99corvette

iTrader: (12)

Ok i tryed to search for this, but the stupid search engine wasnt working so i gave up. What is a LS1 Z28's stock exhaust size? Is it 3in?. This guy i know say that his 1995 Z28 came with stock 3in exhaust al the way back, and that mine should too. This just didnt sound right.

RPM WS6

iTrader: (3)

It's not a true 3". More like 2.75" actually. That goes for Z28/Formula/Trans Am/WS6/SS all the same. I've got a stock Z28 and a stock WS6 catback in my basement, they both have the same I-pipe and neither is a true 3". The only difference is, the WS6 system has 2.5" tail pipes and the Z28 system has 2.25" tail pipes.

99corvette

iTrader: (12)

ok does this go for the LT1's too?

RPM WS6

iTrader: (3)

Honestly I don't know 100%, but I would assume so.....

99corvette

iTrader: (12)

I didnt think that our cars came with 3 in stock, because everyone says that putting true dual 3" is a big HP gain

Starz T/A 17

iTrader: (6)

its pretty close to 3 inch b/c a 3in cutout will fit on our cars, but its the crappy bends on the stock exhaust, pretty much all the aftermarket exhausts have ALOT better bends...Maderal is the word im thinkin in lookin for but not 100% sure

JL8Jeff

iTrader: (14)

Stock is 2-3/4" for the intermediate pipe but it does flatten out as it goes over the axle. Most aftermarket exhaust is 3" so that is where the power increase comes from. Some of the SS cars might have a true 3" intermediate pipe since that was an SS option with the optional exhaust.

99corvette

iTrader: (12)

thanks guys

RPM WS6

iTrader: (3)

Right, I forgot to mention that. SS cars with the SLP Y2Y optional dual/dual catback did get a 3" I-pipe.

BLKWS.6

The main issue is that durring assembly my Y-pipe on the driver-side got run over by a fork-lift or other piece of machinery and is like .75" thick. Poor QC. Every LS1 I ever saw seems like the same "accident" occured as well... WHY!? Come on GM...at least make it an oval...

RPM WS6

iTrader: (3)

They are all like that, and beleive it or not, it's really not much of a restriction on a stock motor with stock manifolds and cats. This has been proven by many who have swapped out the stock Y-pipe for something more round like the SLP Y-pipe and have seen little to no gains.

BLKWS.6

Other than the shorty header=stock manifolds, what is the main restriction? Muffler?

ChocoTaco369

just remember that big gains aren't seen from switching to headers and an aftermarket catback or true duals because of flow. the stock muffler is the flow bottleneck, and switching them out results in ~5-10 hp. the reason why people see 35+rwhp gains from headers and a catback/true duals is NOT because of a huge increase of flow, but because of the scavenging you get from the setups. the biggest problem with the stock exhaust is the lack of scavenging, not flow. i've said it before and i'll say it again: flow is overrated. big gains are gained by the scavenging effect, not by adding more unnecessary flow. you can "flow" 400rwhp through the stock catback.

RPM WS6

iTrader: (3)

Even more than that.

One of our club cars was a procharged, big valve heads/custom cam '02 WS6. It had ported (port matched to the heads) stock cast iron manifolds, cat bypass pipes, SLP 2.5" Y-pipe, and the stock WS6 catback. The car dynoed 580rwhp through that exhaust @10+psi with an aggressive tune.

ChocoTaco369

damn, that's impressive. hats off to that guy! it's like being beaten by a gust of air. there's something about a car that'll lay the smackdown on a ferrari without even making a sound that's...well, damn, i gotta change my shorts.

RPM WS6

iTrader: (3)

That is exactly what it sounded like! Imagine taking a large bag of air and squeezing one end very tight. Then, poke a pin hole in the other end and keep squeezing.... that's what the exhaust note sounded like at WOT on that car, only it would take a REALLY BIG bag of air to make that much noise.

Funny part is, I think the exhaust note was more quiet at WOT than at idle. All you got was whooshing air at WOT, but at idle you could clearly hear the cam with a nice little burble through the stock muffler, probably because we pulled the cats. The blower was much louder at WOT than the exhaust.

There's just something cool about watching/hearing an LS1 run a 10 second pass at 130mph without barely hearing it.