Volumetric Efficiency of Commandos?

Volumetric Efficiency of Commandos?

Lot of calculators ask for VE but I've never seen any figures for Nortons to generally plug in 90%,which I think is conservative. Does any one have a ballpark numbers for various Cdo engines?

Well anyone with a realistic ballpark of VE in Nortons?

:roll:

This is really an incomplete question. I suggest you reverse engineer this to understand it.

Max volumetric efficiency is at max torque. Max horsepower is past max torque where the incremental rate of increase of rpm is greater than the rate of decrease of torque. So the question "Volumteric Efficiency of Commandos" needs to be qualified. Are you asking maximum volumetric efficiency (which is at max torque) or volumetric efficiency at maximum horsepower (but then you would need to know the rpm in either case).


A couple of data points you can play with are from my Commando road racer (standard stroke, 10:1 comp ratio, Megacycle 560-020 cam, stock AMAL carbs, 1-3/8" headers to reverse megaphone). Numbers were RWHP off of an inertial dyno so you will need to make some adjustments using your judgement.

Maximum torque of 49 ft-lbs at 5,200 rpm (rear wheel). The HP curve was virtually flat from 5,800 rpm to 7,000 rpm while the torque dropped off at a steady rate.

You should be able to plug these numbers in to derive the MAX volumetric efficiency which is what I think you want.

Another data point is from one of the initial dyno pulls on the ultra short stroke 750 Norton.

Max torque of 55 ft-lbs at 6,500 rpm (rear wheel)

Let's hear what you get.

Ok, I guess i'm on my own again, oh oh. My vac gauge will help.

Volumetric efficiency is basically a measure of how well your car breathes. As the piston goes down it creates a vacuum which draws air into the cylinder. In an ideal engine the cylinder would fill at ambient pressure, this would give a V.E. of 100%. But due to restrictions in the flow, (those pesky things like air filters and throttle bodies) the cylinder will never fill at atmospheric pressure. There is always a vacuum in your intake. Except for the boosted folks who are running over 100% volumetric efficiency. There are many ways to calculate V.E. but the quickest and dirtiest is to attach a vacuum gauge as close to the cylinder as possible, most probably the intake manifold. Record the amount of vacuum and subtract it from the ambient pressure. Now divide this number by the atmospheric pressure where you live. This will give you a rough estimate of the V.F. of your engine.

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Ambient PSI 14 PSI
- Vac PSI 2
-------------------
12 PSI / 14 PSI = ~ 86% V. E.

Bingo into the ballpark.

What you are suggesting (citing by others) is cruder than crude for naturally aspirated engines and is subjected to so many distortions.


You are better off taking the actual power/torque @ rpm numbers and back calculating but this is all a dog chasing it's tail excercise unless you know whether you are looking for Max VE or what.

So at what rpm were you measuring the differential pressure at. Is that maximum VE or VE at max power?

Hehe, yeah its just mental masturbation to play with online calculators while project stews in my living room and California and Colorado. Down and dirty is my middle name so pleased to learn the concept of measuring the ambient over the vacuum level at various throttle and rpm to judge V.E. Its a sliding scale but interesting to see where Norton lands in V.E. ranges by this crude method. I don't remember the exact vacuum levels but Peel didn't have much vacuum showing at manifold at WOT. Have not put gauge on factory Combat but will soon to see what range it shows to entertain me. Of course Peel's gauge also reads to 20 PSI over ambient. This turbo gauge brought on one of the most funny events in Peel's un-believable performance when I couldn't see her walking back from peeing after a run ahead of a Ducati Monster squadron, then were all arguing and squatting and squinting trying to find the hidden turbo charger!!! When I said it ain't installed yet they almost feel back on heels in wave of shock. I'm sure past Peel couldn't keep up with your racers, just them balloon tire wheelie prone unstable newbies out there.

hobot said:

its just mental masturbation to play with online calculators

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Fair enough but I think this differential pressure drop is next to worthless for estimating VE.

