Kandied91z

iTrader: (7)

who has or believes in 4" exhaust and why?

i'd just like to hear some thoughts on why it may or may not be necessary and what the real purpose of such a large application would be.

25THRSS

I don't think it is necessary until extremely high hp levels. My LS1 has an estimated 550 or so hp and I only have a 3.5 inch exhaust. I do agree though that there are cases when it can be necessary, like when you have a sick sick amount of hp.

Marc 85Z28

iTrader: (3)

I certainly do. I had a Hooker 3" system on the car. A few months back I installed a Mufflex 4" setup. Not only did the car feel faster, I proved it to myself. I can now keep up with my friends modded 96TA from a roll. Before - from a 40mph punch I would consistently lose by a 1 - 1.5 cars to 100. Now I can keep pace. No other changes; and that's with an optimistic 280HP. You don't need 500HP to benefit from larger exhaust. Why would anyone run a cutout then?

johnsjj2

I am planning in putting a T64 turbo on. When I do, I am going to run a Homemade Motorsports 4" single system.

Kandied91z

iTrader: (7)

good question....many have lost power with cutouts around here.

Matt87GTA

That is what we call lack of tuning.

I don't think it is even remotely possible to have too much exhaust flow when referencing the cat-back or similar portion of the system....

I just swapped from 3 to 4 (Mufflex) and the butt-dyno seems to like it... I would verify it with a G-tech time or the like but I will be putting in the 383 this weekend....

KenV

...put up a sound clip as soon as you are done, Matt. I just named you in the latest Exhaust post about choosing a muffler because of how that sucker sounds now. It's like the music we all wish we could play

Peace,

K

25THRSS

people put cutouts on to eliminate all restrictions in the exhaust. If they have a 3 inch exhaust, they put a 3 inch cutout on, not a 3.5 or 4 inch. When going to an exhaust piping that is too large you can actually slow down the exhaust velocity to the point where it actually creates backpressure. Cutouts don't do that because once the exhaust has exited it is gone forever. If you are gonne go 4 inch you better have a lot of hp, aka, a hell of a lot of exhaust gasses being pumped out of the engine, or else it will do nothing but slow down the exhaust velocity too much and cause a loss in hp.

Matt87GTA

Will do Ken . Thanks for the compliments but they really should go to Flowmaster - they made it! My 4" from Mufflex has the 30 series Flowmaster on it and I love the way it sounds too . Even better than the crossflow 80 series.

I'm not even going to get into the debate on backpressure... It has been beaten to death, brought back to life and beaten to death again about a thousand times here and some people still don't get it....

Kandied91z

iTrader: (7)

flowmaster is nice i really like my spintech too. i'm happy with my 4" but i feel sometimes i might have been just as happy with my 3". i do think the lt's helped though. it's hard to guage doing so many things at once. i changed my suspension, motor, trans, rear, exhaust, wheels, and many other things all at once so i couldn't truly guage the difference in exhaust unfortunately.

TunedPort 335

I gained 21rwhp and 8rwtq by opening my cutout in 2nd gear.

Kandied91z

iTrader: (7)

21 rwhp huh.....that's pretty damn good. definately see more cutouts then airfoils sold if that were the case.

KenV

But, who built the engine?


Agreed. You can look straight through the Dynomax, and the force of the fumes coming out are much stronger than on the Flow. Did it affect power? Enough to make me have to feather the throttle in places where I went full-bore with the Flow.

Peace,

K

25THRSS

I have seen several increases of hp and torque with a cutout. It is a proven mod, unlike an airfoil. Don't even compare the 2. If you want even more dyno desults than on here, go to LS1tech or ls1.com and you will see many, many positive results, and not much if any lossed with a cutout.

calroc

I will atest to a definite power increase with an open exhaust. I don't have a dyno sheet with open exhaust, but I do have many timeslips. They all say average .27 sec/2.2mph(12.58@109.33 to 12.31@111.55) improvement with open exhaust.
I run the old SLP Tri-Y headers with a 3.5" Random cat & Mufflex 3.5"/Spintech exhaust. It's an 85 with the four bolt flange at the collector/cat. Easy to drop the exhaust.

Kandied91z

iTrader: (7)

don't turn this into a discussion on cutouts please.

