Thread: Big Block Vette Nitrous/Fuel Issues

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I recently picked a '78 Vette, with a stroked 427, roller cam, rectangular port cast iron heads, dart intake, 1150 dominator, and a big shot nitrous kit.

The car was put together pretty well, but has been sitting for awhile, and needed freshening up. I had the front end aligned, replaced the heim joints in the ladder bar setup, added some new rear coilovers, and just finished installing the nitrous bottle.

It has a fuel cell in the rear, with two seperate systems: a Mallory 140 pump on the carb system, and a Holley blue pump feeding the nitrous side. I tightened up all of the fittings, opened the bottle, and made a few passes the other day. The fuel pressure on the nitrous side was only getting up to 6psi, and fading to 4 on occasion. My single shot nitrous plate has the 225hp pill in it, and was not coming on when I put it to the floor. I checked the micro switch on the carb, and it was working fine. I found out that the car has a fuel pressure safety switch, so if the pressure is too low, then the nitrous solenoids will not ground. I picked up a black pump today, and that should take care of my pressure issues on the nitrous side.

My question is this. The Mallory 140 should be adequate to feed the carb side, but when I am just on the motor, the pressure starts to drop as well. It creeps down to around 4psi on the big end. Both sides have a fram cartridge-type fuel filter right after the pumps. Does anyone know if these filters should flow enough to feed my rig? I have heard that I should pull the elements out, and run an in-line filter, such as the stainless mesh type, with the aluminum bodies.

Does anyone have any experience with this type of an issue, and any help/guidance would be greatly appreciated.

--Monza

well not to much .but if i was you i would go to a stainless mesh and the pump could do the job but i ran a mallory 500 that was going to be with a blue holley for the Nos with a safty swich set at 5psi .a 140 pump to me sounds like it is just getting by for the engine. but with Nos i would want more pump then 140 even with the holley blue feeding the Nos

Run a holley black on the NOS side and you will be fine. Install a BG inline fuel filter. Set your fuel pressure on the NOS flowing thru your fuel jet. You must set the pressure flowing.

I pulled both fuel pumps today, and found the fram fuel filter on the nitrous side to be a mess. The cartridge was rusty, and about half full of crap. I am sure the Holley blue pump that is on there should be ok with a new filter, but I will install the new black pump just in case.

Once I get the fuel system straightened out, then I can start bumping up the nitrous pills, to see how it does.

Nothing against small blocks, but it is nice to have so much torque on the bottom with just the motor.

I have not weighed the car yet, but I think a fiberglass 1978 Vette, with a ladder bar setup, 9", and an iron headed big block is going to be pushing 3800lbs with my 200# arse in it.

I plan on heading to the scale next week.

Thanks,

--Monza

i never been with out a bbc since the 1980s nothing like a car that is 3800+ and can still hauls a$$

I know it will not be an 8sec. door slammer, but I would be happy in the 9's on the bottle in the quarter.

I hope to have a few time slips in the next month or so.

--Monza

Dont forget to set the pressure flowing.

I will make sure to set the fuel pressure while the car is running. I swapped out the Holley blue, and replaced it with a black pump yesterday. Much more consistant. Now the nitrous engages with the microswitch right when I floor it.

I am going to replumb a few more things on the fuel end. I see that the nitrous fuel dead-heads at the fuel gauge. I drive the car on the street a bit, and am going to "t" a smaller braided line from the regulator, to the other side of the primary bowl on the carb. This should take care of any lack of fuel on the big end on the nitrous, and keep the fuel on the nitrous side fresh.

Probably overkill, but what the heck.

Then I can do a little carb tuning, hopefully get it to the scale, and then the track to see how it does or doesn't go.

Thanks again.

--Monza

A 3800 lb car running 9.5s would need ~ 850 hp .........................

Kitz

What I mean by setting the NOS fuel pressure flowing. Is you set the pressure by flowing thru what ever size NOS fuel jet you are using. Lets say you have a 73 fuel jet. You need to set the pressure as the fuel is flowing thru the 73 jet.

I apologize for my ignorance, but I am still not understanding how to set the fuel pressure on the nitrous side. Do I remove the small AN line going into the plate, somehow hold the jet in place, manually actuate the solenoid, and then set the regulator?

Here is what I have for a fuel setup: I have a Mallory 140 pump going thru a Fram filter, then into a 1/2" line up to the regulator. Then I have seperate lines coming off each side of the regulator, up to the carb bowls. There is a small NOS gauge right off of one side of that same regulator, and a smaller line coming off the other side of that same regulator, which goes to a fuel pressure gauge up by the windshield.

On the nitrous fuel side, I have a black pump flowing thru a Fram filter, then up through a braided line to a regulator. One side of the regulator feeds the fuel solenoid, and the other has a small NOS gauge, a smaller line going up to a fuel pressure gauge up by the windshield, and a smaller line that goes to the other side of the primary carb bowl.

The only thing I need to add, is a checkvalve in that smaller line that feeds the other side of the primary bowl. If I am only running the main pump, it tends to push back thru the nitrous side.

Any guidance would be greatly appreciated on setting the fuel pressure.

--Monza

I apologize for my ignorance, but I am still not understanding how to set the fuel pressure on the nitrous side. Do I remove the small AN line going into the plate, somehow hold the jet in place, manually actuate the solenoid, and then set the regulator?

Yes. The way I set mine is. I remove the small braided line after the NOS fuel sol'. Then I made a special line just for flowing the fuel. The line screws onto the Fuel sol' & the other side I made a fitting to hold my jet. Then turn on your pump & set fuel pressure as it flows thru the NOS jet. Or if you want you can just remove your NOS plate, an leave your jet in it and flow thru the plate.

I do not feel like pulling the plate off, so I will pick up another line and try it that way.

Thanks again.

--Monza

Originally Posted by monza406

I do not feel like pulling the plate off, so I will pick up another line and try it that way.

Thanks again.

--Monza

Glad I could help.