Y pipe to a 4 inch mufflex on a 538 big block......

How much will this kill if I were to run this setup? Im trying to quite it down but dont want to kill any power.

How much will this kill if I were to run this setup? Im trying to quite it down but dont want to kill any power.

Well I would imagine you would be looking for AT LEAST dual 3 1/2" on a setup like that, so I would imagine single 4" isnt going to cut it.

4 inch mufflex would do ok, but I would fab a 3.5 inch y pipe for it.


David

I've seen 1,125HP of blown 383 smallblock pushed through the Mufflex 4" with a 3" Y-pipe. When they removed the complete exhaust and changed to collector mufflers, there was no change in HP. Biggest gain was deleting 50# of exhaust piping and muffler.

Interesting I might just do that 3.5 Y pipe and then to a 4inch. Thanks guys for the info.

ive got a 3d gen, but i dont remember ground clearance being a whole lot better on 4th gens[been a couple years since i worked on one].Hooker longtubes roadsurf the collectors,so im having some custom bent and im gonna make my y pipe out of 3 in OVAL tubing,as the y pipe will become the lowest point with the new collectors.Just something to think about.
I love the way my 4 in mufflex[flowmaster] sounds above 3000rpm.

Be weary of the mufflers that Muflex offers. Both the Spintech and the Flowmaster have both been proven to be underwhelming on the dyno. Gains of 30 to 40 hp are common when getting away from those on 450 - 500 hp applications.

Mike

Fwiw, I have 3in downpipes (y-pipe), to a 4in intermediate pipe.

It went 149mph through a 4in exhaust and magnaflow muffler, 24lbs boost.

It went 149mph through an open y-pipe and the same amt of boost.

With the 4in intermediate necking down to 3.5 over the axle into an slp two on the left muffler and tailpipes it went 146mph at 22lbs of boost. (lost 2lbs of boost through that exhaust at the same boost controller setting).

Be weary of the mufflers that Muflex offers. Both the Spintech and the Flowmaster have both been proven to be underwhelming on the dyno. Gains of 30 to 40 hp are common when getting away from those on 450 - 500 hp applications.

Mike
Then how do you explain a dyno test that showed no HP gains (5,000-8,000rpm ragne) when the entire 4" Mufflex/Flow system was deleted, and replaced with the best-flowing header mufflers they could find? That was an 1,125HP LT1. I had a similar result with dyno testing on my lowly 800HP nitrous 381 LT1.

Be weary of the mufflers that Muflex offers. Both the Spintech and the Flowmaster have both been proven to be underwhelming on the dyno. Gains of 30 to 40 hp are common when getting away from those on 450 - 500 hp applications.

Mike


I might tend to believe that on a crossflow type muffler, but not a single inlet/outlet muffler of the same designs on a 4 inch system.


David

Then how do you explain a dyno test that showed no HP gains (5,000-8,000rpm ragne) when the entire 4" Mufflex/Flow system was deleted, and replaced with the best-flowing header mufflers they could find? That was an 1,125HP LT1. I had a similar result with dyno testing on my lowly 800HP nitrous 381 LT1.
was the whole system replaced with a larger diameter/area or did it go strait to open headers?
apples to apples

Then how do you explain a dyno test that showed no HP gains (5,000-8,000rpm ragne) when the entire 4" Mufflex/Flow system was deleted, and replaced with the best-flowing header mufflers they could find? That was an 1,125HP LT1. I had a similar result with dyno testing on my lowly 800HP nitrous 381 LT1.

Well. . . for starters that dyno test was on a blown engine, which can sometimes benefit from backpressure because it will reduce overscavenging. Or, actually, the hp increases due to reduced overscavenging were negated by increased pumping losses, so the net result was no hp gain or loss.

I, personally, had a 3" in/out Flowmaster on my '89 N/A Firebird low compression 355. When I switched to a SLP "straight-through" muffler, I gained a dyno proven 40 rwhp with no other changes.

