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MG MGB GT V8 Factory Originals Technical - 1.5 vs 3.5 psi fuel pressure in Weber 500

Hi Folks,
Having just recently gotten my V8 Wings and is starting to get used to the power. I wonder, is there any powergains to collect by upgrading to a high pressure fuelpump? At the moment I am running the OEM SU pump putting out 1.5 psi. The Weber/Edelbrock says that maximum fuel pressure should be set at 3.5psi, if I remember correctly. The car does not suffer from fuel starvation. Do I bother or is there any gains in upgrading?


I'm running the 500 cfm Edelbrock on my Rover 3.5 and using the electronic SU fuel pump. I haven't had any problems with fuel delivery so far but only have 1000 miles on the car.

Had the car on a dyno a while back and from idle through 4000+ rpm, fuel was flowing freely.

Simon Austin

It's all about supply. Once the float bowl is filled, the needle valve shuts off the supply until the valve opens again. You don't want so much pressure that it overpowers the float, but you want enough volume to keep the float bowl full under all conditions. If your 1.5 psi pump provides enough fuel to do this, then it's good enough. Edelbrock recommends about 6 psi for their carbs.

Run your car through the gears hard, up to say 5K rpms with the accelerator pedal floored, shift fast and floor it again. As you approach the top of third gear, you should know if there's a fuel supply problem. The idea is to run the carb out of fuel if the fuel pump can't keep up.


Wayne Pearson

Simon and Wayne,

Thankīs for your answers. It seems that my fuel pump is up to the job. I did as Wayne suggested and there wasīnt any hesitation or stumble. Iīll keep up the fine tuning and will soon have a very nice car. I have readjusted the exhaust fittings, ignition and are fine tuning the carb. I have to cut a little recess to be able make smoother gearchange into fifth.

Thankīs again

Erik, If it doesn't start to starve on continued full power; then it is OK. The pressure is less important than the flow rate as long as it doesn't exceed the reccomended pressure (which would flood the carb). My 302 car with a MGB SU pump would stumble on full throttle after 10 seconds or so and a change to a double-ended SU (like Jags and Astons used in the carburetor days)cured the problem completely. Bob.
Bob Elwin

Thankīs for the tip. I have gotten fond of the SU pumpīs ticking and will persue your route if needed. At the moment itīs oīkey, but who will know if I start porting and power tuning.


I got by with the stock SU with normal driving. Thing is, I don't do much in the way of normal driving. Severe bog developed when cornering hard in 2nd or 3rd gear and standing on the gas pedal. Uprated fuel pump is the cure.
Carl Floyd

Late in July, Iīll do some track driving. Then I will see what symptoms I get. My car isīnt set up for hard cornering, so I guess that a multitude of weaknesses will show up.



This thread was discussed between 08/06/2005 and 16/06/2005

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