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Performance Exhaust?
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JKRM2K10
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Joined: 17 Jan 2008
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PostPosted: Wed Jan 23, 2008 11:46 pm    Post subject: Performance Exhaust? Reply with quote

What is the best way to get the maximum performance out of a Dyane that isnt tuned or when fixed, will be lightly tuned (gas-flowed and lightened flywheel)


I have heard from numerous people the best way is to leave the crossbox alone and remove the silencer but I now have been told that you strip the baffles out of the crossbox and have a small backbox coming exiting out just before the end of the wheelarch. Another thing I have been told is that sertain motorbike exhausts fit on the same size pipe, remove the original silencer and remove baffles out of the motorbike box and mount it on, again, exiting just before the back wheel. I though about getting a mini backbox, removing baffles in crossbox and fitting mini backbox on without removing baffles as they are 850cc (not 100% sure) so it shouldnt be restrictive and it may remove some of that classic 2cv exhaust note?

What is used on a race car?

What would use and recomend, I dont want anything loud, chavvy and sounds rough, instead I would like something not soo loud but so people realise something special has been done and something not restrictive with possibly a wider exit pipe for a bit of style?

Appreciated
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Rusty
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PostPosted: Thu Jan 24, 2008 2:34 pm    Post subject: Reply with quote

make a double exhaust, so make an extra outlet on the crossbox and 'mirror' the exhaust on the right side. With this setup the engine still has the backpressure it needs and also will be able to breath better!

greetzzzzzzzzzzzzz

Rusty
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Etienne
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Joined: 25 May 2007
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PostPosted: Thu Jan 24, 2008 2:43 pm    Post subject: Reply with quote

The original exhaust is really good to get the max power of the engine!

If you want it sounds better, just move away the silencer under the floors. And make the exit on the side. It sounds louder than regular but not too much and make a nice sound!
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Malte
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Joined: 11 Dec 2007
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PostPosted: Thu Jan 24, 2008 5:28 pm    Post subject: Reply with quote

Etienne wrote:
The original exhaust is really good to get the max power of the engine!

If you want it sounds better, just move away the silencer under the floors. And make the exit on the side. It sounds louder than regular but not too much and make a nice sound!


can you prove that? Very Happy

*gg*

at least it sounds like more power :)
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Bart
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PostPosted: Thu Jan 24, 2008 5:56 pm    Post subject: Reply with quote

Emptying the crossbox as well as replacing the second silencer for a straight pipe does definitely help for power, but the price you pay is noise....

Generally the standaard system is not bad at all, at least it is a good compromise when you don't like it to be not too loud when driving full throtle.

Nevertheless, when you are looking for more power a well designed 2 in 1 system migth work wonders. Watch out, might. I had a 2in1 on my car and it didn't work, empty crossbox and straight pipe were much better than this 2in1 crossbox replacement.

No matter what I think in most cases noise is, till a certain extend, the price for power... from noise point of view the double exhaust suggested by rusty is defnitely wurth a try cause that type might as quite as original.

Quote:
What is used on a race car?
On UK racers I have seen either empty crossboxes with no further silencer or 2 in 1 systems of which there is one really good on developed by 2cvracer and some of his mates, but this is quite expensive as far as I'm aware. Besides Belgium racers have all sorts of home designed 2in1 systems.

Ciao, Bart
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Etienne
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Joined: 25 May 2007
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PostPosted: Thu Jan 24, 2008 6:45 pm    Post subject: Reply with quote

Malte wrote:

can you prove that? Very Happy


Yeah, I've seen some power graphics with different kinds of exhaust...
Result was really interresting, in best case, when you modify exhaust, you don't loose power!
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Kustombart
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PostPosted: Thu Jan 24, 2008 8:15 pm    Post subject: Reply with quote

You are right Etienne, I have heard the same things all around. If you are leaving the cams and compression original, exhaust or air cleaner will not have much effect. I had equal-length 2 in 1 pipes instead of first damper on an earlier Acadiane. Apart from noise, no difference.

Besides, in a Dyane, there is already the "tuned" engine, with the "power tube" on the air cleaner. That DOES really work.

Much improvement can be gained from re-jetting your carbs, especially on later (emission controlled) cars. I have seen several cars on the rolling road gaining as much as 5hp with only different jets.

No need to say that before any tuning is done, it is vital to make sure the engine is in top condition, so get an electronic ignition box, set the timing and valve clearance just right, clean carbs etc. etc.

ALso, blueprinting and balancing the engine and weighing pistons etc can mean much higher revs, therefore, more power. Then you need also stiffer valve springs.

The later 2CV engines are already mostly tuned to the max without losing driveability and flexibility on the road. Real tuning involves much more than changing one part. Changing cams will improve high end power but this will always result in an engine less flexible. For example, the sharper race cams leave you with a much narrower power band and less torque at low revs.