1badblue87z

Kandied91z, first off, I saw the pics of your car at autorama and the new hood looks great, secondly I was wonder how much louder the 4" exhaust is over the 3 inch, I am dropping a 355 with the full edelbrock performer rpm kit in my car sometime in the next few weeks and I def need a new exhaust setup, the dyno sheets for that engine say it produces 425 hp at the crank but my heads are modded more so I should make a lil extra power plus I will be running a 75 hp shot of nitrous at the track, could I benefit from the 4". thanks for your help and keep up the good work with your car, it def is the nicest 3rd gen I've ever saw.

ShiftyCapone

iTrader: (7)

25th is exactly right. You want a nice combo of exhaust velocity and flow. To small and you have great velocity but poor flow. Too big and you have great flow but poor velocity. Exhaust velocity helps pull the exhuast out of the chamber, it's a suction effect for lack of being too nerdy here. 3" exhuasts have been proven to support around 400rwhp before they become a restriction. A 4" exhaust on the same car will make different power but it just shifts the curve a bit and the area below is about identical to that of the 3". Past 400rwhp and things change and favor the 4" all around. If anything you want large collectors and medium sized piping relative to collector size. Your long tubes are a big help. They collect the hot gasses that are at a maximum volume and have a big space for them to fill (I assume 3" collectors). As the exhaust cools before it exits the rear of the car it does not need 3" per side. The two 3" collectors can dump cooler ehxuast into a sinlge 3" since it has less volume. So in essence you are fitting the same amount of gas just as effectively in a smaller tube size because of the temperature difference downstream. This smaller size will also increase velocity and help draw the exhuast gasses out of the collectors.

Chris89GTA

iTrader: (2)

Kandied... A buddy of mine that is on this board just got a 4" Mufflex, and will be putting it on soon. He now has the SLP 2OTL setup, and at the least will have track results for what he gained by going to the 4". He has a 383, fully ported AFRs, 230/236, Minirammed motor... should be interseting. I will post what he gets when he puts it on...

Kandied91z

iTrader: (7)

sounds good, hard data is always nice.....

paul_huryk

Try running a cutout on any day at Englishtown and see how fast they throw your a$$ out. Noise is a no-no nowadays even at the track.

SweetS10v8

I read somwhere Tory Hess runs it on his Formula. Best ET 9.39/149

jocww

im runnin 2.25 on the elco and im pushing 430 at the crank with delta flow 40ss no x or h pipe dont believe in that stuff. no cut outs yet. will get elctric ones soon hopefully. i will not go to a 3 in untill i get 430 at the rear or 450 at the crank. i believe that to many people think that exhausts are like engines bigger is better. and its true to a certain point. but look at the jap crap cars 5 in exhaust dont do jack. my collectors are 3in and then stepped to 2.5 then 2.25 at teh muffler and then of course big tips but thats just for show.
o and its a loud ladie. nick named her loudmout molly amongst other names. but mr peace officer said he could hear me from more than 3 miles in traffic and my dad can hear me get on the freeway and thats over 5 miles.

Dante93GTZ

iTrader: (5)

Not being an expert with exhaust, I'll just explain what I have.

I bought a complete setup at a swap meet. I bought a set of 1 5/8" Hedman headers, 3.5" y-pipe, cutout where muffler used to be and 3" -catback and a Flowmaster muffler (been told 1 or 2 chamber) and 3" since tailpipe. All pipe is Mandrel bent.

The guys I bought the exhaust off of have been modifying their 3rdgens for about 10 years. One has an 86 IROC with a highly built 400 of some sort.

The other has a blown '85 SC with a 400 as well I believe.

The exhaust I have was specially built for these guys and they have run it on both of their cars. I saw the 85 SC go low 11's with it and the IROC I saw go low 12's with it.

Its overkill for my puny 305 right now but I couldn't pass it up at just $300 COMPLETE.

DARCOM

i love my 4" i noticed a better 1/4 times and better gas mileage.
you can see it on my home page at:
http://darcom.org

jocww

better gas mileage with a bigger exhaust.

Kandied91z

iTrader: (7)

1badblue87z thank you for the kind words. only reason i'm running 4" is because i have an extreme amount of power for a street car. with your setup i would think a 3" would be fine and even if it is slight constricting the price difference between the two sizes is well worth going smaller. that is if you get a mandrel bent system.