First off, you would need to get the bike on a brake dyno and take DP readings at max torque or max HP and know the rpm for each to use the swag at VE from DP. But putting the bike on the dyno more or less answers the questions you are probably asking - right.

Air is a compressible fluid and there are so many things happening in an intake tract throughout the cycle including taking on heat energy from the surrounding intake tract. I would say a final word on the matter would be a mass flow measuement; this would measure exactly how much air is going in and you could plot it against rpm. I suspect it would probably shadow/follow the torque curve but be skewed a bit by the increased friction losses as the rpm increase.

And it's called mental exercise.

Ugh I was hoping someone with detailed dyno charting of Norton would give a range of V.E.'s, but as you state its calculator bench racing numbers substituting for real time torque/rpm on a dyno. I don't yet know how to use raw dyno data to come up with a max V.E. One interesting fun thing about calculating V. E. on various engines by same method is the pecking order of sorts. IIRC a quik check of dyno accuracy is the torque and hp are equal at 5252 rpm. Also should not use a percentage of drive train loss to judge crankshaft power, drive train loss don't go up as a percent, its a set amount per rpm, which in Nortons takes about 10 hp - I think. Using a percentage loss factor inflates actual crankshaft hp calculations.

If I get more bored I guess I could extrapolate the mixture cfm to produce the hp calculated in your examples, then subtract that from the theoretical volume potential pumped though and come up with a V.E. for each engine. Not tonight.

hobot said:

I don't yet know how to use raw dyno data to come up with a max V.E.

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Steve,

Pick a point that you want to know about VE (max torque or max power) and do some trial and error testing on your online calculators until you match one of the torque, power & rpm data sets (that you adjust for drive line loss) that I gave you above . Simple as that. Assuming the online calculator is correct it should give you an indication of VE.

All night party in the woods and half a day Commando repairing ain't feeling so fond of them right now to do much mental math exercises - but your data points leave me hanging on Mass Air Flow and Temperature Density. I could guessimate of course for vacuum gauge accuracy. Extrapolate the fuel/air flow from the hp calculations and just take a stab of a few air temp ranges.

http://www.installuniversity.com/instal ... 012000.htm

The results you get from your calculations should help you better understand how your car will react with future modifications.

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A couple of data points you can play with are from my Commando road racer (standard stroke, 10:1 comp ratio, Megacycle 560-020 cam, stock AMAL carbs, 1-3/8" headers to reverse megaphone). Numbers were RWHP off of an inertial dyno so you will need to make some adjustments using your judgement. Maximum torque of 49 ft-lbs at 5,200 rpm (rear wheel). The HP curve was virtually flat from 5,800 rpm to 7,000 rpm while the torque dropped off at a steady rate.

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Theoretic 100% efficiency:
745cc-45.52cid x 5800rpm = ~150 cfm

Calc of mass air flow:
49 rw lb-ft @ 5800 = 54 hp + 10 hp for drive train =64 shaft hp. [dang ok for mostly a real Norton]
1.5 cfm per hp x 64 = 96 cfm

96 / 150 x 100 = 64% VE.

I don't believe this is even in correct ballpark, but don't know what's wrong with the data or my calc's or your Norton should of made like 80 hp into drive train if it had even 80% VE. Its over my little head to proceed further.

ok here's a down and dirty calculator that implies your 49 lb ft engine is just over 100% efficient which I can believe better than only 64%. It still over me little head so that's about it for me on this sideline dead end exercise.

http://www.ajdesigner.com/phpengine/eng ... ciency.php

hobot,

You are mixing up numbers in your analysis, the 49 lb-ft torque is at 5,200 rpm, not 5,800 rpm

After reviewing your reference link above I can say with confidence that............."you can't get to there from here". None of the equations reference power or torque/rpm. I am sure there are other online calculators that do.

A big reason this ain't working out as hoped is the VE is mostly based on the air density and volume pumped I've is no data points for that on Commandos, and all the modern things use a temp and mass air flow senders to measure air density and amounts of it inhaled. Not much hope for me either if I can't even transpose your basic rpm figures, ugh. We can't use the rwhp results as it ignores a good percentage of inhaled power lost to the drive train and tire and we only assum. Hardly any VE info on motorcycles so essentially only automotive direct crankshaft dyno results w/o any drive train or tire drag to compensate/guessimate or in our case 'argue' over.

