Mods for 90's Citroen Break (STW for folks in US))
 

My vehicle is perhaps bit unknown to US market as Citroen did pull out from US market before this car was introduced if my information is correct.

Here it is considered being small family car in US it would be probably something smaller than compact class?

Specs as follows:
Citroen ZX Dturbo Break 1997, motor code XUD9TE
1.9 litre turbo diesel motor, producing 90 HP and ~250Nm of torque that is 184.37lb/ft at 2250rpm.

length 4m (13.12 feet) width 1.7m (5.8 feet) height 1.4m (4.6 feet) 0.13m (0.43 feet) of ground clearance and we have legal limit of 0.075 (0.246 feet), tire flat and suspension compressed fully.

Car without modifications is now getting around 53MPG(US)

My driving is on highway, however our roads are not as nice as in some other countries, so we have lots of hills and curves, roads are narrow and often speed is limited to 50MPH, also my car has 50MPH limit on it's back.

I usually don't drive less than 100 miles when I start the car, so warming up does not affect so much to me.

Steep long hills do cause need of bit more cooling than flat areas, but it is rare that we get temps over +25C.


Took roof railings off and filled hood gaps, also gaps around front lights and taped lower portition of upper grille, upper portition brings cool air to intercooler that sits at top of motor.
Next weekend I should know if those had any effect, however conditions have been very windy so even to get same MPG as before is going to be less fuel consumption.

Photo is from Allcars.com

Here is how car looks as standard:
http://jtbo.pp.fi/images/ZX/ZX_side_standard.jpg

I did poor job of photoshopping what I would like to do:
http://jtbo.pp.fi/images/ZX/ZX_side_aeromodded.jpg

From front:
Airdam, to limit airflow underside of car and to block part of lower grille, Plan is to run it straight down from foremost edge of bumper and to follow bumper curvature to sides, also lower edge of airdam should be bit lower than current front bumper is.
Issues with here can be that I'm increasing frontal area too much to have any benefits? Underside of car is rather ugly.

Front wheel well cover, just small one to make gap bit smaller, don't know if it would have any meaningless value, but I will be testing it with duct tape and cardboard.

Hood spoiler thing at back of hood, from red circled areas I hear lot of wind noise, I hope to guide air over those places, but I'm unsure if drawn location is good (it is bit similar in aerocivic), or maybe at front edge of hood it would be better?

Rear wheel well cover, top of wheel well is already made straight by factory, but I have seen many putting good covers there and probably for reason, should be rather easy to do and test.

Lastly, but not leastly, is extension of roofline, bolted to trunk lid, shape is what I thought would give some separation help and should perhaps function, but I'm the newbie here, don't know about much, I have read about 15 degrees, but I think it should also be bit curved as in original Kammback vehicle of 30's?

What is not seen is bottom of car, from front axle to front and from front of rearaxle to rear bumper area is a real mess, those I hope to cover with some material, I don't think that we have coroplast over here, so have to be creative about it. From rear I think little less angle and bringing bottom out a bit, so it is past bumper line, might work out well enough?

I have mudflaps and I'm hoping to make some miniboattails for front wheels so that I would not get so much penalty from mudflaps, car gets really easily very muddy from it's sides so I hope to get improvements to this area too.

Car has cd of 0.36 as standard, don't know how much roof railings add, but at least there is bit less noise, however wind still grabs car very hard.

This vehicle has no value as of money, it is very beaten up by unknown persons at the parking lot and during winter huge chunk of ice that flew towards me from big rig, took part of front bumper with it, so it is very ugly and nobody wants it, so it is pretty much same what I do with it now, however it is my main transportation and I need to haul lot stuff in it so trunk need to be usable as it is now. Good point is that there is full year of MOT (we have yearly inspection of vehicles here), probably will not pass next MOT without major work so this is rather free experiment.

Primary goal is to get off from boost at 50MPH, it is now 0.05-0.1bar on boost at that speed and getting any of boost will increase fuel consumption radically as that is nature of old tech diesels. Second goal is to get under 4l/100km consumption, that is to get into 59MPG(US), I don't know if these modifications will get it any better than that as shape, motor and gearing is what they are. Bigger tires did not go so well, added consumption by over 20%, car had not power to go up hills.

I'm interested in hearing your opinions as it is perfectly possible that I'm thinking something completely wrong here, I'm just 'going with the flow' meaning air flow and what others have done.

Beauty is in functioning form, ugly are chrome fashion and bling.

Your thinking is correct but your wording is a bit odd.
You mentioned your country’s roads but didn’t say where you live. Your garage says Monaco; is that where you live?

Coroplast is not an exotic material. It is just corrugated plastic board and it will survive rain much better than using cardboard. A good source in the US is political election signs that you can pick up for free after voting is over. I don’t know if they have that sort of thing where you live but it shouldn’t be difficult to find for purchase.

