Fuel required does NOT depend on horsepower; it depends on trapped air mass. And so does horsepower.
The amount of fuel that can be burned is totally dependent on the trapped air mass. Adding more fuel may serve some other
purpose such as cooling or detonation control; but it is not being burned.
The OP defined the problem by indicating the VE of the engine. Thus the air mass is defined at the indicated rpm.
Viewed another way:
We can calculate the fuel required per stroke to define torque.
Or we can calculate the fuel required as a function of time which must include rpm.
Fuel Requirements
Moderator: Team
-
David Redszus
- Guru
- Posts: 9633
- Joined: Tue Nov 27, 2007 9:27 am
- Location: Chicago
- Contact:
-
CharlieB53
- Pro
- Posts: 223
- Joined: Fri Nov 22, 2013 2:44 pm
- Location: Wright City, Missouri
Re: Fuel Requirements
In the marine world a general rule of thumb is fuel required equals 10% of HP.
Like fbird said, 420 HP generally requires 42 gph gasoline.
Your mileage may vary.
Like fbird said, 420 HP generally requires 42 gph gasoline.
Your mileage may vary.
Re: Fuel Requirements
Agree. The best real life answer seems pretty obvious when one looks at the dyno sheet.
We can see the range of fuel consumption measured by the flow meter, along with the rpms, VEs, and calculated HP.
The OP, Bobby B, wanted to be within 10%. He estimated 33.5 gph and this is close to David's estimate, Fisher & Urich, and the example dyno run.
Urich & Fisher used .5 lb/hr hp
From the dyno sheet posted above.
.44 when VE was 101.2
.54 when VE was 95.2
So an engine that is more efficient, as many race engines are within their operating rpms, the estimates around 32.5 gallons per hour seem quite good.
The Urich and Fisher based estimate would be for a a bit less efficient engine, pretty common in the hot rod world, and even some forms of racing.
so 35 gph seems fair enough as well.
I don't like putting factors of safety in until I know what the purpose is. That's the main reason I wouldn't use the divide by 10 rule of thumb in this instance. If I was planning time between pit stops or something similar, then adjust accordingly.
We can see the range of fuel consumption measured by the flow meter, along with the rpms, VEs, and calculated HP.
The OP, Bobby B, wanted to be within 10%. He estimated 33.5 gph and this is close to David's estimate, Fisher & Urich, and the example dyno run.
Urich & Fisher used .5 lb/hr hp
From the dyno sheet posted above.
.44 when VE was 101.2
.54 when VE was 95.2
So an engine that is more efficient, as many race engines are within their operating rpms, the estimates around 32.5 gallons per hour seem quite good.
The Urich and Fisher based estimate would be for a a bit less efficient engine, pretty common in the hot rod world, and even some forms of racing.
so 35 gph seems fair enough as well.
I don't like putting factors of safety in until I know what the purpose is. That's the main reason I wouldn't use the divide by 10 rule of thumb in this instance. If I was planning time between pit stops or something similar, then adjust accordingly.
Re: Fuel Requirements
A very widely used general rule for normally aspirated gasoline engines is 0.5#/HP/HR. The marine rule quoted is equivalent to 0.6#/HP/HR. It's not a bad thing to bake in such a safety factor; 'more is better' within limits.CharlieB53 wrote: ↑Sat Sep 21, 2019 6:48 pm In the marine world a general rule of thumb is fuel required equals 10% of HP.
Like fbird said, 420 HP generally requires 42 gph gasoline.
Your mileage may vary.
A friend of mine was having fuel pick up problems below 1/4 full with his 850 HP Trans Am Series Corvette. The problem turned out to be that the return line was far from the pick up (normally a good thing) and that with low fuel it was taking too long for the return fuel to find its way through the cell foam to the pick up area. Why would that be? Because when I tested the system I found it had enough capacity to support 3,600HP!
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
Re: Fuel Requirements
The system is installed...What is the best and easiest way to test it? The car is a street car that might go to the drag strip once per year.
A 100 gph, 15psi electric pump is mounted at the tank.
A 3/8 aluminum line feeds a 6an filter & Areomotive SS regulator.
A 6an line feeds the 650 carb through a 6an-6an to 1/4 NPT male run tee.
A 6an line feeds a fuel to the Super Power Shot nitrous noid through a 1/8NPT tee.
There is a .032 jet in the nitrous fuel side for a 50 hp shot. (Nitrous jet is .037)
There is a .033 jet in the 5/16 return to tank line.
There is an electric fuel pressure gauge mounted at the carb inlet that can be seen while driving.
There is a hobbs low fuel pressure switch on the nitrous that will stop the nitrous, and give a warning light in the car.
