Muffler Needed?

[Fprodget]

I plan to run my crossle in C Mod at some SCCA autocrosses when my son takes his FJA Kart out this year. My question is if a muffler of some type is definitely needed to meet the sound requirements?

In the Philly Region they require sound to not be in excess of 96db "A" weighted slow response at the measuring point. Their rules also state that the sound measuring device will be located 50 feet from the driving lane.


Does any one out there have any experience if I would be okay with nothing at all???

Thanks

[SWMyers]

You will need a muffler. I did some sound testing with an FC several years ago. An open pipe was 100-103 dB at 50'. I tried several commercially available mufflers with results ranging from a low of 90 dB to a high of 98 dB. Your best bets will be either a Supertrapp or a straight through muffler with at least 250 cu. in. volume.

[Dick R.]

For my autocross FF1600 my "sound sensitive site" exhaust pipe has a super trap 2 inch "250" cid end with no glass pack . . . just the max number of baffles. A local race shop built two easily removeable tailpipes which connect just to the rear of the header collector. I swap tail pipes based on the needs of the event. The setup uses a Kawasaki muffler spring to hold the "tail pipe of the day" to the header. Interlocking tabs are on the mating parts. The race team was IMSA GTU Datona 24 Hour winning Team Highball. They held the mufflers for rotories on with those springs.

Disclaimer. I've never been to an autocross where really strict/accurate sound measurement was done so I don't know if my setup will meet your rules. When I went to events at Harrisburg, PA I don't remember if mufflers were required.

However, even a unmuffled FF1600 is quieter than many ST cars unless they have a serious muffler :-)


Dick
CM85
Van Diemen RF-85

[rickb99]

Fprod,

Has the Crossle been run any place in the past? Should have had a sound reading taken on it to give you some idea of where you need to be for muffler.

Obviously there's a difference between the Pinto and the Kent. But, we run the 17" Supertrapp glass pack 2 1/4" inlet with ZERO baffles/diffusers. Sound is 92 dB.

[Fprodget]

I have not yet run it anywhere. I bought it last may and have been restoring it. I am nearly complete now.

[Jim Garry]

What model Crossle is it?

[gmmls]

an elbo pointing the exhaust at the ground may be enough

[Fprodget]

What model Crossle is it?

Jim,

It is a 62F.

[Fprodget]

an elbo pointing the exhaust at the ground may be enough

I was thinking of trying the elbow trick first.

[rickb99]

Well, if no muffler came with the car you may be okay using an adjustable elbow to point away from sound station. Straight through or the elbow works on most Kent's and Pinto's where the sound limit is 103 dB but I dun-no about 96 dB.

If you don't want the expense of a racing muffler (if not needed), go down to your local Midas shop. Ask to look in their scrap metal bin. You can sometimes find a short old blown out glass pack that would get you through the weekend if needed. Find the right person and they'll keep an eye out for one just for you and set it aside from the recycle bin. Worked for finding a 'garage muffler' here.

Don't know about about "back there" but, out here, we run into some odd stuff. Portland International has a sound limit of 103 dB which, as I said, can be met by open exhaust Kent's and Pinto's. HOWEVER the track supps. state you MUST run a muffler on all cars. Well shucks. P.S. - rule not really enforced

[WAM]

I run a Lola T540 FF at San Diego, famous for their sound control program. They require 95 dB max @ 50-ft, so not so different from your case. Biggest lesson learned is nothing convenient works all the time. I'll go thru a half dozen events without even hitting the 90 dB warning threshold, and then one day the sound police walk up and tell me I'm illegal. Bottom line is sound measurement is complicated and involves factors that seem to be beyond our total understanding. So that said:

I normally run a SuperTrapp glasspack, about 20" long and no disks at all. This gives less than 90 dB almost always.
On a bad day, I add the 20-disk package to the end.
On a really bad day, I cut the disk count to maybe 6.
And if I've had a few bad days already, and they're starting to get irritated, I change to a Walker DynoMax mini turbo muffler that doesn't fit well at all and looks just wrong.

None of the above is a recommendation -- just data.

-- Bill

[Fprodget]

Thanks for the replies. I am going to try an event with nothing and go from there. It seems I might likley end up with a supertrapp.

[Chas Shaffer]

The coast muffler is excellent. For $250 buy it and forget about it. It doesn't impact performance at all. The 4.5 x 14 will quiet the car nicely. Order it with the stainless steel scrubble instead of the fiberglass pack.

http://www.coastfab.com/ultralightweight_mufflers.html

[Dick R.]

Bringing this back to life with a question:

Does anyone have any power reduction and/or noise comparison between a SuperTrapp with NO muffler, just the discs and a SuperTrapp "glass pack" style with no discs? I currently own a "quiet site" exhaust pipe with the 4" OD, 2 " ID, 250 cid disc only unit with 12 discs. I'm curious whether the 12 discs offer any significant power reductions for a 1600 FF and, of course, how much relative sound reduction. None of my local events measure sound that I know of.

Thanks!
Dick
CM 85

[Jim Garry]

Dick,
I don't have back to back numbers. All I've got is that at Lincoln I was measured at about 102 dB with no muffler. I believe that was taken at 75' but I'm not certain.

Meanwhile, at Devens using a Supertrapp which has a glass pack and about 10 plates (?) I've never been over the dB limit which is 90 at 75'. Oh, wait, one time I was over and when I examined the fiberglass it was really beat up and burned out. Replaced it and haven't had any problems (although I do carry a spare package of it).

[Dick R.]

