How much does the fuel pressure drop on launch and for how long .
-On mine with a ally 2 carb setup with mechanical pump is dropping from 10 psi to 3 psi for about .05 of second before it slowly climbs back to 10 at the strip . Is that normal ?
-at the same time my AFR reading goes from 4.6 to 8 then inches back up as it goes down the track . This is on a dragster .

This message has been edited. Last edited by: abitz,

Rear mounted cell?

As stated below, where's the fuel cell? Also where is the pressure pickup installed on the system? But it sounds like your picking up air from slosh in the tank. Another thing you may want to check, where is the fuel return to the tank relative to the fuel supply bung? The return should not just dump fuel back in the tank without a line that extends below the fuel level, otherwise it will airate the fuel in the tank and if it is right over the supply bung, to can really mess up the fuel delivery to the pump.

AFR at the hit will move around a bunch. Both single carb an dual carb setups have fuel slosh issues which cause the move, its the nature of the beast! Not saying what your seeing is normal though. Can you post a picture?

This is on a dragster , the mech pump has internal bypass regulator so one line in one line out . Fuel pressure gauge is tapped in back of fuel log to a gauge on my dash .

if tank mounted in rear this is normal. it is nothing more than the weight of the fuel in the line vs acceleration of vehicle. I was told once that if your car 60 footed faster than 1.32 the cell should be in the front. hard for the pump to pull the weight of the fuel during lift off until it stabilizes g force.

mine would drop to 0 but never gave a problem

ep

would not think you should see a drop on a dragster with the cell in front of engine. unless acceleration is affecting the fuel in the line as it goes forward back to the dash.
does that make sense.

ep

I run a apd pump in my 74 nova, pump up front cell in the rear. Been as fast as 1.27 60s with the nose in the air will solid fuel pressure. It has 20 foot of line between the pump and the cell.

With that said, you need to check your fuel lines. If the lines are not methonal rated, it will deteriorate then over time and they will start to collapse. I am getting ready to replace the lines on my car, because I am seeing a dip in fuel pressure, and I am getting pieces of rubber in the filter.

quote:

Originally posted by pauley:
would not think you should see a drop on a dragster with the cell in front of engine. unless acceleration is affecting the fuel in the line as it goes forward back to the dash.
does that make sense.

ep

Hmmm never thought about the little line full of fuel trying to make it back to the gauge in front cause during the burnout it on’y Drops 2 psi .

Banjo...the 1.32 60' was a recommendation from bo laws which is the pump I run. I just kind of use that as a reference not saying it is gospel. even when mine would drop to 0 the bowls would not run out before the pump could recover.

ep-just something most do not consider so was just throwing it out there

I posted a video on utube with camera on dash . fuel pressure gauge is just under the tach

https://www.youtube.com/watch?v=piJLZXr7rak

Then i remembered i had done the same test a few years ago to check stall on my converter ... u can clearly see fuel pressure is solid in this video :

https://www.youtube.com/watch?v=KdlV95kNm1M

Please dont take anything I said as dimising what you were saying. I was just giving an example that I don.'t experience any dip. 1.30s is always the number I have heard.

no offense taken banjo.

ep-

pump volume is low,could be built in reg.try a different pump no reg and use bypass reg .areomotive makes really good regulators

While I do think your gauge suffers from action/reaction, after you fix whatever you think needs fixed, remove gauge, sleep better.

Justathought.
Isn't there a rule against pressurized fuel lines in the drivers compartment.