Done this before!

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Wish I'd known about extending the collector pipe !!
That alone is just a start. The gutted megaphone with the SuperTrapp disc setup makes the exhaust tunable to a greater degree. It took a lot of discs to get my motor to wake up where I wanted it to, but every motor is different.

BTW, I got the extending the pipe idea from an old Norton road racer I talked to at a motorcycle show and swap back in the late 70's. I didn't tell him it wouldn't work. I tried it instead.
 
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Fast Eddie

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I never said it won’t work… of course it will work!

But as to whether or not it works any better or worse than a dozen or more other permutations, that’s another matter entirely.
 
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I never said it won’t work… of course it will work!

But as to whether or not it works any better or worse than a dozen or more other permutations, that’s another matter entirely.
If I changed my name to Maney or Comstock, would it work better than other permutations? :)

It works much better than it did new. Bubb did a good job with the look though. It's a very tunable exhaust now. Should be straight forward and simple to understand why it works better with the gutted megaphone and SuperTrapp.

Edit: Forgot to mention there are no other permutations of the 2:1 exhaust on my P11 in the world as far as I know. It's a one off I had made for my P11 by Bubb Enterprises in San Jose CA. I later modified the length behind the collector and installed the SuperTrapp setup, so it was tunable. Very unlikely anyone else had Bubb make one for a P11.
 
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Fast Eddie

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Steve and Jim spent dozens of hours on the dyno with their pipe designs. Trying numerous permutations of length, diameter, bend radius, megaphone shape, etc, etc, etc, it’s such permutations I’m referring to, why weld in 4”? Why not 2,3,5,6,7 etc, etc?

So yes, when they say something works, it’s usually very well proven. So yes, I’d tend to believe them.

I put a Maney pipe one mine and it gave a 5 BHP difference, even more in the mid range. After having the head ported and the followers radiused to reduce duration, all of those gains disappeared, there was virtually no difference between it and stock pipes and peashooters anymore.

What this taught me was that a surprisingly small difference in cam operation can have a huge impact on exhaust function. A simplified rule of thumb is, the more radical the cam, the more sensitive to exhaust tuning.

So, as Chris‘s pipe is of unknown make, and certainly not the same as your one off, and he is using a radical race cam, etc. I basically stand by my point that modifying it would need to be done carefully.
 

gortnipper

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Steve and Jim spent dozens of hours on the dyno with their pipe designs. Trying numerous permutations of length, diameter, bend radius, megaphone shape, etc, etc, etc, it’s such permutations I’m referring to, why weld in 4”? Why not 2,3,5,6,7 etc, etc?

So yes, when they say something works, it’s usually very well proven. So yes, I’d tend to believe them.

I put a Maney pipe one mine and it gave a 5 BHP difference, even more in the mid range. After having the head ported and the followers radiused to reduce duration, all of those gains disappeared, there was virtually no difference between it and stock pipes and peashooters anymore.

What this taught me was that a surprisingly small difference in cam operation can have a huge impact on exhaust function. A simplified rule of thumb is, the more radical the cam, the more sensitive to exhaust tuning.

So, as Chris‘s pipe is of unknown make, and certainly not the same as your one off, and he is using a radical race cam, etc. I basically stand by my point that modifying it would need to be done carefully.
One thing I have been wondering about the exhaust dyno sessions you did, is if there were any jetting changes with the exhaust changes?
 

Fast Eddie

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One thing I have been wondering about the exhaust dyno sessions you did, is if there were any jetting changes with the exhaust changes?
Yes there were. Using the AF probe gave an indication of what to do (I say ‘indication‘ as I know there are opinions about how accurate such methods are, distance from the port, etc).

The Maney 2:1, and the Brooking850 Maney replica both required the same changes: they needed considerably weaker needle settings compared to the peashooters.

The needle covers a broad range on the FCRs though. None of the runs indicated a requirement to change mainjets interestingly enough.

Neither were any changes required post the comnoz head work.

The engine is now very different, being a 920 with Maney race cam and Maney stage 3 head. I haven’t been back to the dyno yet but do intend to soon (ish).

Obviously, being a full Maney motor, the Maney pipe should work at its best on the current set up. But I’m currently running peashooters again as I prefer the noise. My arse Dyno says there’s not much noticeable difference, but I learnt not to trust that a long time ago !
 

gortnipper

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Was there any difference between the two "Maney's" or were there confounding changes in between?

