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Re: Help me get my mind around this...accurately. [Re: Cab_Burge] #202563
01/24/09 03:28 PM
01/24/09 03:28 PM
Joined: Jan 2005
Posts: 1,260
Las Vegas NV
moparmanjames Offline
pro stock
moparmanjames  Offline
pro stock

Joined: Jan 2005
Posts: 1,260
Las Vegas NV
Quote:

Someone made a comment recently(in the last year, if I remember correctly) that they wanted the fuel pressure set at or under 5.5 to 6.5 lbs to reduce the possibility of aerating the fuel from the tank to the carbs I had my fuel pressure set at the regulator with the engine running at a idle at 9.5 lbs, I reduced it to 6.5 lbs and didn't see any noticeable change at the track or on the street My car is not real fast (10:34 best ET in the 1/4 mile) so my results may not carry any weight, your results may vary I did find out later using a O2 wide ban that the car didn't have a good enough fuel system to allow me to fatten up the carbs big enough to slow the car down until I switch pumps from a Magnafuel 275 to a Magnafuel 300 pump,whch did slow the car down with no other changes made to the car except the pump switch My message is if you can slow the car down in 1/4 MPH by fattening the mixture up enough until it slows down your fuel delivery system is probally okay, no matter what the fuel pressure gauges reads during the run, if you can't fatten it up enough to slow the cars MPH down you probally have a fuel delivery problem. I did not say fuel pressure problem Air in the line can compress showing pressure when it is not all fuel in the line flowing




I believe what you are referring to at the pump is "cavitation", which forms bubbles in the media by going from a liquid to a gas state due to a pressure drop. This happens when the vanes or rotors of a pump form a low pressure area on the suction side. This usually occurs if the pump speed is too high (which does not apply here since the speed is not variable) or the inlet is not large enough and a low pressure area results. These bubbles will quickly collapse when they enter a region where the pressure is sufficient to become a liquid again.
Another cause is heat and vapor lock, which is what you were referring to with a vapor bubble in the line.
What has always concerned me with these fuel pumps is that most are "deadheaded", meaning that we have a high volume pump that is pumping fuel to nowhere while the needles are closed. This builds heat in the pump and produces cavitation fro the heat buildup.
I have been contemplating some type of pressure bybass flowvalve back to the tank to avoid this type of cavitation and also avoiding a warmer pocket of fuel reaching the carburetor and affecting consistency.

Last edited by moparmanjames; 01/24/09 03:37 PM.
Re: Help me get my mind around this...accurately. [Re: moparmanjames] #202564
01/25/09 02:20 PM
01/25/09 02:20 PM

A
Anonymous
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Anonymous
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A



The way I look at it is, if the gauge is moving around, then the float bowl probably isn't staying full............and if the float bowl isn't full, that means that the engine would have to suck harder to get the fuel up the main well........It's like trying to drink a pop with a ten foot long straw......You'd have to work harder to get it up that far............so, in my opinion, so I can sleep better at night, I'd want it to be rock steady..........

Have any of you guys seen where a guy will raise the float level on a motor that's on a dyno to fatten the fuel curve? I've seen guys pick up power by just changing the float level.......

Will it make your car any faster? Who knows......it depends on whether your motor needs the extra fuel or not.........

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