I'm about to finish my build and I have a 3" downpipe but the Waste gate dumps into it and the turbo I'm getting is v band the downpipe is 4 bolt. So there are some modifications that need to be done for the downpipe to work.

That being said I was thinking about just going for a new 4" downpipe. It's a h22 fully built (fully built head, sleeved, cp pistons, ect). A Borg Warner S366 ETT will be going on and I'm shooting for 550whp on pump and maybe 650whp race gas.

What do you guys think 3" or 4" downpipe?

Thanks
Matt

 

4" wouldnt hurt'...depends on your budget....personally considering your set-up at hand i doubt the budget is much of a concern...id just go 4"....

 

do you run exhaust? id just keep the 3" unless you dont run any exhaust

 

Yeah I'm going to be running exhaust IDK which one as of right now.

Thats another qustion I had. If I did go with a 4" dp would I have to stay 4" all the way or could I taper down to 3".

 

550whp on pump? Hope you have a great tuner thats real high....id stick with 3" or go with 3.5" if you have clearance issues

 

There's no reason too run a full 4" exhaust. If you need to relieve that much back pressure, don't run an "exhaust system" at all. On an S366, 4" will not help you any.. 3-3.5 is all that is necessary. 550whp on pump gas with an S366 is highly unlikely. That is for race fuel.

Good luck.

 

Jef Evans is my tuner... Why is 550 unlikely?

 

ON PUMP GAS... Not likely because you will get into detonating territory from the fuel being used. I responded to your PM about it.

 

alot of people use 4" to help spool the turbo faster, the s366 flows pretty nicely, its what i have and i went from a 3" to a 4" and it spooled 500rpms faster, and as far as clearence issues go, i made mine and when i was done fabbing it i put the part under the oil pan in a vice and pinched it