FrontEngineDragsters.Org Forum
Technical => Matt Shaff's Engine Shop => Topic started by: Pat Johnson on February 01, 2017, 09:43:12 AM
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We have had this happen too us on numberous accounts , we have installed new baffels in fuel tank , once we do our burnout and get on the brakes, it seems like we get some type of air pocket through out the fuel system that allows the engine to die, making us look silly out their, we sure could use some help with this issue .we had Spud go through the pump and mag over the last season , motor runs great up till then .
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I had the exact same problem.
Ended up with a new fuel tank with a trap door in it to keep all the fuel from running forward when braking after the burn out.
I did read that you put baffles in the tank.
The trap door solved my problem
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It could be a multitude of things but my first thought was; where is your fuel tank vent? Could it be that the vent is getting plugged/restricted from the fuel sloshing in the tank?
A few pictures would help.
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everybody has a pigtail loop de loop 3-5 coils in the vent lines and I do not know how they even run--those act like a sink trap and when filled with fuel actually PLUG the vent line --just like a sink trap
We use the 3 1/2 gallon Moon copy from Speedway and have it raised enough in the chassis to solve that issue--not enough to look odd or out of place but it seems to work well no baffles at all
We have about a half a curl on the vent using clear tubing on a 2 inch copper tube stub that way you can see if it
never have a slosh issue just don't overfill the tank is key
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We have had this happen too us on numberous accounts , we have installed new baffels in fuel tank , once we do our burnout and get on the brakes, it seems like we get some type of air pocket through out the fuel system that allows the engine to die, making us look silly out their, we sure could use some help with this issue .we had Spud go through the pump and mag over the last season , motor runs great up till then .
Does this still happen if the tank is 100% full?
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If it's a long tank and fuel moving away from the pick up. You could try extending the pickup forward about a third to half of the tank.
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could if be to much fuel? had this prob with drawthrough turbo setup on vw... do the burnout, then close the blades and motor would die. it was flooded basically. motor still wicked up, still sucking fuel, but throttle blades closed so no air. also, been reading where guys on boosted apps where they are wanting less fuel during burnout. i could only think of same issue we had with the drawthrough turbo setup.
whats the normal size for the feed tube from tank to pump too... like 1.25" or ?
is this n/a or boosted setup?
dean
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I have learned to not get on brakes real hard. Nice short burnouts and a slow stop. Works every time. Killed it a few times...
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1" dia (OD .065 wall alu tubing) is plenty big for fuel line to pump for blown, 3/4" for norm asper alc.
Simple tank test--- remove tank and set on bench outside, fill with water and open feed outlet and watch flow coming out the fitting, nice smooth flow and your good, surging flow and the vent is to small or blocked. I killed a fresh pump once by not checking the connection free-play after an engine rebuild and jammbed the impellor into the front cover, It would fire up just fine, but after the burnout it would loose just enough vacuum to allow the fuel to break seal. If you can spin the pump with your fingers with very little resistence, you need to send the pump back in and then check the spacing.
Long skinny tanks are not that good because the fuel "Head Pressure" is not that great (a funny car by example has great Head pressure because of the amount of fuel above the outlet) and the further out the tank is away from the pump the harder the pump works. You did not mention pump size, an 80A is a 6.5 gal and a 110 is a 13gal to which the vacuum signal is stronger.
Also when building a dragster tank and mounting it, its built in such a way that the front is higher then the back so that the fuel always flows downhill to feed the outlet and not relying completely on head pressure and vacuum. A trap door baffle in a long tank placed between 25%-33% of the tank length is essential. A proper vent should go from front to back and then "T" off the middle. When the tank is full, under acceleration the tank breaths from the front, decell and the fuel moves forward, breaths from the back. "Cork-screw" vent lines (if so desired) should lay flat, so they can drain, as mentioned, standing them up will become a trap and the tank will become a vacuum lock before it will suck the fuel out the tubing vent. Another issue we had on out blown alc dragster, was with humitity, it was so high that the air coming thru the butterflys would ICE them up and the engine would die. Come back to the pits and everything was normal, Since then would always carry a can of windsheild de-ice and give it a shot after starting. If this symtome persist, have a crew member stand at the wall where you stop to see if engine rpms increase, if they do its a fuel starvation issue, and he can quickly jump the wall with a primer bottle and feed the motor till the fuel catches up