Torque, Horse Power and Acceleration (2014)

yes its well known if combustion engine can be kept in its max torque rpm-flow then a constant variable transmission would be most efficient sliding ratios for acceleration power. I have looked into this for some years and if hydualic pump/motors were not so heavy and rpm limited with fluid heating shear and flow Ms Peel would have a bulldozer type drive trans. In the end its how much power can be developed over time and the mass its shoving, so horse power or watts an engine or motor can produce is the main number to plug in with mass to get idea of how long to get going to some speed. The P!! didn't need any brake application to run through all 4 gears and only move a bike length, nor did my Mercedes 6.9 or my hot rod van. The small Brit engine wheelie barred supriser was a Triumph on Nitrous other lists told me. Our ancient engines just can take much rpm over 7-8000 so nothing left but pack more mix in somehow in bigger bores.

My feeling is that moving power up the rev range and lifting the upper limit is a futile and expensive exercise with a commando engine. Better and cheaper to fatten up the mid range even if the gearbox is expensive. What puzzles me is the effect of the heavy flywheel. The motor seems to have a tendency to spin up at the same rate regardless of the gearing, and where I expect a lag, there is none.

acotrel said:

My feeling is that moving power up the rev range and lifting the upper limit is a futile and expensive exercise with a commando engine. Better and cheaper to fatten up the mid range ........

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I get what you are trying to get at but I don't know of a Norton engine designed for race that ever had gains in the mid range and not the top end. Maybe a Norton where you only up the compression ratio; that might be a candidate.

Every Norton race engine I built and/or raced did not take a hit on the low end, the torque was increased across the whole range. Even my ultra short stroke has plenty of torque in the low/mid range that is up there with the best of the long stroke race engines. If you can safely, reliably and efficiently spin it faster to increase the air/fuel mass flow rate (ie power) than why not. Nothing futile about that.

I ain't level of Shrapnel dodger but the two 750s I had that were hot rods to race level were more responsive down low than standards and just got better from there. Its only if over cammed level Jim Comstock experimented for absolute peak possible power that it bogged below its narrow tune zone. That's not to say its also highly likely each mod hurts power some where until the whole combo finally dialed in, sometimes by trying stupid things that end up with surprising joy.
I don't know if its torque or hp but its sure nice to have to be careful at times not to give it full power as not traction enough or wheelie backs ya down. I prefer lower rpm power delivery through tall gearing as so seems the rear tire too, so I'll take my power equation skewed to the torque side more than spin side thank you.
Locomotive steam engine like driving big wheels each turn.

I haven't played much with the commando engine mainly because the inlet and exhaust timings cannot be set independently, and when fitting race cams I would be depending too much on the work of others. If you use a two into one exhaust system on a 750 commando, how much different are the cam timings you use compared with those for separate pipes and megaphones ? Years ago I played with many 650 Triumph engines fitting different types of cams. Like Dances, I also found that fitting full race cams gave a substantial power increase right across the rev range, the difference was that the increase in power was dramatic above the cam spot. What I did not do was test the pulling power due to the various cams at revs below the maker's recommended 6,300 RPM limit by increasing the gearing and changing the exhaust and timings. What have you found when you increase the gearing without changing anything else and the bike accelerates faster ?
There are not many 650cc Triumph engines left in Australian historic racing - they will cop 8,000 RPM for only so long, then they say goodbye. I worry about my 850 Norton engine revving to 7,000 RPM. The internal accelerations and resultant forces are squared relationships.

My Peel gave me the same sensation Al, I couldn't wait to get past 3rd for the better pull of 4th, so I'd of liked a bit lower 3rd ratio not closer to 4th, and a bit higher over drive 4th. I tended to wring her neck out in 1st, 2nd, then short shift 3rd and hang on tucked down in 4th. For some reason 3rd gear seems most famous to show up Cdo clutch slip issue and in Peel case weakest teeth to take torque. C'do cams can be made any way ya like if pockets deep and time enough. On my SV650 vtwin its good pull was over after 4th gear out of its 6. I got all the peddle bike shifting to speed out of my system thank you so lost interest in hopping up SuVee but they can 'easy' be spend on to make 100 hp and beyond with quickly decreasing life span though. Dragster reaction is hindered by a heavy flywheel which is very interesting to me after reading how Norton road racers went around quicker with closer to factory issued. For me to safely use the tire spin on tap it both vital to have a sense of how far to snap/crack throttle but no more, plus how long-far before bike catches up with the hook up reaction. Its the spurt of fuel showing up right now I want and get the flywheel effect a bit later from the wheel spin and sudden pay back. If ya have to go to WOT to spin tire instead of just a blip crack throttle some, then ain't got enough torque on tap to really enjoy so implies ya need to spend a lot more.

acotrel said:

I haven't played much with the commando engine mainly because the inlet and exhaust timings cannot be set independently, and when fitting race cams I would be depending too much on the work of others.

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Unless you are planning on re-inventing the wheel every time, that sounds like a flaw in the plan ?