Monaco is actually trim level of my car, but I indeed live in Europe and in here it seems to be not so common material. It seems that our politics are still stuck into cardboard and paper.

I do have a welding machine and sheetmetal, so maybe using that, but it is lot of added weight then, I must research a bit if I can find something similar for coroplast.

First tests I'm thinking of doing with cardboard and duct tape, that way I get samples which I can cut more rigid material.

If it rains, cardboard will 'melt' so that is not good for anything else than quick testing. I really wish to find local source for coroplast or alike as it would be really easy material to work on.

Unfortunately our politicians last for much longer than the cardboard they print their mugs on:rolleyes:

Try looking for coroplast at shops that make advertisements, Groar found a batch of circus signs on the roadside. I found a plastics company which offered it - it's not called "coroplast", so I had to look through the pictures in the catalog. It's usually made from PP, PE or PVC, in different colors, sometimes you can find something that's UV resistant.

Before you start any welding, not only get the shapes and sizes right, but also find out what your local laws are. The US is much more relaxed about what you do to your car, while in Europe you must have all sorts of homologations and certificates for pretty much everything. It's supposedly safer that way, but for many it's just a royal PITA.

Only their promises disappear faster than their carboard ads :rolleyes:

Kammback design is perhaps one that might be bit shady ground according to law, rest I think should be ok.

This one was before Kamm, so maybe it really should be Ledwinka back? ;)
Tatra 77 - Wikipedia, the free encyclopedia

Our police has been replaced by speed cameras, so much that even I spend 3 times more on road than average person, can't even remember when I did saw police last time and if there is a police they seem to be not very interested from mods, so even I get bit illegal side, there is much of real danger of getting caught.

However, I understand well other side, if someone drives over me and I have illegal mods, then I'm not getting much if anything from insurance.

I know that I can block rear window, but then I must have passenger side mirror too, which I do have.

It is also possible to have 'cargo' that is safely secured and not extending more than 1 meter over outline of car, if extending more, red warning flag is required.

Trunk lid/door is made from plastic, it is not metal at all if I'm not mistaken, so I'm thinking of screwing right trough it to mount that kammback thing.

I will try to find corrugated plastic for belly pan and front airdam might be good to be made from that too.

edit: I did found something that looks similar to Coroplast, it is made from pp, 6.56 feet x 9.84 feet is 62.05 toymoney (euros) + delivery which is not cheap either, probably over 20 and still I need to pick it up from 15 miles and I don't have anything to transport such big sheet, that was 8mm thick, there is smaller sheets that are 5mm thick, but those too are too long to fit into my transportation methods, maybe I could get them precut from them, that would save bit of hazzle.

I plan to contact whatever institution is responsible to find out how to make permanent versions of my mods legal. Just in case. So far the police has only been interested in taking pictures of my car, though I was close to failing my inspection once. If a police, border patrol or customs officer decides that you might be trying to hide something with your bellypan, or that your wheelskirts may fly off in traffic, then having papers for it will put you in a much better position during the discussion.

When I bought my coroplast I believe it was 2x3m (it cost around 30€, iirc??), so when I went to pick it up I had to cut it up in the parking lot. My advice is to know beforehand exactly how you'll want to cut it so that later you don't end up with bits and pieces you can't use.

If you make the kammback so that it doesn't extend beyond the rear bumper then you won't have to worry about red flags and such. I would love to have my rear window at the rear of the kammback to slightly increase trunk space. I've needed that space on more than one occasion...

Just because you don't see them, doesn't mean that they don't see you...

That is probably best plan to cut it when picking it up, have to make plans for it before ordering then.

I spend so much time on road that I can spot their unmarked cars quite well too, but it is better to have mods perfectly legal.

I don't think that here they actually will even mark those mods even if asked, pedestrian safety is something they are bit frantic about, but with these older vehicles it is much easier, when it is well secured and has no sharp edges where person could hurt themselves, then it is ok by inspection.

But if one adds even bit of horsepower to engine, that is where things get problematic.

It would be nice to have officials to understand that it is best for all to make these improvements to vehicles, they should be helping instead of limiting, imo.

Reduction of police on road is supported also by statistics, resources are really low and they have priorized things quite a bit.

I'm going to put bellypan only under engine/gearbox and to rear part of car as between there is rather flat area, but I will need to put some sideskirts as there is so large area between tires that is curved too much inside.

Coroplast like material if only 5mm thick and 1.5m x 2.7m in size would be here price similar to what you got, but our prices here seem to be 3 times what they are 1000km from here, so maybe I have to think that I have found it cheap :rolleyes:

I did some prototyping, after reading that airdam should be as low as lowest part underside car and not more, I decided to put sheetmetal airdam, I readlly needed only about inch more over car's stock version and bit wider to guide air past tires, there should of been more curvature at ends, but had no time to make everything perfect, it is some scraps from roof building, screwed into bottom of bumper, it follows arc of bumper and enough for prototyping I guess.

Could use a splitter though.

