Just got a bit of query about running my 202 with straight out extractors. (Off road of course). The engine is fairly warm around 110kw at back wheels I just need to know if having no exhaust can cause any probs with lack of back pressure therefore ruining valves etc. Or is it better to run a shorter exhaust to stop say just before the diff. As I was considering just 2 dump pipes straight off each outlet.
Cheers Chris.
Running a 202 staight extractors.
Started by
_WYLDLC 6_
, Mar 24 2006 02:57 PM
13 replies to this topic
#2
_draglc_
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Posted 24 March 2006 - 04:21 PM
i dont really know about the backpressure problem, but it wouldnt be too hard to just have a setup like the old group c cars used to have, just have about 2 feet of pipe coming out underneath the front door or something similiar.
A1
A1
#3
_Loki_
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Posted 24 March 2006 - 06:39 PM
As far as I was aware.
Backpressure is unwanted when WOT.
When you're just cruising and idling etc. you want backpressure to protect engine.
Someone else able to add insight into the truth of this and why?
Backpressure is unwanted when WOT.
When you're just cruising and idling etc. you want backpressure to protect engine.
Someone else able to add insight into the truth of this and why?
#4
Loui
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Posted 24 March 2006 - 08:09 PM
From what i know you put a piece of exhaust on, paint it with some cheap paint, run the motor, when the paint burns off cut off where the burn stops
Cheers
Loui
Cheers
Loui
#5
_1QUICK LJ_
_1QUICK LJ_
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Posted 24 March 2006 - 09:14 PM
you will prob need to rejet the carb as it will run leaner
#6
Tiny
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Posted 25 March 2006 - 08:15 AM
TO the best of my knowledge if the car is going to be used for drags.. it woudlnt matter ( short duration of time its being used for ) if its a track car then yes.. from what ive bene told you'll burn out exhaust valves.
I'd probably suggest using a short side pipe similar to the bathurst race cars, that will get you away from these problems as well as having the exhaust exit the side of the car which would be better for a variety of reasons.
What's the car going to be used for?
I'd probably suggest using a short side pipe similar to the bathurst race cars, that will get you away from these problems as well as having the exhaust exit the side of the car which would be better for a variety of reasons.
What's the car going to be used for?
#7
mrlctorana
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Posted 25 March 2006 - 09:20 AM
Some good info here, just taking it all in!!! Never actually knew anythin about this, I've been running mine straight out the extractors when at the drags, would it be better to just have a short pipe out the side to bolt on?
Cheers
Les
Cheers
Les
#8
Tiny
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Posted 25 March 2006 - 09:23 AM
Les: At the drags i dont think its a problem, As i mentioned the short time ( relatively) that its running for wont damage anything, I belive its when it runs for quite some time the exhaust valve heats right up and gets a hammering.
#9
FastEHHolden
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Posted 25 March 2006 - 09:27 AM
what will happen is that it won't scavenge properly...the exhaust pulse has a "vacuum" behind it and it helps draw a fresh mix of fueland air into the cylinder when the valves are on ovelap....you need some pipe...loui said about the paint on the pipe....thats an old motorbike tuners trick and I have heard of it but never done it. don't go too big in the pipe...no bigger than the secondary of the extractors.
This whole thing about "back pressure" is straight out wrong..pressure is just resistance to flow...if the system is big enough it will not build up pressure..but it won't necessarily run properly...an exhaust system does more than just provide a means for the removal of exhaust gas.
This whole thing about "back pressure" is straight out wrong..pressure is just resistance to flow...if the system is big enough it will not build up pressure..but it won't necessarily run properly...an exhaust system does more than just provide a means for the removal of exhaust gas.
#10
mrlctorana
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Posted 25 March 2006 - 10:22 AM
Cheers Tiny, might as well leave it as is then, and just make up a pipe when i start hitting the circuit.
Les
Les
#11
warrenm
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Posted 26 March 2006 - 06:50 AM
Agree with FastEHHolden, back pressure story is wifes tale. The paint trick does work,you need to use black exhaust tube not coated & use "tire black" as it burns really easy.
#12
_73LJWhiteSL_
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Posted 26 March 2006 - 12:12 PM
My understand was that backpreassure give a car driveablity, appart from keeping the noise down.
I used to run a 2 1/4" exhaust and extractors off my stock 173. Well it would rev out nicely in the higher rev range (with a stocky we are talking 3900RPM
) but it was gutless of the line and used to bog pretty easy.
I had a 2" exhaust installed with the same extractors, and the difference was very noticable. Firstly the bottom end. I gain a heap of torque down low, so the car didn't bog anymore taking off, however it got a fair bit more asthmaticy in the higher rev ranges.
This sort of stuff probably doesn't apply to race cars, but for street cars the importance of getting the right sized exhaust probably makes a heap of differents in driverablity or lack of.
Steve
I used to run a 2 1/4" exhaust and extractors off my stock 173. Well it would rev out nicely in the higher rev range (with a stocky we are talking 3900RPM
) but it was gutless of the line and used to bog pretty easy.I had a 2" exhaust installed with the same extractors, and the difference was very noticable. Firstly the bottom end. I gain a heap of torque down low, so the car didn't bog anymore taking off, however it got a fair bit more asthmaticy in the higher rev ranges.
This sort of stuff probably doesn't apply to race cars, but for street cars the importance of getting the right sized exhaust probably makes a heap of differents in driverablity or lack of.
Steve
#13
_WYLDLC 6_
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Posted 27 March 2006 - 03:18 PM
Thanks for the feedback guys. The car will be used for drags, but since I've never run the car on the track I thought I might find out first. As for re-jetting the carbs that really isn't an option as I'm running tripple webers. As for the side pipe what will work better, my headers are 2" dual outlet with flanges on the end of each will it work better with twin side pipes or use a 'Y' piece and then into one pipe.
Cheers Chris.
Cheers Chris.
#14
FastEHHolden
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Posted 27 March 2006 - 08:33 PM
its not "back Pressure"..its a correctly sized exhaust....and how can you have "no back pressure at WOT" yet have it at idle?
If the system is too big it won't allow correct scavenging...that is what aids driveability.
If the system is too big it won't allow correct scavenging...that is what aids driveability.
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