Nitrous Theory

[40k Later]

I have a question for any of you currently using nitrous. I have a crate 535HP 460 from Ford Motor Sport with a NOS Cheater. I have installed it exactly how the directions state, with two fuel lines coming out of the fuel regulator one of course the the Demon 850 and the other to the nitrous solenoid. A few different self proclaimed experts at the track assured me when I hit the switch the car is going to lean out and those aluminum heads will fit loosely in a 5 gallon bucket. I have an MSD 6AL and an MSD timing controller with the correct timing retard chip for the 180HP jet. I have one colder range plug and as soon as summer gets here I will also have the racing gasoline that is required.

I spoke with NOS and they've assured me it will be fine but the "experts" say I need to run two pumps and two regulators.
Isn't it Bernoullis principle that pressure is equal on all sides? 6PSI coming out of the regulator is the same in both lines. Is it because one line experiences a pressure loss (solenoid) due to an increase in volumn?
Any thoughts

[HighPlainsDrifter]

Hi,
You are starting to get up there in fuel volume. One fuel pump may not have the volume to feed a big block + 1/2 again with the nitros. If you have a 120 GPH pump and 1/2" fuel line it will be barely enough. It's kind of like Russian roulette, if it's not enough fuel and it runs lean....well melted pistons are not fun, if it's enough fuel then hang on for a wild ride.
I have dual carbs and a 110 GPH pump and 1/2 way down the track my fuel pressure drops to 3psi from 6 psi. No big deal as 3psi is enough for my application, however if I had NOS on it ,goodbye pistons.
You have all winter to add a dedicated fuel system for a couple bucks and save an expensive engine, I would go with the dedicated fuel system for NOS.
Good Luck,Perry.
ps- Nitros Tip - You will have to shorten the spark plug gap to about .030 as the extra cylinder pressure will not fire a large spark plug gap, even with msd.

[Mr.Fixit]

You didn't say what pump you are running, but I doubt it will feed a 750 HP motor enough fuel. It's recommended that you run a dedicated electric pump in addition to the pump that feeds the motor. Otherwise you'll need enough pump for both, running all the time.

[40k Later]

I have a 110 gph holley electric, and 3/8 braided line, when you say run a dedicated fuel pump, It would only be dedicated system after the 1st fuel pump, or am I missing something? I would have to T-off my existing fuel pump as I have only one pickup in the tank itself.

[750hp]

You won't have enough fuel volume with that pump to support both motor and nitrous system. I would look at a COMPLETE new fuel system for the NOS. New pickup, new pump, separate lines, etc. Also, I'm assuming your 3/8" line is after the regulator. If you're running 3/8" from the tank, I'd say that would be more cause for concern...

[40k Later]

I have a 3/8" all the way from the tank. It does just fine with the 850 Demon, but from the sounds of it, I'd better re-think this. I'm glad I gave this forum a shot. When advice is this overwhelming, it's obvious I have come up short in the fuel delivery department.
Thanks for all who replied.

[bremillard]

Nitrous is real touchy and the parts it hurts are expensive to fix. The pump you are using now is barely adequate for your motor alone(in my opinion it is inadequate). If you use a single pump you will need one that is rated a mininum of 250 gph. You must follow installation instructions to the letter. You will need a #10 feed line and with a pump of this size you will probably need a return line(BG has a high volume pump out now that they claim does not need a return line). If you go cheesy with nitrous it WILL BITE YOU. -Bob

[ItBites]

Everyone who has chimed in here is correct and you need another complete fuel supply circuit (pickup, pump, lines, regulator). This is almost always done when modified engines use nitrous also.

You should also consider a low fuel pressure - nitrous cutoff switch. These devices are available from NOS and others and can (but won't always) prevent a bad day.

Also: HPDrifter mentioned spark gap earlier. Listen to him, he is right. My PSCA buddies that run BIG nitrous have found they have to run gaps as small as .025 in order to get consistent firing. I have seen this to reduce ETs by over .5 seconds in back-to-back runs in those cars.

[40k Later]

Excellent advice, I have decided to run a -10 line and pump for the nitrous alone and change the 3/8" to -10. Which leads me to my next question. Does anyone have the need for a 3/8" BG fuel Y-block, about 12' of braided 3/8" line and numerous -6 fittings?

[Richard Hudgins]

Hi Folks,

First I know nothing about NOS systems. Or for that matter drag racing which is where one would apply this system.

But, I have small problem with the pump size thing.

The question was the size of pump with a 535 hp 460 engine with NOS. (Remember, I know nothing about NOS.)

OK. Here goes. Lets assume that the above engine is running on the rich side at .48 lbs per hour per horsepower.

Therefore: 535X.48=256.8 lbs of fuel per hour at peak output.

