All right thinking of of Doing a diy turbo for my 99 cobra gone to run the stock manifolds and run the pipes forward like the hellion kit. Would you go with 2, 2/14 or 21/2 pipe from the manifolds to the merge looking at gone with a PT 7675.. Car has 03 cobra cams and is a stick with 3.55 other then that the engine is stock short of a forged I beam rods and forged pistons not looking for a all out race car just something that runs better then what this slug does now.

 

id stay on the conservative side with tubing size,, iirc 2" is good for about 900hp

 

It depends on the outlet size of the manifolds. If it's 2.25", then run (2) 2.25" pipes, merging into a 3" section into the turbo.

Is that PT 7675 a T4 or T6?

Al

 

Neck it down to 2" if you want the best spool... I'm running a 370" motor at around 900whp with 2" piping. No reason to go larger on a mild build. I easily spool a 1.32 T6 with 2" piping going to each side of the scroll on an S480 turbo with the big 96mm exh wheel. I have to use all sorts of power management to limit how quickly I build power.

 

Thanks guys kind of thinking the same and my engine builder is saying the same thing he also a turbo head.

 

For a setup that has the turbine close to the motor/header ie within a few ft of the header flange I like to keep stock size of the pipe which is usually 2.25"-2.5" on a v8 header collector depending on application. So forward facing single where both banks merge right in front or low twin where the turbo comes right off the header next to the trans. No lowend loss in spool and overall less back pressure and egt this way especially on a higher pressure ratio setup.

If its a remote mount or has more piping snaking around ie more volume/distance to the turbine, I like to step down to 2" and then flare up to match the turbine flange. This helps with heat loss and the exhaust slowing down when it has to travel 2-3 times the distance to the turbine.

For a drag application no need to shrink size imho as you want max top end with a proper setup.

 

I don't agree.

I can tell you first hand 2.5" spools much slower than 2". For the OP's power goals there is zero reason to go larger than 2" IMO. You would be giving up spool time, and aren't losing any top end at the OP's power levels. Also you can actually run less overall back pressure with smaller piping. The turbo is the restriction, not the 2" pipe before it. By going with 2" and keeping the velocity up you can run a larger turbine housing while retaining the same spool characteristics as a smaller housing. This nets less system back pressure and more power per pound of boost.

 

Some of what I aslo understand the turbo is the restriction and the smaller pipe will help with spool. I was told to remember you only have one exhaust pulse at a time. My engine builder has very small pipes in his 50 Hudson stroker flat Head in line 6. Worlds apart from a mod motor but he is saying it is still a turbo engine and nothing more the a air pump.

 

Don't mean to steal this thread, but figured since you guys were on topic of pipe size. What about the size coming out of turbo to intake? Is bigger better on that side? Or can too big do harm?

 

Same deal, though not as critical. The more volume you add the the system the less responsive it will be.