Fuel Pump Cavitation?

[z-ya]

Here is a good one I have yet to figure out.

 

Been running the road race car for a number of years now, and have never had a fuel starvation problem (at least that is what I think is happening). Trail braking into hard left turns the engine looses all power. This never happens on right hand turns. I have not logged O2 (didn't bring laptop to track yesterday), so I am not totally sure that it is going full lean, but that is my suspicion.

 

Now after getting the suspension dialed in, I am turning faster lap times, and definitely pulling more Gs in the turns. So it is possible that I have uncovered a problem with my fuel cell. But, it was completely full for my first session, so I don't see how the fuel pump inlet could be sucking air.

 

In the road race car I have a custom fabricated fuel cell. It fits in the spare tire well, and has a sump that protrudes about 4" through a hole in the bottom of the well:

 

 

As you can see there are two barbs that face the front of the car. One is the send, the other the return. The sump goes up about 6 inches into the tank:

 

 

There is a single pump, no surge tank. there is a fuel filter on the inlet to the pump (25 micron), and a stock 280Z filter in the normal location. All fuel lines are -6AN braided. Fuel rail and FPR are stock 280ZX.

 

Maybe some crud in one of the filters is coming loose and blocking flow? Maybe because the return is entering the sump close to where the pump feed is? Note that I have looked into the tank when the pump was running and see that there was no cavitation happening.

 

Maybe the fuel rail and FPR is getting hot where bubbles are getting into the return line, cause cavitation on the pump feed?

 

I can take the top off the cell, and install a return in the top of the tank as a test. I may do that before the next event.

 

Thanks,

 

Pete

[Tony D]

Normally the return line is up higher in the pickup well angled downward and tangential to any housing.

This insures that air bubbles go UP and away from the lower pickup for the fuel pump. Looks like you are set up for a dual-feed setup. I think moving your return to the top of the surge tank in the cel and pointing it down and in will eliminate the possibility of air ingestion.

 

If they (suction and return) are close to one another, or on the same level, any air bubbles coming down the return line can get ingested into the suction of the main pump.

 

The #75 IMSA Car Millen drove had six pumps and two surge tanks, each 4" in diameter and almost the height of the car! Something like 42" tall...want to guess where the fuel return was on those tanks, in relation to the suction for the main fuel pump?

 

About 40" vertically above the suction point!

[grumpyvette]

first the questions

BTW NICE CLEAR PICS

WHY does the tower extend that far above the fuel cell floor level?

ID have it extend no more than a 1/4" above the floor and have a reversion or slosh washer/baffle in the top to trap fuel once its in the sump under (G) forces.

FUEL PUMPS are VERY in-efficient at pulling or sucking fuel and far more effective at PUSHING fuel, so the closer to the tank and the lower the pump location the better.

when you say the engine looses power in turns of one dirrection but NOT the other, my first thought was whats your OIL PRESSURE in the turns in BOTH dirrections?

whats YOUR FUEL PRESSURE AT THE CARB INLET in BOTH TURN DIRRECTIONS?

 

most chevys use a oil pressure sender that cuts the ignition voltage at somewhere between 4-8 psi and a oil pan with a wet sump can sometimes slosh enought oil up into the baffles on hard sustained turns to momentarily drop the oil pressure as the pump pick-up sucks air for an instant, since the pick ups rarely centered and baffle designs vary wildly its comon for an engine to work fine in one dirrection of latteral (G) forces but not the other.

 

THOSE APPEAR TO BE 3/8" fuel line fittings,(the internal dimensions less than 5/16" , if your hp exceeds about 450 hp your probably restricting fuel flow and need to change to a 1/2" fitting and lines

 

this might help

 

http://www.chevytalk.org/fusionbb/showtopic.php?tid/189285/post/1432855/hl/fuel/fromsearch/1/#1432855

[z-ya]

first the questions

BTW NICE CLEAR PICS

WHY does the tower extend that far above the fuel cell floor level?

ID have it extend no more than a 1/4" above the floor and have a reversion or slosh washer/baffle in the top to trap fuel once its in the sump under (G) forces.

FUEL PUMPS are VERY in-efficient at pulling or sucking fuel and far more effective at PUSHING fuel, so the closer to the tank and the lower the pump location the better.

when you say the engine looses power in turns of one dirrection but NOT the other, my first thought was whats your OIL PRESSURE in the turns in BOTH dirrections?

whats YOUR FUEL PRESSURE AT THE CARB INLET in BOTH TURN DIRRECTIONS?

 

most chevys use a oil pressure sender that cuts the ignition voltage at somewhere between 4-8 psi and a oil pan with a wet sump can sometimes slosh enought oil up into the baffles on hard sustained turns to momentarily drop the oil pressure as the pump pick-up sucks air for an instant, since the pick ups rarely centered and baffle designs vary wildly its comon for an engine to work fine in one dirrection of latteral (G) forces but not the other.

 

THOSE APPEAR TO BE 3/8" fuel line fittings,(the internal dimensions less than 5/16" , if your hp exceeds about 450 hp your probably restricting fuel flow and need to change to a 1/2" fitting and lines

 

this might help

 

http://www.chevytalk.org/fusionbb/showtopic.php?tid/189285/post/1432855/hl/fuel/fromsearch/1/#1432855

 

The part of the sump that extends into the tank acts like an additional baffle. There are also vertical baffles on driver and passenger side.

 

The pump is under the tank, about 6" from the sump.

 

I don't have a ignition cut from an oil pressure switch. I have an iol pressure switch in my toolbox though . I watched oil pressure on the high G turns, and it stays constant. I am adding an Acusump soon.

 

It is a 200HP L28, so 3/8" is cool.

 

Thanks for the input.

 

Pete

[z-ya]

Normally the return line is up higher in the pickup well angled downward and tangential to any housing.

This insures that air bubbles go UP and away from the lower pickup for the fuel pump. Looks like you are set up for a dual-feed setup. I think moving your return to the top of the surge tank in the cel and pointing it down and in will eliminate the possibility of air ingestion.

 

If they (suction and return) are close to one another, or on the same level, any air bubbles coming down the return line can get ingested into the suction of the main pump.

 

The #75 IMSA Car Millen drove had six pumps and two surge tanks, each 4" in diameter and almost the height of the car! Something like 42" tall...want to guess where the fuel return was on those tanks, in relation to the suction for the main fuel pump?

 

About 40" vertically above the suction point!

 

Tony,

 

I have not had any problems until now, but I will take your suggestion and move the return to the top of the tank. I looked under the car tonight, and the feed fitting is on the driver side. So maybe it is G force related.

 

Pete

[z-ya]

Problem resolved. Here is the surge tank I installed: