High hopes
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Jim,
My understanding is that as a rule, peak volumetric efficiency is where peak torque occurs yet your simulation indicates peak torque of 76.1 ft-lb at 4000 rpm (VE=104.4%) and peak VE = 106.2% at 5500 rpm (73.4 ft-lb). In general it follows the rule but looking closely in this simulation it does not seem to exactly follow it.
Could increased friction with increased speed be a factor? What say you?
My understanding is that as a rule, peak volumetric efficiency is where peak torque occurs yet your simulation indicates peak torque of 76.1 ft-lb at 4000 rpm (VE=104.4%) and peak VE = 106.2% at 5500 rpm (73.4 ft-lb). In general it follows the rule but looking closely in this simulation it does not seem to exactly follow it.
Could increased friction with increased speed be a factor? What say you?
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Dances with Shrapnel said:Jim,
My understanding is that as a rule, peak volumetric efficiency is where peak torque occurs yet your simulation indicates peak torque of 76.1 ft-lb at 4000 rpm (VE=104.4%) and peak VE = 106.2% at 5500 rpm (73.4 ft-lb). In general it follows the rule but looking closely in this simulation it does not seem to exactly follow it.
Could increased friction with increased speed be a factor? What say you?
Peak VE is going to be determined by the camshaft and intake and exhaust tuning. If it were not for the rapidly increasing friction, the peak torque on this engine would occur at the the maximum VE point of 5500. Jim
PS, That rapidly increasing friction as the revs climb makes a wall somewhere around 7600 above which no feasible tuning can create a HP increase. I banged my head against that wall for a long time before I figured that one out. Jim
johnm
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comnoz said:
Goodness. Ill have to dig out my spread sheets but if your wanting to get back to the equivalent to a standard first gear road ratio and need a 3.25 to 3.5 range you must be gearing for about 140 - 150 mph in top ??
Your right - I have certainly never seen a 3.25 ratio.
John
slimslowslider
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I wondered where the parameter "clearance volume", with a figure of 50.8, in the sheet stands for.
With a displacement V1 of 914.6 cc, and a compression ratio of 10,
that would mean a smallest volume V2 above the piston of 101.6 cc (twice the clearance volume by coincidence?).
Assuming compression ratio here is (V1+V2)/V2.
With a displacement V1 of 914.6 cc, and a compression ratio of 10,
that would mean a smallest volume V2 above the piston of 101.6 cc (twice the clearance volume by coincidence?).
Assuming compression ratio here is (V1+V2)/V2.
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comnoz said:Dances with Shrapnel said:Jim,
My understanding is that as a rule, peak volumetric efficiency is where peak torque occurs yet your simulation indicates peak torque of 76.1 ft-lb at 4000 rpm (VE=104.4%) and peak VE = 106.2% at 5500 rpm (73.4 ft-lb). In general it follows the rule but looking closely in this simulation it does not seem to exactly follow it.
Could increased friction with increased speed be a factor? What say you?
Peak VE is going to be determined by the camshaft and intake and exhaust tuning. If it were not for the rapidly increasing friction, the peak torque on this engine would occur at the the maximum VE point of 5500. Jim
PS, That rapidly increasing friction as the revs climb makes a wall somewhere around 7600 above which no feasible tuning can create a HP increase. I banged my head against that wall for a long time before I figured that one out. Jim
I have never thought about friction losses being a major factor. However I believe that at about 7000 RPM with that stroke and rod length the piston speeds are close to the level at which ring flutter occurs. In any case my budget doesn't extend to billet cranks, massive crankcases and Jim Schmidt's excellent rod and pistons, so I concentrate on increasing the power at lower revs (increase torque). A power increase at 7000 RPM often does not mean that the rest of the rev range is stronger. That first gear problem really had me flummoxed. I bought the TTI box, however I think that realistically the old 4 speed CR box would have been sufficient if fitted with a low first gear and the rest all high. I think I've got enough gears in my shed to provide a three different firsts for that old AMC box. - DERRRR ! !
