Exhaust Experts Unite - need help for racing exhaust !!!

[RPMClassic]

OK here are the basics - 2.5 liter race motor with 46 Webers that currently has open megaphones. Need to find alternative that will get me in the 90+ decibel range.

I have tried and do not like:

phase 9's
bursch
sebring
dual supertrapps
dual megaphones with restrictor plates
dansk dual pipe

There have been mentions of Coast Fabrication and Burns, however most of the case diameters available would interfere with the lower valve covers.

Open to any and all suggestions that you guys have experience with!

Lets hear it...............

[JohnT]

I believe you have to be more specific than 90+. Noise measurements are geometric rather than arithmetic. i.e 100 is nearly twice as loud as 99, etc. Nobody I know like or tries to get to 90.

I think the limit at Laguna Seca on the most restrictive days is still 93 and most folks get there with driving technique because the muffling to get to 93 is so restrictive that the car becomes so unpleasant to drive that it's not worth the bother (run-on sentence alert!!!). People simply upshift for #5 and then 1/2 way up to turn #6 they downshift and continue around the track. 96 at Laguna is difficult, but can be met.

The material used to fabricate the exhaust has an effect. Stainless steel unfortunately produces a higher pitched "metallic" sound than good old (rusty) mild steel. Higher frequencies produce more decibels on sound meters than lower ones. You can experiment with combinations of materials in the exhaust to try to cut down the pitch of your favorite SSI headers. BTW heat exchangers will cut the noise somewhat too.

Also remember that you can do a lot about noise without goiong after the exhausts. Porsches throw off a lot of valve train noise below the fenders. 930 valve covers and some creative "deflection" sheet metal may help here. And then there is fan noise. We have used sheets of F1 air filter material attached beneath the grille to cut some of these emissions.

Attacking valve train, fan and tire noise are good ways to get inside 96 or 95 without having performance suffer too much.

johnt

[sithot]

Jashford has Coast Fabricators "mufflers" (hah!) on his '71 PCR car. They look the part and are well made. The sound is quite nice as well. He's running them on heat exchangers with extensions. I saw no interference issues on his car.

I believe Rob Oriente is the guy at Coast. 714-842-2603

Good luck,

Tom

[RPMClassic]

John -

Thanks for the detailed response. I will amend my posting with " have to be under 100 decibels" for sure. I am at 117 now and am NOT welcome back to any auto x's in my area until I find a solution.

Driving technique is surely part of the solution, but my 2.5 liter loves to rev that its difficult to have that self discipline to keep cool, even though I want to drive at WOT whenever possible

Header size is 1 7/8. I would like to find a solution that does not requires that I have a 30" muffler hanging off the rear of the car. Even 24" is a little long measured from header flange. Ideally total length would be about 21"/22". That leaves me 10-12" of length after I clear that bottom valve covers. From that point total diameter couild be in the 3.5-4.5 inch without having interferance with anything.

I believe James Pachard(?) has found a solution with Coast. He works at Limerock and is able to pass restriction. Maybe he will chime in??

With all the motorcycle megaphones on the market ( and ones that look cool without being to dramatic) - there is sure to be something out there that could be retrofitted.



Thanks John.

[RPMClassic]

Tom -

Do you have a picture of Jashfords set up?

[Steve@Rennsport]

John:

You'll get a lot of opinions so I'll just throw mine in FWIW,........


First,....why are you using 1 7/8" headers? Those are appropriate for 3.5-3.8 litre racing engines,.....even 1 3/4" is too big for a 2.5 litre motor. Headers that are too large simply kill all the mid-range power without a payback on top. 1 1/2" to 1 5/8" headers work best with the larger size used for applications over 8000 RPM. Camshaft choice (RPM range) dictates which one to use.

Last,....we've had good luck with a Series 80 Flowmaster which is a dual-in/dual-out muffler that can be configured to fit a 911 and with turn-downs, will work at Laguna. Plus, this muffler operates as a crossover, something which is even more critical for carbureted motors using aggressive cams.

This setup, proper done, actually has better usable power/torque than megaphones,....

[jashford]

I agree with Steve, 1 1/2" headers would probably work a lot better for you. Attached are some pictures of the Coast units I'm using on my 2.2S with SSI's. They are 4 1/2" dia, 12" long with a 2 1/4" opening. They have a great sound especially at full song and have met noise restrictions at WG, SP, and VIR. I don't recommend them for a long trip, sounds like a sport muffler on steriods.

Good luck,

John

[sithot]

I don't recommend them for a long trip, sounds like a sport muffler on steriods.

Good luck,

John

I don't recommend riding with him (John) for very long either. But does it ever sound good when it gets humming!
Ear plugs work good in the car, especially if you have no carpet, no sound deadening material, headliner etc. etc.. It allows you to have a conversation.

Best of luck,

Tom

[Eric911S]

Hello; Why did you not like the Phase 9's? You can add a turn down pipe to deflect the sound down. You can also use dual Flowmasters with turn downs and they work great. The sound is good as well and they are cheap to buy. If all else fails use a sport muffler. Thanks Eric

[cosley]

I've been using the Flowmaster 80 on my 3.4 race motor. I'm showing 92 db at Sears (Infineon).