My good friend had a Mufflex 3.5" system on his '88 N/A IROC 406. It had been running consistent 116 - 117 at the track one day when I convinced him to remoove the Spintech muffler. The next pass was 120 mph, which it consistently did after that.

Naturally aspirated engines have totally different exhaust system requirements than blown, turbo'd, and Nitrous'd engines. I believe INTMD8 has made 750 rwhp through a stock LT1 muffler (turbo). Try that N/A!

Mike

Well. . . for starters that dyno test was on a blown engine, which can sometimes benefit from backpressure because it will reduce overscavenging. Or, actually, the hp increases due to reduced overscavenging were negated by increased pumping losses, so the net result was no hp gain or loss.
But your Flowmaster (40HP) loss, acted like you had a potato stuffed in the exhaust.... hard to understand how you could force the exhaust from an 1,125HP engine through a muffler that constricted, without losing a bit of power.
I, personally, had a 3" in/out Flowmaster on my '89 N/A Firebird low compression 355. When I switched to a SLP "straight-through" muffler, I gained a dyno proven 40 rwhp with no other changes.
Which Flowmaster muffler were you running? Was it the same series Mufflex uses? "40rwhp" boggles the mind.

My good friend had a Mufflex 3.5" system on his '88 N/A IROC 406. It had been running consistent 116 - 117 at the track one day when I convinced him to remoove the Spintech muffler. The next pass was 120 mph, which it consistently did after that.
I can't (and didn't) speak to the Spintech, since I have never owned one, or personally seen a dyno comparison done on them.

Naturally aspirated engines have totally different exhaust system requirements than blown, turbo'd, and Nitrous'd engines. I believe INTMD8 has made 750 rwhp through a stock LT1 muffler (turbo). Try that N/A!

I routinely dyno my setup both with and without the nitrous.

My Flowmaster was a 3" in/out, 2 chamber model. The car not only gained 40 rwhp on the dyno, but it also dropped about .5 second in the quarter and gained 4 mph by getting away from the Flowmaster. It went from consistent 12.70's at 109 to consistent 12.20's at 114 and eventually ran a best of 11.96 at 115 with the SLP muffler.

Those gains and many more have been reported at Thunder Racing when switching from Flowmaster and Spintech mufflers. I'm quite surprised you haven't heard of this. In fact, some of the Thunder Racing cars have Mufflex exhaust systems, but with Hooker Aerochamber or other mufflers welded in.

Mike

I've got to say, I've seen similar results with flowmaster and spintech.

I recently dynoed a heads/cam LT1 car with a 4in mufflex/spintech exhaust.

After seeing the exhaust, I wondered why the hell did it have a cutout (in the intermediate pipe).

I don't remember the exact numbers, but It picked up somewhere in the range of 30rwhp with the cutout open.

Cars making similar power (around 400rwhp), that I have dynoed, picked up between zero and 5 rwhp between an SLP exhaust (2OTL or dual/dual), and open cutout.

I'm dealing with some of those same issues currently. I just finished a solid roller Cam Motion 383 with AFR 220's and running through a 3" intermediate and Borla XR-1. Power is way down currently and the car isn't making power past 6k rpm. We are going to drop the y-pipe and see what effect is has on power. I'll report back but I expect some pretty big gains (hoping). I think on larger cams with a significant amount of overlap, that the exhaust back pressure makes a big difference. We'll see when the car is dyno'd again by the end of this week and I'll let you guys know what we find when the guys at Thunder get back to me.

Just as an extra tidbit. . . my last 550 rwhp combo gained only 5 rwhp when dropping the single 3" Hooker Aerochamber.

Just as further support of the oppinions already listed:

On my car the difference between full exhaust (Ghetto 3in y pipe, stock I pipe and flowmaster muffler) and open cutouts was 31rwhp. We couldn't figure out why the car wasn't making what we thought it would, then we opened the cutouts and it all made sense. 31rwhp gain for the car N/A.

Flowmaster = :no: