I have a 67 Conv. with a 383 and Turbo350. Once the engine gets hot my fuel pressure starts to drop. I have tried all kinds of things...new tank,new sending unit, diffrent standard pumps, electric pumps, fuel cooler, plate under the carb. I cant figure out where the problem is, has anyone seen this before?

 

pressure drops based off what type of guage? if it's those little tiny ones that mount on the fuel rail then i wouldn't trust it at all. buy a real guage and test it out that way out of the engine bay heat

 

what fuel rail? lol

ok here's the scoop, fuel pressure may drop because of crappy pump at high rpm, but apparently not, since you've tried many pumps

now if you arent leaking fuel, i'd check you float levels while it's hot... i wonder if your needle seats are heating up and not sealing as they should or something.... it's a curious problem. but if the float level is good cold, and then super high hot, i'd wonder if your seat is still leaving fuel pass even when it's closed...

now when fuel gets hott, it should expand, and it should increase your pressure, which would lead me to believe that a warming fuel line, combined with an old hose clamp or something starts bleeding fuel out when you warm up....

with a carb you should be running 6-8 psi, with an injection system, i assume your retrofit kit would come with high/low specs, if it's still within spec at all rpm hot or cold... i would leave it go... maybe the pump just doesnt wanna do it, maybe you are sucking more gas hot, maybe your pump, pumps more cold until it warms itself up...

just for reference though, my inline pressure gauge reads 7.5 psi at all heat and rpm i've tested it at with a chrome holley performance 80gph er somethin crazy like that mechanical pump... which is on the high side of what i need, but still spec and it runs fine....

EDIT: some of those pressure gauges may use spring constants... those may easily vary with heat transfer, other types may too, but if the gauge is room temp it should be accurate

 

You were right, I held some ice on the guage and the pressure came back up, damm thing. I did have a fuel problem before, since the car would die on me but I think its all gone now. Thanks

 

You were right, I held some ice on the guage and the pressure came back up, damm thing. I did have a fuel problem before, since the car would die on me but I think its all gone now. Thanks

 

If you 383 is anywhere near 400hp, I would replace the fuel line with something larger. You may get by if you have 3/8" line but with the 5/16" you will probably run out of gas if you pull hard though 1st and 2nd.