Are you guys still limited to dual 2 1/2" exhausts and "must sound stock-ish?"

It's been a few years since the fun times I was involved with all of you, just wondering with the low 10 and high 9 second et's you guys are running; what could you possibly be doing to keep the Db's reasonably down and be low low restriction; do you guys have a db requirement? There easy to check since there's a pretty cool iphone db meter app out....I just used it to measure the improvement of my new AC outdoor units, lol. I'm thinking you guys must have loosened the requirements just a tad since my time away.

Thanks guys, trying do come up with a quiet and super low restriction system using 3 mufflers (2 conventional parallel and one more off a Y (which just functions as an H when capped) pipe bridge (actually cut outs)that will weigh overall not much more than 2 larger mufflers and be super quiet. Each of the tailpipes will have header type flanges for caps and/or reducers, I want to do this as an experiment that can be tested for cause and effect back to back and should be fun.

I remember the story of the Silver bullet running 4 Cadillac mufflers, that must have weighed a ton!

Also I've heard good things about the summit Cheapo turbo mufflers and race welded mufflers too as far as performance, any feedback from anyone on those?

I ujsed to have a 73 duster that had a warmed over (very low 12 second) 69 440 that ran dual 2 1/2"s that were tucked in behind the rear wheelwells (similar to a 68-72 nova) and tapped in a 318
single "bait" pipe on the passenger side....used to sucker the 5.0 stangs in like flies to Stink, lol. Anyway I ran 2 1/2" Sears Muzzlers on it that probably cost some power but no more than that Newport exhast manifold I angle milled to fit the driver's side, the pass side ran a magnum thet fit perfectly after 20 minutes of fenderwell massaging with a couple hammers. I was going to look at sectioning 2 ( a left and a right )Newport manifolds and weld them back together in the center so I could have a dual outlet (at the ends) manifold since I could snake another 2" pipe up past the front of the steering box but I would up selling that motor to build a 451 low-deck...which was a lot faster but wasn't nearly as fun since I abandoned all my sleeper stealthy tricks...fun times! Remember this was a time long before all the kits and cool stuff we have today.

Dyno-Max Ultra-Flow is what I thought most of them use. Ron

Ultra flow SS

So I guess the answer is "Yes", you've obviously had to loosen up the FAST DB rules just a tad. Of course the UF's are great mufflers but with a 13:1 roller cam (even with a really wide LSA) they're comparatively loud by the "old days" Early 2000's FAST standards. The UF is basically a bullet core with a full packed case around it. I know the manifold kill some db's but with a 572" hemi I can't imagine the UF's wouldn't be objectionable to some of the old "letter of the law" guys we had back then.

I was wondering if the Dynomax VT's would work since it's basically an Ultraflow with a flapper valve, would make for a (by comparison) very quiet idle.

Is it still a 2 1/2" dual system? Anybody caught running a 70mm ( which isa common Euro size that is 2.75" but looks close to a 2 1/2" without a caliper in hand.

You know it's funny about a lot of the old muscle cars, with very few exceptions in stock form I could tell what kind of car it was by just the tone, and that was for most brands. With mopars 340's and 68-69 383's can be harder to tell apart but they're distinctly different from more mellow sounding 440 mags and solid or hydraulic hemis'( they sounded different themselves). But my favorite exhaust tone ever was the 73-74 Trans Am 455-SD.

I went from the magna flow turbo mufflers to the Ultra flow SS's in the duster and it didn't pick up a bit. If I drove it on the street more they would not be on the car....

Wize.
If you have been following the "Real World weight loss and its costs" thread on here, you've probably seen my all aluminum constructed exhaust system complete with carbon copies of the Ultra-Flo welded mufflers in all aluminum construction. I don't have a recording as of yet, but my car which before had a tattle tale signature raspy/tin sound, especially under power, now is really humble sounding. Almost two quiet since aluminum tends to tame the savage beast.
If they (Aluminum versions)survive the test of time, they would prove to be a rather stealthy sounding design as well as super lightweight.

Stock sounding, no, but the UFs with 2.5 system might be quieter than you think.

I've heard the UFs they won't be stock sounding (like a reverse flow) since there's nothing to dampen the overlap and especially the 'chirp' of a well tuned roller cam.

Probably not really quieter than I think but I know what you mean...DBS are related mainly to compression overlap and the overall size of the system and if FAST is still limited to 2 1/2 inch duals they may well be quieter than a comparable 3" reverse flow or similar 'non' straight through design.

