Well, the 3 inch single setup was fine for the old 305 but it sure was choking my 350 bad just like I thought it was. The night before I went to the track I cut the exhaust off at the end of the y-pipe just to see how much it would help. The gains were way beyond what I had expected Last year my best run on the motor was a 13.42 @ 102, Saturday night I ran a 12.22 @ 111. Yeah it would have been nice to cut everything off at the track but not a whole lot has changed during winter to my setup. Not enough to pick up a whole 1.2 seconds and 9 mph at least Now it's time for full length headers and duals or a big single setup

 

Hmm! I have a single 3inch pipe on mY CaR! WondeR if I shoUld do tha same

 

I have a nice 3" setup with a SLP muffler. Like I said in my other post I'm going to the Mufflex 3.5 inch system. I will let everyone know if there are any improvements. Just looking for horsepower where I can find it. By the way Mufflex also makes a 4" system. Allen

 

i did longtubes and true duals with an h-pipe for under $300. just incase money is an issue, it's a better deal than the mufflex. my father is running the hedman headers like i am and is running 11.7x's with a powerglide. i imagine with a th350/400 it'd be in the low 11's.

 

couple q's

what hp are you running (ballpark it if ya dont know)

and what was your exact set up with the 3", like which headers cat (if any) and cat back

thanks

-chillen

 

I figure it's putting out about 430 hp at the crank going by the times it ran over the weekend. The old exhaust setup was....

Edelbrock shorties
Edelbrock y-pipe 3"
don't know the brand of the converter
3" in and out Spintech Pro Shootout muffler

The bends were not mandrel bent so that probably hurt me good too :/

 

Cartman that seems alot more reasonable for your setup, i knew there was something holding you back. Throw the juice into it now

 

There is something wrong there, Mufflex told me that going from a 3" to a 3.5" exhaust would pick up about 2mph, you shot up 10....

Maybe your cat was 90% clogged up (if you had one)?

 

well 3" to 3.5", but not necessarily cut off at the y-pipe. there is way less restriction when cut off at the ypipe..obviously..if you go with duals i wonder if you could bring the exhaust all the way back but still pick up significant gains with dual cutouts. havent yet tested the difference between and open y-pipe and an open cutout (at the ypipe with no cat) on a full exhaust. something to consider though?

 

I would be tickled to death if my just ordered 3.50 inch Mufflex system gave me a 2mph increase over my existing 3.00 inch system. Thats like a 20HP increase. Allen

 

The cat wasn't clogged at all, you could see right through it no problem

TunedPort 335, I need some taller tires before spraying again Crossing the line at about 6700 - 6800 right now.

 

That is what Denny told me when he installed the system on my car - thing is that my car has 400hp - lower power motors will gain less.

 

i think you should have cut the exhaust off at the track after a run. im not syaing you didnt run those numbers, but theres NO WAY you picked up 9 mph just by cutting the exhaust off. first off its not that heavy so weight couldnt be it. and its not a flowstopper so it wasnt impeding flow THAT much. ls1 guys are making 400+rwhp with y-pipe exhausts and a cutout. some are int he 420+range without a cutout. a really good friend of mine made 419 with hooker long tubes, ORY and a cutout on his 01 WS6.

i think you had better air at the track this time around. which would account for most of the gains. but you didnt get 9 mph from hackin the exhaust off.

 

Just because you don't believe it doesn't mean it isn't true.I believe most of his restiction was his unknown cat,and non mandrel bent pipes.From what I've heard the spintech muffler he had isn't much better than a flowmaster either.Once he puts longtubes on and a dual exhaust set up he should pick up a few more tenths.

 

The 3.50" Mufflex system I have ordered comes with a Spintech muffler. I'm not going to take any chances and will order a Magnaflow 3.5" race series muffler. Mufflex would not let me substitute another muffler such as a Dynomax or Magnaflow. Allen

 

well im glad i read this before i posted.

wanted to see how much my headman 1 5/8 shorty y pipe and single 3" mandrel exhaust would hold up the 450hp 383 (and 150hp n20). but i guess now if i ran the car with this exhuast on id be extremly dissappointed. time for a full custom dual 3" and longtubes.......but damn thats another thread. ground clearance on my car = ZERO!

 

im still saying that most of the gain came from different weather or something. unless its clogged you probably arent gonna pick up 9 mph running without a cat and aftermarket exhaust.

on a side note, shorties and a y pipe arent bad for most. there was a guy that went i believe 11.0s at like 120mph (this is off memory) with a ZZX cammed 383 with a mini ram in a 91 z28.

