Fuel sense (or lack of!)

[Vez]

Yup, the -6's are way to small!

[bigmack]

I've also Tee'd my two tanks together and run just one fuel pump. I use just the Stack fuel sender on the tank that my fuel pump is run from and double the value in my head to determine how much fuel I have in both tanks. I'll probably break down and purchase a seperate VDO fuel gauge for the other tank someday. I'm running just the standard AN6 fittings as have most people. The fuel doesn't level all that quickly from tank to tank, but its not that bad really. I don't really like the idea of running 1 pump and 1 backup pump, especially if your running an EFI pump that costs $350. According to this www.russellperformance.com/tech_center/manualwhat_hose.htm they recommend 8AN for 400-600hp applications. This isn't exactly easy to change for someone who has already built their cars. Here's a thought for those of us who have already built our cars. Monitoring a lean condition is easy. Fuel pressure gauge or lambda sensor will do the trick, and we can monitor it in the cockpit. Probably even set an alarm for it some how. The best fuel arrangement I've seen, utilizing the AN6 fittings, is on John Castle's Sport. He's running the Edelbrock fuel injection system. He has linked the tanks, but he has a small fuel pump installed, that transfers fuel from one tank to the other that he activates with a switch when needed. On the tank feeding his fuel pump, he runs another transfer pump that feeds into a surge tank, and then runs his EFI fuel pump from his surge tank to his motor. I think this would be an excellent solution for some of us who are worried about the 6AN fitting size. It would take a little research to figure out, but I don't see why you couldn't run an 8AN fitting from the surge tank to the motor(as long as the surge tank stays filled). An underfilled surge tank would be the concern. We could take care of an overfilled surge tank with a return line going back into the main tank and we'd probably want to vent this small tank as well. I'll probably take this approach.
Cheers!
-Mack

[Steve_D]

Mack
You say John Castle's set-up transfers fuel from one tank to the other then pumps it to a surge tank, which then supplies the EFI. If this is so then the max supply is still restricted to –6 because it is only coming from the one tank.
I like the surge tank idea but think you would need to pump both tanks to the surge in –6 with return pipes to both tanks. Then pump to the engine from the surge using –8 or –10.
I don’t know enough about it yet but believe the Stack dash will take a fuel pressure and can have a warning set.
Steve

[bigmack]

You are correct. His addition of a surge tank was for track purposes. He hasn't had any problems with his engine running lean with the AN6 fittings, but he's also running 450hp. If anything, I'd say he's running on the rich side. Not sure if he's using AN8 or AN6 on the surge tank to motor path. My thought, however, is to use a surge tank as a means for giving us an AN8 source for higher output applications. I really think it can be done. This is a similar concept to a water supply system that I'm investigating for a small subdivision. I think it would all depend on the size of the surge tank. I'm thinking that mounting a .5 to 1 gallon surge tank, with an AN8 fitting on the bottom, and three AN6 fittings up top (one that fills the surge tank from something like a Holley Red fuel pump, one that links back to the main tank for overflow, and one that returns unspent fuel back into it from my injection system). I've seen the idea that your speaking of in Carroll Smith's book. Use two pumps from each tank to fill a surge tank, and then run a pump to the injection. This would be another way to do it, but I don't know how necessary it is with using a larger surge tank, and fuel filling the surge tank by both the holley pump and my return line from the injection. I'll probably talk to Kinsler about it and see what they have to say.
Cheers!
-Mack

[bigmack]

p.s.His addition of a transfer pump was just to transfer fuel to his main tank when it got low. It wasn't meant to boost performance to his surge tank or motor. Just a way to speed up the transfer process to overcome the small AN6 link pipe size.
Sorry for the confussion.

[james]

Depending on your ECU, you may have a fuel pressure input, which can be set to an alarm level. If the fuel pressure drops below the chosen level, the ECU cuts the engine. It's a lot more convenient for the engine to automatically shut down, than explode a few seconds later.

Of course, it all depends on your ECU, but I don't think it's a particualrly rare feature.

