Bonneville America Forums Forums Technical Forums Exhaust Modified Stockers...the sound of sweet success!

Call me a mad man, call me..well most anything but I let my 19 year old son ride my Bonnie America last night as a special treat for helping me fix a flat on it's rear tyre (picked up a nail and BTW this job of remounting goes much better with three sets of hands!)

Back to the tail at hand. As the lad pulled away, I listed to that beauty as she rumbled down the road. Not in obnoxious thunder of the impending apocalypse, but a beautiful, mellow rumbling sound that was unique to any bike I have ever heard. It was clear this was no "little toy" rolling away!

And I listened as it rolled down the road out of site and heard it un-interrupted as he drove two miles down and then two miles back. It was so cool to hear because that was my "Bonnie" piercing the quite night air! MAN, that sounded soooo cool!

Let us hope that you and he celebrated with a bit of yeast samples!

how did you modify them? how about a write up for us who want to try

My mods were done using Mikesr's hole saw into the first baffle and bmwhd's idea of drilling half inch holes into second plate. He reccommended 4 but I goofed on first hole so I had only room for 3 holes and that is what I stuck with.

After a summer of riding it has mellowed even more.

That was it. If I had the bucks I could sneek away from my accountant (wife)I would buy some Thunderbike pipes, but there are a lot of other things ahead of that and stock mods are the least expensive option.

ed

Did you remove the baffle and drill the holes all at the same time? Last year, I removed the first baffle only, and the sound is nice and mellow. Just wondering if I drilled holes in the second, if there would be that much difference. I too, would like to go the Thunderbike route, but not right now.
Dad

Hey Dad,

The difference between the first baffle and the second is as notable as the first from the stock, in about the same increment.

Not scientific, but notable. Everyone who hears it says it sounds just right. I didn't want something to make me deaf, just something to sound cool. I heard an America with Bubs on and they were too loud for my taste. That is the only comparison I have to make.

I had bought a set of pipes off eBay in case I didn't like teh sound....well I still have the back up pipes tucked away!

Congratulations on your birthday, Ed!

Thanks Piper!

I did my stockers in two stages.First I remove the rear baffle with just a drill motor and bit,drilling repeatedly till the baffle was free.This sound is nice,A bit louder than stock with a much throatyer sound.So I thought if small increase was good more would be better.I drilled 4, half inch holes in the next baffle with a standered bit just held in the tip of the drill chuck,it just reaches.I am varey pleased with the results,Not much louder but a deeper richer tone.It remindes me of my 70 bonnyville.

I'm considering doing a similar mod to my stock exhaust also. I'd like to know what I'm drilling into before I start. So anyone care to give a more detailed description on how these pipes are constructed internally. Here's what I think know from reading various posts. There are 4 baffles in the pipes. Start by cutting out the rear most baffle and go from there. It's obvious to me that the rear baffle is welded in and I'm going to cut it using the hole saw method. How are the remaining baffles held in the pipe? How far are the baffles spaced from each other? Is here 1 or 2 plates holding each baffle? Any info would be great and if anyone cares to post a diagram of the construction, even better! Thanks for your help.

Dave

Hey Dave,

The distance between the end baffle or end plate and the second baffle is 6.5 inches. I left the edges of the first plate 1 1/2" hole at that diameter to act as a "restrictor" rather than cut it back to the full diameter of the pipes themselves.

Baffles not only quiet it down but help generate back pressure to heat the exhaust to add in combustion which factors in the process some way. But even if this was bad advise (From Helicopter mechanics) I chose not to get too close and risk damaging the outer wall of the pipes. I shot some black heat paint up there and darkened it up and it looks great, sounds great and has worked great for me. The tone issue mentioned is the real treat and the tone drops with each baffle you tap into. But I stopped at two as in the picture below.
Baffles

Thanks for the info that helps a lot. That picture is great. I agree with you about leaving lip, not so much for performance reasons. If I decide to remove all the stock baffles and put in an after market one, then the lip leaves a nice stop and a little meat to anchor the aftermarket baffle into.

