Fuel Requirements

[F-BIRD'88]

The carb feed is not the problem. The carb will work well over a big fuel pressure spread....
It's the nitrous fuel side that is the issue.
The fuel pressure of the nitrous side has to be kept in a narrow window to keep the nitrous-fuel ratio tight..
Your test setup method is all wrong for DYNAMICALLY setting up the nitrous fuel pressure regulator.

[GARY C]

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?

You never mentioned nitrous... maybe this will help confuse you. Top is Fogger, 28 nitrous 32 fuel, bottom is NA. Right click to view image that's worth a s#!+ due to new forum controls.

[BobbyB]

Thanks for your input Fbird, please tell me why you think my test procedure is wrong. Is it because you believe the opening of the nitrous fuel noid will cause a drop in pressure that the fuel pressure regulator can’t accommodate?

[F-BIRD'88]

When piggy backed with a riasing fuel flow to he carb bowls ans rpm increases yes.

Not so much at the 50hp shot level. you will get away with many evils at jsut 50hp shot.
But at higher shot levels you will hit a big brick wall in your flawed method. it will be a expensive brick wall.

But at your planed level you need to tst the piggy baked system flowing and set both the careb fuel regulator and set the nitrous fuel regulator accuratly while simulating the flow of both accuratly at the same time. 1/4 psi regulator set difference in the nitrous fuel side makes a BIG difference in Nitrous to fuel ratio set up. The carb draw on the system will effect he fuel side of the nitrous system as rpm rises and carb fuel flow demand. rises.

you do not want the nitrous side to progressively lean out as you progress down track.

I don't know why you are not seeing this as obvious.


2 big no-no's with nitrous.
failure to dynamicly set up the nitrous side fuel delivery for correct pressure and flow.

Failure to use a fuel with enough octane to avoid detonation.
The higher the shot level the more quicker you get to the edge $$$$$$$.
Get yourself a fuel pressure gauge that is actualy accurate and will re +/-1/8th psi change ACCURATLY for setting up the nitrous... learn to use it orrectly.
You will save a TON on Ford SB engine blocks , Rods and pistons....

50hp shot is nothing.. you will get bored of a 50hp shot before you finish your first nitrous bottle.
Develop correct set up method now...... save a ton of money and grief and go fast on reasonable nitrous levels.. cause you will want to raise the power level from 50HP.

[BobbyB]

Thanks Fbird. It is not obvious to me.

My understanding is that the pump and regulator can deliver far in excess of the fuel required by the carburetor, plus the nitrous, plus the return to tank, while maintaining the required pressure to the carb and to the nitrous. I am only using one fuel pressure regulator. I plan to use jets to tune the fuel flow to the nitrous after reading plugs.

My understanding also, is that with 37 nitrous and 32 fuel jets in the super power shot set up, if the supplied fuel pressure at the fuel selonoid is 6.5 psi, the mixture will be very rich. In fact, I think think the set up will be safe down to 5 psi at the fuel selonoid. Is my understanding wrong on the safe fuel pressure with the 37 & 32 jets?

[F-BIRD'88]

You are not going to do this on a piggy back system with just one single pressure regulator.
You are headed to a very expensive first impression of nitrous oxide injection.
Get 2 regulaotrs.
better just install a dedicated fuel system for the nitrous.
a nitrous fuel system capable of supporting a 300hp shot is not expensive.
at all. it is very basic.
Think of all thsoe Ford engine blocks you will save.

ah hha.
You got this all wrong.
You need to rethink this thingy.... $$$$$$$$$$$$$$$$$

I'd like to see you go fast with nitrous , have fun and not eat parts.

Start on the right foot.

[BobbyB]

Gary, thanks for the Dyno sheets. Are you posting them to show me the change in fuel consumed per hour?

[Geoff2]

David R.