4" is also alot heavier and your clearance becomes worse so lowering can be an issue. i like my exhaust and i'm glad i have it but if it weren't for the power i have i would have kept my 3".

as far as sound i really couldn't tell because i went with a bolt on modded L98 to a highly built 383 and i also changed mufflers so i couldn't compare. now i have a 388 with the same 4" and i wish i could find a way to quiet it down.....definately have to limit night driving.

christian

Do you have any links to picks or info about this car? What type of motor and y pipe does he have?

Randel '86

might as well run a 4" if you got the money, certainly won't lose power. And if you do end up later making some sick hp, it's one less thing your gonna have to dick with.

HiTech5

iTrader: (4)

I have 2 systems for my TA. The first is 2 3" tubes coming out of the headers into dual 3'' cats that merge into a Mufflex 4" at the rear axle. The cats help keep the exhaust decible down and actually has a good sound at part throttle.

The second system is the complete Mufflex off road 3" into single 4". What I do not like about this freeflowing system is the sound at part throttle. It is not crisp. Somewhat iritating.

Under full throttle, it sounds like a NASCAR. I am actually looking to place a Dynatech cone into the exhaust at the bend before the rear axle.

I really want to improve the part throttle.

By the way Kandied, nice ride!


www.geocities.com/dzperf

Fastbird

iTrader: (5)

I have the the 4" Mufflex system with the Flowmaster muffler and love it.

I also have the Hooker LTs which flow directly into a 3"x3" -> 4" y-pipe and then through the system.

I had to put my 305 back in the car for a while and ran the 4" system on it. It slowed the car down by about a tenth.

However, with my normal setup, this exhaust is needed:

406 spinning 7000 rpms

toddlsf

HiTech5 --- When you put that dynatech cone in there, reply to this topic and let us know how it worked. I am not happy with my 4 " mufflex either. At idle it sounds great. Full throttle sounds great. About 10-20% throttle it is good too, but about 50% throtle, mine is downright obnoxious. I don't like it. I even added a small bullet muffler where the cats would have been.
Todd

Kandied91z

iTrader: (7)

spintech, so nice....

EvilCartman

iTrader: (1)

camarojoe

I tried these in my HookerLT's/TrueDuals/Flowtech mufflers setup and I have to say these dynatech cones were the biggest joke ever. There was no noticable difference so I immediately sent them back to Summit and got my money back. This was after calling dynatech and asking them how much these cones are supposed to reduce noise levels. They told me between 1-3 decibles! Like this matters on a car that's putting out around 120 decibles...

toddlsf

Camarojoe -- Thanks for the input. I'm glad I didn't buy any of those cones. I didn't figure they would help that much.
Todd

CrazyHawaiian

I don't want to sound dumb, but what parts of the exhaust setup are you guys referring to here? Are you guys talking about a 4" y-pipe, a 4" pipe to the back or a 4" muffler setup? Because I've always been under the impression that the components need to be matched to get the full benifits. If you run the same headers and y-pipe, but changed from 3" catback to 4" catback, how much of an increase will you really see? Wouldn't the headers and y-pipe be a restriction at that point? So to have a true 4" system, wouldnt you need some custom made headers and y-pipe? Cuz if I just replaced my 3" midpipe (from y-pipe back to the muffler) with a 4" pipe, I wouldn't really consider that 4" exhaust, and I wouldnt expect much of a performance increase. What you guys think?

Marc 85Z28

iTrader: (3)

Its simple:

What would you rather have? Two 3" header collectors going into a y-pipe with 3" inlets and a 3" outlet to a 3" catback (effectively reducing exhaust size from y-pipe back in half)?

Or...

The same two 3" collectors going into a y-pipe with 3" inlets and a 4" outlet to a 4" catback?

thecoolone

iTrader: (1)

Didn't read the posts, but 4"? I don't think NASCAR stock car's run that big, and they are pushing 900hp. And trust me, they spend millions to find 1hp....

Kandied91z

iTrader: (7)

guess you should have read the list then....no big deal really since my truck has 5"

ShiftyCapone

iTrader: (7)

But by the time exahust gases get to the I pipe they are considerably cooler and take up less volume and don't need the huge size that they did when leaving the header. Going too big with not enough power can kill scavaging.