Maney in '02 reports his 920 with 100 hp at the crankshaft but don't know it that's by direct hook up to brake dyno or an extrapolation from rolling dyno guessing at the drive train loss to put on crank shaft power.

I'd expect some of your race engines to have over 100% VE at some rpm coming into cam ram port effect.

So do good Nortons make 1 hp per 1.5 cfm with half a lb of gasoline or do they need 1.6 cfm and over half a pound fuel per hp?

hobot said:

A big reason this ain't working out as hoped is the VE is mostly based on the air density and volume pumped I've is no data points for that on Commandos,

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Pick/assume Standard Temperature and Pressure (STP) conditions and focus on volume pumped. The dyno number I gave you were nearly at sea level (~900 ft AMSL)

hobot said:

I'd expect some of your race engines to have over 100% VE at some rpm coming into cam ram port effect.

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I venture to say maybe +110%. From what I have read about historic race engines, the upper limit is maybe 120%.

hobot said:

So do good Nortons make 1 hp per 1.5 cfm with half a lb of gasoline or do they need 1.6 cfm and over half a pound fuel per hp?

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The rules of thumb I have read are 1.5 to 1.6 cfm per hp yet I do not know if that is at peak torque or peak power. Once past peak torque, the VE drops off so VE at peak power will always be less than at peak torque. The 1.5 vs 1.6 represents only a 6.5% spread so pick a point and go with it all the while keeping this 6.5% uncertainty in mind.

The real challenge is trying to use VE for anything meaningful unless you know the specifics of the engine. Just as in the case of trying to estimate losses between the engine and rear wheel, the same applies to the engine internals. You have heard the term "brake mean effective pressure" (b.m.e.p.), well there are many elements to this including mean effective pressure of pumping, mean effective pressure of friction etc. So two engines of identical cam and head flow may have identical VE profiles yet have different crankshaft torque profiles due to differences in internal friction.

See Chapter six (pg 149) of The Internal Combustion Engine in Theory and Practice (Volume 1) by Charles Fayette Taylor. for Air Capacity of Four Stroke Motors. Also look up the elements of Mean Effective Pressure.

http://books.google.com/books?id=E_...weugsG1Dw&ved=0CD8Q6AEwAA#v=onepage&q&f=false

Also good reading for those few who may be interested in engine design (particulary crankshafts) is Section 11 of Volume Two

I had to assume the generalized data points on air density was STP, 14.696 sea leve PSI @ 70'F room tiemp. I got that each engine can vary but as my understanding clears, bottom line for my satisfaction would be the power potential per displacement that Norton range in. Good point about where to measure this so peak torque and peak power would be better to judge pecking order by. I do sorta have a practical use for this in calculating how much water to spray in Peel to bump the 87 octane up enough to take full ignition timing for best "brake mean effective pressure" (b.m.e.p). But good engines all fall in upper 80's to 90's over normal operation rpm with racers on cam good port header etc get over 100%. I've used conservative numbers for a safety factor in octane excess but still getting closer to optimal means I can carry less water per boosting. Plan A is 1/2 gallon tank @ 15% H2O to fuel mass that clac's implies should be goo for 20+ min WOT on 2 or so gallons gasoline.

CR adds/subtracts 2-6% VE over the range Norton likely to use, ie: 9 to 11+sh.
in real life I'll be tickled pink with the grunt of a cammy 920 in a light rig but something ya feel like a nut so best way I know is build a low down torquer and blow past the torque peak VE drop off. Digital tire spin response opens a whole 'nother world of thrills, if its controllable.

In practice we can't really isolate engine and drive train, just look at the tire out put per the fuel and air consumed. At least the Norton drive train is a pretty close constant comparing Norton type engines. Daylight and stuff to do, may dive back into your dyno data to re-figure cfm's used vs 100% VE cfm's calculated.