Jim, Thanks for the response. The rule books specifies 50 feet from the course lane for the sound measurement. Does this seem reasonable given the site layout?

What length SuperTrapp do you have (10" or 17")? Is it held on with a clamp?

I have a welded disk only (12 disks) tailpipe assembly that may be adequate for most sound controlled sites but am considering a clamp-on 10" for my open pipe for stricter sites. I think the pipe is short enough that the extra 10" inches will be OK per the 8" extra allowed for "95 dB or below" sites. If you have a 10" that would be good news.

Thanks!

Dick

[Jim Garry]

My muffler is 10" (I had to edit my original statement which was "mine is 10" ).

Welded a bolt thru plate to hold it on.

[rickb99]

...What length SuperTrapp do you have (10" or 17")? Is it held on with a clamp?

We have a noise limit at Portland and Pacific Raceway of 103 dB at 50' from the track.

With NO muffler on the FC and a straight pipe (no turn away end) we are smack at 102 to 104 dB and occasional 105 dB.

Use a 17 inch SuperTrapp with ZERO baffles (straight through) and we're at 92 to 93 db. Power loss has got to be minimum.

Last race of 2009 we were getting 'high' readings at Portland again like NO muffler on (strange). Opened up muffler and sure enough, the glass packing was shot. Track side vendor (Armadillo Racing) had a replacement package of glass. Repacked it and back down to 92 dB.

Yes, the SuperTrapp has a 'split' end for clamping on the pipe. But it's TOUGH steel and hard to get a good tight clamping. We clamp it on the pipe. have a safety wire around the clamp to an existing bracket on the bell housing AND have an extra support bracket with clamp off the rear wing. If no wing, use one of the bolts on the Hewland.

With the design of the SuperTrapp, I've been tempted to slide if further on to the pipe to try and get sound UP to around 98 to 100 dB but I haven't played with it yet.

[Dick R.]

Thanks Jim and Jeff for your detailed responses. Lots of good info. Plus Bill M's previous info about San Diego is useful!

"Sounds" like in addition to all the normal sound level variables, a BIG factor is the condition of the "glass pack" for those units.

Does anyone have any data on the power impact of various numbers of discs? If my current 12 disc only unit isn't costing any power, I'm probably fine for ALL events I go to. However, I don't want to start doing that without some facts.

If the disc only unit isn't a good solution, the next option might be the 17 inch long, 2 inch inlet glass pack with zero discs or maybe around 20 discs (which SuperTrapp says is effectively open).

Thanks,

Dick

[Dick R.]

I emailed SuperTrapp with my FF1600 specific questions and got the following succinct and to the point response:

The 'disc only' units do VERY LITTLE in sound reduction and I don't think
would do anything for you.
You need a muffler to absorb sound, the 443-2017 would be a perfect choice.
The small motor, 12 discs will flow way more than enough, probably increase
the mid-range pull, and should quiet it down.

The 443-2017 is a 2" inlet, 17" total length S/C Elite. It comes with 12 discs.

Dick

[Bill Steele]

I use a short (10") Supertrapp straight through (no discs) when I need my Kent engined Crossle below 103 dB. At Laguna when we regularily need to be under 101 dB, I use a Coast Fab. My numbers are regulariy down in the 97-98 range with the Coast Fab muffler.

I got tired of the cost of the repack kits on these units and started buying fiberglass woven matt in bulk from Jamestown Distributors (boat building supplies), much cheaper, works great.

Good luck.

[Dick R.]

Bill,

Thanks for the info including the alternate fiberglass source.

Based on Jim Garry's experience with the 10 inch SuperTrapp I may pick up one to clamp onto the straight pipe when the current disc only unit is not enough. My wife really doesn't want the car to "routinely" have any muffler visible plus she thinks a formula car should be loud when allowed to be . . .

At least now it appears from SuperTrapp's input that 12 discs won't cost power.

Dick

[Bill Steele]

.... My wife really doesn't want the car to "routinely" have any muffler visible plus she thinks a formula car should be loud when allowed to be . . .

Some guys have all the luck...

[TedV]

10” supertrap with 16 disks, attached with T-bolt clamp. Was 93 to 94 DbA at last local event. Nice thing with Supertrap, if you are over, all you need is pull out a few disks for your next run. Yeah you have to have the right sized hex driver handy, gloves help too. I was over 96 once with 20 disks, pulled out 4 and was at 92 that day.

I also run sound control for our local events. I’ve had folks ask “what’s wrong with your car, it’s not as loud as other mod cars?”

[Lynn]

I was just re-reading this thread and there is something that really needs to be mentioned. The road race rules require that the sound meter be set to fast response. The solo rules require the meter to be set to slow response. What I have found on various sites concerning sound levels is that the same sound pressure (loudness) will have a 6dBA difference between the fast and slow settings. The road race standard of 103 dBA fast response at 50' is the same as 97 dBA slow response at 50'.

[t walgamuth]

I had a resonator left over from my 99 mIata which i put on my FF. It weighs 6# and is stainless body and I am legal. It will work for now.

[jdp526]

I put an inexpensive stainless, 'carbon fiber wrapped' muffler on my FC that I started autoxing back in Jan. It's pretty quiet and club hasnt had any noise issues with my car. Muffler does have a removable 1" baffle but I havent had to use it. Looks like I could drill out the rivets if I need to repack the thing. And it does come with a ss clamp. Cost me $50 with shipping. It weighs around 3.5 lbs. I made a simple bracket to mount clamp to side of trans.

http://shop.ebay.com/i.html?_trkparm...4.l1581&_pgn=3#