Marc 85Z28

iTrader: (3)

Sometimes. However, that's not the rule, and my car is an excellent example. I've posted this SEVERAL times before - even on my mild (320HP) SBC I noticed a SOTP gain from a 3" to a 4" catback. And since I went from a Hooker Aerochamber to a Flowmaster, the muffler was if anything giving the advantage to the 3" Hooker. Do a search on this topic. You'll find a link I posted that referenced an LS1.com user that upgraded a 3" aftermarket catback to a 4" Mufflex setup. With NO OTHER MODS he put another 10-12rwhp down on back to back dyno runs.

And to the guy with the NASCAR comment. Please read the entire post before replying. We are talking about a SINGLE exhaust setup here, not dual And you're about 150HP generous on that rating there

CamaroMike

Just some food for thought. I run SLP 1 3/4" shorties with a 3" cutout in place of the cat. My cat back is an Edelbrock. At the track when I open my cutout I can reduce my 1/4 mile time by .3 sec. Opening my cutout is like increasing my cat back size. Hence a power gain. I have to agree with Marc 85Z28.

25THRSS

Opening your cutout is nothing like increasing your catback size. It's still a 3 inch cutout and once the gasses escape they are gone forever. If you increased your catback size the gasses are still in the pipe and if your engine doesn't need the extra size all it's gonna do is slow down the velocity. My 305 tbi runs faster with a cutout, does that mean it needs a 4 inch exhaust?

CamaroMike

The 3" y-pipe will keep velocity sufficient in this instance. Although, a complete 4" system would hurt velocity if the engine were not designed for it.

Camaro_nut

Ok, we talked about 3" vs. 4" systems. What about
the 3.5" system? Wouldn't this be good for a high
hp car? I am expecting only 300rwhp on my car, but
I want to get the 3.5" Mufflex system. It's not a common
system. I want to get Spintech muffler for it too. Any
suggestions? Is this over kill? Or is it just fine for my
application?

CrazyHawaiian

Well yeah I understand the concept, but I was trying to say that I dont see many header / y-pipe combos sold off the shelf that would fully accomidate the flow of a 4 inch cat back system. It would be nice to have a y-pipe with two 3" inlets and a 4" outlet. Can you direct me to where I can buy one? Because when I was buying parts for the exhaust system I want to put on my 91, the biggest y-pipe I could find was the MAC 3" pipe. Two 2.5" pipes into a single 3" pipe. Do they make bigger y-pipes? Or does a huge dual 3" into 4" y-pipe come with the 4" Mufflex cat back system? (I have never seen the Mufflex 4" setup). And if there is a y-pipe that size, what headers would you recommend to maximize the potential of a 4" system? I'm not trying to disagree with you, I'm just interested in maximizing the potential, and in all honesty I did not know the product existed. Cuz if there is a better setup than my current plans, then I'd rather go that route.

Camaro_nut

Try here: http://www.mufflex-performance.com/fbody_8.html

It doesn't state if the off road Y pipe for 3rd gens is dual 3"
pipe to a 4" collector, but I assume it is, cause the 4th gens
are. But email or call them to make sure. They fit the
Hooker Super Comp. long tube headers. Hope this
helps you out. You can get them with or without 02 sensor
bungs.

Marc 85Z28

iTrader: (3)

Well, since the only company that makes a 4" catback for our cars is Mufflex, you'd expect them to make a y-pipe to accomodate that large catback, and they do - just like I described above. Follow Camaro_nut's link.

Most run the Hooker Super Comp LTs (thats what Mufflex recommends). They have a 1 3/4" primaries with 3" collectors. Mufflex's y-pipe and catback are designed with these headers in mind, for all the 82-02 cars.

And I'm telling you, my mild 355 gained hp from the 3" to 4" catback swap.

There have been nearly a bazillion Mufflex y-pipe threads, how did you miss them all?

Camaro_nut

Wow, I was going to buy the exact setup that you have
for a mild SBC. I will be using a GMPP crate motor that
is 350hp. I am buying the SLP 1 3/4" headers w/no AIR,
Random Tech. high flow cat. and 3.5" Mufflex exhaust
with a Spintech muffler. But, they told me (Mufflex) to
use 3.5" for anything under 400hp. Should I just go with
3.5", or should I get the 4"? Also, is there any ground
clearance issues with a 4" system?

It's true that Mufflex should make a Y pipe designed to
work with their existing systems. But, it has only been
very recently that they made these available. I browsed
through their site weeks ago. And at the time, there was
no Y pipes available.