poor quality repop silencers

[Oldhaven]

Also i tried to make it 58" from the ex' valve to the end like L/ning pipes, Always looking for more power !!, But it does seem to make more noise. Cheers Bill.

Hi Bill,

How is that measurement taken? Outside curve?, centerline of pipe?, and you seem to say you measure to the inside of the exhaust port at the valve seat for the 58"? Rough measurement of my std twin exhaust shows the rear longer than the front by 3 1/2 " measuring from the outside of the tight exhaust nut on the outside curve. The length for the front pipe is a little over 61 and the rear is likely 64.5 or so. If you add inside the port it must be a couple of inches more. Hard to measure. (Probably last century news to most of you, but I never thought about it. I was just pleased if they fit well.) BTW the new pipes I am fitting, of unknown origin but from the 1980's, are 15 Ga., .o67 plus 2 thou chrome for .069. They go right on without a struggle and were bought by my brother, who owned the project at the time, at the same time as the Toga, probably from Coventry Spares. Metal thickness must have a lot to do with sound dampening. I am sure that is well researched also and far more complex than I care to know much about.

Ron

 

[Oldhaven]

I just measured the beat up exhaust pipe that came with the B project, probably not original, and it is 18Ga. so not as thick as the one I am using. I wonder if the pipe bluing is greater with this thinner wall thickness?

Ron

 

[Bill Thomas]

Hello Ron, It was only an aprox' Measure, I am not clever, Just a bit of fun, And it was on my Comet, I just thought it looked too long, So I may as well take a bit off, And try and get it close to the race pipes length, I have done this all my life, Sometimes it works sometimes not !!I would take the measure on the centre line, Years ago on my Blue twin road bike, I had two pipes with alloy ends, Sprinting 1/4 mile did 13.5 sec' Rain or shine !, I got my brother Ron to weld 6" on each end, It killed it, !! 14 .5 sec' !!, Did not know if it was something else, Got the saw out, Took 3" off, = 14 sec !, Saw another 3" off, Back to 13.5. !!. On Twin front pipes, I have seen a lot of differance, Some of the ones in Aus',The front one goes a long way forward, I have a set on my road L/ning that nobody could fit !, They were very cheap ! so I made up a stub fitting, If it is going Blue, Is there a hot spot where the gases are getting stuck ?, I have seen this on twin pipes where they go two into one, Some are very bad there. Soon be spring, Cheers Bill.

 

[Howard]

I got myself a Db meter but as I have said previously* it depends where you use it.

Too true. At a Cadwell track day last year Richard Kettle's twin on open pipes registered 95 dB but my road twin scraped in at 105 !!! We think one of Richard's pipes (one on each side of the bike) is screened from the meter - my rev counter may have been reading low.

Regarding pipe length. Early 80s I read a Piper tuning manual, and calculated the exhaust length from their formula for the Comet at 6000 rpm, and that came to 34" on an open 1 5/8" pipe (reached about the RFM pivot point). The difference in power over the usual pipe reaching to the rear wheel spindle, was so great other Comet riders set about their pipes with a hacksaw. Checking the usual length suggested it was tuned for 4000 rpm, which confused me until sometime later I found race regs from the 50s that said exhausts had to reach to the rear spindle as a minimum. Like most things, it doesn't matter how much power it makes, if it doesn't make it where you need it, and times have changed from the good old open pipe days.

H

 

[b'knighted]

Got the saw out, Took 3" off, = 14 sec !, Saw another 3" off, Back to 13.5. !!.

Did you consider taking off another six inches to get down to 12.5?

 

[Nulli Secundus]

Did you consider taking off another six inches to get down to 12.5?

Maybe that is what they did with the Combat Commando.............

 

[Bill Thomas]

Always Ian !! But you must remember this was a road bike, It took me many years to get down to 12. 5. And a differant bike !, But same engine !, In the end I went with two pipes going into a home made silencer, With a huge end hole !, Now that did work, But it was also a road bike, I did what Howard said and it finished at the wheel spindle, But it was very loud. Cheers Bill.

 

[usefulidiot]

well i got the Spares Co. silencer in the mail today. Started the bike with the Cambells, then swapped for the Spares Co. one to have the difference fresh in my mind. HUGE difference in sound. Definitely a lot louder (which i like) and the crispness is there as well. Sounds impressive! Unfortunately i ran out of spare time before i could do some test and tuning but so far i am very impressed! will report back!

 

[usefulidiot]

Well I am impressed. Re-jetted to 180's this morning and went for a test ride. It now pulls cleanly in top gear from as low as 50mph! It never would have done that with the awful Cambell's silencer on it. My cruising speed of 70-75 i no longer have to downshift to pass someone its pretty effortless! Couldn't be happier. I hope this info helps someone.....the Spare's Co. silencer is good.

 

[Bill Thomas]

Hello, You have made the same mistake as I always do !!, You have changed two things at once !, Now you will have to put that old silencer back on!!, To see if it was the rejeting that made it better, Just a bit of fun, Bill.