I getting ready to order my exhaust pipes. i just put on a set of hooker long tubes. Now i plan to run a tru dual set up in oval pipe. Aside from the obviouse delema of routeing the system what size pipe would be best. The engine is a fully built tpi engine intercooled super charge, with a red line of about 6000. estmated hp is around 380 to 400 at the wheels. Is 3" too big dual, should i just go 2 1/2. I dont want to loose any bottom end torqe.

 

2 1/2

 

you are the first person I have ever read to say...2.5 exhaust for a built motor pushing 390+ rwhp...

why?

 

I have seen alot of cars with 2 1/2 inch exhaust. I would use anything with about 500hp and under 2-1/2 and anything over 3 inch.

 

I am in the same spot right now and talked to a guy I know who has done performance exhaust for years now.

He just came back from a school in Ohio and they had a mock up with a clear adjustable diameter pipe with back pressure , velocity , and flow meters .

They tested with a given CFM comparable to a 400 or so hp motor and colored the air going through the pipe .

They started out w/ 2.5" and had a steady flow .
When they went to 3" you could see the pulse start to swirl back ( reversion I believe is the term ) toward the " motor" . The velocity dropped and the back pressure increased .

You would not think that short of a pulse would make a difference but seeing is believing.It is just enough to kill the velocity which is needed to draw the "dead"air from the exhaust pulse.

He said he has seen hp loss when going bigger and now understands why.

You may not notice the small hp loss but I want all I can.

He also has a GN w/680 HP to rear wheels on 2.5" pipes.so I know I'll be good w/ my little 450 hp baby.

Now I am still learning myself so this is just second hand knowledge but I'm in the HVAC field and understand CFM , velocity and flow and it makes sense to me .

He suggested 2.5 from the headers to the cat into 3" single to be good to 600 hp or so and still be legal.

As said just passing some 2nd hand knowledge I'm sure others have their own opinion.
Please tell me if this is wrong and why it is .

good luck Mike

 

hmm> that is very interesting.........I still have yet to run my exhaust on my 383.....but I will have it going to a 3" Borla catback. My exhaust consist of 1 3/4 long tubes, no cat....so after reading this ....Im stuck with what to do.

I need to run the pipe from the headers to the y-pipe and then to the 3" tube of the Borla system.

 

Nice post raptor....I live in Ohio too...Hmm anyone know any exhaust shops in Ohio...that can make me a custom y-pipe?