Therefore the gallons per hour required is: 256.8 lbs divided by 6.5(What gasoline weighs)=39.50 gallons per hour.

So, my question is this.

Why does one need a 110 gph pump?

Of course there is the question of: are the pumps guys telling the truth?

Or are your fuel system pressure drops so severe that you are not getting the output assumed.



I would really like the answers to the above. Help me out here.

[BMK]

ItBites and HighPlainsDrifter,

...Just reading your comments.

Thanks guys for the tip on the spark plug gap. Will try this and see what happens.

Cheers

Bernie

[HighPlainsDrifter]

Hi,
There are many variables to the fuel pressure/volume theory.

-locaion of pump has a big impact, if it's lower than the tank and close it's best.
- fuel line size and restriction, like 90* bends, necked down fittings at the regulator,carburator needle and seat restriction is a biggie.
- #1-voltage at the pump, is it fed with a #10 wire to a relay directly to the battery? if not a 16 gauge wire from a toggle switch will have a major voltage drop across it and that will kill the voltage to the pump. say there is a 30% drop in amperage available to the pump windings, your pump is not working at 100% to start with, 110GPH is FREE flow, not under load. Say 80 GPH under load and a poor wiring feed,now your down to 50 GPH output Now add the other fuel filter and elbow restrictions and you have enough fuel volume to start a lawn tractor,haha.

At best there is the old drag racer trial and error method which says to me anyway that he needs 2 pumps.
Please don't be offended by my ramblings.
Perry.

[Richard Hudgins]

HighPlainsDrifter,

I think that you have the answer.

Just poor plumbing. Too much pressure drop and flow restriction.

In other words, lack of attention to detail system design.

Plagues us all.

[SCOBRAC]

This may seem a little silly... I know WHY you did it, because you can... But how are you going to use 750 hp? Drag racing? you are going to be in the low 9's and need a full cage.

If you think you are going to hook that much power up with street tires you being a little optimistic, especially at the point you'll hit the button. 3.2 pounds per horsepower is a handful. NASCAR runs 4 pounds per and runs on racing slicks.

Good luck in any case.

[Excaliber]

Yeah 750 hp does sound a little on the low side.

Maybe you should kick up the nitrous and try for a 1000?

[Jay]

My two cents. This is probably obvious, but do not forget to check the sizing of your pickup. I have pretty much the same set up as you and I almost forgot that little part. I am only running a 125 hp shot, but a little prevention is worth a pound/$1000's of expense. Also, most of the injector ratings in the instructions are for a small block which would be conservative for that much displacement.

[bremillard]

HPDrifter pretty much summed up why the need for what is seemingly overkill but he left out one point. When the car accellerates the fuel in the lines must overcome the rearward inertia of the accelleration. (You feel it as extra weight in your seat) That is why the need for high pressure up to the regulator with the regulator being as close to the carb as possible -Bob

[ItBites]

Bremillard,

Just the point I was going to add. The fuel column in the line has significant mass, especially if you've sized-up the line to gain flow capability. This is why you shouldn't run bigger than a #10 line in most cases. In fact #8 will usually work for a drag car just as well as a #10. My PSCA buddies often put the fuel tank in the front of the car just to prevent starvation due to acceleration loads.

Also, I think the pump makers lie...

[HighPlainsDrifter]

Hi,
I see that you have retard,set to retard timing about 6 to 8* for that level of nitros. Easiest way is to hook up a msd retard module to the nitros soleniod so that when it's on ,the timing is retarded otherwise you will have detonation and probably lose the head gaskets.
One question though, why do you want to 'hit' the nitros so hard? A 75 hp shot would act like a mini intercooler and give the most efficiency, probably still blow away the tires.
Good Luck,
Perry.

[40k Later]

Michael you ask Why Nitrous? of course because I can but the other is in a word, IMPORTS" Lots of heads up racing out here.
I won't be experiencing 750hp at the rear wheels and of course it's for Drag racing. I seem to have pretty good luck with the Nitto 555 extreme drag radials. I will be fortunate to see mid/high 10's with 3:55 gears. All of the formulas and software seem to confirm this as well.
Just browsing over the nitrous installation manual again to see what I was thinking and here is a quote from NOS.

"Under most operating conditions, it is SUGGESTED (maybe imperative would be stronger language!) that a separate 3/8" fuel line and pump be dedicated to the nitrous system. If you choose to use a single line fuel system to feed both the engine and the nitrous system, follow these instructions but remember-at higher power levels this fuel system MAY ("will" would be better here as well!) be inadequate.
I deliberately stayed away from the 250hp jets because the context in which these instructions were written lead me to beleive if I stayed away from the high HP jets I would be fine.