weestro

I've read and searched ad nauseam and can't find the answer I'm looking for. I'll be doing LTs soon and will be building a custom pipe to tuck nice since I'm lowered. Duals are out because I'd want to run them out the back and that exceeds the budget for this so I plan to keep the B&B. I see that a lot of people run 3" Y's merged and run through a single 3" catback. It SEEMS that two 2.5" Y's merged into a 3" catback would make better use of the single 3" I-pipe. But what does the motor really need?

Here's what I'm thinking:

1) reduce at the header collector to 2.5", run 2.5 pipes through 2.5" Random tech hi-flows, merge into a 2.5x3" collector.

or

2) 3" Y, 3" cats, merge into 3x4" collector and reduce to 3" at the outlet


I want good flow and clearance and don't want to restrict the motor when it's time to run a cam in the future. Does anyone have any data that supports the use of 3" over 2.5" when merging into a single 3" pipe?

Other thoughts?

RevGTO

iTrader: (12)

Read this thread: https://ls1tech.com/forums/generation-iii-external-engine/394839-how-much-power-can-2-5-ypipe-handle.html. To me the idea of going from 3'' collectors to 2.5" Y to a 3" I pipe seems like a better way of managing flow than to squeeze dual 3" down to a single 3" at the I pipe.

eric01ss

iTrader: (13)

get the 3 inch

weestro

Thanks Rev, yeah I ran across that one in my searches, good stuff! I was just hoping for more "expert" data that, for instance, backs up the claim that 3" piping isn't needed until 500PH, etc... The only thing I can find here or on the web is info on sizing the primares.

rollinna65

iTrader: (18)

I think that you're thinking of 3" true duals with the whole 500hp thing. A 3" y-pipe and catback should be just fine on a stock motor.

RevGTO

iTrader: (12)

Isn't there a link in one of the posts on that thread to some "expert" type theory on that kind of thing?

weestro

There was one from an NSX site that makes this statement:

I don't know about the validity of this statement but if it's true I'm hosed, 4" will never happen.

rollinna65

iTrader: (18)

If this is true than you really shouldn't go anywhere past stock with a 3" exhaust. I don't think this is true unless your exhaust is bent and wound of like a coil spring.

I'm glad I went for the 3" TD's .

Viper

iTrader: (6)

I'm lowered and went 2.5" headers ( Stainless Works makes them ) to a 2.5" y-pipe to a 3.5" exhaust. No scraping or banging over the rear.

weestro

Nice numbers Viper! I guess the pipes flow plenty for your cam...

Viper

iTrader: (6)

Thanks

With 3" flp and 3" y-pipe 4 years ago , TR224 112 , S2 heads made 400hp, 380tq.

Combination, combination...