Then I modified mudflaps and made them smaller.

I did put 'spoiler' on hood, rear part of hood I duct taped some cardboard, bit less of angle than what windshield is, it is about 6 inches long (font-rear wise) rear is lifted about 2 inches. Maybe tiny bit less wind noise, but no really big effect, imo. Maybe it should be more towards rear so that it is almost touching wiper arm, but I was afraid it would interfere with wiper then. Must examine this bit more before building final version, there is no more than inch of gap.

Then I did turn passenger mirror against window, cardboard and ductape made nice shield for hinge mechanism so it would not be so horrible aerodynamically.

Antenna was removed, that was forehead of roof.

Hubcaps installed to front.

Rear wheel wells were covered with duct tape and cardboard, also made bad attempt of partial kammback from cardboard and duct tape, cardboard was not best quality and it was curved, could not straighten it so sides were higher than middle, even I did added some supports that did not helped to get it straight from middle, so it might be better too.

Had not chance to make extensive testing, I did test that they should stay on place safely, there was quite bit of wind with very strong gusts so any proper testing would been pointless.

Can't really feel huge change, but then again at 50MPH there probably will not be huge change, however I did constantly overshoot my estimates when coasting, making need to use brakes where speedlimits did change, also wind seemed not to grab car quite so strongly as before, but I consider these feeling rather pointless, it can be that all changes just added as much weight than what possible gain there might been if any and as weight improves coasting too, it might been that also.

Forecast shows no rain for long time, so I'm hopeful that I can keep prototypes on for my next business trip, then if weather really stays similar, I could get nearly 600 miles of test driven on same roads that I did last tank of fuel, maybe improvement shows there or then not.

However for that trip I will need my passenger side mirror as it is really difficult to drive without one, it is like driving one eye closed :eek:

This means the mods are working, but you haven't adjusted yourself to them yet, and so you don't gain as much as possible from them.

I hope that it is so, it took whole roll of duct tape and lot of waste cardboard, lucky me I don't throw anything away :D

Sadly one butterfly lost his life, first start to fly around here and this one hit my windshield, I could not see any change of it's erratic path to point from noticing to impact, that was under 2 seconds but more than 1 second. I remember reading from Aerocivic that bugs fly over the car and not impacting to windshield, but of course angle of windshield is different, don't know if I should even try to get air to run over the windshield.

There were also some very red birds on road, they seemed not to notice my car very early, had to steer to avoid hitting them when they did set to fly, I did observe clear bump to one, not a hit but air from front of my car kind of boosted the bird up, clear sudden lift as poor bird tried to escape flying to car's path, but still bit too low.

Usually birds fly off earlier, but this species was not the most common that I have seen, so probably it was just species not so used to cars.

I tested also on dusty road, dust behaves differently, I would say dust is now lifted up, bit mixed, but it is not like before where dust did spread all over the road, it is more controlled if one can say so.

Also I did notice that rear window is not getting much of dust or water spray as I did notice when there was wet section of road, water spray is really great for carboard body parts :rolleyes:

Not very scientific, but I think they show that there was some change.

Back of car, underside is quite ugly in aero wise, there is car jack and spare wheel hanging from bottom of car, front of those is diesel tank and some other shapes that are not making surface really rough. I did eye that area and if I put some kind of plane there, it will be almost vertical, so that there is not much rise towards rear, this is perhaps good, was 4 degrees for that area some number to seek?

There is not going to be too much of decrease in diameter of car even I put all parts that I can, but I guess that if I can make air leave the vehicle cleanly that would be something worthwhile of effort.

Making such 'fins' as Volt has at rear has been on my mind all the time, maybe I try to create such to near rear lights.

I'm hoping of making kammback addon from clear plastic of some sort, there is 3rd brake light at top of rear window and I wish to leave it visible to other drivers, I think it was 20-30% less chance of being rearended if you have 3rd brake light.

Tomorrow I have 6 hour test drive, I hope to fill up after the drive to see changes immediately, also will be interesting to compare how much I can drive engine off, most of time I drive 50MPH but there are those slower speed areas which are mostly 37.3MPH they are usually very short ones. My average speed on that journey was 46.6MPH to there and back last week according to GPS, average speed is around there for all my trips really, I could go slower, but my trips are so long that I sacrifice bit fuel for time.

A diffusor would help with a sedan or a sloping liftback design, but it increases drag on a station wagon / break / estate kind of car !

I'd keep the belly pan more or less horizontal right up to the rear bumper.

Ah, good to know, thanks :)

So I will bolt it to level of tow hook as that is lowest spot and it should be enough low to let everything living above it, then need to check front airdam that it is about to same level with splitter, when I get that far and it should be nice and straight route air to pass.

Sideskirts are perhaps then more important in STW design to keep air properly underside.

One thing I have still not quite decided is cooling of engine, I have now upper grille blocked, there is hole size of quarter for intercooler, lower grille has two holes, lower I have blocked, upper is open, cooling is enough now, but will not be when summer comes.