I am considering just setting the regulator to 6.5 psi and driving the car. At WOT on carb only, if the fuel pressure stays above 5.5 psi I could try the nitrous.
Or, I can remove the 6an-6an 1/4NPT tee from the carb and put on a ball valve and hose to a catch can. With the regulator set to 6.5 psi and fuel flowing back to the tank and through the 5/16 line, I can adjust the ball valve to flow 42 gph to the catch can. If I can maintain above 5.5 psi under these conditions, I should be safe to try the nitrous.
With the ball valve to catch can set up, I can also test to see what the max fuel flow can be while maintaining 5 psi or more, which might be good to know.
How should I test it?
A 100 gph, 15psi electric pump is mounted at the tank.
A 3/8 aluminum line feeds a 6an filter & Areomotive SS regulator.
A 6an line feeds the 650 carb through a 6an-6an to 1/4 NPT male run tee.
A 6an line feeds a fuel to the Super Power Shot nitrous noid through a 1/8NPT tee.
There is a .032 jet in the nitrous fuel side for a 50 hp shot. (Nitrous jet is .037)
There is a .033 jet in the 5/16 return to tank line.
There is an electric fuel pressure gauge mounted at the carb inlet that can be seen while driving.
There is a hobbs low fuel pressure switch on the nitrous that will stop the nitrous, and give a warning light in the car.
I am considering just setting the regulator to 6.5 psi and driving the car. At WOT on carb only, if the fuel pressure stays above 5.5 psi I could try the nitrous.
Or, I can remove the 6an-6an 1/4NPT tee from the carb and put on a ball valve and hose to a catch can. With the regulator set to 6.5 psi and fuel flowing back to the tank and through the 5/16 line, I can adjust the ball valve to flow 42 gph to the catch can. If I can maintain above 5.5 psi under these conditions, I should be safe to try the nitrous.
With the ball valve to catch can set up, I can also test to see what the max fuel flow can be while maintaining 5 psi or more, which might be good to know.
How should I test it?
Re: Fuel Requirements
Get or make a test orrifice (AREA) that equals the carbs 2 needle seats size. AREA not diameters.
Flow that into a bucket with the regulator set to the working pressure for the carb fuel feed side.
I believe that 2x .110" needle seats equals .156" flow orifice equal AREA.
.156" equals 5/32"
If you make / drill the test orifice be sure to bevel the entry and exit sides of the test orifice to break that sharp drilled edge so it flows correctly.
Making the slight beveled entry exit bevels with a bigger size drill bit works.
flow test thru the orrifce, at the working pressure, into a big wine bottle that you have pre-marked to show a 1 quart US) level on the bottle. Measure how many seconds time to flow 1 quart fuel into that bottle..
Repeat 3-4 times and average the test times. Do the math for GPH.
It is a very bad idea to piggy back the nitrous fuel feed off the same fuel pump as the engine fuel feed.
Do your self a favour and get a dedicated fuel system for the nitrous side fuel system.
At low NOS shots it can be piggy backed but on always effects the other when piggy backed.
You will SOON WANT to step up to bigger more NOS shots to go fast.
You are setting yourself up for a bad experience $$$$$ ny having a piggy backed system.
$$$$$$$$$$$$$$$$$.
Flow that into a bucket with the regulator set to the working pressure for the carb fuel feed side.
I believe that 2x .110" needle seats equals .156" flow orifice equal AREA.
.156" equals 5/32"
If you make / drill the test orifice be sure to bevel the entry and exit sides of the test orifice to break that sharp drilled edge so it flows correctly.
Making the slight beveled entry exit bevels with a bigger size drill bit works.
flow test thru the orrifce, at the working pressure, into a big wine bottle that you have pre-marked to show a 1 quart US) level on the bottle. Measure how many seconds time to flow 1 quart fuel into that bottle..
Repeat 3-4 times and average the test times. Do the math for GPH.
It is a very bad idea to piggy back the nitrous fuel feed off the same fuel pump as the engine fuel feed.
Do your self a favour and get a dedicated fuel system for the nitrous side fuel system.
At low NOS shots it can be piggy backed but on always effects the other when piggy backed.
You will SOON WANT to step up to bigger more NOS shots to go fast.
You are setting yourself up for a bad experience $$$$$ ny having a piggy backed system.
$$$$$$$$$$$$$$$$$.
Re: Fuel Requirements
When testing this be sure of the FUEL PUMPs electrical supply VOLTAGE (12V dc).
This effects fuel pump performance. More voltage is better. But you want minimum real 12V dc. at the fuel pump
This effects fuel pump performance. More voltage is better. But you want minimum real 12V dc. at the fuel pump
Re: Fuel Requirements
Thanks Fbird
I had a stand alone system and did not like some things about it, so, I am trying this.
