[Nicks67GTO]

Hey guys. I'm posting this here because the traffic is best. I built a custom exhaust last year for my GTO. It has dumps that exit right behind the door at a flip if a switch. It's pretty cool but overly loud. It sounded like a low compression truck engine with my old mild 455. I would like to baffle these somehow to kill some of the sharp noise that comes with an open exhaust and give it a bit more of that racecar exhaust punch this year. I've got PaulK building me a strong 4"stroke 400 and I want to Crack these while I'm autoXing or running road course and let it sing the song of its people. I'm aware I'll be cutting the dumps back apart to do this. For what it's worth, later on I'll be finishing the tail pipes out the back but that's for a later project. Does anyone have any suggestions?

[Skip Fix]

Slide some Supertrapps in? I know some of the Prepared class guys used them when I autocrossed but they were close to the dB rating.

http://www.supertrapp.com/product_se...t.asp?CatID=27

[David Jones]

SuperTrapps came to mind for me too.

[Nicks67GTO]

So how do supertraps work? Do they muffle things a bit?

[ta man]

Start fresh,use a x pipe with your dumps.

[Nicks67GTO]

I had an X pipe and got rid of it. There's not much if any major audible difference between the X and H and the H can be tucked up under there a bit where the X was hanging down and very noticeable.

[77 TRASHCAN]

Dynomax and others make real short "racing" mufflers that have minimal sound help

[David Jones]

http://www.supertrapp.com/product_se...auto/index.asp

I used to go over to the IMSA races at Road Atlanta...back in the day. Many of the RX rotary Mazda's ran a Super Trapp muffler. It made them...bearable.

I'd call and see what they suggest.

[NeighborsComplaint]

http://www.supertrapp.com/product_se...t.asp?CatID=27 ? Tunable by number of discs installed.

[Formulajones]

For what it's worth, I run 2 cars with cutouts like this and had 2 different locations. They are supposed to be loud but to answer that question, they simply sound better the closer you get them to the headers.

Having them that far back in the system does make them sound a little odd, almost tractor like. I think muffling them is going to defeat the purpose of having them.

[Nicks67GTO]

Originally Posted by Formulajones

For what it's worth, I run 2 cars with cutouts like this and had 2 different locations. They are supposed to be loud but to answer that question, they simply sound better the closer you get them to the headers.

Having them that far back in the system does make them sound a little odd, almost tractor like. I think muffling them is going to defeat the purpose of having them.

The kind of racing I do require the exhaust to exit behind the door and in some areas to come in under 103 decibels at a given rpm/distance. They do check too. I'm just trying to take the edge off of them. Not necessarily muffle. Think 67 427 corvette sidepipe sound

[rohrt]

Originally Posted by Nicks67GTO

The kind of racing I do require the exhaust to exit behind the door and in some areas to come in under 103 decibels at a given rpm/distance. They do check too. I'm just trying to take the edge off of them. Not necessarily muffle. Think 67 427 corvette sidepipe sound

Just curious why that is required?

[Nicks67GTO]

Originally Posted by rohrt

Just curious why that is required?

On cars and cones last year Natonal Corvette Museum was checking. They made Ryan and I shut his side pipes in his 63 Nova and DSE had to shove baffling in the side pipes in their white corvette or they were done. I'm not 100% sure what all the reasoning there was but I believe it was a city ordinance and angry local residents. The exit behind the door is probably to keep noise down too I'm guessing.

[Harry The Hammer]

Maybe some Vortec inserts would work?

http://www.speedwaymotors.com/Dynate...-In,58203.html

[Sirrotica]

Schoenfeld makes race mufflers for sprint cars etc.

http://www.schoenfeldheaders.com/mufflers.html

[Tom Vaught]

Put a simple Balance Pipe right at the entry point to the to cut-outs where the pipes "y" off and see what you have.
More exhaust pulses seems to change the sound a lot and the sound is NOT like a X pipe sound when the Cut-outs are open.

Tom V.

[Schurkey]

Are you going to tune the carb 'n' camshaft for the 2% of the time that the exhaust is "open", or for the 98% of the time that they're closed?

"I" would scrap the exhaust dumps, build a proper, low-restriction muffled exhaust system, and tune with the mufflers in place. But then, I have an exceedingly low opinion of exhaust dumps.

[goatless]

I've got admit that I'm a little confused by what you are trying to accomplish? The only thing behind your cutouts is a muffler and a turndown? I'm not sure using the cutouts gains you anything other than noise… and now you want to muffle the cutouts?

I would think eliminating the cutouts and going with a good flowing straight-through muffler would perform the best… and eliminate unnecessary weight and complication.

[Skip Fix]

FWIW my car runs 10.90s through an X pipe mufflers AND full tailpipes-and it was identical to open headers. I'd just run it through the mufflers to meet dB specs. I would almost guarantee the 5-10 HP difference cutouts might make in an autocross your driving,tire pressure will make a bigger difference in track time.

When I autocrossed in N CA and here in Houston SCCA they would occasionally have a dB meter near a stretch to be sure you met noise.

Supertrapps slide in pipe and as they said number of discs changes sound.

[Tom Vaught]

He wants to have that "two mode" set-up, apparently.

I attempted that deal for some period of time in the 70s.
I needed a semi-quiet mode for street driving and a go fast mode for the vehicle to properly perform in acceleration contests, not Woodward stop light to stoplight racing.

So I welded up some 3.5" marmon flanges on to the 3.5" collectors and the large diameter 3.5" head pipes. The head pipes were 3.5" until right before the to 2.5" inlets to the mufflers. Then low restriction mufflers and short down pipes.

No noise restrictions where we were "testing" our engines.

The head pipes had twisted wire connections that allowed removing the marmon clamps and the head pipes would swing out of the way of the now open 3.5" exhaust path.
15 seconds is all it took to be in "test" mode". You carried the weight of the rest of the exhaust system but no different in that respect vs the OPs design.

30 seconds or less (if you had a friend and extra gloves to hook things back up) and be on your legal way.

But that was a optimized Dual Mode set-up, not a "compromize dual mode" deal and it was quicker to use vs dumps. and no exhaust was constantly passing thru the normal exhaust system. Deal is you can't play noise games like "The Humbler" at the drive-in.

Tom V.

ps In the Trans Am racing days with noise restrictions and Sound Guys/Race Muffler People helping we would monitor track numbers until the noise limits were barely met at the sound traps. The Race Muffler People would remove the loud mufflers, swap in a different set based on our readings and the car would try again. Usually we could get the racer legal and still keep 99% of his power on the course. But it was a Trial and Error deal.