Sumped tank or fuel cell?

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73Scamp318

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On my last trip to the track, I finally ran through jet tuning on my Holley and discovered that I may have a problem. I ran through sizes from 72F/78R to 84F/90R with a power valve in the front and only found a total .5 MPH difference through the range. With the biggest jets I put in, I would've expected it to be blowing black smoke like a tricked out diesel, but it seemed fine.

I run 1/2" line front to back with a big 100 micron screen filter before the Mallory 140 electric pump, which goes to a Mallory bypass regulator at the front of the car with a 1/2" return line. From the regulator, it goes through a good sized 40 micron filter and -8AN braided line before going to the -6AN carb line. I'm currently using a 1/2" sending unit, which I think may be causing the problem because the pump has to suck the fuel out of the tank instead of being gravity fed.

I'm thinking that I should either put in a sumped gas tank or a fuel cell. Anyone have any opinions of one over the other? Or is there another electric pump that might work better for this? This is a street/strip car and is about 50/50 at this point.
 
if you want your gas gauge,sump the tank.i have the jegs kit on my car it works good.but dumbass people always ask is that for nos....
 
If you are talking about an external electric fuel pump you need the inlet to the pump below the bottom of the tank -as much as possible.... I see many people with a pump in the trunk - and it will work, as long as you have a decent level of fuel in your cell. These pumps are not intended to suck fuel from the tank and need to have a good gravity head above the pump intake - at least several inches. That will probably bring on an arguement for the many that run trunk mounted pumps but I believe it is a fact.
Secondly, a 1/2 " fuel line is pretty big for a street car, IMO -and a 1/2" return is really, quite large. I would drop the return line down to a 3/8 at least. Lots of potential for cavitation after the pump.
Line size is all about line velocities (after the pump). In just about any flow situation the ideal flow rate should be a minimum of 5 ft/sec to a maximum of around 12 ft/sec. Too many glasses of wine in me tonight to figure this out in more detail but if you can calculate it out you can figure out the best line sizes for your pump size and fuel consumption (gas motors use fuel at a pretty close ratio of 1/2 the Hp they put out , in lbs/hour). A 500 hp motor uses about 250 lbs/hour of gas at max output. Divide the lb/hour by the density of gas of around 6.5 Lb/gal to get the fuel used in gal/hour - times 60 to get it to gal per minute.

I'm starting to remember too much fluid dynamics so time for another glass of wine....:)
 
As it is right now, pump is mounted on the frame rail near the rear bumper and the inlet side of the pump is at the same level as the middle of the tank. It could definitely stand to be lower on the rail, but it'll still need to pull fuel up through the pickup currently. I'll be fabricating a mounting plate to move it closer to the bottom of the tank, depending on whether I go with a weld on sump or a fuel cell.

As far as the feed and return line, I'm going off of Mallory's recommendations for sizing.

http://prestoliteperformance.com/Po...eshooting_fuel_system_size_4110_4150_5250.pdf

The fuel system may be a bit overkill, but I wanted to be able to support a stroker small block or big block if I decide to go that direction someday.
 
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