2 in 1 exhaust system (2010)

lcrken · Nov 30, 2015

+1 on his book. It is a great read for any Commando fan.

Ken

acotrel · Nov 30, 2015

Where did the cam come from which was used in the 500cc Domiracer that Tom Phillis rode in about 1962 ? It must have been a race cam to get the lap speed he achieved.

acotrel · Nov 30, 2015

I find the comparison between Norton and Triumph twins interesting. As a kid I always had 650cc Triumphs as Norton twins were very rare and most did not have provision for twin carbs. A friend had a new 650cc Manxman which was faster than the standard unit construction Bonnevilles. The Triumph cams have a race history. The inlet cam of the Bonneville is the E3134 while the exhaust is the E3275 Tiger 110 cam. When the E3134 profile cam is fitted to both inlet and exhaust of the Bonneville, the bike is much faster. Triumph twins were raced as far back as 1948. The first profile was the GP cam which was a valve dropper. The E3134 replaced it in the 1952 Tiger 100 race kit. I still wonder how the cams for the Norton twins were derived.

Rohan · Nov 30, 2015

acotrel said:
I still wonder how the cams for the Norton twins were derived.

The story of the Domiracer that Tom Phillis rode is about, it had some trick bits in the engine.
The cam ran on needle bearings for starters.
It has been discussed here before too, in some detail.

Since Doug Hele and Burt Hopwood and Jack Williams and Dennis Poore and Phil Irving and Joe Craig etc had ALL worked or raced for about nearly every factory going at the time (!), there was probably a fair interchange of ideas. !

Has anyone compared the race Triumph cams with the Norton cam profiles.
Racing motorcycles didn't just start in 1948, if anything bikes were faster back before the war, when fuel was higher spec.
Prewar racing motorcycles were allowed to be supercharged too, and that had spurred some cam development...

BSA, being the biggest, had done an extensive program of testing prewar - on all manner of subjects.
Some of even their 350 bikes would lap Brooklands at 100+ mph before long.
Amongst other things, they had acquired a strobe light, and were amazed to see all manner of parts bending and flexing in use.
They also extensively researched all manner of things metallurgical - the Army insisted on the bikes they bought doing 10,000 miles before an overhaul was needed - something the existing designs needed considerable work on in various aspects before they would meet this spec.
A lot of this appeared in the motorcycle press of the time, they shared it around...

But we diverge, slightly...

acotrel · Nov 30, 2015

When bikes are supercharged the exhaust cam timing is usually retarded. It is common to use road cams instead of race cams, it is a different game. It doesn't depend so much on sonic resonance to get cylinder filling. In that situation you ARE probably talking about FLOW. Vertical twins pretty much started racing in 1948 with the GP Triumphs. The best effort was the Domiracer. It was the only pushrod twin to get near the 500cc Manx in the Senior TT.
I'd be interested to know what cam timings Steve Maney uses with his two into one pipe. With that large diameter, it might not matter much.

SteveA · Dec 1, 2015

acotrel said:
I'd be interested to know what cam timings Steve Maney uses with his two into one pipe. With that large diameter, it might not matter much.

Just search on here and you will find comparison charts for cams including Steve's cam, which is what he used in his own build.

But I am pretty sure that purchasers and copyers have used all sorts of cams with it!

Brooking 850 · Dec 1, 2015

I was running 2 x 1 3/8" ID headers into 'straight through' peashooters and now with a copy of the Maney set of 1 1/2" ID into 1 I have increased my power and torque without changing the cam or cam timing. With the new system I am making power all the way to the rev limiter which is built into my crank mounted ignition system. Just a slight jetting change, although that can change depending on which track I race at.
Regards Mike

acotrel · Dec 1, 2015

I wonder how many of the road race guys have vernier adjustment on their cams and have tried progressively changing the cam advance to see the effect with different exhaust systems ? I did it years ago over several race meetings with my 500cc short stroke Triton. It is amazing what does NOT make a difference. However in the end I had a pipe and cam timing which worked very well. My main competition had an excellent 650cc Triton. I could get level with him, however I could never convincingly beat him. 'Torque wins races'.

acotrel · Dec 1, 2015

Brook, I notice that your max. torque is at about 5,500 RPM are you pulling very high overall gearing with a close box ? I think with my bike I get max. acceleration by keeping the revs between 6,000 and 7,000 RPM. I tend to keep the heavy crank well wound up. When I can afford it, I will buy some dyno time and have a look at where the max. torque is in my motor. It is a very handy thing to know because short-shifting can sometimes make you go faster.

SteveA · Dec 1, 2015

Brooking 850 said:
I was running 2 x 1 3/8" ID headers into 'straight through' peashooters and now with a copy of the Maney set of 1 1/2" ID into 1 I have increased my power and torque without changing the cam or cam timing. With the new system I am making power all the way to the rev limiter which is built into my crank mounted ignition system. Just a slight jetting change, although that can change depending on which track I race at.
Regards Mike

Mike, I am convinced that the Maney system is a good design, probably the best 2 into 1, and very effective and I really have no criticism of it even if I didn't choose to use or copy one.

What we don't know is if you had fitted a separate pipe system of a good design, would you have gotten similar improvements? I would suggest that you would have. I use a separate pipe system by choice and I am convinced I am losing nothing on my 750 Short Stroke due to exhaust design. I am running a standard Fullauto with standard valve sizes, long inlets and 34 Mikunis.We didn't run it on the dyno above 6750 since it hadn't been run for more than an hour all told, peak power would only come at around 7000, however I am inclined to believe the power and rideability would make it competitive with your figures using the full 8000 I have take it to.

Like Alan, I love the way my motor pulls between 6 and 7...and that is where I like to keep the motor, but it doesn't die above or below those numbers, unlike Alan I have a light flywheel Steve Maney crank.

