Fuel pipe size

Simon · 11-04-06, 12:18 PM

I'm stripping down the GTD I have bought with a view to rebuilding it with a 302 in.
the fuel tanks are NOT standard GTD, they have been built by an outside engineering company. Before I re-install them, I want to check that the pipe size is ok for a mildy tuned 302.
The fitting is on top of the fuel tank with a connection for goodrich braided hose to the fuel pump. The INTERNAL diameter of the fitting is 4.18mm and the INTERNAL diameter of the pickup is 6mm.
Is this going to be ok to supply fuel to a 302 engine running a 600cfm holley?
Thanks
Simon

Bernard · 11-04-06, 01:29 PM

Hi Simon
Your fuel fitting looks very small in order to supply your fuel pump. It looks like a 4-AN that is used to connect a fuel return line coming from the fuel pressure regulator (when it is used). Common practice for AC Cobra is to use at least 8-AN braided hose from the tank to the fuel pump as well between the fuel pump to the fuel pressure regulator (internal diameter is about 9.7mm). Large displacement engines (427 and more) use 10-AN. Then you can use 2 6-AN braided hose from the regulator to supply the carb. However, as for a GT40 fuel lines are shorter, you may use 6-AN everywhere. Due to the very short length of the internal pipe, the small diameter is not critical, but according to your engine characteristics a 4-AN plug is not recommended. In the same way, you should have at least a 70 gal/h fuel pump. Have a look to the fuel pump input connection and compare it to your tank, I will be surprised if it was shorter than 6.4mm (6-AN). Last point if you use a fuel filter, put it between the fuel pump (discharge side) and the fuel pressure regulator. Ha ve a good job

Simon · 11-04-06, 02:07 PM

Thanks Bernard,
The pumps are Facet red tops. I think these are rated at 45GPH. this was fine in my last 302 engined '40 so I'm hoping they will be ok in this one!
Simon

Big_Si · 11-05-06, 07:21 AM

The other thing to remember is that the fuel pumps are very rarely working flat out. Just think how hard you'd hve to drive to use all of the capacity of a 70 g/h pump! 70 g/h is a whole lot of fuel! Many pumps only really run slowly/occasionaly to top up the float chambers. I've got a classic mini that has 3 times it's original power, but runs just fine on it's standard mechanical pump!

Bernard · 11-05-06, 11:44 AM

It is obvious that maximum fuel flow capacity is only requested for the maximum power demand. Then I am not talking about fuel flow average but about fuel flow peak. It is a fact: if you expect a powerfull engine performances you have to design all parts of your car according to the stronger requirements. I don't have any experience about classic mini, but I have some knowledge about SBF engine. If you have a 302 stock engine (about 225hp) I agree that a 40gph fuel pump is good enough to feed it. However, if you have like Simon a modified engine (remember that SBF engines are able to exceed 500hp), you have to provide a fuel feeding sized accordingly. Many after market manufacturers such Edelbrock have a complet package to improve engine performances. Edelbrock mechanical fuel pump first RPM stage is rated at 110gph!
Edelbrock.com - Fuel Pumps
I agree, Edelbrock fuel pump looks too large for a 289/302 and it is more appropriate for a strong 351 engine but may be the truth is at the middle, between 40 and 110 gph

Howard Jones · 11-05-06, 02:10 PM

AN-6 (5/16 inch diameter internal) will work fine up to about 400ish HP. AN-4 is too small. It might work on a mild legal speeds street car but I wouldn't want to invest in fittings of that size only to replace them later. If you are using a duel feel carb like a Holley Double-pumper on a motor a lot over 400 HP I would run AN-8 from the tank to the pump and on to the carb where you split the line to the individual float bowl feeds and then go down to AN-6.

I have a drag friend (no not that kind, a drag car friend!) who has a 1100 HP 600 inch chevy and I believe he uses a 3/4 inch main feel line from the tank to the pump and on to the carbs Y blocks. Two BIG holleys.

In the end if you match the size of the pump fittings throughout the system and the pump will supply enough gas then you should be fine. I would use pump(s) that can deliever no less than 50 gal/hour. That fuel delievery rate will work fine with AN-6 lines and be plenty of fuel for 400HP street/track motor.