All of the variables you quote contribute to the HP the engine makes: comp ratio, inlet temp, ign timing, etc. When these are OPTIMISED, max HP will be made. The HP is the RESULT of these factors all being optimised. Incorrect timing, less HP produced, less fuel reqd.
Maybe you should go on a fool's errand & tell the Holley engineers they are dumb a**es who don't know what they are talking about...

[BobbyB]

Please help me rethink it Fbird. I don’t want to burn my new engine up, but I do not think I am on the path to do that either.

Lets say the pump is a Holley blue & the regulator is the one Holley puts in the box with the pump. Let’s say you built the induction system with a tunnel ram and two 750 Holley vac secondary carbs. (4.88 gears too!) Let’s say you figured the engine might make 650 hp. There are 4 needle& seats on your set up. Do you think you must have 4 regulators to feed 4 needle seats? I don’t think you would think you needed more than 1 regulator. D.Vizard says something like “ a Holley blue will fuel 750 hp with bad plumbing and 850 hp with good plumbing” in one of his books. I think most people would tell you that your Holley blue pump and regulator will flow enough fuel at the pressure required to feed 650 hp whether you have 2, 3 or 4 needle seats. You don’t need another regulator just because you additional circuits for fuel to flow through.

So, all I am trying to do is prove to myself that, with 1 carter hp4601 pump, 1 Aeromotive SS regulator, proper plumbing, & proper jets in the nitrous fuel supply and return to tank line, that I can SAFELY flow 5 gallons per hour to the nitrous plate while feeding the carb and returning 5 gallons per hour to the tank.

I feel sure I can prove it to myself using your wine bottle test, and I might end up testing it that way, but I bet there is an easier way.

I want to find an easy way to test it without getting fuel all over myself!

I bet you when it is all said and done that my system will be able to deliver more than 50 gph to the carb, while feeding 20 gph to the nitrous and while feeding 5 gph back to the tank. I just have to figure out how to prove it to myself.

By the way Fbird, what make you think this is my first experience with nitrous?

I really appreciate everybone input and concern.

[David Redszus]

David R.

All of the variables you quote contribute to the HP the engine makes: comp ratio, inlet temp, ign timing, etc.

Agreed.

When these are OPTIMISED, max HP will be made. The HP is the RESULT of these factors all being optimised.

Again, agreed. Maximum horsepower requires that these factors be optimized.

Incorrect timing, less HP produced, less fuel reqd.

Now you are wrong. It is frequently the case where incorrect timing, both ignition timing and combustion timing, may require additional fuel to be used to prevent destruction and maintain power. Even with all identified parameters being optimized, we still experience a cylinder to cylinder variance in mixture and power. Same is true for cycle to cycle variances.
Since not all cylinders perform the same, some change with rpm) the fuel requirement per cylinder will not be constant. If we allocate fuel on an average power basis, some cylinders will be over fueled and some will be under fueled.

The use of inlet air temperature sensors and inlet pressure sensors, per cylinder along with Lambda sensors and
EGTs in each pipe, will give a much clearer picture of actual engine behavior.

Perhaps a major flaw in the rule of thumb is the lack of specificity regarding type and properties of fuel being used. How does that rule apply to methanol? Nitromethane? Diesel?

Maybe you should go on a fool's errand & tell the Holley engineers they are dumb a**es who don't know what they are talking about...

I've been there and done that many times. I was tuning fuel injection systems well before most Holley engineers were born. The more senior engineers know very well of what I speak.

Amateur racers have the tendency to seek simplification of highly technical issues. Some need oversimplication which invariably leads to incorrect understanding.

So let's simplify.
Fuel mass required is dependent on air mass ingested for any engine or state of tune.

Consider fuel required, per stroke, for an engine with constant torque compared to increasing power.

The point of this forum is to provide helpful and sometimes useful information, and not to sling darts at those with whom we may disagree.

[BobbyB]

Thanks David R. I hope you did not think I have been slinging darts at anybody.

I would appreciate it if you read my post from 8:15 this morning and tell me how you think I should test my set up before using the nitrous.