I plan not to increase holes at front, but I plan to change way air exits, I could make it exit upwards, or downwards, if I make it down, then airdam could be lower and belly pan under the engine bay would need to have holes where air could leave, it would be needed to have bit of bump front of holes at bottom side so that air could leave freely without air coming from front being disturbing, also such creates small vacuum that would help air to exit, same is with hood vent.

Natural direction of warm air to exit is upwards, proper location for exit vent is at front half of hood, at least that is what I have read, but that means more noise escaping from engine bay to pass trough windshield and less noise is one reason I'm modding.

Currently there is nothing under engine bay, so it might be little less cooling when I cover bottom of it, but maybe holes with bumps at front of them will be enough to restore cooling.

If not, then I just need to open up lower part of bottom grille, only hills are causing that heat to build up a bit, not very much, but a bit of increase over normal temp and it is now fridge temps outside.

Cooling is actually now bit too much and bit too little, it would be enough and too much if I would keep throttle at same position on uphills, but it would mean getting speeds so low that I would need to gear down and that kills fuel economy. Maybe need to have adjustable grille block too.

I should also monitor bit of intercooler temps to find out how much opening that needs as it does affect to engine temps too.

Oh yes, as this is diesel turbo will be on boost at certain rpm even without a throttle, diesel is squirted by amount of idle all the time, so as long as engine runs there will be some fuel burnt and together with rpm that seem to cause boost. That is at least what boost gauge shows.

Tuning is interesting part, getting all working right and together, like getting good cooling with minimal amount of added drag :)

Dust and rain are great real world indicators of air flow like smoke in a wind tunnel. It sounds like you have made a big reduction to the trailing vortex. :thumbup:

You may want to try adding streamers to visualize airflow over the surface of the car. Check before and after modifications. Unfold the passenger mirror, watch air flow on side of car, and fold it again to see what improvement was made.
I'm toying with the idea of rigging a video camera outside of vehicle to see how water mist acts around wheels and under the car. I drive a truck so the underside airflow is far worse than a car.


I'm also wondering about the best way to control airflow to radiator/intercooler but I'm more concerned for where the air goes after passing through as you are. I've read that with my truck the engine bay actually pressurizes with air to the point it restricts flow through the radiator so reducing air coming in will help in my case.

How much air is needed to keep engine bay cool?
Underhood temperatures are a bigger concern with a turbo. Exaust wrap is not cheap but not expensive either. That will go a long way to help with temperatures. It would be very difficult to install without removing the exaust first.


Everyone likes to see pictures. Please post some if you are able to.

Use an aftermarket LED stop light.


As for overheating, use an openable glille block. Keep it closed when starting, open the intercooler side once the engine warms up, open the radiator side only when needed (A/C use, climbing long hills, etc.). Here's mine:

After driving about 320 miles with mods, I must say that if there was any gain, it is not showing up at all, I'm getting precisely same economy as I did before, good part is that I'm not loosing any economy either, only thing I could notice was tiny bit less wind noise and different airflow behind of the car, but there just was no any change in fuel consumption.

So to get mods work, more work is needed at planning and designing, maybe underside is more important than top side.

At 50MPH or less there really has no effect, could be that at faster speeds there has been some effect.

So next will be making underside flat and hoping that to bring some change that could be noticed.

To get 59MPG instead of ~53MPG seem to be a lot harder than what one might first think, even conditions were better, but still no help.

Thanks from pics, they tell a lot, also those mods of yours are always pleasure to see as those are made so well :thumbup:

At same route I got 4.2MPG difference with mods, that is something around 0.3l/100km, but wind was from behind and from side instead of front, I would imagine that it is wind that gave me most of that, so technically there was a difference, but really there was not a difference because it was wind that did the change.

Piwoslaw, I did read about thread of your friend, who has Megane diesel in France that he has got really a lot better mileage with his mods, and it has given me idea of buying a Megane Coupe, just need to find finance for that. Megane Coupe has quite nice rear shape and I will need a new car in a year anyway as this my current one has bad gearbox by sound of it.

Anyway I would like to test aero mods bit more, pics of 307sw do show that I should of made my kammback bit differently, also when I look others there was one great flaw in my design, there was big gap to sides of vehicle, also most of others seem to have it dropping down at higher angle.

So next version I hope to make from clear plastic, following sidelines of boot lid and maybe getting it to curve downwards bit better.

I think it should be possible to shape acrylic clear plastic with heat gun, of course to get all angles and shapes right is bit of challenge, but maybe it is possible to heat many times to make small adjustments. Attaching it should not be too hard as I'm not afraid to punch holes to boot lid.

There perhaps should be clear improvement from such kammback mod so that I could clearly see it's affect from hundreds of miles driven with it?

Edit: Oh yes, forgot to mention that I had 150kg less load too, so that + the wind helping and still not noticeably better, it must be that mods have not done much to help, maybe effect was even opposite.

