Join Date: Mar 2002
Location: Austin, TX, USA
I took some measurements off of three accellerator pump cams I had on had. Here are the results. The three cams I have on hand are a white cam (with two holes), a pink cam (with three holes), and a brown cam (with one hole). I clamped an old holley carb in the vise, installed a protractor on the throttle arm and measured the lift with a dial indicator.
I won't present the full result here, but rather will summarize my findings and ask for comments on a couple of observations I made. My nomenclature is P for pink, W for white, and B for brown. The letter is followed by two numbers separated by a colon. The first number is the hole number in the throttle lever (1 or 2) and the second number is the cam hole (1, 2, or 3).
The W2:2, W1:1, and B1:2 settings showed a similar result that was logrithmic. The lift was higher and more agressive at lower throttle angles and leveled off around 40 degrees. Full throttle was at 76 degrees.
The P2:3, and P1:1 settings were more linear throughout the range of settings, although the P1:1 setting provided nearly 0 lift below 5 degrees. I suspect an adjustment of the actuator lever might correct the problem. At low angles, the arm was contacting the clock spring on the throttle shaft.
I apparently had my carberator setup with the B2:2 setting which is impractical. It provided nearly zero lift at low angles and over 0.350" lift at 76 degrees. All other cams / settings topped out between 0.130 and 0.200" lift. This must be why I couldn't get the acc pump geometry set according to the procedure.
Now for the questions. There were two predominant profiles - logrithmic and linear. The logrithmic profiles were more agressive than the linear profiles below about 50 degrees. On the other hand, the linear profiles surpassed the logrithmic profiles above 50 degrees by about 0.050". Which of the two general profiles would be most desirable for a street engine.
My engine combo is a 350 +0.030 with an Edelbrock Performer RPM package (heads, cam, and intake) running 11:1 compression. The carb is a Holley 4011-3 (750CFM vac sec).
I am currently trying to fix an off-idle hesitation problem. Timing and jetting should be Ok now - I think the acc pump is the last issue before fine tuning the other things.
If anyone would like to see the results of my measurements, let me know and I'll send you an excel (or ascii) file. I currently don't have a web page set up - sorry.