240ml per minute, how much HP?

[911st]

How much Horse Power will 240ml per minute support at 12.5/1 Air Fuel Ratio (Turbo)?

This is over my head.

Thx.

[cmonref]

Assuming you mean 240 ml/min for each of 6 injectors, according to the calculator on the Megasquirt Manual, about 235 HP.

[911st]

This if for CIS. This is the max delivery of fuel possable to one cylinder.

Somthing must not be right with that number unless is it for one cylinder.

Could that be for an injector rated at 240 ml/min but dose not exceed somthing like a 70% duty cycle?

[WinRice]

I'll take a stab at this one:

240 ml/min = 240 cc/min

Which should be close to a the same size as an EFI injector at 100% flow.

So using a calculator like this one:

http://www.injector.com/injectorselection.php

BSFC = 0.65
# of cyl = 6
Duty cycle = 1 (100% flow)

HP = 211

Which seems awfully wimpy!

So I looked at it another way.

Using the weight of gasoline as 6.073 lb/gal, the conversion comes out to:

240 ml/min = 23.1 lb/hr, which still seems a little wimpy.

I've been following Stup's test also, and this seems way off for the HP levels of a 930.

[beepbeep]

Using my calc:

3.3L engine turning @ 5500 RPM at 0.7 bar, producing 300 HP at AFR 13.0:1 (CIS goes lean on the top, remember?) at 92% VE, 50 deg. C intake temp and 29% efficiency will gulp 33,7 lb/sec of air and have per cylinder fuel flow of 262cm^3/min


I also used 0.75 kg/L density and 43.8MJ/kg energy density (gasoline)

Also, remember that control pressure will be lowered at boost, so what was 240ml/min might go up to more when boosting. So fuel flow seems OK to me.

[WinRice]

Originally Posted by beepbeep

Also, remember that control pressure will be lowered at boost, so what was 240ml/min might go up to more when boosting. So fuel flow seems OK to me.

Yep, that's what it has to be.

Typical EFI pressure is about 3 bar, and the turbo CIS runs a system pressure of 6.2 - 6.5 bar on early models, 6.9 - 7.1 bar on later models, so that will give a little headroom under boost, possibly even double the flow.

So with my rough calcs, that would be about 422 HP.

With Goran's better calcs, that would be around 550 HP.

That makes more sense.

[911st]

Originally Posted by WinRice

I'll take a stab at this one:

240 ml/min = 240 cc/min

Which should be close to a the same size as an EFI injector at 100% flow.

So using a calculator like this one:

http://www.injector.com/injectorselection.php

BSFC = 0.65
# of cyl = 6
Duty cycle = 1 (100% flow)

HP = 211

Which seems awfully wimpy!

So I looked at it another way.

Using the weight of gasoline as 6.073 lb/gal, the conversion comes out to:

240 ml/min = 23.1 lb/hr, which still seems a little wimpy.

I've been following Stup's test also, and this seems way off for the HP levels of a 930.

Is that 211hp for one cylinder?


Also, control pressure only effects the position of the metering plate relitive to air flow.

The test was done manually pushing the plate down to its max position. Thus, control pressure on boost is not a factor.

[911st]

I had the weight per gal of gas wrong so I tried it again.

OK, I am new to this so I may not have done it right but I will try.

240 ml/min = 14400 per hr =486.9 fluid Oz = 3.8 gallons. 3.8 gal at 6.073 = 23.08 lbs.

It takes .55 to .6 lbs per hour to make one HP.

Thus, 41.82- 38.47 HP per cylinder or 250 to 230 hp total.

What am I missing or what mistake did I make?

[donporfi]

I think you need to calculate in mass not volume.

[beepbeep]

Originally Posted by 911st

What am I missing or what mistake did I make?

240ml/min that stup measured is value measured with control pressure being in high "N/A" mode. If you really want to calculate fuel flow at boost, you must pressurize the WUR to 0.7 bar (which will lower the control-pressure) and measure flow again.

[911st]

Metering plate was pushed to full travel by hand. This bypassed the WUR function so that was not it.

[WinRice]

Originally Posted by 911st

Metering plate was pushed to full travel by hand. This bypassed the WUR function so that was not it.

Looking at figure 17 in the Bosch K-Jetronic Technical Instruction I have, it looks like the Primary-pressure regulator has a Control-pressure connection on the opposite side of the plunger, to reduce system pressure as the control pressure increases.

It makes some sense that Stup's tests show 240 ml/min, which would be fine for NA mode, then under boost it would be higher.

The best test for maximum flow potential would be to take the WUR out of the circuit, giving 0 control pressure, then checked at full metering plate travel. Also, monitor the system pressure from closed to full open on the metering plate, to get a base pressure reading at closed, and to see how much pressure drop at full travel occurs. This would show if the fuel pumps are keeping up with the flow, or limiting the overall flow.

[911st]

Control Pressure is behind the metering pin pushing on it to control its rate of movement relative to air flow.

System pressure it controlled by a pressure regulator built into the head where excess fuel exits the head and is not variable.

Differential Pressure or lower chamber pressure is controlled by the advancement of the metering pin as pressure is bleed off around the metering pin slit.

The larger the differential between the upper and lower head the more the diaphragm deflects and the more fuel that passes through the orifices and out to the injectors.

The fuel head is just a big pressure regulator and valve, fuel flow is only a function of how far the valve is opened not changes in system pressure.

At least that is what I understand but I have been wrong before.

[WinRice]

Yep, that's pretty much the understanding I have also. But we're missing something somewhere, so I was doing a little digging.

The manual I have shows the basic system pressure regulator, with only an inlet and outlet, controlled by spring pressure only. Later in the manual it shows the same diagram, but this time with a control pressure line on the opposite side of the regulator from the other two.

Looking at the small Porsche 'White book' of technical specifications for the 78-81 911sc and Turbo 3.3 I get these numbers:

System pressure adjusting value

4.7-4.9 SC (USA)
6.2-6.5 Turbo (later Turbos with lambda use 6.9-7.1)

Control pressure warm

3.4-3.8 SC (USA)
3.45-3.85 Turbo

The first observation, is the twin pumps of the Turbo run much higher system pressure, the second is the control pressures are very close warmed up and off boost for the turbo, which makes some sense.

That extra fuel is coming from somewhere, just haven't figured out where yet.

[911st]

I am stumped.

Is it coming from somewhere, or are we using the right math the convert the fuel delivered to HP, or are the delivery numbers off for some reason.