So, I bought new tool for pop rivets (that is how we call them, expanding rivets maybe in english?), that did allow me to easily attach new roof 'spoiler', it is bit short I think, but that is because I really would like to get transparent one, so that I could make angle to decrease bit more for last 50%.

Here is first 50% in poor photo:
http://jtbo.pp.fi/images/ZX/science/..._roofext_1.jpg

It is plywood, I had it around and it is easy to work with, when painted it is not too bad, I just need to use bit filler to make it so that there is not sudden 'step' where it starts.

Maybe such roof extension does some good?

I also did see that car has roof and side separated by small edge, so I thought that I maintain that edge in my roof extension spoiler thing, also putting edges to same position would of cause quite lot of stress to parts.

Top part is curved same as roof, it comes down slightly steeper angle than roofline, next 50% made from clear plastic, I plan to make so that it comes down bit steeper.

Now maybe I should make last inch of clear plastic to go horizontal level so that it promotes separation of airflow? It should be possible with heatgun to make such form.

Groar is getting amazing fuel economy:) His mods (and those a few other ecomodders) inspired me to go ahead and make my own mods.

Iirc, the Coupe version has slightly lower frontal area, but I have no idea if the Cd is better, and by how much it can be improved. Unless you need a new car, you might want to keep the ZX for a few years and ecomod it to death;) Since the transmission needs replacing, maybe it can be regeared with taller gearing?

The rule of thumb is a 12°-14° drop, and the same for the inward angle of the Kammback's sides. Slightly more towards the rear end if it's a long boattail. Have you seen the aero template floating around the forum?

Looks nice from that angle. Do you have a side view?

Here is side view, I did put one extension on, which brings it out by same distance the original piece did, but still left to do is to add sides and I think getting extension piece cut to get bit more angle to meet that 12-14 degrees inward angle.

http://jtbo.pp.fi/images/ZX/science/...lippa2nd_1.jpg

Trunk door is made from plastic, really easy to attach things to it as no worries of rusting.

Unfortainely here gearing transmission is several thousands of euros, even used box would be worth of car, which has severe rot problem underside.

Might squeeze one more year out from it if box is staying together, but in my line of work can't risk too much, car's value is 1000 at most, new old Megane Mk1 is around 2000.

This long roof break has bit too long roof for good aero, I did do teardrop photoshop test and according to that I should chop last window section to half at it's rear part to keep it within teardrop shape, so even by adding kammback shape to rear which should be in proper angle, well that is what I hope at least, it is bit too late, might be that there is more to be gained from underside then, spare wheel is underside of the car for example, quite ugly underside means of course lot of losses there.

In megane Coupé rear angle should be such that adding kammback should not be too difficult, I'm restricted to inside bumper level, can't have anything poking outside of that, same for sides and lowest point of vehicle is limited too, so it is quite difficult to get most from the break/stw shape, I at least think Megane Coupé might be easier as it has original shape closer to optimal.

I'm sure you with Groar have gotten your share of young guys with baseball cap sideways pointing, taking pictures and laughing?

I think lost are ignorant ones, but maybe it is us that get the last laugh, in next 10 years not all have chance to drive because of increasing price of fuel and too slow introducing of alternative fuel options.

My first test mods did wake up some unwanted attention for sure, but I hope to make current mods such that those are bit less 'screaming' if you get the idea, I think that is why Groar likes black tape better even it is not so well sticking from what I did read.

My solution, get matching paint to car and paint over silver tape :D
That is until I get around to fill gaps with plaster of some sort.

I have gravel everywhere in my car, also radiator was quite filled, some of our roads are not so great during spring, so my front air dam transformed to twisted metal after impacting with road at some 40-50kph, got engine bay also filled with mud, air filter soaked and muddy, rocks and mud flew to wind shield too. It was no more than a inch lower than standard bumper, but road was soft and wheels did sank into it quite a bit at that spot.

That occurrence lead me to think about putting metal belly pan, I'm sure anything less will just be broken.

Oh, how nice it would be to lower the roof. If the car is a goner anyway, then why not have some fun?

As for the Megane Coupe, I checked that is has Cd=0.33 and frontal area only 1.9m2 (as opposed to my 307sw's 2.55m2). Iirc the ZX's FA is closer to mine and has Cd=0.36, so getting the Coupe would score you a lot, especially if you don't need a big car. You could also look for the convertible version and make a custom aero hardtop, as proposed here.

Much more than we would like, but that's the price we pay for being better than the rest:D

I try to make some mods, but have to keep car legal and usable, also I'm mostly using scraps for parts, so that even there would not be much gain from mod, it will not cause more load to world, even I'm not really eco person, I try to do things reasonable way and there is no point of buying much new stuff for vehicle that is going to be replace by christmas if all goes according to my plans.