Regards
Dave

Made a better picture of the baffel.

Baffel modification

I was thinking about a way to finish the end plate once there is a 1-1/2" hole in it. Here's what I'm thinking. Take a cheapo 1-1/2" chrome exhaust extension for a car. Maybe a turn down style. Weld up some mounting tabs on it and then screw the tabs into the remaining lip on the original baffle plate. So what you would have is a slash cut with a turndown comming out of it. Obviously a straight or slash cut extension would work too!

I'm getting ready to do this mod as per the picture.
Two questions first though.
I was going to use a 1-1/2" hole saw to cut the first baffle, but could not find one deep enough to fit over the stock inner pipe on the first baffle. Every hole saw a found was about 1-3/4" deep. The tube is about 2" long. I modified a hole saw by cutting it in half and welding on a length of pipe like I've seen elsewhere. Just wondering if that's what everyone else did or is there a better way?

2. If my math is correct then the four 1/2" holes in the second baffle have the same area as a single 1" hole. Any opinions as if a single large hole would perform better than the 4 smaller holes? I'm thinking along the lines of which would flow smoother (turbulent vs. laminar exhaust flow).

vintage6t, The wholesaw rig you made you sounds similar to the ones I have seen pictured on this site. I just drilled a bunch of 3/8" holes around the center pipe and then connected the dots with screwdriver and hammer.The end plate is very thin so this took very little time and effort. The remaining ring of metal is only attached by three or four tack welds, again short work for your screwdriver and hammer. After drilling three 9'16" holes in the next end plate I was not satisfied so I ended up removing the next baffle altogether using pretty much the same technique as the first baffle removle. I now have exactly the sound I was looking for, the bike runs great and I did'nt have to mess with the carbs. I hope this helps, good luck and have fun!

OK, I'm confused. What about the tapered section at the rear end of the stock speedy pipes? Do you guys cut that off? Then start working on the baffles? Or, is there some trick to cutting a bit enough hole in the cone to get a 1.75" hole saw up to the last baffle?

I was thinking the same as I have only seen it done on America's, has anyone done this on the standard SM pipes and is there any pictures?
I too would like the Thunder pipes but can't justify the cost to my accountant (the wife)yet

Dinqua have a good (as always) step by step writeup of removing the baffles on the Speedmaster pipes.

Pat´s site

I've modified my Speedmaster pipes. No photos I'm afraid. Being a cheapskate I decided to do it with the tools I had to hand. Here's what I did:

1 - Drilled a series of 5mm holes as close together as possible around the end of the exhaust (in the black bit between the tube and the outside of the exhaust).

2 - Hit an old screwdriver with a lumphammer to pierce the metal (the black bit) and connect the series of 5mm holes together.

3 - Insert the old screwdriver down the "slit" I'd created in the black bit and hit it with the lumphammer until the plate the driver is pushing against is pierced. The plate is approx 8" inside the exhaust. Gradually work round in a circle until the plate is pierced all the way round.

4 - Pull the inner tube out of the exhaust. It should come out with part of the inner plate attached to it.

5 - Use a small grinding wheel attached to the end of a drill to grind the inside of the exhause exit smooth.

It worked for me, honest I've got a few minor scratches around the inside end of the exhaust, but nothing that you'd spot unless you were looking for it. The result is an exhaust that sounds just right IMO. Not too noisy, but a bit throatier than standard.

I bought a secondhand set of standard pipes as insurance before I did it.

If I was doing it again I think I'd use 2 hole drills on the black bit - one just big enough to go around the exit tube, and the second one almost the full diameter of the inside of the pipe. That would leave you a nice neat circle to work in when removing the inner plate, and should mean less chance of scratches.

I'm looking out for another cheap set of standard pipes to test my theory

Simon,

Hello, my name is Mike Sr. and I'm a cheapskate.

