I have a carbed 355 Vortec that puts out 330 hp at my 6000 foot elevation. I have ordered the Edelbrock performer nitrous kit (50-75-100) and I want to spray my motor this friday at the track. I am worried about fuel starvation. I don't have a fuel safety switch, nor can I get one before friday. I am using a fairly new TBI in tank pump that goes to a mallory 3 port reg. and to the carb. It is regulated at 5.5 psi for my edelbrock 600 carb. My carb is leaned out 8% in order to work right at my elevation(dyno tuned). I want to just run a tee into the carb supply line for the N2O fuel side. I could also run a separate line from the last port on the mallory regulator(I don't think it would make a difference).

Will the TBI pump give my engine enough fuel for the nitrous at 5.5 psi?

I will be running a 50 shot, but I want to know if it would be fine for the 100 shot in case I decide to turn up the shot.

Shouldn't the TBI pump easily provide enough fuel since it is at such a low psi?

 

If you read the TBI stickies, you'll see this:

"How much power can my stock fuel pump support?

"The answer to this is not much. A stock pump can support a full exhaust, intake mods (manifold and air cleaner) and a very mild cam. Once you have all of these mods and you go with a nice set of heads or decently sized cam the stock pump will not be able to deliver the necessary PSI at wide open engine load. A high flow unit will supply enough power to your TBI system no matter what mods you go with. Popular choices include, stock GM TPI pumps, Walbro 190lph and 255lph, and the Holley 255lph. Each of these pumps can support gobs of power but will work safely with your TBI set-up because your fuel pressure regulator will keep the fuel entering into your TBI unit where it needs to be."

The difference in TBI and carb pressure is only 3-5 psi. And that should be 3 if you want to stay on the safe side. Seems to me you'd want to be safe and get a different pump.

 

I just thought of a partial way to test it. What if I hooked up the carb spray bar plate to the fuel side and held it over a bucket and with the car on hit the button to activate the soleniod and watch to see if the psi on my gauge goes down while it is spraying. If it is strong, and doesn't even budge for 12-13 seconds then I think it would be ok to run it. But if it fluctuates then, I won't run it.

I know I have to consider that the carb will also be using some of the flow to refill the bowls, but it shouldn't be using THAT much fuel on only 330 hp. I can run my car at the track all day, over 20 passes, and still have plenty of gas to get home.

How does this test sound?

 

It would be a ball-park test. The part that the carb isn't using during that test could be the straw that breaks the real-world camel's back.

 

I wouldnt risk it. I'd either get 1 good pump and regulator or keep the stock fuel system and hook up a secondary fuel system for the nitrous using a small fuel cell and a Holley blue pump. Overkill is always good when it comes to fuel systems, especially when using nitrous. Your stock pump may work just fine, but is it really worth even trying? I'd rather buy a Holley Black pump or something and call it a day.

 

A friend and I are going to do the test and I will keep you all posted on what happens. I have been searching all day about fuel pumps and I think it is funny how all the TBI guys swear that their pumps will never go past 230 hp, even with a carb setup. Then I dynoed at 410 HP and 435 torque at the engine and A/F was solid and so was pressure to the carb at WOT.

 

That could be the 3 psi difference.

Or, perhaps you could come clean and admit that the in-tank pump has been replaced sometime in the past...

 

I wouldn't trust it. Although the TBI pumps do run at low PSI's they also run at low flow. With your motor NA you are about at its max. I would not trust it with spray. You will need a solid boost of fuel for that large of a power jump. Remember N02 is not a fuel but an oxidiser and you need enough fuel for it to be effective. Anything less will be death. Do you still have your return line intact? I would go with a high flow low PSI unit just to be safe. You can get them as low as 80 bucks. They will support the power levels that you are looking at with ease.

 

I did replace the pump because mine used to be TPI then I read that it is hard to regulate a TPI/MPFI pump down to 5-6 psi so I changed it. That was before my exhaust system was welded in place, now I don't want to go through the work of replacing it. I may just install a small fuel cell with a dedicated pump for the N2O.

