New Member, Muffler Question (CMod)

[BRODA]

Hello fellow CMod competitors,

I have been wanting to try CMod for several years, and I finally took the plunge. I just purchased this 1983 Reynard FF1600 (former autocross car, currently set up for road racing):


Previously I had an STX car, so there is going to be a *huge* learning curve for me. I have already learned a lot from this forum, so thank you very much to everyone who contributes.

I have a question which I am hoping someone can help with. I did some searching but could not find anything conclusive.

The car currently does not have a muffler, and I am trying to decide what size I need. I have had great experience working with Coast Fabrication in the past, so I plan to buy from them again (they also make the Burns mufflers).

Our local site has a very strict sound limit of 90dBA measured at 75'. My question is what size muffler do I need?

Here are the three options available for a 2" pipe:
3.5" O.D. x 14" L = 91 in^3
4.5" O.D. x 11" L = 140 in^3
4.5" O.D. x 18" L = 230 in^3 (custom size)

Obviously the biggest muffler would be the most effective, but I don't want to go any larger than necessary for cost and packaging reasons.

Does anyone have any first hand experience with Cost Fab / Burns mufflers who can make a suggestion?


Thanks in advance,

Dave T
New to CMod

[chrisw52]

I have a supertrapp muffler on my CMod car.

https://www.pegasusautoracing.com/pr...asp?RecID=4302



Without any disks installed, I am right at 90db.

[BRODA]

Thanks Chris. Seems like a lot of CMod guys are running SuperTrapps. Without the disks, that's just a 4" diameter glasspack, so that's a good reference point. Just to confirm, that's 90 db @ 75'?

Thanks again,
DT

[Barry Ott]

Welcome! You'll love C Mod!!

I had a ~20"x4.5" coast fab muffler on my '88 Reynard and measured ~90dBA @ 50'. Our limit was 93dBA @ 50' and I was never over. Those numbers are from a few years ago, we've since found other sites that we don't need to sound control. My current '95 VD/Honda has a 12" x 4.5" coast fab muffler, it's only been measured a couple times but it's generally in the mid 90's. I measured high 90's in the VD/Honda once and found that the packing material was nearly gone, fresh packing material made a noticeable difference!

I'm sure you know that sound measurements in autocross are never simple, absolute, or repeatable. Margin is a good thing :-) If I were you, I'd pick the 4.5" O.D. x 18" L and give yourself some margin and peace of mind.

Good luck!
Barry Ott

[chrisw52]

Thanks Chris. Seems like a lot of CMod guys are running SuperTrapps. Without the disks, that's just a 4" diameter glasspack, so that's a good reference point. Just to confirm, that's 90 db @ 75'?

Thanks again,
DT

I believe so. But like Barry Ott said, the measurements are subjective. I like the supertrapp because if you do have issues, all you need to do is add disks and quiet the car down until you pass.

I saw the ad on Race-cars.com and your car looks to be in really nice shape. Good luck with it, you will absolutely LOVE CMod.

[BRODA]

I had a ~20"x4.5" coast fab muffler on my '88 Reynard and measured ~90dBA @ 50'. Our limit was 93dBA @ 50' and I was never over.

Thanks Barry, for both the warm welcome and the great info. Based on your experience, I think you are probably right that I should just get the big one and find a way to make it fit. Better to be under than over.

I saw the ad on Race-cars.com and your car looks to be in really nice shape. Good luck with it, you will absolutely LOVE CMod.

Thanks Chris! I didn't know my car advertised was on that site (I found the car through ApexSpeed), but I do think I got a good one. I just have a few small things to get the car ready for the season, which is rapidly approaching at this point!

[-pru-]

Dave,

Welcome to the class! When you have a chance, let me know your details so I can update the competitors listing.

Regarding sound suppression, I'll add to what Barry and Chris offered noting that we run a 14"x4.5" CoastFab muffler which works great on the DB1 (registers ~85-88 dB). As only half of events we run have sounds limits, my muffler is a slip on type only used when needed. As such, the packing lasts a long time; I just replaced the packing this off-season after 6 seasons in service (packing was still in decent shape with only ~20% missing).

Looking forward to hearing more about the car and your experiences going forward. Let us know how we can help.

[-pru-]

Regarding sound suppression, I'll add to what Barry and Chris offered noting that we run a 14"x4.5" CoastFab muffler which works great on the DB1 (registers ~85-88 dB).

As follow up, I will note that the sound readings given above were at 75' (i.e. SCCA National Event standard) and the muffler is a custom sized unit that was built and shipped with the HyTech header I ordered for my DB1 in 2010.

[BRODA]

Hi Chris,

I'm not 100% sure, but I think I met you at Nationals last year. I was there selling my RX8 and scoping out a lot of CMod cars.

Thanks for the info on your muffler. I think I will talk to Gary about getting something custom. The 21" dual core listed on their scratch & dent page doesn't sound like what I want.

Appreciate the help from everyone

DT

[PDM075]

Dave don't think you'll need a dual chamber....


On my RF84 Van Diemen and Crossle 50F both are the shorty 4" 14 inch overall (8 inch body) single chamber Coast Fabs.

We have a strict 92 dB at 50 feet rule up here in Vancouver, and I've never blown over yet.

VD runs 2.25". Crossle will be 2.0".


I run a Dual Chamber 3" on my SM 240SX (400 whp) and it fits just behind the downpipe. To make sound I add a 2nd 3" single chamber.

