Torque curves

acotrel said:

If you fit E3134 cams into a 1955 Triumph Thunderbird, you get a radically better performing bike. But if you do it to a 1958 model which has the ramp cams, the difference is not so great. The compression ratio makes no difference. A Thunderbird on 7 to 1 comp. will still go faster with the race cams. What you lose with the race cams is bottom end, but overall there is more torque from bottom to top. When you have race cams fitted, the way you ride the bike is usually different because you tend to ride the bike with the revs above the cam spot (the point at which it comes on song ). So if you do it to a road bike, you fall foul of the law. You need to try it, then you won't speculate about what happens.
A Commando engine is a completely different kettle of fish. You need pull from go to whoa, and whoa is at lower revs. A Triumph 650 engine will cop 8,000 revs - for a while. The race cams usually give a power band from 4 to 8, if you use the specified pipes.
With unit construction Triumphs the E3134 exhaust cam has a different number. I fitted one to a 1963 Bonneville which already has the E3134 inlet cam. The bike became much faster. Nothing else was changed.

If you fitted a similar cam into a Commando road bike, you would turn it into a piece of shit. Peak revs for most guys is 4000 rpm - you wound never be above the cam spot.

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"Peak revs for most guys is 4000 rpm" !!!
I'd say you are about 2000 rpm too low on that one mate

baz said:

"Peak revs for most guys is 4000 rpm" !!!
I'd say you are about 2000 rpm too low on that one mate

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With a hot cam, higher compression, and a dynamic balance it is more like 3000 too low.

baz said:

"Peak revs for most guys is 4000 rpm" !!!

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Speak for yourself !

Fast Eddie said:

Speak for yourself !

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So you never get past 4000 rpm Eddie?
Ha ha I bet you don't!!

I will still bet that most of you guys do 90% of your riding on public roads, using less than 4000 rpm. A proper race cam would be horrible - you'd be riding with the motor jumping about, with no instant power. A proper race cam usually gives slightly more torque below 4000 rpm, but then a big boost. When I used them in road bikes, I used to ride like an idiot, so they were sort of OK. With a Commando engine , you usually have smooth power there all the way from bottom to top, even without the 2 into 1 exhaust.

With my 500cc short stroke Triton, I had virtually nothing below 5,500 - then everything. It had a high first gear, then four close ratios. So everything I did had to be full-on. If it dropped below 5,500 at 70 mph in a tight bend, it would drop of the cam - then came fear and trepidation as I slipped the clutch and went sideways. When it had 4 inch megas, it was almost impossible to ride any way near safely. Long before I got it, it had stuffed my mate who built it, into the guard rail on Skyline Corner at Bathurst. It broke both his arm and leg. I didn't know that when I was racing the bike back then. I was only told much later.
The Seeley 850 is a soda - just too easy. I don't even like to think about what that Triton was like - it turns my stomach.

If you want to try something interesting - fit four-inch megaphones to your Commando and go for a ride. Even on that, they would give you a kick up the bum. You'd need to jet up slightly.

I had been thinking about doing an E3134 race grind on a commando cam. The usable rev range would be about 3000 rpm, but there would be nothing much below 4000, then bang. You would not want to get balked during a race. In the end I just handed the cam to my favourite cam grinder and said ' just give us your best Norton grind'. I don't even know what it is and I am too lazy to map it. All I know is that it works extremely well. ( But so does methanol ).

Al, the E3134 was a race cam, in that you are correct. BUT it was a race cam designed in the early 1950s... for a 500cc twin.

There’s no way a E3134 type profile and timing would be considered a race cam in an 850cc twin today.

It was a production cam by the 1960s in both 650cc and 500cc twins.

The stock Norton Commando cam lift and timing is more aggressive than the 3134 is in a Triumph.

Regarding race cams in road bikes, again, there are race cams and there are race cams. I’m running a Steve Maney race cam in my 920 and, so far at least, I’m extremely pleased with it. Having more experience with Triumphs than Norton’s, I was surprised how aggressive it seemed when I timed it, but it works very well.

The 920cc’s and the 2:1 pipe probably compensate for some low end losses that might otherwise be apparent. I have, of course, got the higher CR that a cam like this needs in order to function as designed, and the combined effect of all the parts in the motor (and the pipe) make for an engine that spins up SO quickly.

I think people forget this. Sure, getting to 6k rpm on my bike when I first got it (cw it’s single 36mm Mikuni) was genuinely hard work, and it felt hard on the engine, and it seemed to take forever, and it was a waste of time. If THIS is what people envisage it’s like with a race cam then A) I understand their hesitation but B) they’re wrong!

My motor seems to get to 4K rpm as soon as you’re off the line. Then 4k to 6k comes in a flash! The idea of riding a motor like this around all day chugging along below 3k is abhorrent. It would genuinely be hard work keeping it at those revs. And no fun at all.

I’m NOT saying that everyone should fit a race cam. I fully ‘get’ the strengths of a stock Commando motor and do believe it suits more people more of the time. But it’s definitely a case of ‘different horses for different courses’.

Actually, it seems to me that the answer is that everyone should have two Commandos. One in stock tune for touring / commuting / etc. and one that’s ‘breathed on’ for FUN !!

Fast Eddie said:

Actually, it seems to me that the answer is that everyone should have two Commandos. One in stock tune for touring / commuting / etc. and one that’s ‘breathed on’ for FUN !!

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Take your new motor 1500 mi on motorways and A roads and then let's talk about touring fun.

Just fit flat bars first...

