750 Exhaust

chrisk

chrisk

Hero member
Location
Brisbane, Australia
I purchased some 50mm perforated tube for my SFC 2/1. Any thoughts on whether I should pack the "muffler" with muffler packing, or just weld in the bare perforated mesh?
 
Depends on whether you're going to have an open entry into the perf tube section or close the end and put all the flow through the perforations...Which again, depends on how long the perf section is in relation to the overall length of the muffler.

If it's straight through, yes, pack it. I've put a short muffler section on the end of reverse cone megaphones using perf tube with a closed entry end and no packing. It's worked on race bikes. Legal where you are ? Couldn't say.
 
Hi Chris,
I have a Shorty Megaphone on the triple that I got from Queensland.
It has a 57mm inlet / outlet with a straight through perforated core.
I think they packed it with steel wool.
Doesn't sound too bad.
Phil
 
Hi Chris - on my proddy racer Sf - i used a 2" (50mm) piece of tube stuffed to where it would go no further. i then drilled 6mm holes all along the length of it - with about a 10mm (3/8") gap between rows and left the rough material that had been broken through by the drill. i then belled it out a tad and bronzed it into the mega cone. The sound was reduced enough to get through scrutineering. your "proper" baffle tube should do the same - I noticed no drop in power either. At some tracks i had to "adjust" the needle position on my rev counter ! - regartds - Phil
 
chrisk said:
I purchased some 50mm perforated tube for my SFC 2/1
Click to expand...

Hi Chris,
Interested to hear about your results..
Please keep us informed.

Curious to learn about a convenient solution that doesn't kill perfs and design.

Cheers,
St?phane

 
phil37 said:
Hi Chris - on my proddy racer Sf - i used a 2" (50mm) piece of tube stuffed to where it would go no further. i then drilled 6mm holes all along the length of it - with about a 10mm (3/8") gap between rows and left the rough material that had been broken through by the drill. i then belled it out a tad and bronzed it into the mega cone. The sound was reduced enough to get through scrutineering. your "proper" baffle tube should do the same - I noticed no drop in power either. At some tracks i had to "adjust" the needle position on my rev counter ! - regartds - Phil
Click to expand...

Phil, there's a guy here - Graham Harris - a sidecar racer and lecturer in physics who's, I think, patented that layout.
Only difference is that he holds the center tube in with 3 TIG welds at the small end of the megga. They break ultimately...

They work quite well when it's one muffler per cylinder, quite low revs - he's made a lot of money off Harley owners...
Higher frequency, eg small fours, not so much. A twin with 2 into one is probably the limit of this layout.
 
phil37 said:
Hi Chris - on my proddy racer Sf - i used a 2" (50mm) piece of tube stuffed to where it would go no further. i then drilled 6mm holes all along the length of it - with about a 10mm (3/8") gap between rows and left the rough material that had been broken through by the drill. i then belled it out a tad and bronzed it into the mega cone. The sound was reduced enough to get through scrutineering. your "proper" baffle tube should do the same - I noticed no drop in power either. At some tracks i had to "adjust" the needle position on my rev counter ! - regartds - Phil
Click to expand...

I did the same thing when I built a 316 stainless muffler for my Honda 750/4 ......... too many 8mm holes, packed with boiler KO wool. It was as quiet as a mouse, and wasn't what I wanted.
I don't want to make it much quieter, just take away the raspiness, as heard without anything in there. (give it a nicer deeper note) The holes in the tube I have are about 3mm.

Makes me wonder what was inside WA Mikes Redax/Motodd mufflers? By all accounts it sounds great.
http://s1222.photobucket.com/user/redax5/media/14th%20July%20MN%20Motodd%20silver%205_zpsjxdqft8d.jpg.html
 
Keep in mind when you change from the stock OEM exhaust system be prepared to play with carburetor jets and timing - Less you melt pistons.
 
IMHO you can't fiddle with the factory 2/1 with its matching 5C (and maybe 6C) cams without SOME effective drop in efficiency. I ran a factory 2/1 with my 5C on the road for several decades. Initially I made up a tapering inner sleeve from std perforated baffle sheet, starting at the 50mm OD(?) after the collector and expanding to about 25mm smaller than the OD of the megaphone at the exit, so it still utilising some taper/megaphone effect with the original reverse cone. This ran really well, and curbed those raspy decibels very nicely (unbaffled they're almost louder on the overrun at +5000 than on full throttle!!). The perforated tapered baffle doesn't go all the way to the reverse cone, but ends with a blank, level with the widest part of the mega (which is the widest part of the reverse cone as well, of course!). The cavity is packed with glass fibre with stainless mesh underneath.

Later I added a parallel baffle flowing directly from the large OD of the tapered baffle. This also worked very well, even quieter (dare I say 'legal'!!!???) without killing the top end. For the 270 motors I'm going to experiment with twin systems with a short siamese section under the motor - two large ID baffled straight through mufflers.

BTW, I once ran it with the 2/1 with an open megaphone (ie no reverse cone) and it felt like a 450 Honda twin!! Zero powerband and nothing anywhere in the rev range - and noisier than the ugliest Hog you ever had to endure  :-* :-* :-*
 
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