(Apologies for the rat hole)
 

Fast Eddie

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Was there any difference between the two "Maney's" or were there confounding changes in between?

(Apologies for the rat hole)
I tested the Maney and the Maney replica back to back quite early on and detected no differences between them and they both needed the same needle changes.
The Maney pipe was on loan though (from Chris, the OP) and I only compared them that one time. All subsequent work has been with the stock pipes, 1 1/2 big bore pipes, peashooters, and the Maney replica.
 
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At the risk of repeating myself: There was no welding required for what I did. I started with an 8" length of 2" pipe swedged at one end so it would slip on to the collector tight, and be cut to length. The megaphone slipped over the extension at the other end and is clamped on the extension. That 8" piece made for a 5" extension. I ended up with a 6.5" length of 2 inch pipe that gave me a 3.5" extension. Some trial and error took place, but not much. The SuperTrapp made the biggest difference for after the fact tuning. If I pulled half the discs out of the SuperTrapp, the motor wouldn't run as good as it does. I should have made that clearer. Picking on the extension as not making much difference gives you guys something to talk about though. Bonus

Anyway, easy modifications to try. The handful of guys that still have Bubb 2:1 exhausts on their Nortons could benefit from the SuperTrapp change if they are having difficulty getting adequate top end out of their motors with carburetor jetting changes. The extension mod could be skipped, and results should still be good enough. Ron Wood Racing sells a better looking SuperTrapp arrangement than what I have. Down side to the discs is the exhaust note is sharp once the motor is up on the cam. Well, with my little 2S cam it is. Going slow is a mellow note though.

Carburetor tuning was also being done at the same time, but the Amal 930's I had on there were not cooperating. The Mikuni needle trick might have helped, but I didn't like the old small Amals anyway. Good excuse to take them off. I only tuned my bikes (now bike) as a personal hobby, not for a living. None of the bikes I owned ended up running slower after I got done. Can't prove it of course. No trophies, or dyno charts.

On Topic: Nice bike to play with Chris.
 

Fast Eddie

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Yes, I quite like the Supertrap idea too. I made an adaptor to play with that on my Maney replica. Got kinda shelved currently though until I can find the time and motivation for another dyno day.

C646DB54-2BAC-4CDC-A86C-261225385E8B.jpeg
D29D309A-66E1-412C-A505-65527FF27CF0.jpeg
 
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Steve and Jim spent dozens of hours on the dyno with their pipe designs. Trying numerous permutations of length, diameter, bend radius, megaphone shape, etc, etc, etc, it’s such permutations I’m referring to, why weld in 4”? Why not 2,3,5,6,7 etc, etc?

So yes, when they say something works, it’s usually very well proven. So yes, I’d tend to believe them.

I put a Maney pipe one mine and it gave a 5 BHP difference, even more in the mid range. After having the head ported and the followers radiused to reduce duration, all of those gains disappeared, there was virtually no difference between it and stock pipes and peashooters anymore.

What this taught me was that a surprisingly small difference in cam operation can have a huge impact on exhaust function. A simplified rule of thumb is, the more radical the cam, the more sensitive to exhaust tuning.

So, as Chris‘s pipe is of unknown make, and certainly not the same as your one off, and he is using a radical race cam, etc. I basically stand by my point that modifying it would need to be done carefully.

Steve and Jim spent dozens of hours on the dyno with their pipe designs. Trying numerous permutations of length, diameter, bend radius, megaphone shape, etc, etc, etc, it’s such permutations I’m referring to, why weld in 4”? Why not 2,3,5,6,7 etc, etc?

So yes, when they say something works, it’s usually very well proven. So yes, I’d tend to believe them.
Unless it is Comnoz cam info quoted by me :)
 
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I brought a Bassani road rage for my stage 3 Harley bagger it was loud with the equal lengh primarys reverse cone megaphone built into the muffler then around 8 x 3 inch perforated baffle to the fake reverse cone. I fitted a suppertrapp baffle 22 x 4 inch baffles closed end cap it lost some top end but picked up mid range power and it sounded wicked on the gas. The beauty of the supertrapp mufflers is there tunable for where you want your torque HP.
 
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