Fuel Pressure
#4
Pressure is meaningless except on EFI. Flow is important on a carb.
I will never understand why carb guys endlessly farque around with pumps, regulators and gauges. Close the hood an drive it.
I will never understand why carb guys endlessly farque around with pumps, regulators and gauges. Close the hood an drive it.
#5
Burning Brakes
Mike I agree with you for the most part, though fuel pressure can be an issue for a carburated system particularly if you run too high a pressure. For instance, Qjets don't typically like over about 7psi. Over that can cause all sorts of BS. Depending on the pump you run, you may need a regulator to hold down the pressure. If that's the case, then obviously you'd want a guage so you know where your at. For stock (or mostly stock) systems, I agree pressure shouldn't be an issue...
#7
That's exactly my point- guys reading too many Hot Rod magazines and falling for the glossy 'racing pumps' that give the impression that somehow a higher pressure pump will deliver more HP. As you correctly pointed out, too much pressure will just overwhelm the needle and float.
#8
Burning Brakes
I run a pro-systems 750cfm (custom built holley hp) and the carb builder said to make sure fuel pressure stays around 7-7.5psi throughout whole rpm range.
last year I had a 750cfm mighty demon carb with a 80gph mech pump and it made 7.5psi of fuel pressue at idle/cruise but would drop to 3-4psi at WOT. It made 327rwhp 380rwtq on chasis dyno. I swapped to a 110gph mech pump at the dyno shop and power went up to 365rwhp 410rwtq and fuel curve looked alot better. I still get a drop from 7.5psi down to 5psi... The dyno guy and carb guy told me i would make more power with bigger pump and holding 7.5psi. I'm swapping to an aeromotive electric pump and bigger feed lines soon and will be going back to dyno. I have a reg set for 7.5psi...i plan on adding 125hp shot of nitrous to my set up so I have upgrade fuel system anyway.
last year I had a 750cfm mighty demon carb with a 80gph mech pump and it made 7.5psi of fuel pressue at idle/cruise but would drop to 3-4psi at WOT. It made 327rwhp 380rwtq on chasis dyno. I swapped to a 110gph mech pump at the dyno shop and power went up to 365rwhp 410rwtq and fuel curve looked alot better. I still get a drop from 7.5psi down to 5psi... The dyno guy and carb guy told me i would make more power with bigger pump and holding 7.5psi. I'm swapping to an aeromotive electric pump and bigger feed lines soon and will be going back to dyno. I have a reg set for 7.5psi...i plan on adding 125hp shot of nitrous to my set up so I have upgrade fuel system anyway.
Last edited by L-82kid; 06-21-2011 at 12:59 AM.
#9
Pro
What carb do you run?
For my Holley the recomendation is between 5 and 7 psi.
At ALL times (from idle to WOT).
If you have a higher pressure there is a risk of the fuelpressure pushing down the needlevalves/floats and the carb is flooding.
//Ricky.
For my Holley the recomendation is between 5 and 7 psi.
At ALL times (from idle to WOT).
If you have a higher pressure there is a risk of the fuelpressure pushing down the needlevalves/floats and the carb is flooding.
//Ricky.
#10
last year I had a 750cfm mighty demon carb with a 80gph mech pump and it made 7.5psi of fuel pressue at idle/cruise but would drop to 3-4psi at WOT. It made 327rwhp 380rwtq on chasis dyno. I swapped to a 110gph mech pump at the dyno shop and power went up to 365rwhp 410rwtq and fuel curve looked alot better. I still get a drop from 7.5psi down to 5psi... The dyno guy and carb guy told me i would make more power with bigger pump and holding 7.5psi.
#11
Burning Brakes
#12
If two pumps have the same flow capacity but the 'performance ' version simply does it at higher pressure, nothing is gained.