That of course limits a bit what I can do, so far only paint, tape and some rivets have been bought for mods, rest are odds and bits left out from other projects that have had no other possible usage, new tool I needed anyway and fiberglass I needed anyway to repair bumper.

Latest improvement was to add side supports for that last 50% of kammback, this time I had no more plywood available so found scrap pieces of thin metal, it was bit too little really, but I made supports from that anyway.

After driving some 30km on gravel road I did notice that it is not very good, supports are getting dusty from outside facing surfaces, so they are too much inward.

Other thing I did notice is that now dust swirls, there are two swirls at sides, like in aeroplane when landing and at middle there is tiny gap where dust is not rising so high.

Swirls rotate inwards, also rear window is still gettin bit dusty, not so much as before. Hard to really tell much of difference as there was not enough dusty roads to see full effect, only small areas of dusty roads. Rain would be rather good test.

I must still add 3rd brake light to lower part of window, so that it is seen by other drivers, I think that I have one unused one that I got free years ago as it was going to dumpster, yeah, I'm a hamster :rolleyes:

ABS got broken again, just few weeks ago was fixed, did cost 180 euros, one of the gremlins in this car.

I was wondering if that cd value in database is for break or normal ZX? If it is for that hatchback then break would be bit more 0.02-0.04 is perhaps typically added for break/stw compared to hatchback, sedan being somewhere in the middle.

Megane and ZX are same size cars, imo, only that I now have break, but I really don't need one as I do have a trailer, aerohead would probably get excited about that one and if I would need to pull it more than once in two years then I might do full mods to it for sure :D

Okay, I don't know if I did anything right, but I added now few things, to front I made small lip, barely visible in a photo, then I added wheel well covers, rears need still bit of work, some support so it does not look like curtain, but I'm yet to come by appropriate scrap metal.

You can see in photo that my kammback attempt, I checked that car's sideline is straight in gimp and measure bit under 11 degrees for first section and around 13 degrees for latter section (that has red metal supports). I think that those red parts could of been larger, but metal piece was so small that I got barely those two out from it.

http://jtbo.pp.fi/images/ZX/science/...eromodattu.png

Added new 3rd brake light too:
http://jtbo.pp.fi/images/ZX/science/...romodattu2.png

Yes, car is covered in clay, mud and who knows what, it is this time of year and these roads, no point washing car until about month or so.

I did some Flow Illustrator testing, but I don't think that it really tells much, front lip could be lower, but it is already around 60-70mm from ground and is touching ground on bad roads, good thing it is still flexible, might need some supports to that one too.

Black material is vinyl carpet, used in house floors, this one had lot of mould and it was rather small piece, just enough for car.

Rear belly pan and sideskirts are perhaps next that I will do when I will have time again. Underside is horrible, rear bumper is like U-shaped air brake, there is spare wheel too, I'm thinking of leaving spare wheel out and getting one of those bottles that promise to fix tyre, then I could put cover to that area so it would be smooth, probably largest effect.

I also did the ultimate mod:
http://jtbo.pp.fi/images/ZX/science/.../old_trick.jpg

Got to get the engine to run hotter. Evans Coolant ( biodegradeable, 375 F boiling point ) and raising the operating temp will help you gain mpg. Turn the engine fuel delivery down with smaller injectors ( I saw the hitch in the back, do you tow with it? ).
Heat the fuel up so that it reacts better inside the engine ( diesel needs all the help it can get to go from ambient to auto ignition point ), add propane or cng assist as a range extender. If you are feeling real frisky, get a cam ground or find a factory camshaft that brings the torque peak in at 1600 or lower rpm, and modify the fuel delivery so that the powercurve peaks quickly and falls off ( like a semi truck engine, car diesels keep the powerband flat and long so that it accelerates well ); see if your engine is used in commercial apps that require that type of powercurve and use it.

Fuel is heated to coolant temp before injecting into motor, filter is in same housing as thermostat is, so when cylinder head warms, also fuel warms, it is great in our winters, where temperature can drom to -40C.

To heat air, that is easy as it requires only limiting air flow to intercooler, however it is very easy to to loose power and get excessive diesel consumption with that.

I don't tow too much, once in two years, but most of time I have 200-300kg of load in trunk, so I'm pretty much always driving near gross weight limit, this means that climbing those long hills means lot of load to engine and this means again lot of heat. Current grille block is about maximum I can have and still be able to climb hills without crawling, but when coasting temps tennd to get bit lower, that engine is producing quite a bit of heat for a diesel, also headgasket is common failing point so I'm bit afraid to get too much of heat there.

There was one valve for turbo cars, which lets pressure to wastegate actuator only after set pressure is reached, this causes turbo to spool up earlier as wastegate is not open at all until pressure is reached and such would bring more torque to lower rpm if I'm not horrible mistaken.

