Bowtieman4life

iTrader: (1)

LS1 Speed makes a catback in 3.5 and 4 inch. You can choose a Flowmaster or Spintech race muffler. Has anyone seen gains from increasing the exhaust size?

I8AFORD

iTrader: (4)

Mufflex makes a 4inch system. You can choose from a flowmaster or spintech muffler

Bowtieman4life

iTrader: (1)

Perfect! WHere can I buy it. What kind of gains can I expect running a 4 inch catback. I am thinking of running a 3 inch into 4 inch collector.

boomcase

That is a huge pipe do you think you really need that.

Bowtieman4life

iTrader: (1)

My car makes 400 RWHP and 380 RWTQ. I've read that anything over 350 hp requires a 3 1/2 or 4 inch. I just want to know if anyone got decent gains from this mod.

NIRVANA

4" is probably too big. The LS1 likes a little backpressure. I would say anything over 3.5" is not going to help you much if at all.

1999_SS_M6

People are going nuts with the big pipe craze.. The rule of thumb has always been when to go from 2.5" to 3" based on HP. The consensus is, 500 engine HP makes an argument for 3" pipe. As far as 4", 5", 17" or whatever the exhaust company of the day thinks up, it sounds like a lot of over-kill that is going to have really bad sound characteristics.

By my rough math, 400 RWHP will be right around 500 FWHP, give or take.. I'd say you're only gambling with 5 hp between 2.5" and 3" catbacks.. I seriously doubt there is anything beyond that to be gained at that power level with 3.5" or above. IMO

someday

1999, ur right on ur numbers, but they r basing that on going from a 2.5" to a 3" running DUALS, not a single 3" like the F-bodies do... dual 2.5" is equal to a single 3.5" in actual area...

Bowtieman4life

iTrader: (1)

Exactly someday! We are talking about a single exhaust system.

XFACTOR

You dont want to go to big then you could possibly loose horsepower Dont want that.I have 410 rwhp and am running 3.5" makes great power let us know what you choose-also have you thought about a bullet muffler or borla xr1-those are good too.

BurnOut

iTrader: (1)

Something to be aware of regarding the performance through a Spintech: https://ls1tech.com/threads/showflat...31&fpart=1

I'm not saying that it won't work for you, I'm just sharing my experience.

redz_02

iTrader: (4)

stick with the 3", the only time i have seen alot of 4" is on turbo lt1's, where they want the higher exhaust velocity. If you are going to change out exhaust i would go true duals, a 4" is mainly when you have a power adder.

John B

iTrader: (10)

We have a lot of opinions here and zero facts and data. The reality is that when you have ~500 FWHP you need the equivalent of 3" true duals. The 4" single comes the closest to this. To say that "the LS1 likes some back pressure" is just foolishness. There isn't a high performance motor on this planet that "likes some back pressure" and the LS1 is no different. If this was the case why wouldn't people with open headers just run a 2" diameter collector to create "some back pressure"?

My exhaust system (oversized according to the uneducated) consists of 3-1/2" true duals running into an "X" pipe and then 3" true duals to the rear of my car producing 426 RWHP & 400 RWTQ with a puny B1 cam. Surely there isn't anyone here that believes I would gain more peak HP with a smaller sized exhaust! Let's get real.

Go with the 4" mufflex, you won't be sorry!

BurnOut

iTrader: (1)

The only advantage I can think of to going with a smaller pipe is that the resulting higher exhaust velocity MIGHT induce a scavenging effect.

Other than that, John B is right... dual 3" pipes are pretty much dead on equivalent to a single 4.25" pipe. Since there aren't any 4.25" cat-backs available (that I know of), the 4" comes the closest. It's a hell of a big pipe, but if you want to run your exhaust out the back of the car on an F-body and you're looking for 400+ RWHP, it makes the most sense.

Vents

iTrader: (9)

John,

thanks for the shot of common sense in the midst of the over opinionated. a 4" mufflex is a great idea for a 380+ RWHP f-body, but duals are ideal. in a perfect world, a collector side 3" x-pipe w/3.5" after the x into some fairly free flowing mufflers, like a borla set, victor's, magnaflows, ect.. would be completely ideal. i've seen this setup on a few 350 rwhp cars run the same numbers on the dyno as when run open headers, just w/o the extra noise. the x adds to the scavenging effect and, after the x flow does not need to be inhibited at all.

the problem here, is that alot of us f-body guys like to take the 3" y-pipe as a standard for making power, when in actual reality, it's the crappiest idea i've ever seen used on any production V8, ever. in addressing the comment about "some backpressure" our cars need to breathe! some cars require backpressure to up the tq production because they are engineered at the factory to do so. however, a V8 15* headed motors dont require it. we're working around a top fuel inspired motor here. do those things need backpressure?

ssdungeon

iTrader: (24)

Great thread and great info I am pretty sure I am going to switch from a 3" y with electric cutout to a 3" X pipe setup. I think I should be happy and my fears of loosing HP are gone now. I doubt I would loose much.
If it sounds like the mustangs its not too loud for me either so I think I am sold on the idea.

Bowtieman4life

iTrader: (1)

THats what I am talking about. True duals here I come.

Vents

iTrader: (9)

;D