Copying what other folks have done successfully is how we moved on from penny farthings.
Trying it at the recommended setting would have been top of most tuners first steps ?

Copying others maintains status quo, trying new things leads to progress and sacrifices too. At one time it was thought a 750 360' twin would always intrude on pilot and frame for instance. Al on boosted applications its the exhaust profile and exhaust system where extra gains are made, so at some point after I understand more what's happening in my special may re angle and profile the exhaust lobes and make its valve bigger instead of the intake. The Truimph racers I've quizzed were more involved with more issues than I've had Nortonneers relate to me.

Rohan said:

acotrel said:

I haven't played much with the commando engine mainly because the inlet and exhaust timings cannot be set independently, and when fitting race cams I would be depending too much on the work of others.

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Unless you are planning on re-inventing the wheel every time, that sounds like a flaw in the plan ?

Copying what other folks have done successfully is how we moved on from penny farthings.
Trying it at the recommended setting would have been top of most tuners first steps ?

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So you believe implicitly in the work of others ? I know of a couple of exceptional bikes which have not followed the same old well-trodden paths. The top end theory works well for a while if you can afford to double the strength of every rotating, reciprocating and containing component in a Commando engine. However let's just suppose that a standard commando engine is a good design if it is never revved over 6,800 RPM. How would you get the most out of it ? As far as cams are concerned I would always try a medium proven one first and go from there without enlarging the inlet ports. The 850 cam seems to work well with a two into one exhaust if advanced a bit before the recommended - now why would that be ? And yet I've never seen anyone on this forum mention they've changed the cam timing after fitting a two into one pipe. Do you believe the requirements for cam timings remain the same when you change from separate pipes with megaphones to a two into one pipe with muffler ?

Well acotrel, that statement on depending too much on others work is a bit close to going over the top.

So why bother with a Norton engine or any engine at all - no, wait, that would depend on the work of others. Must start with a one off design of your own. Cast up those new cases and remember to start with cast iron pistons because those new modern aluminum pistons would be depending too much on the work of others. While your at it, might as well have a go at your local bog and start lifting some of that Bog Iron (limonite) and start reducing in your furnace so you can trial and error your way to getting the right metallurgy. It can go on and on.

The dependent cam is a nuisance, not a show stopper. So many other things that impact the tune of an IC engine besides a cam that you can personnalize and tweak (or is that tweark?).

One thing which I always did which I always did in the old days was especially when changing exhausts, I tried systematically altering the exhaust cam timing to see if there was a different optimum. You can bolt in the best cam ever, if your exhaust system defeats it you are nowhere. With the commando 850 cam, it is obvious the standard setting for the inlet opening is too late. I suggest that it works better using the same inlet opening as the combat cam plus 6 degrees (60 degrees BTDC ?), and for a two into one pipe, the exhaust opening point becomes better. The loss occurs when the inlet then closes 12 degrees too early (about 24 ABDC) - however the set-up seems to work well. Two into one pipes usually tend to stifle a motor, take the top end off - mine doesn't do that. An error fixes an error ?
I suggest that the commando has a few compromises built into it to make it suitable for commuting, fuel economy might have been a consideration when deciding how to time the cams for a road bike ? Is it possible that the cam in the 850 was intentionally retarded ?

I suggest you should have a look at the race cam timings for Z900 kawasakis for the various timings used when four into one pipes are fitted compared with separate pipes. It might be my imagination, however it looks as though the exhaust timings alter to suit the pipes. I do know this - top end was never a problem with Japanese four cylinder bikes - a full race cam made them diabolical - yoshimura cams were bullshit compared with a proper race cam, and everyone back then was buying them. I helped fit a full race Italian cam to a ZIR Kawasaki in about 1978, it was the fastest super bike at Bathurst that year, especially when we helped the baffle fall out of the pipe.

comnoz said:

is it really ONLY max cylinder filling that dictates max rear wheel torque?

It dictates maximum crankshaft torque if the mixture and burn are right.

Rear wheel torque is very dependent on the gearing. Jim

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Out of curiosity how does your VE table compare to a dyno run on your bike? (assuming you are running MAP, Im not quite up with AN)

Cheesy said:

comnoz said:

is it really ONLY max cylinder filling that dictates max rear wheel torque?

It dictates maximum crankshaft torque if the mixture and burn are right.

Rear wheel torque is very dependent on the gearing. Jim

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Out of curiosity how does your VE table compare to a dyno run on your bike? (assuming you are running MAP, Im not quite up with AN)

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How much rear wheel torque do you need ? If the overall gearing is made higher, it is more difficult to make the bike step out at the rear end coming out of corners, especially with modern tyres. So you can afford to have the bike tighten its line. It is when you need a heap of revs to get the bike going, and you have a nasty power band that it becomes more difficult to ride well. This is one reason that Molnar manxes fitted with mufflers are easier to ride and thus faster than the old style manx with the megaphone exhaust. However I might not know what I am talking about - after riding my old short stroke 500cc Triton, the manx with the megaphone was sheer bliss.

acotrel said:

Cheesy said:

comnoz said:

is it really ONLY max cylinder filling that dictates max rear wheel torque?

