why would they use 2.5" pipe from LT headers
TECH Fanatic
Joined: Jul 2007
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Im not talking need, im saying that 3" pipe will actually hurt flow if the motor doesn't need that much. There is a point where having too big of pipe will hurt flow. Bigger isn't always better.
I dont care what size pipe "supports" what power level. Supporting is one thing, but its crazy talk to say that 3" pipe will not make more power than 2.5" on an LS1 motor stock or otherwise. How much more? Maybe only a little, but it will make more and it will continue to make even more difference as the engine is modified.
TECH Addict
Joined: Mar 2009
Posts: 2,099
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From: Texas/Afghanistan
i ran 3" true duals on my car when it had a completely stock motor...it didn't hurt a thing. then with cam only(224r) it dynoed in the 370's. and its a 2000 so it had a shitty intake, and shitty injectors.
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...
I dont see it as a huge deal on a stock internal car. like what was stated above, 3" collectors or larger shouldn't be necessary on anything making less than 400hp. The headers on my 5.3 have 2.5" collectors.
The merge on the y pipe is def the major problem on the sound when it gets raspy under decel. Under acceleration it sounds fine I just wish it was louder I miss the pure grunt when it only had headers I guess. I am gonna run this Y pipe for now maybe just replace the merge or change the whole Y pipe. The mege is a 180 pipe that has a cut out in the peak to fit the 2 sides into the I pipe.
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Verdad Gallardo
Joined: Nov 2003
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From: Wichita KS / Rancho San Diego
His results speak for themselves. It doesn't matter whether the Y pipes are 2.5 or 3.0 if they both choke down to one 3". The greatest point of restriction is at the single 3" I-pipe - no matter how big the pipes are going into it, flow can't be any better than the single 3" I-pipe can accommodate.
Bigger isnt always better.... ever hear of stepped headers? Their is a reason we dont all just slam 1 7/8" primary headers on all of our cars. The idea is to run the smallest pipe while still allowing the most flow possible. It promotes torque... FACT
Joined: Aug 2007
Posts: 24,241
Likes: 89
From: Turnin' Wrenches Infractions: 005
I 100% agree with you as I bought my car with Hedman Torq-step headers. Mid range was insane. However, after running a tr-224 and then switching to a full non-stepped 1 3/4 primary, midrange was down, but I feel above 5k I picked up 10-20 hp. You could feel the pull difference. Also, there is a reason they call it stepped headers and not stepped exhaust. Most would agree, that stepping the exhaust down the line is not near as beneficial as a stepped header, for obviously heat/velocity reasons. And btw, I dont regret one day ditching the Hedmans.
Last edited by 01ssreda4; Apr 24, 2010 at 01:21 PM.
His results speak for themselves. It doesn't matter whether the Y pipes are 2.5 or 3.0 if they both choke down to one 3". The greatest point of restriction is at the single 3" I-pipe - no matter how big the pipes are going into it, flow can't be any better than the single 3" I-pipe can accommodate.
Joined: Apr 2004
Posts: 1,378
Likes: 14
From: Atlanta, GA Ft. Walton Beach, FL
agree w/ 2.5 I agree on a Y 2.5 creates faster flowing exhaust compared to 3"
you need the backpreasure.
even the ricers haven't
figured this out those giant coffee cans reduce the backpreasure.
I would be more concerned w/ what or how they made the Y was it madel bent? did they flange it for removal slip on's w/ band clamps don't seal that great. post images.
here's a image of mine 3" reducers into 2.5" Y Mandel bent into flowmaster merge out to Hooker cat back.flanged front and rear
BTW a Y will sound a bit raspei.
good luck.
you need the backpreasure.
even the ricers haven't
figured this out those giant coffee cans reduce the backpreasure.
I would be more concerned w/ what or how they made the Y was it madel bent? did they flange it for removal slip on's w/ band clamps don't seal that great. post images.
here's a image of mine 3" reducers into 2.5" Y Mandel bent into flowmaster merge out to Hooker cat back.flanged front and rear
BTW a Y will sound a bit raspei.
good luck.
Last edited by badmfkr; Apr 23, 2010 at 04:45 PM.
TECH Addict
Joined: Apr 2009
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If I was op I would just keep the 2.5. Imo I dont think it would be worth the extra money for the extra gain if any.
When i called New Era about the Dynatech's only having a 2.5" y-pipe they told me
there's only a difference of about 5-6 rwhp between a 2.5" y-pipe header system from Dynatech and a 3" header system from American racing. So i guess unless you're looking
for every single HP then it's not a big deal. I had FLP headers for years and ran good times for the small heads/cam setup that i had. Plus there were alot of fast cars that ran MAC headers. Alot were in the 10's. But if i installed a 427cid in my '02 SS then i probably would opt for the larger header/y-pipe setup.
there's only a difference of about 5-6 rwhp between a 2.5" y-pipe header system from Dynatech and a 3" header system from American racing. So i guess unless you're looking
for every single HP then it's not a big deal. I had FLP headers for years and ran good times for the small heads/cam setup that i had. Plus there were alot of fast cars that ran MAC headers. Alot were in the 10's. But if i installed a 427cid in my '02 SS then i probably would opt for the larger header/y-pipe setup.
Joined: Aug 2007
Posts: 24,241
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From: Turnin' Wrenches Infractions: 005
Maybe on a completely stock car. As you mod down the road, and the engine needs to breathe better then what they told you was nowhere near accurate. Classic marketing.
i agree. there is a point in exhaust size where you go from fire breathing muscle car sound to rickety *** farm truck sound. 3 inch just sounds better than 2.5 inch period.
I personally never worried that i only had a 2.5" y-pipe on my FLP headers.
Back in the day there were debates about the y-pipe size, but there were a lot of cars
with MAC headers and FLP's that ran in the 10's. I wouldn't have a problem buying a set of Dynatechs with their 2.5" y-pipe and 3" merge. Unless I was going with a 427cid then i would definately want a larger y-pipe.
Back in the day there were debates about the y-pipe size, but there were a lot of cars
with MAC headers and FLP's that ran in the 10's. I wouldn't have a problem buying a set of Dynatechs with their 2.5" y-pipe and 3" merge. Unless I was going with a 427cid then i would definately want a larger y-pipe.