FI 70mm or 76mm exhaust?
 

hi!

I am building a Stage 3 Turbo GT86 with fully built engine and a GTX30/35 turbo. The goal is 500whp, I'll track the car and get the supporting mods obviously.

I am planning to get a full exhaust from Amuse, the R1000. It is 70mm. It is much larger than the stock, but most high power FI guys run 3" (76mm). There is an awesome deal on a used in Europe on the R1000 full titanium exhaust though and LOVE the sound of it!

Downpipe will be 3" for sure.

Will that be a limiting factor? Does that 6mm matter that much?

Another option might be to put an electronic valve somewhere that releases more exhaust on track, but flames under the car are never good, and that would mean more problems...




I tried to look for full titanium 3" exhausts but only the Expreme 80S which is a straight piped single exit and I do not like that.


Thanks for the suggestions :)

No, it’s not going to matter. On turbocharged cars, bigger diameter piping is more beneficial the closer it is to the turbo

Also if bigger piping is used on catback/axleback side, one has to be ready for sometimes too loud result. For example perrin 3" resonated often mentioned as loud as 2.5" unresonated. +1 for not worth it.
Better think of more robust gearboxes to handle 500whp :)

Thanks!

I think I'll be going with the Amuse then! :)

Yup, gearbox is in the plans as well! That is going to be the hardest part.

~18% more cross section area. now what that does for performance, no idea

I'm curious, why is the Amuse exhaust your only consideration? Most expensive does not mean the best. Just wanted to float this out here, since $3,000 could go so much further on an FI build than titanium exhaust

Yes, that is why I asked how it affects it on the practical side. :) Hope someone tried it...

Yes, I did. Titanium exhaust cost less only with the single exit huge diameter version. There is almost 20k going into the build with the GTX30/35 turbo + fully built big valve engine + oiling upgrades so there is no expense spared already :)

I love how the amuse sounds of all, there is a good used one for much less than 3000 and that is the reason I'd go that way.
The only thing that would make me choose a different one is if it would be a huge issue performance wise. -5HP loss at 500whp is ok. -100 is obviously not :)