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  #1 (permalink)  
Old 09-12-2001, 08:13 PM
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Default Fuel Starvation!!!

Hi--
Just recently finished Superformance #988, and have discovered that under hard acceleration (very rarely encountered!) all the gas will slosh to the back of the wedge-shaped tank, starving the motor (and risking burning pistons).
I don't have the fuel cel, and am running multiport fuel injection, which may amplify the problem. This happens if the tank is less than 3/4's full. Needless to say, I could keep refilling every 45 miles......

Anyone else have this problem? Anyone know of any solutions? Will the fuel cel stop slosh? Or do I need to have the tank modified with baffles, trap doors, etc?

Thanks!
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Old 09-12-2001, 08:39 PM
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Grant, I've never heard of this problem. I suspect you're running your float bowls out of fuel. That would occur much sooner than fuel tank slosh would be noticeable. You didn't say which carburetor you're running, but I doubt very seriously if you could run your entire fuel line dry and cause your engine to starve.

I had the same problem with my float bowls on SPF#770 with a Holley 4160 750DP. The primary bowls were running dry under extremely hard acceleration. But, not until 3800 rpm in 3rd gear! The car would act like it hit a brick wall. You could back off the throttle, and it would catch back up with itself, but as soon as you got back into it, it starved again. If I accelerated easy I didn't have the problem, and even under hard acceleration, I didn't have the problem until I reached 3800 rpm in 3rd.

The fix? Easy...just adjusted the primary float height using the adjusting screws, Raised the primaries about 3 flats of the adjusting nut and it cured the problem. The fix was suggested by Dennis Olthoff, and turned out to be right on target. Raising the float height provided the additional fuel needed under hard acceleration.
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Old 09-12-2001, 08:53 PM
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Freddie--

No float bowls, fuel injection!! Actually, your float bowls allowed you to get to 3rd gear, I run out of juice halfway thru 2nd. Otherwise, your description of the effect is identical to mine.

I've been told fuel injection is more sensitive to fuel pressure fluctuations than carbs.
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Old 09-12-2001, 10:23 PM
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I have the exact same problem with my Superformance and EFI. Above 2/3 to 3/4 tank it's fine, but below it WILL run the pump dry on hard acceleration. Of course I'm running an Aeromotive 1000 hp pump set-up but still. If you've looked in the tank they are poorly designed as far as holding the fuel near the pickup. The shape of the tank alone does exactly what you think it's doing.

A carb set-up is not as sensitive to this as even if the pick-up is uncovered briefly the carb bowls still have fuel in them. On an EFI set-up with bypassed fuel any uncovering of the pick-up is immediately felt.

I am told their custom fuel cells they sell for the cars should fix it (no guarantees) but at $800 and no guarantees, I just keep my tank topped off.

Jody
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Old 09-12-2001, 11:10 PM
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Congrats on finishing the car,

At this years Carlisle, I spoke with Dennis Olthoff concerning this
issue. He said SPF tanks are baffled but the gas will still slosh around. On carburated cars there is always gas in the float bowl so when the line momentarily goes dry, the engine does'nt miss.
Obviously, when fuel injection is presicely metering out the fuel, this is a problem. Also, I believe he mentioned a fuel cell would produce similar results.

I am in the market for an SPF as well. The motor of choice for me will be the LS1 which of course is fuel injected. The gas tank is one of the bigger issues I am looking into. At the show, Dennis and the other dealers were down on the idea of FI. They sited the high costs and difficulty of installation and tried to sell me on the merits of carburation.

I am sticking to my cause because I am sure it can be done reasonably easily. I think one answer may be to get a tank with the fuel pump on the inside such as in a stock production car.
The FFR guys mostly use stock engines with FI and utilize the stock tank as well.

Goodluck and please post your fix or email me with your results.

Rich
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Old 09-13-2001, 12:55 AM
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okay, it is fuel injected, although the remedy for the carb i liked also. i had a problem like this.

fuel injection is a little hairier, as mentioned before:
you need a constant pressure to keep the system operating. you may check fuel cells from stock FI cars to find out what may be suitable for the SPF cell (i have never seen one).

the main principle is that you use a catch tank inside your fuel cell with a volume of about a gallon of fuel. the circulating fuel that runs back into the tank should enter the catch tank first to keep volume aroung the pick-up tube, which obviously should be located in the catch tank as well.

to mount this you need to have access to the inside of the tank. any fuel cell manufacturer like harwood may provide more information.

dominik
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Old 09-13-2001, 08:20 AM
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Dominik makes an excellent point here. All our FI Honda tanks have an internal "catch" area, to guard against fuel starvation when cornering, incline, acceleration, etc.. If changing to an EFI tank is not practical, perhaps relocating the fuel inlet pickup inside the tank would be an option. I'm not familiar with SPF tanks, but if the bottom is somewhat flat, moving the pickup to the rear would seem logical to me. I have been contemplating going to FI, and find this info interesting. Any other ideas?

Dave
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Old 09-13-2001, 09:59 AM
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thinking ...

frankly, i do not know. the idea is to keep the pressure and to get a constant flow without bubbles or vapour locks.

mounting the fuel outlet at the rear may help, but here we found a complaint at 3/4 of tank volume.

one thing is for sure:
the return line should flow easily. that is: enter the tank at the top.
i do not know if connecting before the tank with a T to the pressure side will help.

plus: the pressure line should be thick enough. 1/2"at least.
i had too many customers with the holley fuel injection that did use the stock 3/8 or even 5/16 line with bad results.