If you are really looking for more performance in a ROAD car, just add lightness. Weight is the enemy.
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Pimslet
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Joined: 14 Nov 2007
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PostPosted: Fri Jan 25, 2008 5:05 pm    Post subject: Reply with quote

Hey,

My thinking is that best exhaust is one per cylinders and it is more beautiful to have two exhaust on a 2cv.

More over, making a 2 in 1 is more difficult than 1 per cylinder.

The result you will have depend of the section of the exhaust and of its length.
The longer, the best for low revs.
The shorter, the best for high revs.

For best performance, the rule is that you should never dicrease the section of the exhaust from cylinder head to the end.
If you make a 2 in 1, you have to add the surfaces of the first tubes to know the surface of the 2nd tube.

Because of the rules, all belgians racing cup 2cv must have a 2 in 1.
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Malte
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PostPosted: Fri Jan 25, 2008 5:58 pm    Post subject: Reply with quote

Pimslet wrote:



The longer, the best for low revs.
The shorter, the best for high revs.



i thought this is about the intake?
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Pimslet
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PostPosted: Fri Jan 25, 2008 6:03 pm    Post subject: Reply with quote

The problem of length is right for intake and exhaust.
But the rule is a bit different, what explain the difference of lenght.
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sivipas
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PostPosted: Fri Jan 25, 2008 6:44 pm    Post subject: Reply with quote

I had large bore sidepipes on 652 dyane. there were no silencers, so the car was really loud at high revs, but at lower revs the sound was really great. as I drove down the street with full throttle, I turned on all the alarms on new cars.
then we put silencers, but the sound was not that nice any more. what I would like to have is cool sound at low revs without the car screaming wildly at high revs. many chopper motorcycles have that kind of sound. about performance I can't say, because I put 652 engine and sidepipes at the same time, so the car went much better than with a lousy 602 I had before.
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Kustombart
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PostPosted: Fri Jan 25, 2008 11:32 pm    Post subject: Reply with quote

If you want to have both there is a solution. Make a exhaust with damper and without. Make a valve, operated by cable from the cabin to choose between the two.

Pontiac GTO had that option in the late sixties.
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ami8i
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Joined: 29 Oct 2007
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PostPosted: Thu Jan 31, 2008 12:52 pm    Post subject: Reply with quote

Hello exhaust tuners,

most problem of seat-of-the-pants exhaust tuning is that loud IS NOT fast.

I agree that 2CV OEM setup isn't too bad - it's hard to make real improvements all over the rpm range, also this nice setup loweres torque at the low end: http://www.2cv-power.de/tuning/rennauspuff/rennauspuff.htm


--> we have to think harder:
In my opinion most torque(!) could be achieved if the connections between each runner could be closed/opened automatically!
- For torque at very low rpms the interference pipe which also heats the carb is very important.
- Also it is profen that the cross box is good for midrange and high revs - just sound should be 'improved' if each pipe is lead seperatedf without connection to the rear of the car.
- But what's about interference between thos two lenghts? Take a look to BMWs flat twins and notice the rally fat interference pipe!
- the crossbox is also a 2in1-pipe


My idea is to put in additional interference pipes plus exhaust gas valves which are controlled by a cheap µC.
»a OEM interference/heat pipe
»b One connection in front of the heater
»c One connection after the heater
»d (modified) OEM cross box

Close valves a - c and make 2 road dyno runs (Streetdyno, GSF-Dyno... maybe worth to start a new thread!)
Open just a and make 2 dyno runs
Open just b...
Open just c...
Open a - c...
(For 2CV scientists only: open a+b...
Open b+c...
Open a+c...)

Do some afterprocessing of the datas --> at each range of rpm one valve (combination) should be opened for best torque chart.

Most difficult part (for me) would be to feed a µC (Atmel for 2 - 4€) to control the valves. A TPS (throttle position sensor/switch) should limit the valve work just during WOT - because at cruising we don't need an optimized pipe.


This tuning could be done clean so no problems with MOT/police are expected. No bothering of your neighborhood - and all other people who had to be near by your car.


Finally I'd like to tell you that I removed the inlet sheets from crossbox - but it was done before I had some Streetdyno experience --> difference isn't proofed. At least car's noise didn't increased.
If I would know how I could find some space I'd like to move the S-pipe to the middle of crossbox so that flow is more symmetric. Also I'd like to minimize the turbulences at both pipe inlets into the crossbox. Maybe a shield which leads exhaust along the wall for 5-10cm.



The same tuning steps could be done to find out a reasonable spark advance curve.

»Horst
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Olli
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PostPosted: Thu Jan 31, 2008 12:56 pm    Post subject: Reply with quote

ami8i wrote:
loud IS NOT fast.



I also dont understand why car what is after all slow, should keep
many noise. Silent cruise or moving fast is much more cool! Cool

-Olli
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Etienne
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PostPosted: Thu Jan 31, 2008 12:58 pm    Post subject: Reply with quote

Pimslet wrote:

My thinking is that best exhaust is one per cylinders and it is more beautiful to have two exhaust on a 2cv.


You definetly loose power with two single exaust!
You need to keep a connection between the cylinders to get the max power!
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