So I rebuilt my engine, just a standard 350 with a comp cams 262 in it. Full length headers and I went with 3 in exhaust into 12 in cherry bombs. (Yes I know....) anyway it's just a hair loud for my taste. I don't mind the cherry bomb sound at all but I'd like it to be quieter! I want to drop to a 2.5 or 2 in piping but don't know which one! Any suggestions? Or am I going to just have to get rid of the cherry bombs lol? I also have 2 Xelerator mufflers laying around that I thought I'd try as we'll but have never heard anything about them

 

Smaller pipes won't make it quieter, just slower.

 

just replace the glass packs with a set of 3'' flowmasters or magnaflows

 

Borla

 

Dropping to 2.5" won't hurt a thing.

Single Borlas have very low back pressure, but can be a tad loud for my taste.

if you want quiet, you want an H pipe in there someplace, and either a resonator or second muffler in each pipe.

I have 2.5" full exhaust with an H pipe behind the collector, an empty resonator can (4" diameter by about 10" long) on each side behind the H pipe, and a 12" Borla on each side on the 427 small block in my '61 car. It is very quiet until you open the throttle, then you can hear the car, but it isn't what I would call real loud.

The resonator cans make the headers think they are open headers, though 6" diameter would be better, but they won't fit.

The H-pipe boosted the rear wheel torque from 250 ft-lb at 1500 RPM to 400 ft-lb at 1500 RPM, with no other changes. The torques were equal before and after by the time 2500 RPM was reached.

400 ft-lb of rear wheel Tq from just off idle to almost 6K RPM before it drops below 400 again, in a fairly quiet 2800 lb car can be fun. I have found the more HP I have, the less need I ahve for a loud exhaust.

Doug

 

Typo?

 

No, its not a typo. See the two tq charts. This is with an 8.5 CR motor by the way, it looked like 93 octane was going to hard to get at one point when I put the motor together; if i get the urge, i will raise the CR to about 10.5:1, which should put me at about 500 ft-lb RWTq.

In addition to the massive low RPM Tq boost, the H pipe mellows out the sound between the two sides, which is why i originally installed it, the Tq boost was an unexpected benefit.

Look at the AFR, some sort of reversion was occurring which severely leaned out the mixture below 2200 RPM, the H pipe fixed that. The same reversion existed with the exact same exhaust with an L79 327 motor, i had in there previously, using the same 1.62" primary headers (which are too small for the 427 motor). 1 .75" primaries raised the power band about 500 RPM with no loss elsewhere.

Doug

 

Not always true. I've seen and heard from many sources that 3" will definitely be louder than 2.5", all else being equal. The source I trust most is a guy who has built performance exhaust systems for at least 30 years.

That being said, I'd try a muffler change first before scrapping the 3" system.

 

an H-pipe is NOT going to give you 150lbs tq.... no way no how... something else was wrong...

sorry... but just no way, no how...

 

2.5" mufflers won't sound the same as 3" mufflers.

 

2.5" for a 350 is plenty...

i was running duel 2.5" with no h-pipe or X-pipe on my 383 and i had 460lbs tq at the rear wheels on one of my last Dyno runs before I snapped the crank at the race track.

 

The graphs don't lie.

This was with sequential, port inj EFI, BTW, so we had complete tuning control. Others have noticed similar results. And, the reversions were similar on two entirely different motors.

Nothing else was changed, other than the H pipe was added.

Now, go put an H pipe of your car.



Doug

 

I run an X-pipe now on my 3" 427 650hp motor....
the dyno will be done next week for rear wheel hp

i truly believe, you believe, that you gained 150 lbs of tq with that H-pipe... but I will say again, no way no how.... you say others have had this happen... please do tell, who??? if it were true, every single forum member would have an H-pipe, (Which has been shown to have less of an effect than an X-pipe BTW) I'm sorry, but something else happened to show that much of a power increase, I also run an EZ EFI 2.0 FI with full timing control and A/F.

please, just 1 other member that has run an H-pipe... that says he/she gained near 150 ft tq for JUST adding an H-pipe... ANYONE???

 

They also don't tell the entire truth. Something was drastically wrong with the tune on that engine to raise the AFR above 17. Adding the H-pipe did not fix that.

 

No, we couldn't tune enough gas into it. There was nothing *wrong* with the tune, other than air was pulsing back and forth in the intake manifold and not getting to the cylinders. Adding more gas in the 2000 RPM range caused problems after we got out of the reversion area.

Did you read me say REVERSION?

Something was causing a reversion, two different tuners noticed it, it was less pronounced with the 327 motor. The H pipe eliminated that reversion. The reversion wasn't caused by the resonators, it was there before that, it was there with two different exhaust systems, except I always has the same Hedman 1.62" long tube headers and EFI modified Vic Jr manifold on both motors.

The second tuner told me that he has seen similar low end tq increases with an H pipe added, they do.a lot of work on LS motors in custom builds

Doug

 

We'll I already pulled the 3 in. Didn't like the decreased ground clearance either. So my question is now 2 in ir 2.5? Will most likely weld in H pipe as well

 

2.5"... and of you are going to do a crossover pipe do an X-pipe....
AZDoughas something else going on that is causing him those crazy numbers... but I will bet $500 that the H-pipe was NOT the sole reason for the 150 lbs increase of tq. as i said, I had 460 lbs tq at the rear wheels of my 383 with NO X or H pipe.

 

Sorry... looked at my old Dyno 383 numbers.. 440 tq at the rear wheel, not 460...

 

My (very) warmed over L48 sounds very powerful with Hedmann's (68301) with 3" collectors into 2.5" duals, $50 (in 2002) H-pipe just rearward of trans x-member and then 2.5" duals dumping into a pair of Dynomax Super turbos. I've been running this exhaust over 10 years and headers probably have 2 more years before they have to be replaced.

My 1st H-pipe was on a '90 Mustang LX 5.0. I figured... if Ford positioned the h-pipe that far rearward, it could not be ALL that wrong.

Nice sound... especially with the tops off.