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Old 08-19-2008, 10:38 AM
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Fuel Pump Pressure.

I have been fighting a problem with the secondary float level on a Holley Street Avenger. I have tried new needles and seats, new float, etc. Nothing worked. I ordered a new float bowl for the secondary from Summit Racing and also had them send me an in line fuel pressure gauge. I put the new float bowl on, installed the fuel pressure gauge and started the car. The float level is still to high. The float level was set below the (clear) sight window before installing it on the car. The fuel pressure jumped up to a fluctuating 9 to 12 lbs of pressure at idle. Way to much from what Holley says it should be. Too much pressure must be keeping the secondary needle and seat open and over filling the float. Odd thing is that it does not affect the front float level.

Is there a mechanical fuel pump out there that has been tested and checked to have a max pressure of 6 lbs at idle that I can buy?

Any help is appreciated.

Steve

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Old 08-19-2008, 10:46 AM
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Sounds like you have a later model mechanical fuel pump (1973+) that has a return line. Is there an extra port on the pump that you have capped off?

Old mechanical pump models (60's and very early 70's) don't use a return line to regulate the pressure and make 5 to 7 psi. The later models make pressure like you are talking about if you don't use the return line.
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Old 08-19-2008, 10:52 AM
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Quote:
Originally Posted by 454C10
Sounds like you have a later model mechanical fuel pump (1973+) that has a return line. Is there an extra port on the pump that you have capped off?

Old mechanical pump models (60's and very early 70's) don't use a return line to regulate the pressure and make 5 to 7 psi. The later models make pressure like you are talking about if you don't use the return line.
@@@@@@@@@@@@@@@@@@@

No, it only has the two feeds. Inlet and outlet to carb. It is the older style pump.

Steve
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Old 08-19-2008, 11:09 AM
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excessive gas tank pressure can also increase pressure from the pump. In summer months, heat will vaporize fuel in the tank which makes higher pressure at the inlet of the pump and that is passed on as extra pressure at the output. Take off the the tank cap and remeasure the pressure.

You could try installing a simple "dead head" pressure regulator right before the carb.
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Old 08-19-2008, 11:26 AM
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Quote:
Originally Posted by reflog
I have been fighting a problem with the secondary float level on a Holley Street Avenger. I have tried new needles and seats, new float, etc. Nothing worked. I ordered a new float bowl for the secondary from Summit Racing and also had them send me an in line fuel pressure gauge. I put the new float bowl on, installed the fuel pressure gauge and started the car. The float level is still to high. The float level was set below the (clear) sight window before installing it on the car. The fuel pressure jumped up to a fluctuating 9 to 12 lbs of pressure at idle. Way to much from what Holley says it should be. Too much pressure must be keeping the secondary needle and seat open and over filling the float. Odd thing is that it does not affect the front float level.

Is there a mechanical fuel pump out there that has been tested and checked to have a max pressure of 6 lbs at idle that I can buy?

Any help is appreciated.

Steve
Check out putting a regulator into the system. 6 PSI is plenty for the Holley, but sometimes you've got to wrestle the fuel pump down to that, using a regulator is an easier solution than cut and try efforts of replacing fuel pumps. Check this spot out http://store.summitracing.com/egnsea...382&D=%2D86382 for some choices.

Bogie

Last edited by oldbogie; 08-19-2008 at 11:56 AM.
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Old 08-19-2008, 12:51 PM
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Not wanting to hijack, but this is an issue I too have been concerned with since I had a similar problem with my wife's Corvette. I wound up changing out the pump, and all is now well on that car. However, I am building an older Chev pickup, with a 383. I expect a max of 450 HP (470 Tq) and am using a Carter 4070 (not CERTAIN of the part number -- it's the rotary Carter street pump that delivers up to 70 GPH). I'm sure I won't have too much pressure with this pump, but can anyone tell me if I'll have enough flow? If not, and i go to a bigger pump, it seems a regulator will almost certianly be necessary, since so few high capacity pumps stay well below the 7 PSI a Holley tolerates (my carb is a Demon). Can anyone recommend a fairly priced bypass regulator that can be adjusted to 5 PSIG?
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Old 08-19-2008, 01:01 PM
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Quote:
Originally Posted by PatM
Not wanting to hijack, but this is an issue I too have been concerned with since I had a similar problem with my wife's Corvette. I wound up changing out the pump, and all is now well on that car. However, I am building an older Chev pickup, with a 383. I expect a max of 450 HP (470 Tq) and am using a Carter 4070 (not CERTAIN of the part number -- it's the rotary Carter street pump that delivers up to 70 GPH). I'm sure I won't have too much pressure with this pump, but can anyone tell me if I'll have enough flow? If not, and i go to a bigger pump, it seems a regulator will almost certianly be necessary, since so few high capacity pumps stay well below the 7 PSI a Holley tolerates (my carb is a Demon). Can anyone recommend a fairly priced bypass regulator that can be adjusted to 5 PSIG?
Let's put a little common sense to this. Let's say you can go 60 miles in an hour of driving. Lets assume your vehicle gets 15 miles to the gallon. That means 60 miles/15MPG = 4 gallons burnt in an hour. So will a pump capable of moving 70 gallons an hour be enough?

Bogie
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Old 08-19-2008, 01:08 PM
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Bogie, if I never stepped on the "go" pedal, I'd agree. But most of us don't know how much "milage" we get at WOT, and that is what the pump must support. I don't know how much fuel delivery it takes to support 450 HP. The question didn't seem so illogical to me. Maybe someone else will jump in.

