Thread: fuel pressure

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What would you say would be the correct fuel pressure. I've
heard it all. i'm running about 6 lb psi at idle which is 1500 rpm
on 1050 holly dominator. some say this is too low and some say
it could be raised a little. motor is 468 bb chev
rdobbs

Pressure at idle isn't that accurate of an indicator. What is the pressure at full throttle under load???? If it holds 6, that's plenty. The volume is equally important as the pressure. What size lines and fittings are you running?

3/8 line with an fittings.
rdobbs

That's a small line for a Dominator, but if it's enough to keep the bowls full, should be ok. I always use 1/2" line (-8). On the big inch engines, we run two -6 lines, one to each bowl....

What is the engine doing that you are concerned about the fuel pressure?

On a 1050, Holley recommends minumum 5 lbs, maximum 7.5 lbs.

I agree with Dave, 1/2" lines.

Dave, at times when i really get on it hard, it seems to
want to sputter some especially on a up hill grade.
rdobbs

Could the small fuel lines.....

Unless this is a 1000+ HP 468 then I doubt it is the fuel lines. Especially if you have a fuel pressure regulator near the carb. When I last looked into this I discovered that the pressure drop in a 3/8 line feeding my 502 at full theoretical flow is quite small. Less than 1 psi over 8 feet. So if you have say a 12 psi pump at the trunk the regulator sees at least 11 psi at full flow and chops that to 5-7 psi. 1/2 line makes little difference.


Now if you have mega power your flow requirements increase and there will start to be an impact ............

Kitz

Originally Posted by kitz

Unless this is a 1000+ HP 468 then I doubt it is the fuel lines. Especially if you have a fuel pressure regulator near the carb. When I last looked into this I discovered that the pressure drop in a 3/8 line feeding my 502 at full theoretical flow is quite small. Less than 1 psi over 8 feet. So if you have say a 12 psi pump at the trunk the regulator sees at least 11 psi at full flow and chops that to 5-7 psi. 1/2 line makes little difference.


Now if you have mega power your flow requirements increase and there will start to be an impact ............

Kitz

Kitz, we can always count on you for the No-Bull scientific answer. Thank you.

Doesn't sound like a fuel volume issue. On the street at cruising speed the 3/8" line will supply more then enough fuel. At first I thought we were talking some end of the quarter at 7300 RPM deal. Does the sputtering occur at a specific RPM every time? Sounds more like a timing issue, maybe the centrifugal advance is floating around a bit when it pulls, coming in to slow maybe? All the advance should be in by 1800 to 2000 RPM, though. Maybe a weak plug wire (can check them with an ohm meter), or a plug or two breaking down a bit under load....

The sputtering occurs at 5000 rpm and above. I haven't driven the car
lately but may have stumbled upon part of the problem. I have a msd
ignition system, and I got to looking and I still had the hot line coming
thru the old resister which sits on the firewall. I bypassed the resister.
Like I said, I haven't driven the car since doing this. Could it be the
resister was starving the msd of enough fire? r dobbs