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Old 05-11-2005, 08:43 AM
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Shop Talk on Fuel Systems

I've been installing my fuel system and have been concerned about doing it right based on what I've read here and elsewhere. I suppose with any car, there's what's ideal and what's practical and I'm trying to find the best setup that gets as close to ideal as possible.

In my research, I've found a lot of good information, but not a lot of explanations. So now I'm concerned about inducing a flaw in my application that I will regret later.

Let's say were working with a 10 second 1/4 mile carbureted car for the rest of this.

According to BG, a 10 second car should have the capability to delivery 1 gallon of fuel in about 35 seconds. To make the math easier, let's just change that to 30 seconds. Therefore, a pump that can deliver 120 gph should meet this requirement.

But, from what I've read, g-forces could cause fuel starvation 1/2 down the track, so we want a pump that exceeds the minimum. In order to defeat the loss of fuel due to g-force, the fuel line from the pump to the carburetor should have some length in front of the engine - theoretically to prevent the fuel line from emptying out during heavy acceleration. I don't see how that can occur if the pump is operating properly and providing positive pressure to the fuel line to the carburetor. It seems to me, that if g-forces were so strong to do that, then the entire fuel line would be evacuated and all the gas would be reverse flushed back into the fuel tank. So, in that case, why not use a check valve?

Another thing I have read is that when using a pressure regulator, it should be located as close to the carburetor as possible. There are mounts that allow the regulator to be placed either in front or to the side of the carburetor, but sometimes this is not possible if the intake design prevents it. In that case, second best would be to have the regulator forward of the engine. Third best would be to have it to the side. What's the reasoning for having the regulator as close to the carburetor as possible? If the system is pressurized and the pump can provide the volume of fuel needed, how would there be any problems?

With an in-line canister type filter, it is recommended to place it toward the rear of the car by the tank. A large canister could act as a reservoir (more so than extra fuel line routed in front of the engine), so if that were the case, and if g-forces are a concern, then wouldn't it be best to have the canister filter in front of the engine?

I think the most important thing when designing the fuel system is to make sure it delivers the needed amount of fuel at all times under all conditions. If acceleration affects the delivery, then it's a problem caused by a poorly designed system. I don't see how a properly spec'ed pump could be overcome by g-forces and not be able to keep up with fuel demands.

I'm looking forward to some decent shop talk on this!

Dan

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Last edited by 66Caprice; 05-11-2005 at 08:56 AM.
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Old 05-11-2005, 12:26 PM
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If it makes you feel any better, my Nova went as quick as 10.82 on the juice with an Edelbrock mechanical pump, firewall mounted regulator and the stock fuel line. All that high dollar hoopajoop isn't really necessary until you reach the 9 second threshold. I'd rather spend the money on parts that will actually make a difference in the performance. That's just my experience anyway.
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Old 05-12-2005, 09:34 AM
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Quote:
Originally Posted by coldknock
If it makes you feel any better, my Nova went as quick as 10.82 on the juice with an Edelbrock mechanical pump, firewall mounted regulator and the stock fuel line. All that high dollar hoopajoop isn't really necessary until you reach the 9 second threshold...
That's my thought too - as long as the pump can keep up, the volume of fuel to the carb will remain constant and as the the fuel moves along, its flow rate / velocity may change if it is going through different sized pipe. So if you have the stock fuel line which is 5/16" (I think) going to a -8AN adaptor at the pump inlet, it doesn't matter because the amount of fuel needed is still being delivered.
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Old 05-12-2005, 11:12 AM
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fuel system

Are you using a fuel cell? If you are using a regular gas tank the diameter of the pick up will restrict anything you do. If you use a fuel cell install it with gas fittings to the rear. The filter should be located before the pump to protect it. The pump should be below the gas tank. Use straight fittings where ever possible. Angle fittings are more expensive. Use 1/2" aluminum gas line. You can buy 20' for about 20 bucks. Regulator can be installed on fender well. Holley carbs will handle 9 psi no problem. Branch off regulator with two 5/16ths braided lines to the two float bowls. This will stop restrictions caused by cheap 2 in 1 fuel lines.
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Old 05-12-2005, 11:46 AM
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fuel system

It sounds like you have a real good handle on what you need to make the car work.

I think that the BG formula takes into account the "G" forces on the car according to the et.... I am sure the tech guy will let us know.

I personally have my car over pumped for the et i am running but since i have a faster engine planned for the near future its only a matter of time untill i need it anyway...

It is like many other combos in drag racing. I have seen some off the wall fuel systems in 9 / 10 second cars that i just cannot believe work....

I don't think that all the entire colume of fuel could be pushed back to the tank but you would see a drop in fuel pressure at the regulator if the pump was not up to over coming the "G" forces... If you mount a gauge and watch it during the run you will get a real quick idea of what is going on. With my BG 400 pump the gauge stays rock solid the entire 1/4 mile with no movement at all. Not that its required but it's one thing i know i do not need to worry about....

keith
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Old 05-12-2005, 12:20 PM
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Quote:
Originally Posted by bracketeer
Are you using a fuel cell? If you are using a regular gas tank the diameter of the pick up will restrict anything you do. If you use a fuel cell install it with gas fittings to the rear. The filter should be located before the pump to protect it. The pump should be below the gas tank. Use straight fittings where ever possible. Angle fittings are more expensive. Use 1/2" aluminum gas line. You can buy 20' for about 20 bucks. Regulator can be installed on fender well. Holley carbs will handle 9 psi no problem. Branch off regulator with two 5/16ths braided lines to the two float bowls. This will stop restrictions caused by cheap 2 in 1 fuel lines.
I am planning on using a stock tank customized with a -10AN outlet and a -8AN vent. Then, run -10AN to the pump with a filter inbetween somewhere. From the pump to the regulator, which is mounted on the fenderskirt, I have -8AN braided out with one 90-degree turn and then from the regulator to the carb there are 2 90-degree turns, also -8AN. I really couldn't do it any other way because of the a/c mounts, pulleys, belts, other hoses and so on in the way. It looks nice though
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Old 05-12-2005, 12:25 PM
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Quote:
Originally Posted by k-star
I think that the BG formula takes into account the "G" forces on the car according to the et.... I am sure the tech guy will let us know.
I looked at some fluid flow formulas and got really scared from all the math! And there was nothing about g-forces either. It would take a PhD to figure that stuff out.
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Old 05-12-2005, 12:39 PM
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Simplify, any pump capable of supplying the fuel at the big will be enough to overcome g forces. A ten second ride doesn't require a rocket science. I think you are over analyzing a little.
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Old 05-12-2005, 01:37 PM
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Quote:
Originally Posted by johnsongrass1
Simplify, any pump capable of supplying the fuel at the big will be enough to overcome g forces. A ten second ride doesn't require a rocket science. I think you are over analyzing a little.
You're right, sometimes I just go nuts trying to figure something out.
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Old 05-12-2005, 02:57 PM
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That is exactly why the super hot cars run 2 gallon Moon tanks in front of the engine! A 10 second car should have no problem keeping up with the hi-po mentioned here.
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