Pat

Last edited by PatM; 08-19-2008 at 01:23 PM.
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Old 08-19-2008, 02:08 PM
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Quote:
Originally Posted by PatM
Bogie, if I never stepped on the "go" pedal, I'd agree. But most of us don't know how much "milage" we get at WOT, and that is what the pump must support. I don't know how much fuel delivery it takes ot support 450 HP. The question didn't seem so illogical to me. Maybe someone else will jusm in.

Pat
I'm not considering the question as illogical, just showing how to think about it. If you're racing at WOT for a long time then you need to do the same calculation for those parameters, which I'll get to.

However, I'll admit to getting testy about part advertising. Take "high flow" thermostat for example. Given that a thermostat is an intended restriction that maintains a given temperature assuming the remainder of the cooling system is sufficient to provide the necessary heat transfer against the heat load; then what exactly does "high flow" mean.

For the fuel pump lets say you're doing 140 miles an hour with the engine running continuously at WOT (I'm making this easy on myself) on a high bank oval like Daytona, I'm getting 2.0 miles to the gallon, then I'm burning 70 gallons in an hour. That would make a 70 gallons per hour pump awfully edgy, maybe a 100 gallons an hour pump would be a better choice. Now if this is a street driven can that will see the occasional trip to 140 at WOT and the fuel consumption becomes 2 miles to the gallon; then the car will use the full capability of the pump, but puttin' along in the Power Cruise at 60 mph, the 70 gallon per hour pump has got nearly an 18 to 1 edge.

All I've striven to do is to expose a way to think about this without having to rely on guessing, what "everybody else is doing, or accepting some advertising that says more is simply better. For the most part, people who frequent this forum don't need high out put water pumps, high flow thermostats, nor ultra high flow fuel pumps. All of which are expensive. If you're racing that's another matter. If you're not racing then you can put the extra cash in a better stereo or something.

You can tell that the guy that started this blog, has way too much fuel pump for how the vehicle is used. He needs a regulator or less pump. I like the regulator and over-sized pump because if you use a vehicle over an extremely wide speed range from in town to twice or more the freeway speed limit, then oversizing the fuel pump and managing the needed pressure for the speed variable volume is a good idea. Especially when using a simple electric pump since it runs at one speed and that needs to be selected by the user for the maximum situation. Lesser situations need less and the simple way of getting that is with a regulator. In my opinion a return flow regulator is the best solution as it insures the pump isn't pushing against a nearly static head as it would at idle. This keeps the fuel and the pump cooler and lessens, or eliminates, the cavitation within the impeller which adds component life and reduces entrapped vapor within the fuel.

Bogie
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Old 08-19-2008, 03:04 PM
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Thanks, Bogie

I agree regarding advertising items. That said, in a recent Summit catalog (the pinnacle of advertising) they have pump adds claiming to support "XYZ" horsepower, and a tech letter response that would lead you to believe that the necessary pump for a given demand is smaller than the catalog's specs would indicate. So, I got to questioning the pump that I have. I feel certain it'll offer little, if any, margin above what my motor will demand, but I am just not certain if it will do the trick (barely) or not. I think I'll run EA3.0 (+) tonight. I know it has a fuel demand feature. Maybe that'll help me decide if the engines demand's are going to be greater than the pump capacity.
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Old 08-19-2008, 03:09 PM
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Quote:
Originally Posted by 454C10
excessive gas tank pressure can also increase pressure from the pump. In summer months, heat will vaporize fuel in the tank which makes higher pressure at the inlet of the pump and that is passed on as extra pressure at the output. Take off the the tank cap and remeasure the pressure.

You could try installing a simple "dead head" pressure regulator right before the carb.
%%%%%%%%%%%%%%%%%

This thing is almost a gravity feed. If leave the fuel line from the tank off of the fuel pump the gas will syphon right out. So it is not a problem of excessive pressure in the tank.

Put a new fuel pump on and the pressure came down to 6 lbs. Just got back from a run and pressure is now down to 3.5 lbs. But at least the rear float has not overfilled. Got that problem solved for now.

Steve
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Old 08-19-2008, 03:22 PM
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"You can tell that the guy that started this blog, has way too much fuel pump for how the vehicle is used. He needs a regulator or less pump. I like the regulator and over-sized pump because if you use a vehicle over an extremely wide speed range from in town to twice or more the freeway speed limit, then oversizing the fuel pump and managing the needed pressure for the speed variable volume is a good idea."

*************************************

Bogie,

Actually the best idea was to get a pump that only put out a max of 6 lbs of pressure. That is what I did. If you think my 32 Coupe is gonna ever go twice the speed limit I'll guarantee you that I am not gonna be in it when it does.

Now to bigger and better things. The car seems to run fine and the floats are now OK. Problem seems to be accelerator pump. I've got the Holley book and will look up on how to change the pump cam or if I need to get another cam that gives it a quicker shot.

Steve
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Old 08-19-2008, 03:33 PM
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Quote:
Originally Posted by reflog
"You can tell that the guy that started this blog, has way too much fuel pump for how the vehicle is used. He needs a regulator or less pump. I like the regulator and over-sized pump because if you use a vehicle over an extremely wide speed range from in town to twice or more the freeway speed limit, then oversizing the fuel pump and managing the needed pressure for the speed variable volume is a good idea."

*************************************

Bogie,

Actually the best idea was to get a pump that only put out a max of 6 lbs of pressure. That is what I did. If you think my 32 Coupe is gonna ever go twice the speed limit I'll guarantee you that I am not gonna be in it when it does.

Now to bigger and better things. The car seems to run fine and the floats are now OK. Problem seems to be accelerator pump. I've got the Holley book and will look up on how to change the pump cam or if I need to get another cam that gives it a quicker shot.

Steve
Either I'm way to rummy from this 7 days a week pace I've got going or ya'll are just to funny. Either way I'm totally cracking up with the vision of a 32 coupe doing a 140.

Bogie
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