James

[mkoch1]

I haven't got my gas tanks yet, but from pictures they seem to have 3 ports. 1 high and two low in the tank. Any reason you can use both low ones has supply lines. This would give you 4 supply lines. Most people seem to use the top line, as a ways to balance the tanks, couldn't you put a t in the line and also use it has the return line from the engine.

Any reason this wouldn't work?

mark

[james]

I have a Mk4 Sport, which only has one tank, so this isn't an issue for me. However, if I had 2 tanks with the configuration that you describe, I would assume that the fittings were for the following:

1 low connection for the feed to the fuel pump.

The other low connection would be for the ballance pipe (not much point ballancing the tanks at the top, as once the tanks had a tiny bit out of them, the fuel level would be below level of the pipe, and unable to get to the other tank.

The high pipe would be for a return from the swirl pot.

Hope this helps.

James

[GTRCLIVE]

mkoch1 said: I haven't got my gas tanks yet, but from pictures they seem to have 3 ports. 1 high and two low in the tank. Any reason you can use both low ones has supply lines. This would give you 4 supply lines. Most people seem to use the top line, as a ways to balance the tanks, couldn't you put a t in the line and also use it has the return line from the engine.

Any reason this wouldn't work?



mark

I may be wrong but I think that only one of the bottom pipes has the pickup pipe to the bottom of the tank. But like I said maybe you better ask the factory..

>> Edited by GTRCLIVE on Monday 13th January 14:16

>> Edited by GTRCLIVE on Monday 13th January 14:18

[Stig]

The top fitting is for the return pipe of a fuel injection system, or a balance pipe which is used in the event of the failure of a non-return valve in a dual fuel pump setup. Otherwise the other pump would fill the other tank until it overflowed.

[Stig]

As a footnote re. fuel supply. The Carter pumps that the factory now supply are rated at 100GPH at 7psi.

[Stig]

As a foot, footnote (is that a toenote then?) I found this info. which may be of interest

Extract from Walbro fuel pumps website.

Calculating Fuel Requirements: Determining how much fuel your fuel pump needs to be able to provide is no mystery. It's simple mathematics. The engine in your car takes in air and fuel and converts them to horsepower. The amount of horsepower your engine can make is a function of things like the size of the engine, the compression ratio, the boost (in turbo/super-charged applications) and several other variables. To make this horsepower, your engine will consume a certain amount of fuel. That amount is referred to as the "Brake Specific Fuel Consumption", or BSFC. The BSFC is generally estimated to be between 0.45 and 0.50 for most naturally-aspirated (non-turbo/super-charged) engines, and between .55 and .60 for turbo/super-charged engines.

By way of an example, let's say that you have a naturally aspirated car that makes approximately 200 HP. Using the more conservative BSFC of 0.50, your engine requires approximately 100 pounds of fuel per hour. Now, fuel pumps are typically rated in flow of volume over time and not weight over time, and so we convert this to an international-standard of 63 liters per hour by dividing by 1.58. For a turbocharged engine that makes 300 HP, we use a BSFC of 0.60 to come up with 114 liters per hour.

It is critical that the fuel pump in your fuel-injected vehicle is able to produce at least as much or more volume over time than the engine requires. If the fuel pump is unable to meet the fuel requirements then the fuel mixture will become lean and the engine will go into pre-detonation and will eventually destroy itself. Unfortunately, many stock fuel pumps are capable of providing enough fuel for only the capabilities of the engine as designed and installed by the manufacturer. Users who seek higher horsepower output from their vehicles increase fuel requirements. The stock fuel pump often becomes dangerously inadequate to provide fuel to the heavily modified engine. Since additional flow above engine requirements will simply be returned to the fuel tank, too much flow is a far better thing that too little.

So for my engine, this equates to:
630hpx 0.6(supercharger) = 378
378 / 1.58 = 239 litres per hour

Convert to US gallons = 63.13 Gallons per hour. So the Carter pumps are running at 63% of their potetential capacity - which was nice

So hopefully, my engine won't self detonate This is also the reason that I went for a fuel pressure sender option with the Stack, so I at least get a warning before things go bang!