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

[euromodder]

Originally Posted by jtbo

Back of car, underside is quite ugly in aero wise,
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?

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.

[jtbo]

Originally Posted by euromodder

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

[JMPVW73]

Originally Posted by jtbo

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

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

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.

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.

[Piwoslaw]

Originally Posted by jtbo

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.

Use an aftermarket LED stop light.

(Click on image for link.)

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:

(version 1)


(version 2)

[jtbo]

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.

[jtbo]

Originally Posted by Piwoslaw

Use an aftermarket LED stop light.

---clip---

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:

---clip---

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

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.

[jtbo]

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:


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.

[Piwoslaw]

Originally Posted by jtbo

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.

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?

Originally Posted by jtbo

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.

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?

Originally Posted by jtbo

Here is first 50% in poor photo:

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

[jtbo]

Originally Posted by Piwoslaw

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.



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
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.

[Piwoslaw]

Originally Posted by jtbo

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

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.

Originally Posted by jtbo

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

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