why would they use 2.5" pipe from LT headers
why would they use 2.5" pipe from LT headers So I installed some pretty sweet headers last week but the company didnt have a y pipe for it until now. So I went and had a custom exhaust shop finish it off and they used 2 and a half in piping and its raspy and not loud at allll So im pissed. I am thinking of getting the y pipe and getting a flowmaster merge and go back and tell them to put that instead. The question is am I wasting my time by spending all this money or is it worth it for power and sound?
I just dont understand y an exhaust shop would use 2.5 inch pipes when the header collectors are already 3 inches its just stupid that they would do that and restrict me.
Joined: Aug 2007
Posts: 24,241
Likes: 89
From: Turnin' Wrenches Infractions: 005
yea I am pissed and wish I just would have waited and not wasted my time there so I just bought the Y pipe and I am gonna tell them I want them to install it at no cost.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
...and they will look at you like you've got an arm coming out of your forehead if you even speak about 3" pipe. They've got so many "backpressure" stories under their belt and most of them assume that your car has a 350. 2.5" exhaust has been about the standard size for muscle cars over the years, and unless they've been around LS performance stuff then it's pretty safe for them to assume that you just want them to do what they've been doing to muscle cars for years.
2.5" wont kill your power too bad. You'll have good ground clearance...
TECH Fanatic
Joined: Jul 2007
Posts: 1,516
Likes: 0
If you read a lot about exhaust pipe, having 3" pipe on a motor not needing 3" it will actually hurt flow. Backpressure isn't the only thing to think about.
If you have an exhaust pipe that is too large, it will decrease the amount of heat inside the exhaust pipe. Decreasing the heat inside the exhaust will decrease the velocity. If you have 2 pipes, 2.5 inches is good for up to 500 bhp. 2 3" pipes is good for a motor creating around 700 bhp. Going too big will hurt flow, I have heard this many many times from engine builders.
A customer of ours has a program on his computer that will calculate power for a given engine combination and it is usually close ( within 5%). With that program you can change header primary size, length, and collector size. You can also change exhaust pipe size and length.
We were building an exhaust for an impala with a 502, 500 bhp. Changing the exhaust from 3" to 2.5" created no loss in power. The rasp your are experiencing is most likely in the design of the Y, not in the size of pipe.
If you have an exhaust pipe that is too large, it will decrease the amount of heat inside the exhaust pipe. Decreasing the heat inside the exhaust will decrease the velocity. If you have 2 pipes, 2.5 inches is good for up to 500 bhp. 2 3" pipes is good for a motor creating around 700 bhp. Going too big will hurt flow, I have heard this many many times from engine builders.
A customer of ours has a program on his computer that will calculate power for a given engine combination and it is usually close ( within 5%). With that program you can change header primary size, length, and collector size. You can also change exhaust pipe size and length.
We were building an exhaust for an impala with a 502, 500 bhp. Changing the exhaust from 3" to 2.5" created no loss in power. The rasp your are experiencing is most likely in the design of the Y, not in the size of pipe.
Teching In
Joined: Aug 2009
Posts: 29
Likes: 0
From: Minot Nd
My input is that for my loudmouth it is 3" in an 2 3/4 out. I could run 3" in and out but how would that help its still going down to 2 3/4 on the way out. In a true dual setup it would be worth 3" all the way back with 3" mufflers if I had the power to support it.
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
There's nothing wrong with using dual 3" into 2.5" reducers into a single 3" I-pipe with a good merge. You maintain good velocity and gradually reduce down. It's much better than most of the old style Y-pipes that slammed two 3" into one 3" and then reduced down to 2.75" at the I. That is your greatest point of restriction, not the dual 2.5" pipes going into the merge.
Man, does anyone have a dyno graph of the exact same car laying down numbers with a 2.5" system, and then once again with a 3" system?
I'd be really interested in seeing just how much power you give up in the 4k plus area with a 2.5" setup, on a car with over 500fwhp.
I can only imagine that the city-driving-torque would be better on the 2.5" setup... but how much less would it pull up top on a car that "exceeds" the 2.5" threshold?
In other words, how different would a 450rwhp car feel (or trap) with a full 3" vs a 2.5" setup. I see half an inch of ground clearance being worth the a few ponies, but not a tenth of a second...
I'd be really interested in seeing just how much power you give up in the 4k plus area with a 2.5" setup, on a car with over 500fwhp.
I can only imagine that the city-driving-torque would be better on the 2.5" setup... but how much less would it pull up top on a car that "exceeds" the 2.5" threshold?
In other words, how different would a 450rwhp car feel (or trap) with a full 3" vs a 2.5" setup. I see half an inch of ground clearance being worth the a few ponies, but not a tenth of a second...
TECH Fanatic
Joined: Jul 2007
Posts: 1,516
Likes: 0
There is a point where 3" duals will help power, but if you have under 500 fwhp it isn't necessary.
I guess there is no turning back now that I bought a y pipe from the people who make my headers. I will probably run this 2.5 inch setup until summer nationals when I am gonna cut it all out for the weekend and then install the better y pipe in.
Joined: Aug 2007
Posts: 24,241
Likes: 89
From: Turnin' Wrenches Infractions: 005
A tenth of a second? Really? How many people on here are worried about a tenth of a second? Let me reword that, how many people on here should be worried about a tenth? On a street car, a tenth of a second shouldn't really matter. That is a drivers error amount of time.
There is a point where 3" duals will help power, but if you have under 500 fwhp it isn't necessary.
There is a point where 3" duals will help power, but if you have under 500 fwhp it isn't necessary.
