[Skip Fix]

Heck my original 180 HP 7.5:1 '78 400 with just a cam change started having problems! My Camaro with a 370 HP 383 has done fine with a Holley and a hiflow mechanical pymp stock lines in the 12s.

[Torquewar]

Well ill jump in,had a 1/2 aluminum line bent to stock route with a Robb Mac 550. I also nosed the car over at 100mph so went to Russell 8an from tank to carb . Got the car into consistant 11:60s and was happy.There was that question of maybe running it lean at higher speeds.? I decided to do a check late in the year with a guage and well 6psi until 4k and then 4psi dipping to 3 just above 5k.
Hell with it just bought the Aeromotive drop in sys,so we shall see whwere it goes.
Chatting with Cliff last year on the phone and he said the same thing as he has also commented on this site..build your system for a car 2 seconds quicker and dont look back.

[HWYSTR455]

Originally Posted by Torquewar

Well ill jump in,had a 1/2 aluminum line bent to stock route with a Robb Mac 550. I also nosed the car over at 100mph so went to Russell 8an from tank to carb . Got the car into consistant 11:60s and was happy.There was that question of maybe running it lean at higher speeds.? I decided to do a check late in the year with a guage and well 6psi until 4k and then 4psi dipping to 3 just above 5k.
Hell with it just bought the Aeromotive drop in sys,so we shall see whwere it goes.
Chatting with Cliff last year on the phone and he said the same thing as he has also commented on this site..build your system for a car 2 seconds quicker and dont look back.

Ok, lemme get this straight, you had a 1/2 hard line from the tank to the pump, with the 550 pump, it would nose over, and when you ran a AN8 line tank to carb, it picked up? With no other change? And you had the 1/2" pickup? Ran the same level of fuel? And after you made the changes, you hooked up a gauge and you are still seeing a drop in psi?

If I would have to guess, it sounds like you have a vent problem. You might have been sucking a line flat before you went to the AN8 line too.

Are you running a late model non-vented cap? If so, try switching to an early vented cap. Maybe also try pulling a vent line from separator and leave it open, run the psi check again.

Maybe that's some of the difference from the Pontiacs to the Chevys, the caps the Chevys use are properly vented? Just guessing there, but makes sense.


EDIT: I just looked up part numbers for a 70 GTO 455 and compared to 70 Chevelle 454, non-CA emissions, and the GTO cap is non-vented, the Chevelle is vented.

.

[FrankieT/A]

I have robbmc 1/2 INCH PICK UP, 550 PUMP AND 1/2 INCH LINE ALL THE WAY TO THE QUAD ALL STAINLESS EXCEPT PICK UP TO ROBBMC 100 MICRON FILTER, BODY CONNECTION AND FRAME TO PUMP. My car still goes to zero top of third (manual). My cap is vented, then drilled 1/8 inch hole through cap and then ultimately left cap just laying on. Nothing helps. Im going to a pusher. BTW all connections are tight and all parts are new. Please excuse caps im typing on phone

[FrankieT/A]

I have robbmc 1/2 INCH PICK UP, 550 PUMP AND 1/2 INCH LINE ALL THE WAY TO THE QUAD ALL STAINLESS EXCEPT PICK UP TO ROBBMC 100 MICRON FILTER, BODY CONNECTION AND FRAME TO PUMP. My car still goes to zero top of third (manual). My cap is vented, then drilled 1/8 inch hole through cap and then ultimately left cap just laying on. Nothing helps. Im going to a pusher. BTW all connections are tight and all parts are new. Please excuse caps im typing on phone

[HWYSTR455]

Originally Posted by FrankieT/A

I have robbmc 1/2 INCH PICK UP, 550 PUMP AND 1/2 INCH LINE ALL THE WAY TO THE QUAD ALL STAINLESS EXCEPT PICK UP TO ROBBMC 100 MICRON FILTER, BODY CONNECTION AND FRAME TO PUMP. My car still goes to zero top of third (manual). My cap is vented, then drilled 1/8 inch hole through cap and then ultimately left cap just laying on. Nothing helps. Im going to a pusher. BTW all connections are tight and all parts are new. Please excuse caps im typing on phone

Well, that covers the vent question!

What about bends in the soft lines? Possible any area is getting sucked closed?

.

[RobbMc]

Originally Posted by FrankieT/A

I have robbmc 1/2 INCH PICK UP, 550 PUMP AND 1/2 INCH LINE ALL THE WAY TO THE QUAD ALL STAINLESS EXCEPT PICK UP TO ROBBMC 100 MICRON FILTER, BODY CONNECTION AND FRAME TO PUMP. My car still goes to zero top of third (manual). My cap is vented, then drilled 1/8 inch hole through cap and then ultimately left cap just laying on. Nothing helps. Im going to a pusher. BTW all connections are tight and all parts are new. Please excuse caps im typing on phone

It's not unusual for the pressure to drop 1, 2 or even 3 psi at full throttle with a 550HP pump because a regulator is not required. But if the pressure is dropping to ZERO, something is wrong. Since you seem to have checked everything else, ship the pump back to us and let us check it for you. Maybe a valve is being held open by a piece of debris. What is the fuel pressure at idle?

[FrankieT/A]

I have 6 and a half and 7 at an idle. I even capped off the return to see if that would help, but unchanged.