 

Far as I remember, temps were in the 70's last year and again this past weekend. Also like I said, yeah it would have been better to chop it off at the track but that would have ate up some major time. Chopping the exhaust off wasn't the only change made to the car like I said. Little different jetting still within 2 jet sizes of last year, air pan to seal against the cowl hood, poly motor mounts and bushings in the rear control arms. Those are the only changes to the car that would effect the times besides cutting the exhaust. Both last year's run and this the car dead hooked, both runs were right off the trailer. I'm willing to bet if the exhaust was left on, it probably would have only ran at best a 13 flat if lucky.

 

That would be me.! I went 11.24@123 opened up on Hooker Shorties 1 5/8.
.And as far as the gain not coming from the exhaust..I had the same thing happen to me with my setup when i first did it..I couldnt get out of 12.20s @ around 113..I took off the Blowmaster muffler and went to 3 inch straight out with a Dynomax Bullet Muffler..walaaa..I went straight to 11.50s at 118 the very next track pass.And it continued to get faster from there.So his gain is very belivable to me with his set up.Congrads Evil. Keep it up bro youll be in the 11s n/a ..

 

I am presently running a 3" flowmaster with a cut out before the rear axle. I have been thinking of changing the exhaust. Any opinions on weather I will see gains going with a 3-4" or duals. My car is presently making 350whp/360wtq and runs traction limited 12.90s Mods are in sig.
Thanks for any info
Kory

 

Hey Kory check this chart out. It is on the Dynomax website. Magnaflow has a very similiar chart. With that much horsepower you need a 3.50" exhaust. You need some Mickey Thompson ET street radials. You are spinning off the line big time. I'm running quicker than you with a lot less horsepower and most likely more weight. You should be in the lower 12's. Allen

 

I'll be running 450 hp at the crank so whats that mean i need 4" single piping?? its a 350 5.7l

 

450HP at the crank. Hehehehe. You need a 3.50" exhaust at a minimum. Looks like the 4.00" sewer pipe might be what you need according to the charts. Allen

 

I'm planning on some more power this summer. I hope to have in excess of 400 whp soon. It looks like a bigger exhaust is in my future. Thanks for posting the chart.
I have had better luck at the track lately. I hope to go back in a week or two. I think I can cut a 1.8 60' That should help my et alot. My 12.90 was a 2.14.
Thanks for the info.
Kory
btw I got a street twin and a new rear going in so I should be able to dump the clutch alot higher.

 

That chart is pretty generic. I've seen it on several websites,and it had me convinced that 3" wasn't going to work for me. I emailed dynomax for a recomendation. I gave them the low down on my motor and car set up and told them it was for street strip. To my suprise they recomended their 3" system.So instead of running out and buying a 4" Mufflex I played around with the single 3" system that came on the car. I took the car to the track with the original flowmaster,Then swapped it out for a dynomax bullet, then open headers.With the flowmaster it was a full 5 mph slower than my 80 camaro was with same motor and gears,but a true dual 3" with xpipe system.With the dynomax bullet I picked up 3mph, and open headers I was still about 1 mph slower than my old camaro, due mainly to tuning issues.Its not the ideal comarison, but the two cars are similar in weight, had same gears, and exact same motor. The main differance was a 10" converter in my camaro and an 11" in the firebird. The camaro also had front drag shocks frame connectors and a better fuel pump. This year I have the firebird sorted out a bit better . I put the same 10" converter in and same tires and fuel pump that were in the camaro. I am going to try to take it to the track May 6th.I am pretty sure I can get it to run with in 1 mph of my old camaro with the single 3" system. All that being said i think a single 3.5 would be better than the 3 for my set up, but I'm not going to shell out that much $ for what would probobly amount to a 1 mph gain. I'll keep it quite on the street and just get some cut outs.Oh yeah my old camaro was trapping 118.9 mph on street radials.

 

You are right in that the chart is a guideline. However also keep in mind that Dynomax does not make anything larger than a 3" for a catback. I'm sure if they sold a 3.50" system you may have heard a different recomendation. Allen

 

True, but I was just pointing out that the 3" system did perform much better than I expected,and that its not as much about the pipe size but things like the muffler and cat that will really hurt a single system.So if someone doesn't have the money to buy a $500 mufflex 3.5 and then go out and spend another $115 on a good muffler that the 3" system can work.