If it is possible we will get it on a dyno again in 2016, but it's going to be tricky to fit in with a relocation to France in progress.

acotrel · Dec 1, 2015

When you have short stroke and light crank, you are playing a slightly different game. What I like about my bike is that it does not try to bite me. There is no anxiety associated with it. With my old short stroke Triton I always had to be 110% on top of it. It was always ready to crash me. With a commando based engine you are probably in a slightly better situation, however I would never go back to separate pipes, megaphones and a top end motor. I hope it works for you, but take care.
What I found with the 850 is that everything happens fairly slowly, so it is easy to be smooth. Light crank and top end motor takes a lot more concentration. There is probably no point of convergence between old fashioned twin cylinder bikes and modern four cylinder bikes.

Brooking 850 · Dec 1, 2015

Hi SteveA, no I didnt really try any other exhaust, only the initial high 2 x pipes into the peashooters I borrowed off my road bike, as out of three sets of mufflers I have , those ones gave me more mid range, the other two "original" peashooters robbed my midrange.
Yes you are probably right, Jim Comstock posted several videos of him running up and testing a high HP motor using P11 high pipes, so if I had of opted for the 2 separate pipes, maybe I would not notice the difference.
The reason I went this direction was I had a genuine set lent to me to copy , so did that , and very happy with the improvement in midrange and where the max power tops out.
As I am running a standard crank in Maney cases, I dont have to ring its neck to make power, and also as I am not the quickest rider by any stretch, I can still have usable power low down.
It runs a 5 speed TT gearbox.
Just so you know there is no trickery in the engine, due to class regluations I run standard 32mm Premiers on standard length manifolds with standard sized Vv's in a RH10 head. Standard crank in Maney cases, JS Motorsport JS2 cam, his rods and pistons at 0.040" + I am limited to period carbs, although can change the length of the manifolds and this will be the next area I will work on
It is work in progress, the exhaust is the biggest change since I built it , and I only change one thing at a time and check for results, hence slow progress.
I am building another motor(slowly) , it will have NZ made billet cases, FA head, JS internals including one of JS.s new profile JS2 cams , cast iron 880cc barrels, standard weight hi spec crank. Some of these components I already have, head potential at this stage is 84HP and do some flow testing as we speak.

This motor will need a good exhaust to extract the best out of it.
Regards Mike

Brooking 850 · Dec 1, 2015

Alan, max torque is at approximately 4800 rpm not 5500 rpm, so plenty of low down grunt, very happy with where power and torque are, trying to keep it reliable, although try and keep the revs under 7000 rpm when riding it
Regards Mike

pommie john · Dec 2, 2015

Brooking 850 said:
I was running 2 x 1 3/8" ID headers into 'straight through' peashooters and now with a copy of the Maney set of 1 1/2" ID into 1 I have increased my power and torque without changing the cam or cam timing. With the new system I am making power all the way to the rev limiter which is built into my crank mounted ignition system. Just a slight jetting change, although that can change depending on which track I race at.
Regards Mike

That's an impressive chart. Do you have a direct comparison of peashooters vs Maney system?

acotrel · Dec 2, 2015

Sorry I didn't read the chart correctly previously. Looks like max torque is between 4.5 and 5.0 X1000 RPM ? Do you short-shift to keep the revs near that range ? When I was using the 4 speed close box, I found the gearing very deceptive if the overall gearing was not high enough. Surely max acceleration has to be when the crank is at the revs where max. torque occurs ?
However that created the problem of first gear not being low enough to get decent starts without revving the tits off the motor and dumping the clutch. I was always frightened of bending the main-shaft.

Brooking 850 · Dec 2, 2015

Alan, first gear is quite high, 4000 to 5000 rpm off the start line will see the front launch off if I am not careful, but as I have tall gearing for 1st and plenty of torque I seem to manage very good starts , make up a few places , then get swept up in the first few corners by the quicker guys.
I am happy with the 5 speed I have, also I have a modified standard drum brake that gives me quite a quick change rear hub/sprocket set up if required.
Regards Mike

Brooking 850 · Dec 2, 2015

Hi pommie John, here is an earlier graph with the 2 x single 1 3/8" upswept headers and open peashooters.
Regards Mike

SteveA · Dec 2, 2015

Brooking 850 said:
.............including one of JS.s new profile JS2 cams.....

This is the part I am interested to hear more about in time. I have a PW3.

Rohan · Dec 2, 2015

acotrel said:
Sorry I didn't read the chart correctly previously. Looks like max torque is between 4.5 and 5.0 X1000 RPM ? Do you short-shift to keep the revs near that range ?

The power keeps climbing nicely to +7000 rpms = torque drops off very little too above the max torque point,
so short shifting would likely be the slow pokes approach to life ?

acotrel · Dec 3, 2015

Surely it is the combination of torque and gearing which creates acceleration ? If you have a top end motor, you still need to have the situation where the breeze doesn't make the revs drop. It you are riding near the top of the torque curve, isn't that best if your gearing is as high as practicable ? You need to get out of corners fast, however the bike needs to keep accelerating near the ends of the straights. If it runs out of steam the more modern bikes will out-run you. Short-shifting is a bad answer, however might be necessary - if you don't want to slave over the sprockets and chains at a race meeting.
For many years I always knew where I was going to get beaten. I could choose my poison. My bike was a long way under the allowable capacity. Commandos are not like that. My feeling is that the heavy crank is a major advantage. Once it is wound up, it tends to keep going.
With Brooks bike, I would raise the gearing and try shifting near the revs where peak torque occurs and see if the acceleration is quicker - it can be very deceptive. It helps if you have a reference point such as another rider near you trying hard over many laps.