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When you did you inlet tract flow experiments, how did you get a simulation which approximates what happens at mid-range revs in a real motor ? I had a discussion with a friend the other day about his fast 750cc Triton. He said that he thought that the standard Triumph 650 cylinder head has about the maximum desirable port diameter. He sets his motor up for maximum pull at below 6,300 RPM.
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I like having a very high final drive ratio for the highway which has made the stock low gear too high as it is. I would prefer something in the 3.25 to 3.50 range. Jim[/quote]
Goodness. Ill have to dig out my spread sheets but if your wanting to get back to the equivalent to a standard first gear road ratio and need a 3.25 to 3.5 range you must be gearing for about 140 - 150 mph in top ??
John[/quote]
Without pulling out my spreadsheet I would guess that is about right. I don't run that tall of gearing for the speed particularly.
I like the tall gearing for the relaxed cruise rpm in the 75-85 mph range I generally ride at. Plus the 70 miles per gallon it gives me is really nice.
Of course a rip down the salt flats is not out of the question. Jim 8)
Goodness. Ill have to dig out my spread sheets but if your wanting to get back to the equivalent to a standard first gear road ratio and need a 3.25 to 3.5 range you must be gearing for about 140 - 150 mph in top ??
John[/quote]
Without pulling out my spreadsheet I would guess that is about right. I don't run that tall of gearing for the speed particularly.
I like the tall gearing for the relaxed cruise rpm in the 75-85 mph range I generally ride at. Plus the 70 miles per gallon it gives me is really nice.
Of course a rip down the salt flats is not out of the question. Jim 8)
slimslowslider
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comnoz said:
now definitely need to catch up on sleep..
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acotrel said:
A port that is flowing at it's maximum obtainable velocity is going to fill the cylinder most effectively. If the port is small enough to reach it's maximum obtainable velocity at a RPM that is too low -then cylinder filling will be compromised at speeds above that RPM.
The port needs to be shaped correctly to allow it to sustain a very high velocity at the engine RPM you want peak power. That way it is still flowing at a velocity high enough to be fairly efficient at a lower RPM.
The better the shape of the port then the higher will be the obtainable velocity through the port. So the better the shape of the port the smaller it needs to be to flow enough volume to satisfy high RPM.
I have not done work on a Triumph port so I don't know about it's capabilities. Jim
lcrken
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johnm said:
RGM sells a wide ratio gear set with a 3.28 first gear. They used to sell one with a 3.16 first gear, but I think they discontinued it a few years ago.
You can also get low first gear ratios by fitting the Norton "wide ratio" high gear pair (23/14), which gives a 3.29 first gear when fitted with the standard 28/14 first gear pair, or 3.66 when fitted with the 29/13 first gear pair (if you can find them). With 4 different first gear pairs and 4 different high gear pairs available from Norton over the years, you can have first gear ratios from 1.78 to 3.66. The difficulty will be finding stock Norton gears from long discontinued models, including race bikes, sidecar combos, trials, etc. I haven't checked to see what might be currently available from Andover, but my guess is your best bet would be the RGM parts.
Ken
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comnoz said:
Why an I not surprised? I think everyone realizes by now that the Commando gearbox is pretty marginal for a powerful engine, regardless of the gear set used. Just not enough room in there for decent size shafts and gears, and not enough support for the sleeve gear. Same for the original Quaife 5-speed gearset for Norton boxes. The only thing that I found that saves the gearboxes was going to a higher primary drive ratio (1.75:1 instead of 2.19:1). Spinning the gearbox faster reduces the load on the teeth. I still had to replace gears and shafts occasionally because of wear and cracks, but never had another failure while running. I eventually went to a heavy duty Quaife (complete gearbox, originally meant for sidecars), which I'm still using. From everything I've read, the latest Quaife and the TTI boxes are light years better.
Ken
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