What type of exhaust for power. (2019)

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Theories about producing more power can be great, but it is what happens in practice that is important.
My friend's 650cc Triton is a very quick bike, for what it is. It is fitted with separate pipes with reverse cone megaphones. It is extremely tractable, but the larger capacity and sensible cams must contribute to a large extent. My 500cc short stroke Triton was unrideable when it was fitted with separate pipes and 4 inch megaphones. Another friend had built it in about 1957 and rode it at Bathurst. He got to the end of Conrod Straight and found he could not stop the bike. He had a choice - right into the escape road or turn left and go around. Both were equally as difficult. He chose left and somehow got around. When he got to the top of Mount Panorama, the bike stuck him into the guard rail and broke his arm and a leg. He did not race for 20 years after that. When I started racing that bike, it turned me into an instant dud.
You hear talk about guys having balls - Allan Greening had more guts that any guy I ever knew. He died in a road crash a few years ago when his heart stopped while he was at the wheel of his car. He was an excellent race rider.

The guy wearing the cap :
https://i.ibb.co/3fgy2hV/scan0003.jpg
 
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Pipe Werks, in the UK, do baffles which fit in the Maney "silencer". I get 102db with the closed perforated one. Warm engine and a gentle roll on to 5000 rpm (hard to do!)
 
Moto55UK said:
The upgrades included a crank mounted ignition, new R&D valve springs , 37 from 35 carbs with extra long inlet tracts, JS2 smooth ramp cam & radiused std followers, took 0.040" of the head ( I had been using JS 0.003" copper rings previously but found they were destroyed when the head came off so i shaved the head and went back to the 0.040" copper gasket)( the heads not been off for two seasons now and recently we dynoed it again and it had only lost 1 bhp ) and of course fitted the NRP exhaust system which I had no input , I left the Bike with Nigel and he did his magic. Off to the dyno and when it went over 80bhp i nearly wet myself!!!!
I also spent a lot of time setting the pushrod length to 90 deg to the valve at 65% full lift as per steve Maneys suggestion. What % is due to what I dont know ,im just very pleased .
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Over 80hp, I am guessing its an 850cc plus, I did a search to try and figure it out but lost the will to live, easier just to ask. I had my bike (Maney short 750) on the dyno and got 64bhp. I am thinking maybe not so good now! Still not quite sorted, last outing clutch gave up as did the ignition. Easy fix with clutch, needed new heat resistant trigger for ignition. Almost sorted, had to helicoil the tiny blind holes in the crankcase where its mounted. Hopefully one more test before winter sets in.
 
Steves said:
Pipe Werks, in the UK, do baffles which fit in the Maney "silencer". I get 102db with the closed perforated one. Warm engine and a gentle roll on to 5000 rpm (hard to do!)
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Can you post a link or some info on what you use please ?
 
That’s brilliant Steve, thanks !

Do I understand correctly that th open ended one knocked 1.5hp off?

If so, what about the perforated closed end, did you test that on the dyno?
 
Steves said:
Over 80hp, I am guessing its an 850cc plus, I did a search to try and figure it out but lost the will to live, easier just to ask. I had my bike (Maney short 750) on the dyno and got 64bhp. I am thinking maybe not so good now! Still not quite sorted, last outing clutch gave up as did the ignition. Easy fix with clutch, needed new heat resistant trigger for ignition. Almost sorted, had to helicoil the tiny blind holes in the crankcase where its mounted. Hopefully one more test before winter sets in.
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64 BHP should be quite sufficient to do yourself a mischief. If you end up in a drag race against an 80 BHP bike down a long straight on a power circuit, you might have a problem - but not if you are faster everywhere else.

Getting 80 BHP out of a Commando engine without losing midrange, would not be easy. If the circuit is tight, you need loads of torque, rather than just top end. The problem with torque, is you usually don't know you have it until you raise the overall gearing.
 
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Steve, any chance of some pics of the outlet of you’re Maney pipe? I have a Brooking 850 system and looking at your posts and description I’m thinking mine is different to yours...
 
Fast Eddie said:
That’s brilliant Steve, thanks !

Do I understand correctly that th open ended one knocked 1.5hp off?

If so, what about the perforated closed end, did you test that on the dyno?
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Yes just the reduced straight tube baffle as it was the only one I had at the time when I put the bike on the dyno. I got the other one and the supertrapp as I was paranoid about getting turned away from a trackday.
 