Based on what you said about AREAS, how about this as a first test idea?:
Replace the .033 jet in the return to tank line with a .047 jet. This will give the same area as the .033 return to tank plus the .032 nitrous fuel jet. If I can maintain 5.5 psi or more at WOT on carb only, I should be safe to use the nitrous with .033 jet back in the return to tank line.
I had a stand alone system and did not like some things about it, so, I am trying this.
Based on what you said about AREAS, how about this as a first test idea?:
Replace the .033 jet in the return to tank line with a .047 jet. This will give the same area as the .033 return to tank plus the .032 nitrous fuel jet. If I can maintain 5.5 psi or more at WOT on carb only, I should be safe to use the nitrous with .033 jet back in the return to tank line.
-
David Redszus
- Guru
- Posts: 9633
- Joined: Tue Nov 27, 2007 9:27 am
- Location: Chicago
- Contact:
Re: Fuel Requirements
Perhaps, but perhaps you do not fully understand the real issues.
To use a crude rule of thumb to determine fuel requirements based on horsepower, completely overlooks the effects of compression ratio, ignition timing, fuel specific energy, flame speed, inlet air temperature and several other power influencing factors.
Oversimplification is a fools errand. But then, even a stopped clock is right twice a day.
Re: Fuel Requirements
Let's not overcomplicate it either.
What do you say about testing with a larger jet in the return to tank and posted above?
What do you say about testing with a larger jet in the return to tank and posted above?
Re: Fuel Requirements
No, using the simple crude hp/ 10= gph fuel flow requirements of the system ON THE CAR.
Allows for and accounts for these variations. And variables.
Some of which you do not account for.....
No engineering degree required....
K.I.S.S.
Allows for and accounts for these variations. And variables.
Some of which you do not account for.....
No engineering degree required....
K.I.S.S.
Last edited by F-BIRD'88 on Mon Sep 23, 2019 3:40 pm, edited 1 time in total.
Re: Fuel Requirements
No, because the nitrous system operates and is calibrated to a different pressure than the carb.
A small change in nitrous fuel pressure, in actual operation effects the nitrous/fuel mix. Significantly...
At low hp nos shots you can get away with a lot of evils...
But at higher levels which you will soon seek to go fast using nitrous, you WILL run into big trouble $$$$ fast using that method.
Your test set up method sucks....
Develop and use correct nitrous fuel side set up and fine tuning method now and go faster longer....$$$$...
Piggybacking is just bad... Especially how you plan to test set it up......be ware...
A small change in nitrous fuel pressure, in actual operation effects the nitrous/fuel mix. Significantly...
At low hp nos shots you can get away with a lot of evils...
But at higher levels which you will soon seek to go fast using nitrous, you WILL run into big trouble $$$$ fast using that method.
Your test set up method sucks....
Develop and use correct nitrous fuel side set up and fine tuning method now and go faster longer....$$$$...
Piggybacking is just bad... Especially how you plan to test set it up......be ware...
Re: Fuel Requirements
We will see. I can't run much more nitrous without busting my factory sbf block. So, we will take it one step at a time. I hope to do some testing tonight. Not nitrous, just carb.
Re: Fuel Requirements
Just tested the new fuel system for the first time.
Put a .065 jet in the return to tank line (4 times the area of the .032 nitrous fuel jet for 50 hp). I expect to use a .033 jet in the return to tank before using the nitrous.
Fuel pressure regulator was set at 6 psi according to the engine bay gauge. The in car gauge showed 6.5 psi.
I saw no change in fuel pressure on the in car gauge on a 25 mile trip. I only hit WOT once through second gear but could not see any drop in fuel pressure.
I mounted a thermocouple on the carb to monitor the temp. The car is stored in a basement garage and everything was about 72 degrees when I started testing. Outside temp was about 85 and dropped to about 75 after sunset. The carb temperature stayed below 112 degrees. So, the return to tank line could help prevent vaporlock if no non-ethanol gas is not available on a road trip.
Put a .065 jet in the return to tank line (4 times the area of the .032 nitrous fuel jet for 50 hp). I expect to use a .033 jet in the return to tank before using the nitrous.
Fuel pressure regulator was set at 6 psi according to the engine bay gauge. The in car gauge showed 6.5 psi.
I saw no change in fuel pressure on the in car gauge on a 25 mile trip. I only hit WOT once through second gear but could not see any drop in fuel pressure.
I mounted a thermocouple on the carb to monitor the temp. The car is stored in a basement garage and everything was about 72 degrees when I started testing. Outside temp was about 85 and dropped to about 75 after sunset. The carb temperature stayed below 112 degrees. So, the return to tank line could help prevent vaporlock if no non-ethanol gas is not available on a road trip.