Available engine performance

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As the last A65 was made in 72 how does that work, the Devimead conversion was not factory that does not count and anyway was available in the late 60's as the owner was using A65 engines in his racing sidecar.
I think luck has a lot to do with many things, but an A65 also has a heavy crank. The Triumph Saint has a light crank and is slower then a pre-unit Tiger 110. When I looked inside mt 850 and saw that crank, I could not imagine racing with such an ugly thing. I now believe in it - It actually works. But NOT with the standard gearbox. When you peak the 850 motor out to 7000 RPM in every gear, and race-change with close ratios, the bike really gets mobile. But if your revs drop below 5,500 RPM, you have to wait until they come back up. In most situations, that never happens. Once that crank is spinning high, nothing stops it. I love it.
On Winton Raceway, the slowest corner is a hairpin which requires second gear in the close box. At the slowest point in the corner, my 850 motor never drops below 6000 RPM. How you get around that corner determines how good you will be everywhere else on the circuit. It has 5 straights and 12 bends in 3 kilometres. I run relatively high overall gearing.
With the heavy crank, the Commando is very different to many other bikes. With most bikes, if you lower the overall gearing, they accelerate faster. If you do that with a Commando engine, it usually just does the same revs and the bike does not accelerate faster.
 
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It is difficult to get an exhaust system which will give good performance and a tolerable noise level, without chopping the top off the usable rev range The tail pipe on my 2 into 1 exhaust has twice the cross-sectional area of one of the header pipes. With an absorption muffler, it is too noisy. But my motor will rev straight up and through the top in every gear, if I let it. The Dunstall 2 into 1 into 2 exhaust might be better.
 
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A65 engines are a lot more common than the frames Steve
Not advertised it on the dreaded fleabay yet. Me being helpful don't need another project although a triple might work out nice!
 

SteveA

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I thought we were talking about more engine performance for Commandos, for a large rider, not for racing?

Kinda lost the plot...
Yeah, but read what one of the racers said.....may need interpretation but....

...pretty much equates to.....don't build yourself a race engine for the road!
 

grandpaul

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Yeah, but read what one of the racers said.....may need interpretation but....

...pretty much equates to.....don't build yourself a race engine for the road!
That's why I replied with the modest answer in the first place.
 
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If you ride a standard Commando on public roads do you really want to ride fast ? You make a choice. Making a Commando faster is not really in the engine. A Commando in standard form is a good motorcycle. If you change it, you have to live with it.
If I was going to ride on public roads, I would buy a GSXR750 or a Triumph Bonneville.
 
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A couple of years ago Ken (Fullauto) came to see me in Benalla. He is from Perth. I think he shipped his Commando to Adelaide and rode via Melbourne. He rode the 200 Km up the Hume Highway from Melbourne to Benalla in the rain. He was going to Northern NSW. On that highway, the traffic travels at about 120 kilomters per hour, and with a motorcycle, you need to keep passing the traffic. Ken's Commando is near standard but has a single Mikuni carb. Ken was doing it easily, which says a lot about his Commando. Years ago a mate of mine rode almost non-stop from Brisbane to Melbourne on a Dominator 88, in the rain in 14 hours. When he got there, he fell into bed and slept for two days.
 
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Hi all (again),
Having started this discussion I have found it very interesting where it has led. As with all human endeavours, there has been wide range of views put forward. It’s a case of different strokes for different blokes!
The question has been asked several times of why you would need more power than is available in a standard Commando. I guess for me I would like as much performance as is easily available whilst maintaining reliability and rideablity.
I have always chosen to ride old Pommie iron. If I was riding a smaller capacity bike I would simply move up to a larger capacity. In view of the fact that Commandos (and Tridents) are as about as modern and as powerful a British bike as is available from that era, the only option is to improve their performance if possible. I really like owning ‘classic‘ British bikes and appreciate them as collector items but ultimately for me they are for riding and riding alongside mates with modern road bikes at fast (but sensible) road speeds.
As Nortons were built to a price and had to be robust enough to hopefully cope with the most ‘ham fisted rev-head’ whilst not destroying themselves within the warranty period, they could not be too highly tuned (I guess the Combat is the exception that proves the rule, as was the MGA Twin Cam). Therefore, as I’m hopefully very sensitive to the health of the engine, as are most others on this forum, I believe I could have a few mods that would increase the performance but still maintain reliability. The additional power might only be needed 1% of the time but it’s nice to know it’s there.
Do I need more performance? Probably not. Do I want more performance? Definitely!
Eating up miles on a Commando through scenic country is great but I also want to feel the rush as the bike delivers as much surge as possible when you roll the throttle on.
So, it will be new Premiums, a slight compression increase, the head opened up as much as reasonably possible. Not sure about larger valves and just perhaps a cam. I have no intention of looking for power beyond 6500 rpm.
I also should have mentioned that I live at 3000’ AMSL. That reduces available power by approximately 10% on a standard day.

Al
 
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Hmmm,
Brisbane to Melbourne in 14 hours. And in the rain, and on a Dominator. That must have shaken the fillings out of his false teeth! Amazing effort. I would have taken a week to get over that one. 400 or 500 km in a day is more than enough for me these days.
A couple of years ago Ken (Fullauto) came to see me in Benalla. He is from Perth. I think he shipped his Commando to Adelaide and rode via Melbourne. He rode the 200 Km up the Hume Highway from Melbourne to Benalla in the rain. He was going to Northern NSW. On that highway, the traffic travels at about 120 kilomters per hour, and with a motorcycle, you need to keep passing the traffic. Ken's Commando is near standard but has a single Mikuni carb. Ken was doing it easily, which says a lot about his Commando. Years ago a mate of mine rode almost non-stop from Brisbane to Melbourne on a Dominator 88, in the rain in 14 hours. When he got there, he fell into bed and slept for two day
 

SteveA

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Given all else you have said, I would seriously consider flipping those two parts around in priority.
And then just maybe forget the cam, or go for one of the milder grinds available.

It's always a trade off. Stay mild with the cam, and it's less of a trade-off for enjoying eating up miles on a Commando through scenic country....at which you might spend all day, compared to getting the rush you might enjoy for 10 minutes of a day ride!
 

grandpaul

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Like I said, the Megacycle 560-00 cam is relatively mild, and has a great reputation. No larger valves needed, just lap your current ones if they're up to spec (along with the seats, of course).
 
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Alan,
Good luck with curbing the temptation to do more than you planned on once the motor is apart.

I definitely agree with all the don't build a race motor for the street comments. It'll be easier to ride on the street in closer to stock trim.

I built what is like a low budget flat track Norton engine. Light crank, higher compression pistons, ported head, bigger carburetors, yadda yadda. It was fun when I was 40 years old and fearless. It's still fun, but a lot of wasted potential, since I now have obtained fear. Hence, a closer to stock Norton that doesn't accelerate as quick and has a heavier stock crank and lower gearing would be better for me as a street bike now.

By the way, "accelerate as quick" is relative. It's only a 750 Norton. Only way it would really be fast is if dropped out of a C17 Globemaster from about 3000 feet.
 
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