Chris: Repack the Coast more often..... Andy Hollis found more hp in his STS Civics with quieter sound by repacking at the beginning of each season. (tighter fresh packing made more hp in his dyno testing and kept things quieter.)

The Coast Fab is "marginally" lighter than the Supertrapps.... - I run a Supertrapp in my STS CRX and it's noisier and heavier and more maintenance. (I don't like how Supertrapps literally trap more moisture and the tiny welded nuts gall easier the more you remove and replace the long allen head bolts. (even re-applying Never Sieze religiously) I've gone through 6-8 various Supertrapps on varous cars.

don

[BRODA]

Thanks for the reply Don. I called Coast Fab yesterday and spoke with Gary and decided against the dual core once he explained what it is. Right now I am leaning toward either the 14" OAL or a custom 17" OAL single core at 4.5" O.D. Based the replies here, it sounds like I might be okay with the 14". I am trying to get in touch with a local guy who runs a FF at my site to see what he runs for a muffler, and then I'll place an order.

What I really want to do is get a new Hytech header with a muffler, but I already went over budget on the car/trailer/tow vehicle, so that will have to wait.

P.S. I used to have a 240SX many years ago and bought some stuff from PDM Racing. I hope the business/car/racing are all going well for you.

DT

[DanW]

Thanks for the reply Don. I called Coast Fab yesterday and spoke with Gary and decided against the dual core once he explained what it is. Right now I am leaning toward either the 14" OAL or a custom 17" OAL single core at 4.5" O.D. Based the replies here, it sounds like I might be okay with the 14". I am trying to get in touch with a local guy who runs a FF at my site to see what he runs for a muffler, and then I'll place an order.

What I really want to do is get a new Hytech header with a muffler, but I already went over budget on the car/trailer/tow vehicle, so that will have to wait.

P.S. I used to have a 240SX many years ago and bought some stuff from PDM Racing. I hope the business/car/racing are all going well for you.

DT

I'm using the 14" x 2" Coast Fab muffler on my Zink Z10. It makes 92dB at 50' at Laguna Seca, so at 75' you should be at 90dB or less. It's important to remember that intake roar, gearbox noise, bodywork flapping, will all add to the equation.

Regards,
Dan

[BRODA]

Thanks for the additional data point Dan

[ewcmr2]

I am trying to get in touch with a local guy who runs a FF at my site to see what he runs for a muffler, and then I'll place an order

Josh runs a big street car muffler on Stacey's car. Flowmaster maybe?

[BRODA]

Josh runs a big street car muffler on Stacey's car. Flowmaster maybe?

Yup, that's who I've been trying to contact... thanks for the info. After you posted this, I checked some photos, are you are right. Not the answer I was hoping for, but that's one more data point. Thanks

[Jim Garry]

Dave,

I ran my Citation FF at Devens for over a decade. For the first half of that time period I used a Supertrapp but always with plates in it. Then I switched to Coast Fab because it robbed less HP. Checked on dyno.

Never got a warning about sound with either muffler except for once when the engine was about to blow up.

Have fun. I'll be interested in looking at the car at Devens this spring. Do you know which autocrosser owned the car prior to the road racer you bought it from?

[BRODA]

Hey Jim!

Glad you chimed in. How big was the Coast Fab you ran? Josh is running a huge muffler on his car which is not a great data point.

The car I just bought is actually former NER autocrosser... from what Bill G tells me, this was maybe 15 years ago. It belonged to Kevin Berry, who I believe took it road racing and then sold it to Tod Powers in CT before going to NJ and then Florida where I bought it.

I actually tried to buy your old car from Sho but didn't come anywhere close to fitting. The car I bought already had the frame modified for a taller driver and fits like a glove.

See you in the spring,

DT

[Jim Garry]

Ah. I know that car. It's a nice one.

Can't recall the size of my muffler but I think it was 14? Maybe Sho will see this thread and measure it directly.

See you.

[BRODA]

Thanks again for all the guidance everyone.

For anyone who is curious, I was able to get in touch with Josh and Sho and decided to go with a custom 200x450x17. Based on what everyone has said, that should be well below the limit with enough buffer to cover me on days where the meter is reading high.

Best,
Dave

[CM/FFdriver]

Thanks again for all the guidance everyone.

For anyone who is curious, I was able to get in touch with Josh and Sho and decided to go with a custom 200x450x17. Based on what everyone has said, that should be well below the limit with enough buffer to cover me on days where the meter is reading high.

Best,
Dave

If Dave hasn't found a Muffler yet he get it first but I have a Coast muffler for sale Dave, it's 200x450x14 in total length but 8 inch long barrel length.

$310 new, $250 shipped

Ben

[BRODA]

Hey Ben,

Sounds like a good deal, but I already bought the custom 200x450x17. If anyone is curious, it is very quiet. "Quietest mod car I've ever heard" is what someone said. The club I ran with didn't have sound logs available, but I don't foresee any issues.

Good luck with the sale Ben.

- Dave

[Albatross]

About 3 years ago one of the vintage FF racers tested different exhaust systems on a dyno located in the Portland, Or area. The exhaust system with the Coast muffler produced the best Hp. That driver/owner has never removed that muffler except to repack it once.

[CM/FFdriver]

About 3 years ago one of the vintage FF racers tested different exhaust systems on a dyno located in the Portland, Or area. The exhaust system with the Coast muffler produced the best Hp. That driver/owner has never removed that muffler except to repack it once.

Hmm...something to ponder and I just found out that I would be saving .37 of a pound in weight, so whats the point.

Ben