Is it OK to run without a muffler?

[openwheeler37]

Other than the noise aspect, is there any performance advantage or disadvantage to running an open exhaust?

[Albatross]

Best determined on a dyno. Japanese have spent hundreds of thousands of dollars developing exhausts to increase the performance of their motorcycles. So,too, has Ferrari and others. Exhaust header diameter and length is generally critical as well as over all length of the entire unit.

[Randy Cook]

The only reason to run a muffler is to reduce noise. I've heard of mufflers that have no negative effect on HP, many do however, but they all add weight. If you pass sound and weight regulations, and wear ear protection so you're not deafened by the noise then there's no competitive reason to add a muffler.

PS I'm glad I started racing just as noise restrictions in SCCA began, otherwise I'm sure my hearing would be much less acute today. Please keep that in mind in your decision.

[Daryl DeArman]

If you pass sound and weight regulations, and wear ear protection so you're not deafened by the noise then there's no competitive reason to add a muffler.

Having a car that is not as loud as others in your class can be a competitive advantage.

[ghickman]

In the dyno runs we've done it wasn't the muffler that reduced HP so much as the total length and diameter of the the tailpipe past the collector, that's where the magic happens.

I did a day of testing at WSIR in my old F1000 without a muffler and it took my hearing a few days to recover, even with my ear buds in.

Out here on the left coast it probably is an advantage to be as stealthy as possible, keeps the sound police off your case. Nothing like laying down a good Q lap and having it yanked because you blew over sound. I've seen guys monkey around all day long trying to make sound which takes away from focusing on driving.

[Lotus7]

Changing the back pressure on an engine will change its behavior.... but it is not a given that it will be better. As mentioned above, great effort goes into tuning the effect of back pressure waves in scavenging exhaust ports.

[openwheeler37]

Well I guess that pretty much solves it. So my next question is, what's the best way to repack my muffler. I've taken it apart and 75% packing is gone. It has fiberglass packing in it now. Should I switch to stainless steel packing? I've never packed a muffler before. Is there a right /wrong way to do it. Thanks for the help.

[ghickman]

Well I guess that pretty much solves it. So my next question is, what's the best way to repack my muffler. I've taken it apart and 75% packing is gone. It has fiberglass packing in it now. Should I switch to stainless steel packing? I've never packed a muffler before. Is there a right /wrong way to do it. Thanks for the help.

Stainless steel packing will last an entire season. It doesn't muffle as well as glass but the trade off is worth it.

We stuff ours until it's about 80% full, we don't try to pack it so tightly that the covers are hard to put back on.

[openwheeler37]

Like I said, I've never done this before (so please dont blast me if this is way off) I spent some time googling and it looks like people are using steel wool pads (like you'd use to wash dishes) and packing the can with that. Is that corect or should I be using something else? Thanks again for the help.

[Lotus7]

Stainless steel packing will last an entire season. It doesn't muffle as well as glass but the trade off is worth it. ...

coincidentally, this months "Dirt Bike" magazine has a full page article suggesting why this is NOT a good idea.... YMMV

[openwheeler37]

coincidentally, this months "Dirt Bike" magazine has a full page article suggesting why this is NOT a good idea.... YMMV

So did they suggest to stay with fiberglass packing?

[R. Pare]

coincidentally, this months "Dirt Bike" magazine has a full page article suggesting why this is NOT a good idea.... YMMV

Got a direct link to the article? Looked at their site but couldn't figure out which article it would be in.

Most likely any resistance to using steel wool would be the possibility of small pieces getting sucked back into a cylinder with a reversion pulse.

[Jnovak]

We have used stainless steel pads that are much higher strength than the very fine Brillo style of packing. This stuff lasts forever and works. We also won many National Races in our FB Piper without any muffler at all. We did have a muffler on the car for our Runoffs win.

[openwheeler37]

So is this more like what I want to use?

https://www.pegasusautoracing.com/pr...asp?RecID=3023

[Lotus7]

We have used stainless steel pads that are much higher strength than the very fine Brillo style of packing. This stuff lasts forever and works. We also won many National Races in our FB Piper without any muffler at all. We did have a muffler on the car for our Runoffs win.

the article didnt express concern about durability, it was reiterating the importance of correct back pressure on the engine.... these repackable mufflers generate opposing radial pressure waves into and out of the packing to muffle sound, and these pressures are felt by the engine.

[Lotus7]

BTW, not trying to tell anyone they are wrong, just stating what apparent experts (not me) think :-)

[Marty Nygard]

I always used mineral wool bat. Much more effective than steel wool and lasts longer than fiberglass (but probably not as long as steel wool).
BTW, the radial pressure waves (" these repackable mufflers generate opposing radial pressure waves into and out of the packing to muffle sound") are supposed to be turned into heat energy within the packing between the inner perforated shell and the outer cylinder and should not affect flow within the muffler. But what do I know, silencer design was only part of my job description for over 30 years.
Marty

[openwheeler37]

I always used mineral wool bat. Much more effective than steel wool and lasts longer than fiberglass (but probably not as long as steel wool).
BTW, the radial pressure waves (" these repackable mufflers generate opposing radial pressure waves into and out of the packing to muffle sound") are supposed to be turned into heat energy within the packing between the inner perforated shell and the outer cylinder and should not affect flow within the muffler. But what do I know, silencer design was only part of my job description for over 30 years.
Marty

Where can I get the mineral wool batting?

[racerdad2]

Try your local lumber yard. They may be able to order some. Some call it Rock Wool insulation.

[glenn cooper]

I was told be an owner of one of my accounts, which is a Dinan BMW dealer, btw, that the whole back pressure issue is not as much a concern on our type engines as the throttle bodies are RIGHT THERE at the cylinder head.
On a typical automotive application, the throttle body mounts to an intake, which may then have a plenum, which may then have...

You get the idea.

[tedsimmons2]

Scrubble - Stainless Steel for long lasting muffler repack. Scrubble is a coarse stainless steel wool product that is an excellent muffler packing material. It appears more like mill-shavings than brillo pads. Scrubble is sold by the pound. Please refer to Burns Stainless Steel muffler web site for more details.

[openwheeler37]

Any idea if 1lb is enough? My can is 4"dia and 17"long.

[ghickman]

Any idea if 1lb is enough? My can is 4"dia and 17"long.

1lb is enough.

We turn lots of Stainless which makes nice long stringy curly turnings. We recycle most of it and I stash what looks like good muffler packing.

[Lotus7]

But what do I know, silencer design was only part of my job description for over 30 years.
Marty

thx.
as I said above, I quoted what I read, but glad to hear from someone with first hand knowledge.