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

[Piwoslaw]

I also noticed a reduction of wind noise after adding the Kammback and removing the roof rails. Unfortunately, this is cancelled by the increased road noise when driving without the rear seats.

I think that getting your Cd below 0.28 will need more than a Kammback and bellypan. You might need a boattail. A tail cone like this would be awesome:

[jtbo]

Many sources say that car's cd should be 0.34-0.36, I got measured 0.36, but when I tested rolling resistance at lower speed I got more accurate CRR and cd was 0.429.

I think that I just drop 0.429 out and do estimates from 0.36, with kamm several test's average shows cd under 0.3 so that would be around 18% improvement I guess.

To get under 0.28 I don't need much, reduction of 0.02 would be enough. Because there is now no airdam underside makes more effect when implemented, rear wheel well covers, air guides to front of front tires and some mini boat tails behind the wheels and I think it should be relatively low.

However current cd being under 0.3 now is still subject to error, but it is average of many runs so it should not be hugely off, also I did use GPS to log speeds at every second so it should be really accurate, especially as it is average of several runs, but still, it is so small error that makes so large effect that there is not knowing how accurate that result really is.

It might be autumn until I can test more though as car would need inspection at tuesday and I can't afford it now, so I take it off the road for now. It is few months of cycling for me, oh and also patching the roof of garage and such sort of extra costs that popped up.

[Piwoslaw]

Ah, cycling
Ah, a garage
Double lucky!

[jtbo]

Originally Posted by Piwoslaw

Ah, cycling
Ah, a garage
Double lucky!

Two garages, four cars and five bicycles, so it is lucky but could be luckier?

I'm converting currently city hybrid bike to be highway triathlon type more or less, so then I can use it bit better, actually it has currently in broken state, bearing balls from rear hub came out, so it is undrivable until I get new parts, no gears bicycle from 80's (almost like new condition) is temporarily replacement for that.

That reminds me, I must start updating my bicycling log :P

[jtbo]

I made new mini Kamm for ZX, today I drove in rain with it and I found out that sides of car and Kamm were dry, Kamm was actually perfectly dry from top and sides. So is that good?

Also rear of the car is getting wet from low and center, no longer from tail light areas.

There is also small lip, or more of two lips at front corners of bumper, I attempt to something like some new cars have, to reduce front tire drag but allowing air from center of car to go under the car.

I would need to make flat bottom for rearmost part of the car as well as bumper to engine section needs to be made flat.

Rear brake is binding, poor mileage because of that, will open brakes and lubricate them soon, just need to wait finger to heal as car sliced it, too much energy and I foolishly wiggled finger front of him...

Anyway at MOT they gave green light for my mini kamm, so this time it probably will stay there for winter, just not sure if I can drive much at winter.

[Piwoslaw]

Originally Posted by jtbo

I made new mini Kamm for ZX, today I drove in rain with it and I found out that sides of car and Kamm were dry, Kamm was actually perfectly dry from top and sides. So is that good?

Also rear of the car is getting wet from low and center, no longer from tail light areas.

Hard to say. If the Kamm's sides are totally dry then maybe they are hidden in the car's wake and don't help at all (except maybe in a crosswind). On the other hand you might have nice airflow along the Kamm's surface neatly pushing the water back. If the new Kammy has the same dimensions and angles as the first, then I'd say it's good.

Originally Posted by jtbo

Anyway at MOT they gave green light for my mini kamm

Wow :jealous:

[jtbo]

Originally Posted by Piwoslaw

Hard to say. If the Kamm's sides are totally dry then maybe they are hidden in the car's wake and don't help at all (except maybe in a crosswind). On the other hand you might have nice airflow along the Kamm's surface neatly pushing the water back. If the new Kammy has the same dimensions and angles as the first, then I'd say it's good.


Wow :jealous:

There were few drops of water that had run along the surface of kamm, but without gopro or someone to drive behind it is bit problematic to do tuff testing.

It might be bit steep, but especially from top angle is less than previous setup as now I bended edge of the kamm and that did stiffen it up nicely.


