fueltap with reserve

texasSlick · Jun 2, 2016

Fast Eddie said:
Just for clarity, my 840 Triton produced 72rwp. I assume fuel needs would be based on crankshaft horsepower, so I guess we would have to assume somewhere in the region of 80 crankshaft bhp?

That would put it at 425 ml/m.

@Fast Eddie and all:

If you refer to Fig 2 which I posted above, for the engine given in that Fig (a Ford 6 cyl), the minimum specific fuel consumption rate (sfcr) occurs at about 2500 rpm and is about 0.45 lb/hp/hr. AND THE HP AT THIS RPM IS ABOUT 90. At the max. rpm given, the sfcr is 0.55, and the hp is about 135.

For this data, the rate of fuel consumption at the minimum sfcr is 0.45 X 90 = 40.5 lb/hr. and at max rpm the fuel consumption rate is 0.55 X 135 = 74.25 lb/hr. To calculate fuel consumption rate, the sfcr must be MULTIPLIED BY THE HORSEPOWER OCCURRING AT THE RPM FOR WHICH THE SFCR APPLIES. It is not appropriate to multiply the sfcr at the MOST EFFICIENT rpm by the hp at the maximum rpm.

For your bike, the sfcr at max rpm is unknown, a value of 0.5 is typical of gasoline engines for the minimum value of sfcr which generally occurs near the max torque rpm. If we "guesstimate" a value of 0.8 for your Trident at max rpm, the fuel consumption rate will be 0.8 X 80 = 64 lb/hr. or 1.07 lb/min. or 0.164 gal/min, = 1.3 US pints per min = 620 ml/min.

Slick

Deets55 · Jun 2, 2016

Slick,

Unless I am reading the chart wrong ( and that is very likely ) it shows a 6 cyl uses less fuel that an 8 cyl. at any given RPM, wouldn't that come into play when dealing with a 2 cyl engine. Thus reducing the amount of fuel required?

Pete

Fast Eddie · Jun 3, 2016

texasSlick said:
Fast Eddie said:

Just for clarity, my 840 Triton produced 72rwp. I assume fuel needs would be based on crankshaft horsepower, so I guess we would have to assume somewhere in the region of 80 crankshaft bhp?

That would put it at 425 ml/m.

Click to expand...

@Fast Eddie and all:

If you refer to Fig 2 which I posted above, for the engine given in that Fig (a Ford 6 cyl), the minimum specific fuel consumption rate (sfcr) occurs at about 2500 rpm and is about 0.45 lb/hp/hr. AND THE HP AT THIS RPM IS ABOUT 90. At the max. rpm given, the sfcr is 0.55, and the hp is about 135.

For this data, the rate of fuel consumption at the minimum sfcr is 0.45 X 90 = 40.5 lb/hr. and at max rpm the fuel consumption rate is 0.55 X 135 = 74.25 lb/hr. To calculate fuel consumption rate, the sfcr must be MULTIPLIED BY THE HORSEPOWER OCCURRING AT THE RPM FOR WHICH THE SFCR APPLIES. It is not appropriate to multiply the sfcr at the MOST EFFICIENT rpm by the hp at the maximum rpm.

For your bike, the sfcr at max rpm is unknown, a value of 0.5 is typical of gasoline engines for the minimum value of sfcr which generally occurs near the max torque rpm. If we "guesstimate" a value of 0.8 for your Trident at max rpm, the fuel consumption rate will be 0.8 X 80 = 64 lb/hr. or 1.07 lb/min. or 0.164 gal/min, = 1.3 US pints per min = 620 ml/min.

Slick

Hi Slick, IF I remember rightly, it was 72rwhp at around 7,500rpm...

texasSlick · Jun 3, 2016

Deets55 said:
Slick,

Unless I am reading the chart wrong ( and that is very likely ) it shows a 6 cyl uses less fuel that an 8 cyl. at any given RPM, wouldn't that come into play when dealing with a 2 cyl engine. Thus reducing the amount of fuel required?