I'm running at 1850rpm @50mph which is what I can drive with that car, maximum torque comes at 2250rpm from my memory, however at least before mods putting bigger tires under the car caused rpm to be too low for car to run well, diesel consumption did increase dramatically, even with hypermiling I had hard time to meet rated consumption levels, surely car did have power in reserve, but I had to push pedal down more so that turbo came into play, but if turbo would come in with less throttle, then I think that I could save a bit with bigger tyres.

What kind of injection pump do you have?

Mechanical Lucas, Bosch would be better, but of course car had not that one. Lucas is PITA to tune as screws are hidden under blind plugs and so that one can't see there without tiny mirror.

There is not much electronics in a car, old fashion engine with old fashion mechanical management, that I kind of like, less to worry.

edit: I don't know if I did this horribly wrong, but I got these:
http://jtbo.pp.fi/images/ZX/science/...nt/ZX_orig.png
http://jtbo.pp.fi/images/ZX/science/...odded_wind.png
Perhaps not so good improvement in reality, but at least there is some change.

The mods look quite good on your pics:thumbup:

It appears that the sides of the red Kamm extension are drooping inward. My guess is that they shouldn't be - the airflow will detach too early and they won't help any. But the top looks OK, as do the skirts.

And I love the sponge under the gas pedal: It lets you now when to stop pressing, but still allows max acceleration when needed.

The yellow circle with the '80' is to let other drivers know that you don't expect to go faster than 80 km/h, correct? Does that really help reduce the number of tailgaters?

Ok, so it's a Lucas CAV ( rotary ) pump, similiar to the one used on the early Cummins 5.9. It may be a pain in the butt to get to the screws, but there is gold in changing the settings. Add more timing but cut the fuel back. If you are not comfortable doing it, you are in the best place to do diesel tuning. Between the Germans and the Finnish, there has to be someone that can optimize the torque curve for lower rpm operation.

Yes, just a tiny bit inwards, they are almost straight, but last piece of black top side was bit narrower than first part, of course this is the idea of kammback to narrow towards rear, but it would require rotating sides and that I did not manage to do properly, so there is tiny bit of curve on support, mostly on other side, while other side is pretty much straight, I have only thumbs on my hands, someone forgot to install other fingers at factory :rolleyes:

Anyway dust seem to settle to red support pieces of Kamm so that means they are too much inwards, I could try to bend them more outwards when time permits, it is quite thin metal so easy to work with bare hands.

Sponge is very old trick, they used that already in 60's in here, probably the most effective mod, when tuned properly, it should not be too restrictive but not too easily compressing either, should be set so that when foot is resting on pedal relaxed, then you are travelling normal speed on level road, so it is bit like drive by load cruise :)

80 sticker on back is required here if car is converted to van class, cheaper tax and insurance, but not allowed to drive faster than 80km/h, I have not really converted mine, but as I don't see anymore point trying to drive 100km/h because there is very short pieces of such speed on our roads and even on those sections there are always many drivers driving slower, so I drive only 80km/h.
It helps on faster roads and there is not much tailgaiters anymore as I put that sticker on, they are now kamikazes that overtake at insane places, but I often show when it is ok to pass and usually slow down or go side of road just to make road bit safer, when others seem to be uncapable of doing even small amount of reasonable thinking.

It seems to be rather difficult to cut that last 0.3l/100km, but maybe with mods it will be possible.

I might ask some quotes next week, don't like to mess pump by myself as my job requires to have a car and I need to travel really a lot with it, again tomorrow I need to fill the tank, will be really poor MPG as I have been driving on very soft roads and one night had to forget hypermiling and drive rather quickly, so I would not be surprised to see lowest MPG, but car has surprised me before and now I have mods on, so let's see how it goes.

If you don't clean it, the mods will be invisible in a few days :D

True, and also that will show where aero is lacking so it is easy to make improvements :D

This morning there was no wind as I drove small trip with car, I'm not sure if there really was much effect, but it felt that car did run target speed with less load than before, there was larger difference between uphill and level road, imo. Very subjective of course, so it is not so much of evidence from anything, somehow I just got feeling that at higher speed difference might be more notable, speed was decreasing rather slowly from downhill speeds, but I need to fill the tank and drive more, then refill again, to see difference, if there is such.

Already have heard comments like "who would do that to car" "poor car, it had done anything to deserve that", I guess not everyone can't be above average, that would put average just higher and such is not going to happen probably ever ;)

It was -2C at the morning, more grille blocking would of been good.

I made improvements to front airdam, first I made it too low, it scraped on everything, now I did cut it bit less low, but I still have to be bit careful about where I drive, even there is more than 2 inches of clearance under it.
It has now also side deflectors so that front tires are not seeing direct air stream.

Weather has been great, so can't tell how much effect airdam has had, however now I got some insane half tank, again filling slowly on same station up to filler neck.

67.16mpg, that is too low to be realistic (uhm, high in mpg that is), imo. However I drive again and fill again soon, then we know how it is, if I get unrealistically high reading (uhm, low mpg that is, thinking l/100km here again), then average of those must be closer to reality.

