fuel pressure
 

Iam trying to set my fuel pressure on my N/a bbc to 7 pounds but if I set it to 7pounds at wot it drops to 5 pounds it does not hold the pressure at 7.The only way it will hold it at 7 wot is if I set it at 10 pounds.Is it all right to leave it at 10 pounds and let it drop down? Thanks

3 possibilities come to mind here. A bad regulator. A weak pump. Or a fuel system that cant handle the demands of your engine. Give more details about your engine and entire fuel system. IE: what pumps, regulator, line size, filters, pick up size, heres a good one that many dont think about... do you have any 90* pipe fittings in the fuel lines?

Like these:

http://store.summitracing.com/partde...5&autoview=sku

If so, throw them away and get these:

http://store.summitracing.com/partde...5&autoview=sku

it is typical for most fuel pumps, mechanical, to drop. the only one i have ever used which didnt drop under heavy load is made by C.V Products. the use of a return style regulator mounted after your carb, on the fuel log is essential for proper operation and dependability. the one pictured is from weldon. both pieces are pricey but protect ave save you in the long run.

My fuel lines are from the tank to the pump -10 and out of the pump -8.My pump is a cv product model 2516 and my regulator I got from hardin it is a aeromotive the kit for the holley 4500.I do not have any 90's like the fist pic.the motor is a 603 ci 800hp.Thanks

what size is your return line? It should be at least a -8. If there is too much restriction in the return, you will get a false high reading when you set it.

with the regulator set at its minimum, you should have less than 3 psi showing on the gauge. If its higher, your return is too restrictive, and you need to increase teh size of it. you can use 90* fittings, but they have to be full flow AN, not NPT.

HOLLY DOT COM SAYS ALONG AS THERE IS 4-7 PSI AT W.O.T YOU SHOULD BE FINE IF OYUR RUNNING 10 THAT IS TOO MUCH ON THE SEALS, IF BOAT IS FALLING ON ITS FACE AT W.O.T. YOU MIGHT HAVE TO RAISE THE REAR FLOAT I HAD TO IN MY CAT YOU CAN GO TO WWW.HOLLY.COM AND IT WILL GIVE YOU A GENERAL IDEA

Osen007 the only way I can keep 7 pounds of fuel at wot is if I set it at 10 pound because it drops.Thanks

the first pic is to show location in the fuel system where reg. should be located. also to show brand. and lastly to show correct plumbing and install. the aero is good just not sure if it is as dependable as the weldon. as for the fuel pump which spring do you have in it white or green.
and for the lines i used here's a pic of the seperator and line from the tank they are -12to sep, -12 from sep to fuel pump, -10 from pump to fuel cooler, -10 from fuel cooler to log, and -6 from log to bowl's. the return is -8. and all fitting s are straight with radiused hose ends which do not diminish inside diameter.
-10 is more than adequate for 800 h.p. . just mount reg as shown, this way if it does jam or fail you ll dump fuel instead of lean out, hich saves form grenadeing.

Ray,
I use the CV pump with the green spring and no regulator. It is rated at 7.5 to 8 lbs. Holds pressure at WOT with 750-800HP. You can order the spring separate if you decide to try it.

I opened the fuel pump and it has a white spring.Be for I put this cv fuel pump and regulator on I had a holley pump and it held the pressure at 9 pounds WOT but I though it would be nice to lower the pressure a bit.

You need the volume with the pressure. you can set a 25 gph pump at 4 or 7 psi, and blow up the motor.

Holley's web site is written 100% about cars. their tech on marine is near useless. If they made that blanket statement about pressure settings, they are getting worse.

Ray,
The white spring is rated 10.5-11 lbs at idle and supports 1200HP. My experience says the green spring will work without a regulator and CV and I both say this spring will support 750-800 hp...try it without a regulator and see if doesn't fix your problems.

What kind of fuel filters are you using? If they are not large enough capacity, they would cause this problem also.

i agree with the spring, but the reg would still be nice.

this pump can support more than 1200 too. it is absolutely incredible. the engines pictured above are 1250 h.p . they never loose pressure, and maimtain pressure from idle to 6900 .

like i said incredible.


You need the volume with the pressure. you can set a 25 gph pump at 4 or 7 psi, and blow up the motor.

this is true but with a 800 hp engine usind -10 and -8 fuel line it will never support the volumein the fuel system to produce pressure falsely, aspecially with the return sytle reg.

but good point . very good.