I know with piston vehicles it helps to have some back pressure. If you have to little back pressure on a TII can it cause the turbo to spool much later in the RPM band?

 

Piston or rotary, with a turbo it doesn't make any difference. The turbo already provides a lot of backpressure, and after the turbo you want as little resistance to flow as possible.

 

Hmm, .... K thx.

 

I'm not a piston engine guy, but as I understand it, they need some backpressure to prevent burning of the exhaust valve. Obviously, rotaries don't have this problem. You want as little backpressure as possible, but that doesn't mean to just stick a 4" pipe on there. You need to tune the size of the pipe to preserve velocity, which will increase the scavenging effect. More of an issue for NAs, since in turbo applications you just want to move as much exhaust throught the turbine as necessary, hence the thick downpipe....

 

with a turbo think of it this way:

its the difference in pressure that moves the blades (partly), the lower pressure you can put on the exit side of the turbo blade the better

on an na aaron is right

 

My turbo seems slow to build boost, I wonder if its because I dont have my DP hooked up to my cat?

 

Hook up your cat, and let me know the results

 

my friend has a mkIII supra and just has a 2.5" dp... nothing after it(he says he's too poor to finish it). Anyways, besides being loud as hell, you can hear that turbo spool up crazy fast and once he's into boost all you can hear is turbo. It's definately an experience

 

One thing I was wondering about...how come the down pipe for the good RB exhaust is 3" when the outlet of the turbo is like 2.5". kinda seems pointless to have such a large pipe when the weak link in the chain is the turbo outlet. Just a thought.

Craig

 

It's not the weak link in the chain at all... the outlet of the turbo is 2.5in because that is (close to) the size of the turbine blade, besides any dump pipe built even by a half reputable company should actually have the flange end that goes into the turbo as 2.5in or whatever and then expand to 3in, or however big you think you need to flow a certain ammount of air at a certain RPM while keeping a certain velocity..

You want as large as possible pressure difference over the turbine blades to turn the turbine... like j9fd3s said.

Basiclaly to get the turbo spooling quickest, NO dump pipe at all would be best, trust me, I drove my car 15km's on my way to the exhaust shop to get my dump-pipe made up, and it spooled incredibly quick, also sounded awesome

And on an N/A engine you'd want as least as possible restiction past the tunned section of the exhaust, ie. after where the manifold. meets the collector.... but as has been said already, just whacking ahuge pipe on there or even venting striaght to the atmosphere may cause too much turbulance and that would make it restrictive.

 

Actually, I got under there and it was hooked up. Just no gasket between. I think it just seemed kinda slow because my timing was a but retarded.