Also I found out that pressure in tyres had disappeared, so there was only around 32psi left, put again to 44psi, so now it coasts very very long time compared how car was when I started modding it, too bad there has not been time for really test these.

67mpg? That is insane!

Have you tried making the airdam lower only on the sides, in front of the tires? I believe this is the new trend in OEM airdams. The lack of the middle part reduces frontal area, but the extra air going under the car doesn't increase drag too much because of the smooth bellypan.

It is insane, that is why I can't believe that, not with just one tank.

That modern airdam is what I do if I can get smooth bellypan made and sideskirts added, but before that I think it is best to keep dirty air out from underside as much as possible.

I had lower airdam section at front of tires but there was less than inch of clearance and that was bit problematic with our rough roads, even this 2 inches (50mm) is scraping, but at least it is not scraping on road, just when going to parking places and at most extreme bumps on road, we have quite extreme, but I'm sure you know a lot from those as I remember your beautiful country had quite a few potholes years ago, maybe roads are improved by now?

I think that I'm coasting easily more than 30% of time, also I can pulse and glide in lot more now, so in my car, underside seem to have huge effect.

Must get a pic sometime, airdam still would need to be smoother and better angled, it is bit of variable angle still, but hoping to get it better soon.

I would like to install air guide on hood, to reduce wind noise, but front edge or near windshield, which is aerodynamically better?

Stll, it's what you recorded ;)

Don't make the air dam too low, it increases frontal area, and thus drag.
You could lose the aerodynamic improvement to the increased area.

As low as the lowest major car parts is OK.
Going deeper only adds extra area.

Are you sure it comes from the hood area ?
Wind noise is mainly due to A-pillar and mirrors, or wipers, if they are largely exposed.

I had no evidence from anything else, so until I find some error, I must trust that be correct.

Drove bit more, now 1150km and still 1/4 tank left, if last 1/4 tank in gauge is same as in reality, then it would be again about same kind of FE, but I'm not 100% sure that it is, surely it is very close as I have usually seen 500km at half tank, and each quarter has been pretty much of 250km, that has made 5.5 to 5.8l/100km, but now with my current tank I'm again travelling some insane distances compared to time before mods and hypermiling, just drove slowly.

Frontal area increase is bit of issue of course, but there are parts that are quite low, like spare wheel and rear bumper is like parachute, so I put it quite low and then I hope to add sideskirts to control air entering underside a bit more.

Car's front bumper is not very high to begin with, but I did put it some 7,5cm lower with airdam, it seem to have quite large effect to fuel consumption, but I must gather more data to be able to say anything for sure, it might be that weather has been much nicer than before.

Better Kammback might help more, my current is rather crude with lot of sharp edges.

Wind noise comes from wiper and a-pillars + top of windshield. with air guide that would push air bit upwards, I might be able to reduce wind flow around wiper and also maybe would be possible to make air to hit windshield on bit better angle, at front of hood it did look better in flow illustrator, but that is not much of tool for the job, imo. There might be however point as air directed up would take time to come back down, if it comes down, other way would be to install it right at front of windshield, making cover for wiper blade (I have only one of them).

As I painted wheel skirts there was perhaps bit less rubbernecks, but people still stop and stare when I'm on traffic lights, maybe I should put some text to sides, like "lesser minds can't comprehend." or something as subtle and friendly. Most seem to think that someone would actually do such things for car because of looks, my mind is not enough to understand why anyone would do that, so I did order few stickers that remind with warning that has some strong wording how reading a tuning magazine will turn person to idiot, I think those will fit in very nicely.

This is bit crazy week, I have to do quite few miles on road. Now most recent tank was bit less than previous one, might be because of my right foot too, but still over 64mpg, that is quite good for such car as ZX, front airdam is doing miraclous things it seems, it can't be that there would be error in two fillups and as I managed to get a lot further than before airdam with a tank, I can only point airdam being one responsible from better FE.

That is almost 10mpg change that has happened after I did install airdam, it is quite a lot, imo. might be that it is partly because maybe I have just adjusted to mods, like wheel skirts and kamm + now airdam.

Will see more results by end of a week.

With tanks of 67 and 64 mpg, I'd say that's confirmed :thumbup:

That's a big improvement - I really need to start modding my car ;)


I'd go that way.
The ZX's hood already has a nice upward slope to it, and the angle with the windshield is not excessive either.

Groar puts his fuel mileage on the window.
Something like "3,5 L/100km, et vous ?" might get their attention ! ;)

:cool:

My next tank will be disastrous, it is garden work time and it means I need to haul some supplies, our hills are rather steep here and I need 3rd gear to get up without flooring the car, when I have trailer full of stuff.

Empty trailer is like if I would have handbrake on all the time, full trailer is so heavy that car is really struggling with it, 60kph is ok, but trying to do 80kph is almost impossible at uphills.

Naturally I did put tire pressures to 44psi on trailer too.