Of course everybody should have two Commandos. If you only have one, you juggle between two concepts. A racer and a road bike are usually two completely different animals. Somebody suggeste I should put the Seeley 850 on the road with club registration plates. I would be in jail within a week. When I was a kid, I sold my road bike to buy the Triton. I would have been much better off racing my road bike. At least it was ride-able. The Triton turned me into an instant dud. That is when I started learning how to go faster by modifying my bike.

How can you ride your bike above 4k revs in town with today traffic and traffic lights every 500 m ?
Perhaps only in first gear, because second will take you into forbidden territory.
And to get out of town you have to chose very carefully the best route which still takes 25 km, but could take 50 km if you are not careful.
I had my A65 with "spitfire" cam and big valve / big ports head and this bike was a pain to ride in town with constant gear changes.
Completely different story with a small port head, giving you some necessary torque down low and still 7k revs possibility if you need it.
But the best was Thunderbolt head with one 28 mm carb, sipping gas, one kick starter, loosing some acceleration and speed to small port head version but in real life much nicer bike to live with.
And still holding 90 mph for some time wasn't a problem.
You don't need racing cam in real life, you just need it during a race.

I commute about 30km, combination of half A type roads and motorway. If it is congested it is all 2nd gear.

Still plenty of torque below 4000, it's just the balance has shifted above there. A lot of the difference is also how fast it gets to 4k now.

When I was a kid, I used to really fang the bike. In fact I probably did not deserve to stay alive. As I reached my late 20s, I started having too many near-misses as the amount of traffic increased. So I gave up and went road racing instead. To me, riding a bike in traffic is one of the worst things to be doing. In a road race, you are usually almost completely unrestricted, so you can use an exciting motorcycle in the way in which it was intended when it was designed.
By the time I was 25, I could name about 12 guys who'd died in road crashes of their bikes with cars. In road racing, I can name about four whom I knew, in 30 years and they were really going for it.
For me, road racing is much safer than riding on public roads. I had an RD250LC here in Benalla for a while. I always felt as though I had a target painted on my back.

I know you guys like to trick your Commandos up a bit, but take care. A good rideable bike is always better than the fastest. If you want to race your mates, choose a road which suits your bike. For me, that always used to be a straight one, until I built my Tribsa. Pre-unit Triumphs handle like shit.

If the head flows well the power will be good. The stock cams are often pretty high performance in the older British twins, its the flow of the heads that limit them. I use a stock profile Spitfire cam in my big A65, it's still making power near 8,000 because I copied the port dimensions, fairly closely, of an XR750 oval port, from an image on this forum, into an old A65 head. It was excessively lean on the dyno but the best we saw was 85hp and though I put in richer jets afterward, I haven't re-tested it. It uses a Norton crank bolted at 90degrees with 79.5mm B44 JE pistons. If I was racing the thing I'd definitely go back with some jets and experiment a bit with ign timing to get the best out of it. The dyno guy wanted to rev it another 1000rpm to see when the graph would go over, so you definitely need to be there when it's being tested. It's almost impossible doing it by seat of the pants, even with a data logger it's difficult on the road with speed limits and other vehicles. The dyno guy went to great pains to explain the dyno was not an inertia type, it was a ramp type. He could set a start and end speed for it and it would hold the bike within those parameters. It's definitely worth dyno testing modified engines, it gives you a measure.

That’s a lovely looking port you got there Mark !

This one is around 200cfm @28"w @.410" valve lift. It breaks through in a couple of spots, I can get around 190cfm without breaking through. The 190 head is on a 79.5 x74 stroke 90degree A65 which is the sweetest thing. They use a 38mm carb and 44.5mm valve.

I can get 160 from a 34mm port, 150 from 32mm with a slightly oversize valve, and 142cfm from a 30mm port and stock valve all using the same style of oval port. I've not used the smaller port ones on a bike but they should be good on smaller motors. I'm interested to see what a 30mm oval port head would do to a stock 650. It's the same volume as stock, just flows a lot more.

Fast Eddie said:

That’s a lovely looking port you got there Mark !

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Yes it it.....

If you have a fixed rev limit of 7000 rpm and over-port the motor, the bike would go backwards. What you take out of the port is almost impossible to put back. If all becomes top end, the bike can become very difficult to ride well. If it only pulls from 5 to 9. that is the usable power band with which you and the gearbox must cope.

Nigel, you might be right about the timings of the Commando cam being more radical than E3134. From memory the E3134 was IO at 52 deg BTDC and closed at 70 after. EO was 72 BBDC and closed 50 ATDC. I think the Commando 850 is very close to that. I never rode my bike when it did not have the 2 into 1 exhaust, so I don't know whether it gave a kick at 4000 rpm. The way it is now, I don't think there is a bottom or a top to the power band. It pulls from nothing and goes straight through the roof. But it seems to have most pulling power at about 6000 rpm. I usually try to change up just before 7000 rpm and if probably does not drop more than 1500 rpm.
I don't know about the relationship between comp. ratio and cam timings. What we are talking about are two linked resonating tubes. With organ pipes, it takes less effort to get a note out of a skinny pipe than a fat one. The cam timings set the frequency of the notes. I cannot see how comp. ratio affects that. I think that most guys raise comp. first then fit the hotter cam and don't try one without the other. What you seem to be saying is the combined contribution is greater than sum of the individual contributions of each change. If you lose compression because of the more radical timing, that means the motor has not reach the revs at which the cam cases the pipes to resonate properly. In the case of the inlet port, you don't have enough ram and in the case of the exhaust, the return wave is not strong enough.
That comment about needing higher comp. might have been more relevant to road bikes where you tend to ride them without revving the tits off the motor.