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Discussion Starter #1
which exhaust would be best.3" or 3 1/2".will you loose torque but gain more hp with bigger exhaust :confused:

thanks
 

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Depends what youve done/doing to the car m8 3.5" you will loose torque low down as gas speed will be low on a standard/slightly modded car. 3" wont restrict flow until over 450bhp(roughly)
 

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When the APS 3" & 3 1/2 " were compared a while back as a back to back test on a scooby. The scooby was running 345bhp on the 3" system and 350bhp when they ran it on the 3 1/2" system.
;)
 

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Doesn't that depend on the exhaust though!if you ran a magnex up,a 3" against a 3.5" your going to get a different result,but whats it like to drive in 'real world terms' on the road you want power down low more that you need it up high(unless your an idiot on the road)so having 5bhp more at top end dont count for much if you aren't hitting peak torque till 4k rpm
 

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best option for a turbo car is probably no exhuast at all, just a little pipe with side entry jobbie.

now that is not suitable for a road car so the next best thing is go as big, as straight, and as short as you can. simple :D


small exhuast and low down torque etc etc.... that is on a NA engine. for a turbo charged engine it is the boost (turbo) that provides torque and not the exhuast.
 

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petbeemer said:
Doesn't that depend on the exhaust though!if you ran a magnex up,a 3" against a 3.5" your going to get a different result,but whats it like to drive in 'real world terms' on the road you want power down low more that you need it up high(unless your an idiot on the road)so having 5bhp more at top end dont count for much if you aren't hitting peak torque till 4k rpm
I agree if we are talking in the real world and not on paper ..................when we compared the two on our own car we didn't really feel any difference neither did we notice a drop in torque though, so therefore the variences are minimal when out on the road. ;)

And atm i'm running the 3 1/2" due to the fact that a 30/37 turbo is being fitted this week :D
 

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were would it stop then T i can make anything going in stainless,would you want a 5" system under yer car as short as poss like evo-7 says?
 

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petbeemer said:
were would it stop then T i can make anything going in stainless,would you want a 5" system under yer car as short as poss like evo-7 says?
For us personally we would only ever go bigger if we felt the exhaust was restricting power output, but as we are only going to be running between 450 - 500 bhp, we are happy with the 3 1/2" APS honey ;)
 

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Discussion Starter #12
petbeemer said:
were would it stop then T i can make anything going in stainless,would you want a 5" system under yer car as short as poss like evo-7 says?
if it works,yes.get away with it-no.can get a 3 1/2 aps of the shelf.think thats as big as i would want anyway,for clearing subframe/cradle etc etc.dont think the neighbours would like the sound of a 5" short spout droning out me evo.

thanks
 

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Discussion Starter #13
T1 RSE said:
For us personally we would only ever go bigger if we felt the exhaust was restricting power output, but as we are only going to be running between 450 - 500 bhp, we are happy with the 3 1/2" APS honey ;)
cheers,i'm running 430 at the minute.hopefully get onto 500 ish with new exhaust and cams.will have a busy week to get ready for the dentist to map at the weekend.

3 1/2 aps it is then :)

martin
 

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it is actually very simple when you think about it. with a NA car you want to tune teh exhuast so you can increase the gas velocity and hence increase the scavanging effect of the exhuast. meaning you want to get rid of exhuast gases as quickly as possible.


so the faster you get exhuast gases out, the faster you can put air ( power ) inside the engine from the otherside of the engine ( inlet).


now think about the turbo charged engine. what do you have at the end of your exhuast manifold blocking your exhuast and causing a big restriction!! the turbo :D so what you are trying to do is the same thing. get rid of exhuast gases from the engine so you can squeeze more air from the otherside. only way you can accelerate this on a turbo engine is reducing back pressure. when you reduce back pressure you also reduce the exhuast gases temperature which is a good thing on a turbo charged car obviously. again that is physics and not my opinion here PV=RT (ideal gas law)


now pressure = force/ area which means the larger the area the less pressure we are going to have.

so best thing for a turbo charged engine will be probably very short very big bore. but obviously that will have clearance, and noise implications. so as in everything in life is a compromise go for teh biggest you can fit in there without too many issues.


again this is not my opinion this is science ;) :D


sam
 

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Been here before Sam haven't we :D:D:D

Bigger is definitely better after the turbo.
Before the turbo is another matter though as you need a combination of exhaust gas velocity and temperature to get your turbo spinning.

Andy
 

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suppose the theory stuff explains the RC devs short side exit very fat exhaust then....
 

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AndyF_RSX said:
Been here before Sam haven't we :D:D:D

Bigger is definitely better after the turbo.
Before the turbo is another matter though as you need a combination of exhaust gas velocity and temperature to get your turbo spinning.

Andy
oh yes, i was waiting for you or ( lexus guy cant remember his name) to post something :D

RC were definitely taking no prisoners with their approach ;)
 
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