Running the fuel tank dry

[stickybones]

I'm going to the track this Friday and for the first time, I'm gonna drain the tank of the 93 pump gas and put in some leaded good stuff. With help from the board, I know how to relieve fuel pressue in the rail (by disconnecting the power harness under the rear bumper) and drain the tank from under the hood after installing a hose to the fuel rail and jumping the fuel pump test lead.

My question. Is it bad to run the pump until no more fuel is pumping through the hose attached under the hood? I figured it to be safe for at least a second or two. Heck, what happens if you run out of gas while driving? Are you saying that you'll ruin your pump when you run out of gas. Same thing isn't it?

 

[Steve Wood]

yes, it is very bad. Stop as soon as you start getting bubbles in the output.

 

[stickybones]

Thanks Steve.

About how much is left in the tank when the bubbles start and will it be obvious?

I got a clear hose to do the job per the advice on gnttype.org.

 

[III'S 87 GN]

CURIOUS !!!

STICKYBONES,
WHAT IS YOUR TIME ON THE 1/4 MILE ?
MY SETUP IS SIMILAR TO YOURS AND I HAVE NEVER BEEN TO THE TRACK WITH IT !!!
THANKS

 

[Turbo 6 Justin]

III take it to the track, it is the only way to really see what you run, stock fuel pumps, injectors, power plate stuff like that will not help you run faster 'per say' but will allow a lot more security and more ability to turn up the wick a bit, I have tuned a stock car (turbo, IC, DP injectors) to a 12,70 some of the stock parts run out real quick after that I would say best would be 12.2 with a real perfect tun. Some will say lower but that is getting pretty ragged edge.


Back to the origional question, I drained mine a bit too much one time and I believe that to be the downfall to my 307 pump. if you really want the high octane, go get 2 gallons, drain it till it starts scavenging for pressure put the 2 gallons in drive it a mile or so drain it again then throw 10 or so gallons in for track use. should get you pretty close to pure race gas. I don't like running them that dry the pump gets pissed and the sock gets pissed


as always my .02

 

[stickybones]

III...in street trim (pump gas and street tires with lousy 2.4 60ft times), my car will run 13.9 @ 103. Haven't run it with high octane and strip chip like I wanna do this weekend...hence the original post. I'll still be on street tires though so I don't expect my short times to improve.

 

[Steve Wood]

Probably about a gallon left at most.

A lot of us think you need at least 5 gallons in the tank if you have a hard launching cars to prevent the pick up from being uncovered when the fuel surges to the rear. Others will tell you this is bs and they have no problem with a couple of gallons in the tank....

I would rather be safe than sorry.

 

[striker_29]

When I took my car to the track last weekend, we drained it thru the rail like you said. Well for about the last 5 minutes or so of this process the pump was just shooting it out in spurts. Is this normal? I didnt check exactly but I'd say it "pulsed" a 1/2 gallon to a gallon out before it seemed to run out. I have been chasing a crazy low throttle miss for awhile, but didn't really consider my pump because the pressure is always good when I check it.

 

[Steve Wood]

the pick up was not completely covered so it was sucking air and a little fuel...in the meantime, the pump was overheating which does it no good and shortens its life.

 

[stickybones]

Would anyone believe that after pumping the gas out of the fuel tank from the under the hood via the fuel rail, there would be 2 gallons of gas left in the tank.

When I did this last month after racing, I put a gallon of gas back in the car and drove to the gas station to fill 'er up with 93 for normal driving. It only took 15.xx gallons of gas. With an 18 gallon tank (that's what GN's have right) that means when my pump starts to cavitate, I still have 2 gallons in the tank. That sucks. Really dilutes the octane. No wonder I could only run 22 psi with "111" octane. It was probably closer to 107-108 octane.

Is this a normal amount to be left in the tank when the pump starts spitting our bubbles? Anyone have a picture (cutaway) or sketch of what the inside of a TR gas tank looks like. I was wondering what the baffles look like.

I also didn't do the installation of the Walbro fuel pump. Is it possible the pickup tube isn't low enough?