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?

setxws6

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.

ddelallata

iTrader: (2)

don't listen to him

snake charmer

iTrader: (118)

i run 3 inch on my duals and the ta is running fine

777

iTrader: (21)

go back to this guy and do this

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!

setxws6

Hopefully not a Buick Grand National....if so.....

tim99ws6

iTrader: (31)

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!

TJ

iTrader: (10)

his theory was to increase the size of his exhaust and make yours smaller.
let me guess, he pulled the ole "is there anyway you can drop it off......" routine?

BBQLS1

You would have to be makeing a shitload of power for dual 3inch pipes to be too small. You might loose a little torque from them being so big, but LS1's tend to like big pipes.

soundengineer

iTrader: (16)

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...

tim99ws6

iTrader: (31)

that's interesting that it's a myth, because my dyno results show the exact same results.....

00Z28 Camaro

so 2.5 or 3. for a bolt on car ,this scares me

setxws6

tim99ws6

iTrader: (31)

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.

YsoFast

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?

tim99ws6

iTrader: (31)

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.

Diolar Magnum

he needs to get a new career.

Swang

iTrader: (3)

with the power of an LS1. i wouldnt worry about goin 3 inch, but definitely dont go any bigger.

GuitsBoy

iTrader: (4)

I think youve got the jest of it, but backpressure is not what helps you out, its exhaust velocity. Kind of like over porting a head can kill velocity and hurt power, too big an exhaust can theoretically do the same. Its the reason stepped headers and merge collectors exist. Bigger isnt always better when youre trying to eek out every last possible ounce of power. The slightly smaller 2.5" pipe will boost velocity without creating too much backpressure. The added velocity will create a stronger scavenging effect as the pulses go through the X pipe and down each leg of the exhaust. In order to run at optimum, you shoudl run the smallest pipe without building backpressure. That will keep velocity up and will increase torque everywhere, not just down low.

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)