I still need to cut bit from leading edge to make it match size of trunk, also car will get dark grey to bits that are red now.

Reason for passing MOT with kamm was that there were no rule that could be used to prevent that, but tester clearly did not want to approve it.

I think that kamm starts to work properly only after there is flat area under the trunk, it is now such that rest of the bottom of the car is bit below rear bumper level, but under trunk it is almost at bumper top level, so there is that large empty area and rear bumper acts as kind of parachute.

[jtbo]

I did make new front lip from washer fluid canister that I did cut, still needs few rivets and final paint, then I made rear wheel well covers also, I did use 0.5mm sheetmetal galvanized one.

Then I put spare back under the trunk so there is no such large parachute now there, but there I could really use coroplast which is really hard to come by here, I might put some other material there at some point though.

[jtbo]

Some pics to shook head to, I refuse to use very much time to this vehicle as it is daily ride and also as it is probably not going to live very long because of underside rust issues, so I make rough work without taking measurements etc. Despite I work slower than a snail there has not been many hours put to car.







Front airdam is something I plan to make from sheetmetal, currently it is made from trashes which did run out so it is not going enough near tires at the moment. If there is any luck, tomorrow I might get front air dam made and upper grille block too, just can't block whole upper grille as there is intercooler air pickup from upper holes, so that is bit limiting factor, IC sits at top of engine, which also causes engine to get cooling air stream from above that is not very good thing as temps drop at downhill despite there is quite bit of blocking already, engine just does not produce enough heat while idling and downhills can take several minutes to coast down.

I will also attempt to make front wheel skirts, only partials, to reduce that gap at top of wheel, not so sure that it will handle winter with all those mods, without mods there are already issues with snow packing to rear wheel arches, during 300km trip it was a must to stop 4 times to clean up rear wheel wells as tires had no space to move anymore. Might be really horrible with skirts on, but I don't plan to do long trips at winter.

Sideskirts and rear bottom belly pan would be great improvements along with wheel mini boattails, but not so sure I can make those happen. Especially rear tires have horrible aero around them, behind them there is large openings, whole bumper is hollow from that rear section and car bottom is at level of turnk lid bottom, if I would have proper bellypan there, it might help a lot to have clean flow there and Kamm would perhaps work even better.

With current mods 10kph more speed at coasting down hills on dry weather, 5kph at wet weather (we have had mostly wet weather for many months now).

It might be even better as I have now poor rolling tires at rear, have had two blowouts so had to use free backup tires and those are like brakes.

Painting is not yet complete, I think I will not paint it against winter, at spring paint has more chances to harden before getting harsh conditions.

Driving is actually bit more challenging now, at level road it goes with very little throttle, but when uphill comes I have to push clearly much more, probably level road throttle percentage is just less so there is now larger percentage of change for uphills.

Around 0.1bar less boost at level roads and lot more places where I can glide.

Farmers bring mud to roads, so car is constantly dirty, no point washing until roads will get cleared by rain and farmers get their jobs done so they don't bring constantly new mud, but maybe it servers as telltale of aero working or not working.

[Piwoslaw]

Originally Posted by jtbo

I will also attempt to make front wheel skirts, only partials, to reduce that gap at top of wheel, not so sure that it will handle winter with all those mods, without mods there are already issues with snow packing to rear wheel arches, during 300km trip it was a must to stop 4 times to clean up rear wheel wells as tires had no space to move anymore. Might be really horrible with skirts on, but I don't plan to do long trips at winter.

I don't think that snow will be a problem if the front skirts will only be partials (just enough that the tire doesn't touch when turning): They will be smaller than the rear skirts, in fact only at the front and top of the wheel well, plus heat from the engine will melt any snow that doesn't fall out. I say go for it.

Originally Posted by jtbo

With current mods 10kph more speed at coasting down hills on dry weather, 5kph at wet weather (we have had mostly wet weather for many months now).

That's proof that the aeromods are working! And your fuel log shows it