don't listen to him 
????????????????
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Launching!
Joined: Apr 2005
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From: Thornton, Colorado
???????????????? While checking my exhaust, some guy at this exhaust shop said putting 3" piping is robbing horsepower from the LS1. I have 2 cats and 3" str8ts, and for damn sure I felt the power. Is this guy right? Or just need to find a new career? 
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Joined: Oct 2003
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From: Lumberton, TX
He doesn't have any idea. I have a 3 inch off road y-pipe leading into a 3 inch maganaflow catback with a cutout. Most guys do it. You won't loose any thing with a 3 inch.......Now if you start getting into 4 inch and higher, well, that's too much. Most guys that have 4 inch exhaust have built motors or at least have a heavy heads and cam package. Go with 3 inch and fire your exhaust guy.
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well. His theory is to increase backpressure, and in effect bring the torqu into a more useable range. 2.5 is probably plenty big enough to flow for bolt-on cars. They trick is the bigger the piping, the less the backpressure, the slower a car "feels".....it actually will increase Hp by freeing up backpressure, but with a larger piping, you'll lose some bottom end tq. That's why some guys think that when they open their cutout, their car "feels" slower, but in actuality, you're just sacrificing bottom end torque for top end hp.
The guys theory in effect has some merit, but i seriously doubt he'd be "doing you a favor" by dumping a 3" exhaust for a 2.5 exhaust!
The guys theory in effect has some merit, but i seriously doubt he'd be "doing you a favor" by dumping a 3" exhaust for a 2.5 exhaust!
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Originally Posted by 150shotWS6
Yeah he was saying he would switch my 3" out for 2'5 for free "to do me a favor".........what an *******.. he probably drove a Buick or something! 
let me guess, he pulled the ole "is there anyway you can drop it off......" routine?
TECH Enthusiast
Joined: Nov 2004
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From: Red Stick, LA
Originally Posted by 150shotWS6
While checking my exhaust, some guy at this exhaust shop said putting 3" piping is robbing horsepower from the LS1. I have 2 cats and 3" str8ts, and for damn sure I felt the power. Is this guy right? Or just need to find a new career?
Originally Posted by tim99ws6
well. His theory is to increase backpressure, and in effect bring the torqu into a more useable range. 2.5 is probably plenty big enough to flow for bolt-on cars. They trick is the bigger the piping, the less the backpressure, the slower a car "feels".....it actually will increase Hp by freeing up backpressure, but with a larger piping, you'll lose some bottom end tq. That's why some guys think that when they open their cutout, their car "feels" slower, but in actuality, you're just sacrificing bottom end torque for top end hp.
The guys theory in effect has some merit, but i seriously doubt he'd be "doing you a favor" by dumping a 3" exhaust for a 2.5 exhaust!
The guys theory in effect has some merit, but i seriously doubt he'd be "doing you a favor" by dumping a 3" exhaust for a 2.5 exhaust!
ok..the "loosing low end torque" thing is a big MYTH.... I can tell you from experience that any freeing up of the exhaust crates more torque at ALL Rpm ranges...you do however usually see more gains up top than you do down low..... and you can correct much of this with a little tuning...
just try richening up the low end a little and add a couple of degrees of timing...sometimes you dont need to add any timing at all.... but you can get a little more torque down low with a little bit more fuel with longtubes...
More than anything, it's the restrictions in the exhaust that are what will gain/lose hp/tq. That's why Lt's are such a great upgrade. They are built to scavenge air. The same goes for aftermarket exhaust. I would be willing to bet that a well built 2.5" system would be within 2-3hp/tq of a 3"system at the bolt on level. Just buy quality stuff that has been tested here on ls1tech, and proven to work, and you'll be fine.
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Joined: Apr 2004
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I dont want to highjack but I am having the same problem with picking headers for my Iroc with an LS1. Hawksthirdgen made 1 3/4 to 2 1/2 collector LT for the conversion cars but I am building a 383 LS1 with a G5X4 cam, 90mm intake/TB and think it will need bigger headers. So will these LTs kill my setup and should I have a custom 1 7/8 to 3 collector made?
It will definately be the restriction in that setup, but it's not somethng that will RUIN your setup. I'd run them until someone came out with a off the shelf 1 7/8-3" collector setup. I think the biggest restriction will be the collector. In a large cam, i'd like to see at least a 3"collector. Have you tried calling hawk's and seeing if they'll install a 3" collector instead of a 2 1/2'??? That's the only place i think those headers would be insufficient.
Originally Posted by tim99ws6
well. His theory is to increase backpressure, and in effect bring the torqu into a more useable range. 2.5 is probably plenty big enough to flow for bolt-on cars. They trick is the bigger the piping, the less the backpressure, the slower a car "feels".....it actually will increase Hp by freeing up backpressure, but with a larger piping, you'll lose some bottom end tq. That's why some guys think that when they open their cutout, their car "feels" slower, but in actuality, you're just sacrificing bottom end torque for top end hp.
The guys theory in effect has some merit, but i seriously doubt he'd be "doing you a favor" by dumping a 3" exhaust for a 2.5 exhaust!
The guys theory in effect has some merit, but i seriously doubt he'd be "doing you a favor" by dumping a 3" exhaust for a 2.5 exhaust!
What does all this mean in the real world? Probably nothing. Any change between 2.5" to 3" pipe would be well within the dyno's margin of error, as well as within any drivers variance. The guy isnt necessarily trying to screw you over, but he is a little irrational about how much it will help you (not likely any at all)