2.5" or 3" Y-pipe with LTs?
Thread Starter
Launching!
Joined: Dec 2001
Posts: 222
Likes: 0
From: DFW, TX
2.5" or 3" Y-pipe with LTs? 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?
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?
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
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.
Thread Starter
Launching!
Joined: Dec 2001
Posts: 222
Likes: 0
From: DFW, TX
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.
Originally Posted by 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.
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
Originally Posted by 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.
Thread Starter
Launching!
Joined: Dec 2001
Posts: 222
Likes: 0
From: DFW, TX
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.
Unfortunately, we know of no accurate way to calculate optimal exhaust pipe diameter. This is mainly due to the random nature of an exhaust system -- things like bends or kinks in the piping, temperature fluctuations, differences in muffler design, and the lot, make selecting a pipe diameter little more than a guessing game. For engines making 250 to 350 horsepower, the generally accepted pipe diameter is 3 to 3 ½ inches. Over that amount, you'd be best off going to 4 inches. If you have an engine making over 400 to 500 horsepower, you'd better be happy capping off the fun with a 4 inch exhaust.
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Originally Posted by 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.
I don't know about the validity of this statement but if it's true I'm hosed, 4" will never happen.
I'm glad I went for the 3" TD's
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