It's interesting, I have a Corsa system on my 06 Trailblazer SS and it has got to be one of the best sounding systems ever in terms of tone and it is essentially a straight through pipe with only a slot and about 4" of perforation. Corsa uses a "tortuous path" (almost like a maze) acoustic chamber in the muffler body instead of dampening/absorption that really 'tunes' the sound....again only for a particular application. But if I put a bigger cam or removed the cats on my TBSS it would be almost like the car had no mufler at all, the resonance of the entire system if taken into consideration and when you
alter any parameter the acoustic tuning goes right out the window. So in a way a Corsa muffler is really more like an "instrument" than a muffler in every sense of the word.

@FMJ

Wow that is so cool and I think it could hold up well for a while, the thing that's interesting in all exhaust systems is that the peak hot spots tend to 'walk around' the system proportional to engine load and rpm/airflow, the key is to (by design or otherwise) have enough material to dissipate the heat repeatedly without fatiguing the aluminum (which of course is it's Achilles heel as a structural metal)

Yeah, size matters in aluminum. That is why the muffler fabricator and I decided on 3-1/2" tubing out from the collector to the X-pipe. then it narrows down to 3" from there to the mufflers and out the down turn tails. This size allows for the heat dissipation as you mentioned and keeps the heat to a minimum throughout. I've also attended to the various hangers that hold it under the car so that if it fails on the welds, it won't become a catapult object under power. The aluminum is only used on the tubing from the collector back where the heat seems to be much less than up at the primary section of course.
Ever heard of the Pontiac Swiss cheese doodle cars where the engineers tried to use aluminum up top as headers and at the end of the track, they were met with melted lava exhaust.
So far in idling around in the garage and short drives, this system has held up nice in my car. I of course only did it for weight savings but ended up with a quieter system at the same time.

Greetings and happy new year Wise! Ultra flow ss, non- welded stainless. Quiet at idle, FAST rules says must sound stock at idle. Noisy at WOT, but FAST rules do not address sound at WOT. A quick bead blast on the SS case and it looks galvanized, or close enuff.

Thanks, Joel and happy new year to you and yours as well!! so is the rule still dual 2 1/2" max pipe diameter?

I need to attend a FAST race this year, been way too long since I changed a Hemi clutch on 130 degree pavement!

They don't recommend the VT mufflers on big cammed/high compression motors from what I have read.Mainly due to the flapper flapping with the exhaust pulses IIRC.

George,

Thanks and Yeah, I know a little about the Flapper valve and how it can be upset by big overlaps...kind of like the old 'stove flaps' you used to see bouncing up and down on some 80's and 90's econorails. But that's precisely why I want to try this three muffler system which would Y off the open Cut-out and go to a conventional (either Reverse flow Turbo or similar) muffler.

I ran an H pipe 12" x 3" bullet on the Rocky not for any performance reason, The reason I did it was so that when I was idling the car in my driveway I could cap one of my tailpipes and I could tune the loud motor (I live in a residential neighborhood and I try to make as little "noise" as possible) and idle the car with effectively 2 mufflers in series and it was dramatically quieter...The H gave the blocked off bank of the motor a path to exhaust to the other side. It worked brilliantly for what I wanted to do.

And when it was all hooked up the Bullet muffler did reduce DB's compared to a conventional H pipe, and since it was flanged and right behind the collectors it made it really easy to get a read on the A/F mixture after a pass.

The 3 muff system will be a bit heavier but I plan to replace my pair of 19" Edelbrock RPM's with a pair of 14" VT's, I actually want the flappers to stay more or less 'shut' at idle and they should since more of the flow will go the path of least resistence (through the Y and third muffler.) The VT's will still let a little flow through (after all it's not a seal-tite valve) and should make for a nice noise absorbing pair of resonance chambers.

What I'm debating is whether to make the Y a dual 2 1/2" or 3", the 2 1/2" will be lighter and will carry a higher velocity so I'm leaning that way, I plan to use a 2 1/2 to 3" flowmaster Merge collector to join them before the muffler. I also plan to put a flange and cap on the Y as well as the tailpipes ( which now may not be needed with the VT muffs acting as check valves) just to be able to experiment with the sound.

Again I'm doing this to give me more "tune time" at home all while being respectful to my neighbors who may not share my enthusiasm for motorsports. lol.

I think I got it all sorted in my head, just gotta build it...I got to remove the tailpipes and muffs temporarily anyway to give me more room to work on the fuel pump/system upgrades I'm doing anyway. he goal is to see just how quiet at idle and lower RPM that I can get an 11.5:1 roller cammed stroker small block without costing any appreciable power.