Most power made with a single 3 inch downpipe and when does it really start to become a restriction

 

I've made 631whp turbo ls.
565 whp turbo 4g63
680 whp turbo 420" new gen hemi.
735 408w

Don't feel like in any of these cases the down pipe was a restriction. These runs were all made without an exhaust also, exept for the 4g witch was a 4" exhaust.

 

Made over 650 with my first turbo setup.. 316 ford with a t70 single 3 inch down pipe..

 

680whp on 420 cid through a single 3"? I would think it would relate to the turbine size. A 3" on a small cid high pressure ratio would work much better than on large cid with low boost, where the hp is comparable. Thoughts?

 

The 420" motor had a 3.5" outlet flange, but we necked it down to 3" to get it to fit.
that was kind of my point with the post. All these engines were very different and all made decent power through the 3" pipe. So I don't think the 3" pipe matters anywhere near these power levels. turbine flow is way more critical. I have never sat down and figured out the xsection of a turbine before so not sure when the 3" becomes smaller then the turbine.
The old indy cars never had giant downpipes that I'm aware of and were makeing retarded power for thier size.

 

There used to be a guy here that made 900 with (I think) a pt7675 on a 347 through a tremec. Ran well into the nines too. I don't remember what the poster's name was or if he's even still here.

I agree Mnlx, a smallish DP should pose less restriction on a higher pressure ratio app. It also matters how straight the piping is, and length also.

 

Also a consideration is if the wastegate dumps or returns to the DP.

 

I made 737whp on a 4.6 2V at 25psi. I strongly believe the turbine wheel was a bigger restriction at that point, since it seems the same setup is going to make about the same power with 5-6 less psi, a smaller compressor wheel but much better turbine wheel.

I, or the new owner, will update this thread in the spring once it's dynoed but the car pulled a lot harder at 19lb's than before.

 

@wiplash. what size turbo was that?

 

Went 9.27 @ 146 with a 76mm turbo with 3" down pipe at 25 #'s of boost in a 95 mustang at 3450#'s. Back pressure was choking it as 27#'s did not result in any real improvement in et or mph

 

@turbo pony what size engine was that and was that a 7675 or 7668 turbo.

 

It is a 331 with an old school 7675. I have since put something through the exhaust side and killed the turbine so I am upgrading to Reed's BW T-6 80mm

 

840 at the FW.
274" Stage 2 Buick.
3" dp on a GTQ 70 PTE.
Full 2.5" exh, Dynomax turbo muffs.
A 3" dump pipe allowed a 5 RWHP increase when open.