Fast Eddie said:
Steve, any chance of some pics of the outlet of you’re Maney pipe? I have a Brooking 850 system and looking at your posts and description I’m thinking mine is different to yours...
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I took some pics, uploading is another issue. However it’s pretty straight forward, large can, minimal packing, large internal perforated tube holding the packing against the casing. On the end an alloy cone with a 2 inch hole in it. No baffles, flutes or S bends. So I can put anything 2 inch in diameter in there and it won’t stop until it comes against the exhaust pipe at the other end of the ‘silencer’. The cone is drilled for a small m4 or m3 fastener to secure baffle in the cone. To summarise the baffles just slip in and there is plenty of room inside. The 2” hole in the cone is about 1.5” maybe a little more, long.
 
acotrel said:
64 BHP should be quite sufficient to do yourself a mischief. If you end up in a drag race against an 80 BHP bike down a long straight on a power circuit, you might have a problem - but not if you are faster everywhere else.

Getting 80 BHP out of a Commando engine without losing midrange, would not be easy. If the circuit is tight, you need loads of torque, rather than just top end. The problem with torque, is you usually don't know you have it until you raise the overall gearing.
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Well you may well be right. Still 80hp from a 750 pushrod twin is impressive.
 
Steves said:
I took some pics, uploading is another issue. However it’s pretty straight forward, large can, minimal packing, large internal perforated tube holding the packing against the casing. On the end an alloy cone with a 2 inch hole in it. No baffles, flutes or S bends. So I can put anything 2 inch in diameter in there and it won’t stop until it comes against the exhaust pipe at the other end of the ‘silencer’. The cone is drilled for a small m4 or m3 fastener to secure baffle in the cone. To summarise the baffles just slip in and there is plenty of room inside. The 2” hole in the cone is about 1.5” maybe a little more, long.
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Thanks for the description Steve.

I’ve sent you a PM by the way...
 
Steves said:
Over 80hp, I am guessing its an 850cc plus, I did a search to try and figure it out but lost the will to live, easier just to ask. I had my bike (Maney short 750) on the dyno and got 64bhp. I am thinking maybe not so good now! Still not quite sorted, last outing clutch gave up as did the ignition. Easy fix with clutch, needed new heat resistant trigger for ignition. Almost sorted, had to helicoil the tiny blind holes in the crankcase where its mounted. Hopefully one more test before winter sets in.
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Your dyno figure makes it very similar to my short stroke 750. And it will make a very rideable and enjoyable bike. And if you think about it is very close to the figures Thruxton achieved at the crank, Norman White says best ever on the dyno was around 76 at the crank, with a short stroke. Back in the day my 850 with ex works head pistons and cam was probably making similar figures at a few hundred rpm lower.

The other guys posting here are using 920s so the numbers don't really surprise me too much, but will put lots of other stuff under stress.

I chose a 750 partly to stress my original '75 frame a bit less and partly to get access to European 750 class races.
 
Steve sent me pics of his pipe...

Here’s tha end can:
What type of exhaust for power. (2019)


Here’s the baffle, looks very neat:
What type of exhaust for power. (2019)
What type of exhaust for power. (2019)
 
Dyno figures only give you bragging rights. When you get two bikes side by side on the start grid, there is much more which affects their lap times than the horsepower of the motor. It is really the combination of power, gearing and handling which affect how well the bike races. Theoretically, you could build an 80 BHP Commando which does everything perfectly. But what happens in theory is usually different to what happens in practice. A lot depends on the nature of the race circuit and how well you adapt to it. I usually only ever race on one circuit So my bike is fast around it. A few years ago I raced at Mount Gambier and won a couple. But it is similarly tight. If I went to Phillip Island, I would have a real problem - it is a power circuit. The other circuit near me is Broadford - if I went there, I would probably neck myself.
 
By contrast, here’s mine, some thoughts gonna be required to get my noise down to acceptable levels me thinks:

No wonder mines louder, firstly the can is a lot shorter:
What type of exhaust for power. (2019)


And the inside diameter is bigger:
What type of exhaust for power. (2019)


A lot bigger in fact:
What type of exhaust for power. (2019)
 
I always have a problem getting my head around the difference between a top end motor and one which has loads of torque. If you ride two bikes which have that difference between them, you find that it really changes the way you can race. Over the years since 1973, many guys in Australia have raced Triumph 650 and 750 engines in historic races. Most of them have blown up after going fast for not very long. The better approach seems to have been , to built the motor to pull harder, rather than rev the tits off it to get more power.
I often wonder about the calibration of the dynos which are being used these days - can they measure the difference between the two types of motor ?
 
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