It dictates maximum crankshaft torque if the mixture and burn are right.

Rear wheel torque is very dependent on the gearing. Jim

Click to expand...

Out of curiosity how does your VE table compare to a dyno run on your bike? (assuming you are running MAP, Im not quite up with AN)

Click to expand...

How much rear wheel torque do you need ? If the overall gearing is made higher, it is more difficult to make the bike step out at the rear end coming out of corners, especially with modern tyres. So you can afford to have the bike tighten its line. It is when you need a heap of revs to get the bike going, and you have a nasty power band that it becomes more difficult to ride well. This is one reason that Molnar manxes fitted with mufflers are easier to ride and thus faster than the old style manx with the megaphone exhaust. However I might not know what I am talking about - after riding my old short stroke 500cc Triton, the manx with the megaphone was sheer bliss.

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I think you may have quoted the wrong person here unless you thought MAP or AN were something fancy, just methods of calculating/controlling fuel delivery in an EFI system.

Even if the Manx is like that I know of one bike that was the opposite, FC 600, it had a massive midrange hit and you had to be built like a gorilla to manhandle the thing, so much so that the one I knew of was given a factory race cam which gave much more top end, after that it was much nicer to ride. To be honest I have not ridden any of these old bikes which you mention as having peaky power delivery, as a point of reference have you had a go on a modern 450mx bike? if so how do you think that compares

Cheesy said:

comnoz said:

is it really ONLY max cylinder filling that dictates max rear wheel torque?

It dictates maximum crankshaft torque if the mixture and burn are right.

Rear wheel torque is very dependent on the gearing. Jim

Click to expand...

Out of curiosity how does your VE table compare to a dyno run on your bike? (assuming you are running MAP, Im not quite up with AN)

Click to expand...

The torque curve and the VE curve looks very similar. A pre-injection dyno run will sure help build an initial VE table. Jim

The better power calculators require VE data point, so does anyone have a reasonable accurate figure for our Nortons? I've used 80 to 110% to run them but know just guessitmates though not unreasonable range for scope of Norton's.

I don't know much about MX bikes, I've only ever ridden the older two stroke varieties, and the power delivery requirements are very different from what is used on the bitumen. I can get into enough trouble with a nicely prepared MX bike without trying to ride something nasty on the dirt.

How does rod length affect the torque/horsepower relationship? I know that short rods tend to increase torque by letting the downward force of the piston kind of push side ways on the crankshaft higher up on the stroke. This also causes a lot of side force on the thrust side of the piston and drastically lowers the red line on most motors. They say that on a 400 small block Chevy with short rods you should hold the rpm down to 5000 or less but torque is way up. But if, on an engine like the Norton, the rod is short and the red line is at 7000. How would putting a longer set of rods in it affect that? Would it allow for a higher red line? Does it lower the low rpm torque in anyone's experience?

motorson said:

How does rod length affect the torque/horsepower relationship? I know that short rods tend to increase torque by letting the downward force of the piston kind of push side ways on the crankshaft higher up on the stroke.

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Its perhaps important here to note that rod length can't actually increase OR decrease torque.
It does modify HOW it is delivered - increasing or decreasing the peak values.

If you study the indicator pressure chart of engines - thats the little graph with the 4 sided curve that defines the cylinder pressures - then the TOTAL torque supplied by that engine is the total area of that curve. How that is delivered to the crank is modified by the rod length - but the TOTAL amount of torque can't be altered by the rod length. Its that peak value that alters - and feels different...

I'll let others answer the rest of that, but we note Jim Schmidts lightweight rods and pistons get good comments here.
Longer rods would add reciprocating weight to the plot, which would tend to lower the redline on their own ?
Old type steam engines had loooong rods - this smooothes the torque pulses.
If you note that steam locos are capable of twisting their chassis clean off the rails if you open the throttle HARD, you appreciate how important this can be...

motorson said:

How does rod length affect the torque/horsepower relationship? I know that short rods tend to increase torque by letting the downward force of the piston kind of push side ways on the crankshaft higher up on the stroke. This also causes a lot of side force on the thrust side of the piston and drastically lowers the red line on most motors. They say that on a 400 small block Chevy with short rods you should hold the rpm down to 5000 or less but torque is way up. But if, on an engine like the Norton, the rod is short and the red line is at 7000. How would putting a longer set of rods in it affect that? Would it allow for a higher red line? Does it lower the low rpm torque in anyone's experience?

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Generally speaking short rods will increase the torque in the lower to middle RPM ranges if you have a small fast burning chamber like a Norton.

A longer rod increases the torque at higher RPM because the ideal rod to crankshaft angle comes a few degrees later so the fuel has more time to burn and raise the cylinder pressure.

The differences are very small. Jim