The cams are rated in CC per ten pumps. For instance, if you have a cam that is rated at 22cc then that is 2.2 cc of fuel per full stroke. The cam determines how MUCH fuel.
The cam position determines how much fuel relative to the throttle position. Position 1 is for very low idle speeds say around 600-700. Position 2 or even 3 'delay' the pump action to a 'later' amount of throttle opening. For instance, a car that idles faster. This is of course affected by other things and is a generalization. Think of this as off idle tuning.
Cams also determine when the fuel is delivered relative to the throttle position some cam profiles may deliver all the fuel (think of it as reaching maximum lift on a cam) by say 30 degree of throttle movement while others may go as high as 50 degrees. Think of this like the cams duration.
Here is a chart that shows all the pump cams:
http://www.carbdford.com/tech/pumpcams.htm
There is also a great chart in most holley books and I think with the cam kit.
If you can picture you camshaft for the valve train, you are a long way along to picturing the pump cam.
Squirters. Squirters determine how long, time wise, it takes to deliver the fuel to the engine. The bigger the squirter the faster the fuel comes out. Pour water through a straw or a hose? Over .040 you will need a hollow squirter screw, and over .037 go to the 50cc pump setup, go up and down in about three sizes each time.
As you can see, there are many variables. For some one to say 'use this cam and this squirter' and to have it work on a different car is not a real high percentage shot. Pun intended
Generally, if it stumbles or even backfires give it more fuel. If it hesitates or is not crisp/clean, give it less. Start with the stock cam and pick the right squirter size to give good off-ilde acceleration.
Then move to the cam. Buy the whole lot of them and lay them out side by side and look at the difference. No movement of the arm or not enough off idle. Try position 2 or 3. Off idle good but get a hesitation when you are already at higher speeds, try a longer cam (look at the chart!).
If the car will accelorate smoothly in high gear, then it will in a lower gear. So tune in high gear! Some times you find that low gear is great and high gear is not. Often decreasing the squirter size helps because the engine takes longer to build speed and needs a longer duration shot.
Of course don't forget initial timing, proper idle mixture adjustment and proper throttle blade to transfer slot relationship.
Take the day off for this one, you will need it. Change one thing at a time and take notes.
Rick
Hybrid Mode
