I was just wondering weather to change my down pipe from a 3 to a 3 1/2 with my new set up as i have more porting and a bigger exhaust housing.
I have seen people get very good power with a 3 inch but also a lot of people seem to be using 4 inch now
What do you think?
Bigger will give you more power potential..... My theory is, go overkill then you wont have to upgrade the componant again!!!
Jono
DirectFreak\'s FB with a Cosmo 13B RE lump in it was running 460 RWHP with a 3" exhaust - see here (http://www.youtube.com/watch?v=Suut7tcLOPo) :D
the thing thats worrying me is with the large exhaust housing and BIG ports i dont want it to be too laggy, a more moderate sized exhuast can help it spool a little quicker at the expence of top end power. Although Bramble\'s B/port had a 3 inch exhaust when it made 527 rwhp so i know i should still make good power but i will probably make more with a bigger set up.
The second half of my system is plenty big enough as its two 3 inch pipes from the middle back to two 3 inch straight through rear boxes.
Ooooo that sounds interesting mate..... any pics of your system??
Jono
I\'m looking for 400 ATW\'s so i should be able to do it .........hopefully
its a turbo II, i like the twin exit. 3 inch down pipe into a 3 inch straight through mid box into a Y splitting to 2 more 3 inch pipes to the back
Depends on the tubby your gonna run.
Fish
gt35/40, T4 flange with a .72 comp side and a 1.15 hot side
The t4 flange will help spool up anyway Tony. The 3inch will cope with those sort of power levels but don\'t forget a smaller pipe also keeps the heat in and around the engine where a larger one helps get it away.
Kevin
if it is enough for at least 400hp (as has been shown above) why worry, going bigger will just make it harder to fit in and cost more (slightly) I\'m not entirely sure on turbo\'s but the turbine works as a complete system with the exhaust and is not isolated from it totally ... so it is possible that there is an optimum size and going too big will loose out. You probably know more about it than me (no turbo expert, just thinking aloud) but my £0.02 worth :)
I would say 3" is fine. As the exhaust gas expands on it\'s journey down the exhaust so you have already catered for this with your 2 3" pipes :bandit
I used to have a nice looking but restrictive cat back exhaust on the FD. It made 300FWBHP (would have been around 320 but we never fine tuned it) and its internal bore was just 1.7 inches!!!!!!! :eek :eek :eek
You cannot lose out by going bigger.The only way you can cause a problem is by going too small,or having a poor flowing exhaust,flow is crucial,so nice smooth Mandrel bends are key.
A bigger downpipe does not affect spool up,in fact it may just improve it slightly.
Since the exhaust is after the turbine,even running NO exhaust can only offer improvement.
Put the biggest you can in as long as it is not too much like hard work.
Regards
Carl
Think of drag cars with virtually no exhaust at all on the turbo\'s!
Regards
Carl
Just because an exhaust is after the turbine does not mean it does not affect it, the turbine and exhaust work as a coupled system
In a N/A Mike then yes you\'re right as it relys on the exhaust pulses to scavenge the next batch of exhaust gasses to improve power levels but with a turbo motor the golden rule is back pressure is bad so anything at all that you can do to reduce it is the way to go. Hence why my new set up is 5inch downpipe and twin 3inch main pipes with not a baffle in sight.
Kevin
when you change from one pressure and gas speed to another such as at the exit of a turbine, the interface is very crucial. If you look at an intake on a supersonic jet you will see an inlet diffuser that helps the transition from very high speed (high dynamic pressure) air to much slower but higher static pressure air. The same is true at the exit of a turbine where the gasses have been expanded through the turbine to a low pressure and are being vented back to atmosphere you can improve the efficiency of the turbine by carefully controlling the diffusion of the exhaust.
Reason you don\'t see it in drag cars ... they don\'t have the budget to exploit it?
Lots of cars running 400 with 3" exhaust, when tuning the yellow one it was decided the exhaust was the restriction - on went the 4" and saw an imediate increase, I think bigger is better :D
The exducer on a turbocharger is already designed to be pretty efficient.
That is the part that helps the turbine to work really well.
Of course everythiung can be improved on,but in the case of a turbo,there is no real need for an exhaust for it to be optimum.
Regards
Carl
that makes sense then, didn\'t realise a turbocharger has a built in diffuser in the housing. Interestingly Greddy call their downpipes diffusers rather than downpipes.