 

heres a tip.

look at how much fuel comes out when your spraying your 100 shot.


now imagine 3.3 times MORE fuel going into the motor.... plus that 100.


i can dyno 600hp with a tbi pump...... until the carb bowls go dry.


with nitrous, there are two ways to play it.... play it safe, or play Risk.

i prefer to keep my risk limited to board games.


replace the pump.

 

There's no way to "bench test" your fuel supply like you propose. Results will be meaningless. Engine won't be drawing 300HP worth of fuel and you won't be working against the g-forces of acceleration that basically makes the fuel in the lines "heavier" and more difficult for the pump to work against.

I HIGHLY suggest you rig up a fuel pressure gague somewhere you can actually see it while you make a WOT run and WATCH IT LIKE A HAWK. I actually duck-tape mine to the windshield (temporarily!) while I make a few "get acquainted" runs. You may find your fuel pressure isn't even holding up on the motor alone, or you may find it holds rock steady even with the nitrous flowing. No way to know until you KNOW for sure.

If you're outrunning the fuel system it will be OBVIOUS. Fuel pressure will nose-dive at the top of the first couple of gears under hard acceleration.

 

BTW- my wife's 92 Camaro RS with newly transplanted carbureted 350 seems to be fed adequately by the stock TBI fuel pump and Mallory regulator set at 5.5 PSI. Much like your crate motor, the modest 350 I have installed puts out about 325-345 HP at the flywheel. I have no idea if the stock pump would support an additional 100+ HP worth of nitrous, but I plan to find out next summer.

 

I will only be spraying a 50 shot, NOT the 100. My motor only put down 270 RWHP at the location I will be racing tonight (6500 feet DA). I figure with the 50 shot, it will run like it does at sea level. It sucks running 12's on motor then coming some where hot and dry and you go low 13's. I want to be back into the 12's at least.

A 50 shot will be ok right?

I was just reading the instructions on my Edelbrock kit, and it says that with it's carb and N2O system your fuel delivery should be able to handle 0.10 Gallons per hour, per HP @ 5.5 psi. that is kind of vague but since most kits are rated at RWHP lets say here I have 270+50 shot=320, then x 0.10= 32 GPH @ 5.5 psi that I need for my fuel system to deliver. That is 122 Liters per hour.
With the 100 shot it is 37 GPH, or 140 LPH.

 

OK, let me try this again.....

 

We did the test with the car on and just fuel going in. It was with a 75 shot and the pressure dipped for a split second then the fuel pump/ reg. compensated nicely. I ran it at the track with the 75 and watched my A/F gauge like a hawk. It never even stumbled at all. I ran a 12.8 @ 114 mph on 245 50 R16 kuhmos. Our track is actually at 5500 feet but the DA was at 7800 feet I guess cause it was so hot and dry.

To all non believers, the TBI pump held up easily to the 50 shot and the 75.

 

You only know that your A/F ratio stayed okay. You don't know if your fuel pressure stayed where it belonged.

By the way, "dry" air lowers DA. Higher humidity raises it, as does warmer temp.

 

jus thought id let yall know i got 416 heads with 1.84int and 1.60 valves and a 97 lt1 cam and edelbrock carb and hedman headers ans stock exhaust back from the ypipe and my tbi fuel pump kept up once and only once now when i floor it the a/f ratio gauge like slams all the way to the lean side and i let off and wait for th epump to catch up but i also go 119,xxx miles so yeah that might be why but im getting a 255lph pump and thats the smart thing to do get a better pump.

i bet though that pump will die before any otehr hipo will.

 

See dyno numbers in sig.
All on a tbi pump.
Damn 10:1 AFR screwed me though.

 

A stock TBI pump wont keep enough fuel pressure to handle my 406 on motor let a lone the spray. Like everyone says, get a good intake pump.