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Old 09-13-2001, 10:03 AM
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... or how about a catch tank outside the fuel cell beeing fed by the return line and a pump between tank and catch tank?
sort of a band-aid for a poorly designed tank (in this case for carbs only)

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Old 09-13-2001, 10:10 AM
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The problem with their tank is in the shape and improper baffling. The flat section at the bottom is only 6-7" long and then it goes straight up towards the rear bumper. So if the tank is 30" long, say, the pick-up is still way towards the front of the tank and the shape makes it VERY easy to run up the back of the tank and uncover the inlet for the pump. I'm running #10 feed lines and #8 return and a pump rated at 1000 hp so it's not a problem of line size. It won't do it on a full tank or close. It's worse in first or second gear as the acceleration "G" force is much higher than high gear.

I have heard of success using a remote 1-1.5 gallon reservoir for the pump inlet with an electric pump feeding it. They mounted them in the wheelwell or wherever there was room and it gave a positive source to draw fuel from that wouldn't run out during a run.

Jody
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Old 09-13-2001, 11:02 AM
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The more I think about this, the more I lean towards this: Winter is approaching, ie: Cobra storage time for us Midwesterners. I would remove the tank,( after THOROUGHLY flushing and rinsing it..) and cut a large, "access" panel from the top, to verify the condition inside. If possible, perhaps modifications could be made to the pickup, and baffles TIGed in to control the fuel movement, and the top piece welded back on. If this seems unfeasable, a custom made fuel cell is probably in order. These remote setups seem somewhat unsafe, and a bit redundant, though they may work. Short of this, I don't see any other safe, effective way to resolve the problem.

But, I'm still thinking....(should be working! )

Dave
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Old 09-13-2001, 11:31 AM
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Hey Grant,

I suggest that you contact the good folks at Fuelsafe (http://www.fuelsafe.com/). Check it out! These folks make fuel cells for almost all racing applications. I'm sure that they can recommend a solution for you.

Have Fun,
Randy R...
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Old 09-13-2001, 03:30 PM
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Guys--

Thanks so much for all your suggestions. Me & the engine builder have already gone thru all the ideas you guys came up with (secondary resevoir, baffling, etc.) and it don't look cheap in any scenario. I cannot recall what my fuel line size is, but would estimate it to be 1/2", with adequate filtering and pumping for the application. The problem really seems to lie in the tank's triangular shape, and the ease with which fuel can slosh up the ramp to the rear of the vehicle.
My builder really did a fantastic job of installation, and is a big believer in dfi (we're running multiport Accel). Honestly, with the cam and single plane manifold we're running, a carb would be nearly undrivable.
He's given me an estimate of $1000 to baffle and trap-door the tank, and I still would not have the safety factor of a fuel cell....

I will contact some of the fuel cell manufacturers to get (ouch!) quotes on a properly baffled cell. Any other ideas?
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Old 09-13-2001, 06:40 PM
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Grant,

I would suggest that you fill your stock tank with fuel cell foam. this will stop 90-95% of the fuel movement towards the rear of the tank.

The next thing you can do is to weld in a small reservoir for your fuel pick up point. This will have to be about 2 inches deep by 6 inches square and have very straight sides. When the foam is installed over this you should be able to maintain fuel at the pickup point at all times.

The return line should not be near the pickup point. The returning fuel is somewhat heated and you wish this to go to a location away from the pickup to allow some cooling time.

Hope this helps.
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Old 09-13-2001, 08:20 PM
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Grant,

I made a small sump and welded in bungs for the pickup and return lines.
I cut three 3/4" holes in the bottom of the tank and welded the sump over them.

I'm running a carb, but I have had no problems at all with fuel delivery, or heating of the fuel.

FI may indeed add more heat to the fuel, so you may need to run the return in at another location.
It's still best to run it in near the bottom of the tank to avoid aeriating the fuel.

Good luck,
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Old 09-14-2001, 02:31 AM
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Default external carch tank

Hi Dominik,
Your external catch tank suggestion with a small pump between the main fuel cell and the catch tank is the way numerous Cobra owners have solved this problem in Australia.
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Old 09-14-2001, 07:15 AM
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Richard--

Any suggestions as to where I can get the foam you speak of? Are these solid wedges you stuff down the filler neck, or something that is mixed with a catalyist and poured in?

I figure it's worth a try before committing to ripping into the tank and adding baffles, etc.

Thank You!
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Old 09-14-2001, 09:21 AM
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Grant, Richard designed the fuel cell in my car and he seems to prefer JAZ products. I see on their website that they list fuel cell foam in several sizes. You may be able to use one of these sizes or have to cut it down into smaller chunks.



http://www.jazproducts.com/fuelaccess.htm


hope this helps

Andy
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Old 09-14-2001, 10:10 AM
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Grant,

Andy's link is the right place to go for the foam. I have found them to have the best prices.

Yes, you cut the foam to shape to fit your tank dimensions. I would make the foam blocks the shape of the tank from a side view if possible.

Then you just stuff in the foam piece by piece until you have the tank full. It would be easiest to make a access port in the top center of the tank for insertion of the foam. This is then just covered witha plate. JAZ will have these cover plates as well.

You will only lose about 5% of your fuel capacity with this. But it will stop the fuel sloshing problem.

We used this method in Formula fords years ago, when the rules would not allow a fuel cell due to cost considerations.
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Old 09-14-2001, 12:05 PM
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Just make sure it can handle unleaded fuel as well.
I once used old material from a racer and it deteriorated clogging everything in sight.

(maybe it was just too old)

dominik
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