Get yourself a 1-1/2" carbide hole saw and cut it in half. Weld in a piece of the same size tubing between the 2 pieces you just cut. Make it as long as the number of baffles you wish to remove (30" worked for me). If you go slowly (very important!), you can slice thru all the baffles including the offset tubes. Check to see that you are progressing on a straight path frequently. You will leave enough of the baffle to maintain some back pressure and tone it down a bit. Do not use a big, powerful drill! It will knock the teeth off the bit: Better to go slowly with a smaller drill that occasionally stalls.

Worked for me.

Excellent, I was wondering if something like that would work.

Here are some sound clips of my bike with stock, then after I took out the first baffle (end plate) then the second clip is of the bike with teh second plate drilled with the 1/2" holes.
First file is a ram which may require Real audio second is a wave file.
Stock then first baffle

Second baffle

Hope this gives you guys an idea, at least what I ended up with.
ed

Speedyjon,
I use modified stock SM pipes because I like the taper.
I only used a 3/4" rotary file in a drill to modify my SM pipes. The file cut into the tube at the rear and removed enough of it to wiggle it back and forth to remove the tube from the second plate. I used the rotary file to work down the endplate until right before I got into the chrome. I used a 6" and a 12" drill bit extention to drill a 3/4" hole in all the plates, beside the tubes. I wish I'd have knocked out all the plates except the front two, leaving the connecting tube intact. These plates are thin and the welds break free easily, so a good long chisel and hammer work great. But the SM pipes being tapered creates a challenge for removing the loose metal. Get lots of compliments on sound.
Ride Safe,
Dennis

great info guys, that will come in handy this winter for doing my tba pipes, however once you modify your pipes is it necessary to rejet your carbs ?. i plan on doing 3 or 4 1/2" holes in the second plate (depending on the sound of course)

Hi Celt,
After you drill your little holes, get a hammer & chisel and whack away at the second baffle. Get a few shots of Johnny Walker Black Label and go after 3 & 4. It still won't be real loud, but much deeper exhaust note. My wife hates, I mean HATES loud pipes. She has commented several times on how good my motorbike sounds. My endplate is gone, along with the next three plates in. I have a ¾" hole in the rest of plates. If I can find another set of 99¢ pipes on ebay, I'll remove everything but the fron two plates and their connecting tube. That way, it will have plenty of backpressure, and the gas expansion into a large void which is needed for a deep exhaust note.
Ride Safe,
Dennis

Had the bike three days and just had to get some noise out of her. SO we did the standard mod as dscribed in this thread. All went well - 40mm hole saw, long drill bit for the holes in the 2nd baffle etc.

End result is that she sounds sweet but has a slight cackle when I back off the throttle. Anyone else experienced this ?

Incidently we kick her over with the zorst off and just the headers still attached. What an amazing, loud, beautiful noise !! Could be a bit hard to live with day to day but.

T.

TonyTooTimes, I modified the pipes on my BA and also picked some popping on decel. From what I gather on this site this is fairly common, the nature of the beast as they say. I think alot of that was always there but muffled by the baffles. enjoy and ride safe, Mike

Yeah after riding it today I think I just couldn't hear anything before the mod. Now I can heaar stuff and it seemed strange for a little bit !!

Thanks for the tip.

so after these mods ,is it necessary to rejet ?

Personal opinion, Have it Dynoed if you can.
If not, watch your plugs. Us old guys did that cause there
weren't no such thing availabe to us way back.

Anyone still got copies of these images they can post me

The Kid ? You have created a dream in that boy .

Quote:

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Call me a mad man, call me..well most anything but I let my 19 year old son ride my Bonnie America last night as a special treat for helping me fix a flat on it's rear tyre (picked up a nail and BTW this job of remounting goes much better with three sets of hands!)

Back to the tail at hand. As the lad pulled away, I listed to that beauty as she rumbled down the road. Not in obnoxious thunder of the impending apocalypse, but a beautiful, mellow rumbling sound that was unique to any bike I have ever heard. It was clear this was no "little toy" rolling away!

And I listened as it rolled down the road out of site and heard it un-interrupted as he drove two miles down and then two miles back. It was so cool to hear because that was my "Bonnie" piercing the quite night air! MAN, that sounded soooo cool!

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