Pete

Pete

There is only ONE specific fuel consumption (sfc) curve in Fig 2 which I posted, and that is for a 6 cyl engine. In fact, all the data is for the 6 cyl. engine except an 8 cyl brake horse power curve is shown for a comparison to the six.

Fig 2 is for illustrative purposes .... it matters not that it is for a 6, or a water cooled engine. The reason I posted this figure was to show the sfc if not a constant value as is oft cited, but is a curve that has a minimum. The figure also shows this minimum occurs at the maximum thermal efficiency rpm (not a coincidence, as the two are linked) and the maximum torque rpm also occurs at, or nearly at, the max. efficiency rpm.

Autos are geared so the highway cruising speeds occur at the maximum thermal efficiency rpm, and this is the minimum sfc point. Tables that cite values of sfc usually pick the minimum point on the curve.

Hope this clears it up for you.

Slick

texasSlick · Jun 3, 2016

toppy said:
Ok so i just went into garage an tried measuring flow. Half full roadster tank with two reserve type taps to get every last drop if needs be. Twin Amal Premier carbs with float drain plugs removed.
1tap on 1 carb flows 200ml per minute
1tap on 2 carbs flow 300ml per minute
2taps on 2 carbs flow 400ml per minute

The bike will hold 70mph about 4000rpm all day or 80mph but on motorway its me that gets bored not the bike. It will also go to the ton and stay there but normally you run out of space or my license starts to panic (i have nearly lost it in the past an that would be far to life changing)
So given the way the bike runs and way i ride it i believe i should not worry (unless you think otherwise) and i guess many other owners have same performance.
So my point is really how long do you need to hold max power of flow to be an issue? An if it doesn't seem at any rate to be an issue is it an issue?

Toppy

For most of us, the conditions you cite above, are as you say, entirely adequate. We get on down the road and never suffer any fuel starvation ... or do we? When we wind out the gears with WOT, and the rpm starts to approach the red line, and we feel the engine seem to "run out of breath" and the pull seems to wane, is it because the cam, carbs, and air induction is not keeping up, or is it because the mixture is leaning out due to fuel starvation caused by fuel taps unable to deliver the fuel? There is no simple answer, but this thread has piqued my interest.

The racer is certainly concerned, he has a "racer's edge" if he can eliminate that fall off near the top end.

How long does it take for an engine to feel the effects of fuel starvation? Again, no simple answer. It depends on the bikes fuel delivery system relative to the power the engine can develop. Again, for most of us, it does not matter, but for those who are competing, be it a stop light drag race, a TT race, or a land speed trial, it matters a great deal to get sufficient fuel to the carbs.

Slick

texasSlick · Jun 3, 2016

htown16 said:
The figure I quoted, 300 ml/min per carb was from a fellow that posted on Triumph bulletin boards. His handle was Mr Pete and he was from Australia. He was one of those guys who's opinion was widely respected based on his extensive background working on old bikes. I'm assuming he was mainly referring to 650 Triumphs, but the hp difference between them and Commando's is probably insignificant.
He stated that the 300 ml/min per carb was twice what was required, but because you were measuring max flow with the float sitting in the bottom of the bowl it was a safe margin. Here's a link to the original post. His is the 4th post down.
http://www.triumphrat.net/classic-vinta ... -taps.html

Making flow measurements as Mr Pete and I did with the float resting on the bottom of the float chamber is "somewhat artificial" as the bike could never run with the float like that. A more realistic measurement might be with the float shimmed to some "reasonable" value, but what?

The value in doing it as we did, is to get a "best case" number, which if deemed too low, tells us "we have a problem, Houston".

Slick

Deets55 · Jun 4, 2016

Slick,

Guess I might have misread the chart. It seemed to me the point where to dotted 8 cyl line crossed the fuel line would have been fuel consumption for an 8 cyl motor. Especially when the last written line on the graph says they included an 8 cyl for comparison. My bad..

Pete

fueltap with reserve

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