kyles2000z

iTrader: (8)

im running mods in sig with a 4 inch collector at the end of the Y-pipe and a 4 inch bullet muffler turned down. how much, if any, would this be affecting me as far as power? ive read the debates on backpressure....some swear by it and others just say its myth on LS1s, so i wanna hear your opinions on this. is it hurting me, or helping me, and by how much would yall guess?

the car, with mods in sig dyno'd only 313 hp, 312 tq and im tryin to figure out why the #s were so low, most people have suggested its bc the huge exhaust diameter with no backpressure. it wasnt a low reading dyno bc a 99 SS with lid/flowmaster made 300 rwhp.

bolton98TA

iTrader: (3)

maybe the tune?
i have a 98 a4 with pretty much same mods and put down whats in my sig before duals.

TheBlurLS1

iTrader: (8)

Some cars just make less, some make more. I'd say it's a tad on the low side, but your exhaust is definatly not the problem. What was the AFR and timing?

kyles2000z

iTrader: (8)

not sure, but it was pretty lean it needs more fuel, A/F was 13.4-13.6 durig the runs. all i know its been tuned by someone who knows their stuff so i didnt think the tune was the problem, although the A/F is off a little.

i was just kinda shocked to see thses low numbers, as other LS1s with my mods are puttin down 335-345 on average.

TheBlurLS1

iTrader: (8)

I'd get that AFR lined out, we make the most power at 12.8, it's also safer for the motor.

kyles2000z

iTrader: (8)

yea when i had it tuned i coulda swore we had it dead on at 12.7 but i guess not.

GeorgeR@kooks

4" is way to big for the car. 3" should be max on an app like yours. We would generaly use 4" on a car making well over 700 hp.look at this set up we did and that car was a 455 ls1.https://ls1tech.com/forums/generation-iii-external-engine/599926-kooks-3-true-duals-over-axle-exhaust.html

Ragtop 99

iTrader: (7)

4" isn't necessary for bolt-ons but if the y-pipe was designed properly with a true merge, it isn't a problem. The worst it would do is kill some low end torque by reducing exhaust gas velocity, but it wouldn't really hurt top end HP.

What brand of dyno?

kyles2000z

iTrader: (8)

it was done on a dynojet.........the exhaust, i got it as a package deal with the LTs so i didnt bother swapping it out. its a 3 inch ORY with a 4 inch flowmaster merge and then the bullet. it does sound verrry nice tho, i dont wanna loose the sound!

01 Red WS6

iTrader: (4)

I don't think the 4" is too big. When you look at all the people that run 3" true duals with just bolt ons I think 4" would be about the same level with the right merge. I've seen cars make about the same HP with true duals or a nice 4" setup. I think they may lose a little torque but the HP should be close to the same

Cop Car

iTrader: (14)

3 inch true dual setup on a bolt on car didnt seem to hurt my friend... 4 inch wouldnt be too much IMO

LSGunZ28

iTrader: (8)

Some say its a myth? some say its different on LS1s?

lol...


doesnt matter, the way a car works is still similar.

Backpressure is an unwanted thing... what you mean is scavenging and Honestly I dont think after the headers much scavenging is needed anymore for optimim performance..

lsx24

iTrader: (45)

Actually Dual 3" flow much more than a single 4". So no it shouldn't be any different than 3" duals.

ATwelveSec02Z28

iTrader: (17)

Im running a bolt on car - The exhaust is Kooks 1.75" stepped to 1.875" with 3.5" collectors. The Kooks Y pipe has 3.5" sections at the header ends reduced down to 3" tube with a 4" collector for the mufflex catback.

Lots of people will say its too much exhaust, but with this I've been 11.42@119 with an M6 and just bolt ons. So Im all for bigger is better (within reason)

kyles2000z

iTrader: (8)

thanks for the input guys, i guess i'll leave it on there, cant beat the sound anyways!

JohnnyC

wldesyWS6

iTrader: (2)

if thats the case then why are people so against running just bullets off the headers like i wanted to, cuz if what you said was true, who wouldnt just run bullets or pipe off the headers besides the noise factor/choking exhaust fumes i mean besides headers exhaust would be around $130 and less weight to, wana explain that or is the noise factor/exhaust fumes thing really the only reason nobody does it?

bad6as

iTrader: (17)

did you dyno it with the z06 rims on?
hows your plugs/wires and air and fuel filter look?
what was the temp and humidity that day?
did you do the runs in 4th?
thoes sae numbers?

JL ws-6

iTrader: (50)

The fastest ls1's, wether they be bolton, or full blown race cars are running open headers, maybe a bullet muffler and a turndown, no x pipe, no h pipe, nothing. Hell the fast turbo cars run an open downpipe.

the 4 inch is not hurting you. It's not really nessasary at your level, but it's not causing you to lose power where it matters in the powerband when you are racing.

jam01

yes it does matter.