Don Terrill’s Speed-Talk

What color is the most aggressive Holley pump cam?

Blue.

-here's link to a graph showing Holley pump cams.

http://www.carbdford.com/tech/Holley20PumCams.gif

http://innovatemotorsports.com/forums/s ... php?t=8488

In spite of what that chart says the blue cam is the most aggressive discharge in the least amount of throttle shaft rotation just opening from idle. I just opened a new package and double checked. The chart must have been generated with a pump arm that was bent to an angle that favored the green cam. If the pump arm is adjusted (bent) so as to take advantage of the blue pump cam it definitely has the most initial displacement of the pump.

Where does the Brown one fall in there? Didn't see brown on the chart.

There are two different blue pump cams? Blue #1 and Blue # 2?

The brown is a 50cc pump cam; the chart is for the 30cc pump cams. The #1 & #2 refers to the holes in the throttle lever for the screw that attaches the cams, positions 1 and 2. In the days of `57 ford 312’s and `60 Dodge 383’s the purpose was for a summer and winter setting of the accelerator pump.

Here’s some trivia for you, the pink (330) cam was originally used for the `60 383 Mopar R-1971A which had a mechanical secondary and was the only Holley made with the smaller “AFB” bolt pattern. The pink cam and the Mopar carb have 3 holes so I guess the typical Mopar attention to detail gave us spring and fall as well as summer and winter.

-there is two countersunk screw head locations on the throttle arm----stamped 1 and 2---#1 normally positions most all the cams for slightly less pump shot than #2.
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-brown cams are typically used on 50 cc pumps on 4150 style carburetors---and all these pump cams are for 30cc applications.

-there is also a brown and a yellow (I think) that are specifically for 4500 dominators----where the cutout for the throttle shaft is 1/2" instead of 3/8".
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-This chart shows some typicalness of what you'd expect to see when changing pump cams-----but in all reality when you actually put a degree wheel on the throttle arm and a dial indicator on the pump arm lever and make your own graphs you find the real truth.

-If the throttle shaft was ever loose and repeened or welded back tight onto the shaft, if there is previous wear from the cam friction under the long lever arm, how you position the float bowls back onto the main carburetor body, the length of the override spring, and some other stuff all affect the actual amount of movement the diaphragm moves---and that diaphragm movement basically controls the amount of fuel you'll get out of the squirter nozzles.

In a 30 cc pump cam, the pink on position #1 delivers the greatest volume of fuel, and nearly the least on position #3.

Holley offers the best graph to illustrate the volume delivered across the range of throttle actuation.

Troy Patterson TMPCarbs.net TMP Carbs

Troy Patterson wrote:In a 30 cc pump cam, the pink on position #1 delivers the greatest volume of fuel, and nearly the least on position #3.

Holley offers the best graph to illustrate the volume delivered across the range of throttle actuation.

Troy Patterson TMPCarbs.net TMP Carbs

Where is that Holley graph? I couldn't find any info on their website about pump cams.

Edit: I found the graph, its color coded and they display it in black and white... genius.

BTW, I don't see the brown pump cam on that graph. And the brown one looks the most aggressive to me.



Am I reading this right? Is blue actually the 2nd lightest pump cam?
"Installation Notes
accelerator pump shot relative to cam color from lightest to heaviest are as follows. White, Blue, Red, Orange, Black, Green, Pink and Brown "

The brown is a 50cc pump cam as Tuner said. The graph shows 30cc cams.

I have never measured the results, but I had a application that required a lot of shot quick. This was with the 50cc pump and the blue cam is the one that gave enough shot to take out the lean spot & bog. I tried them all in all possitions just for the learning and on this 50cc setup the blue cam was the most aggressive and the only one that would feed the engine what it wanted. It was a two barrel setup and needed a lot of fuel quick which the blue cam gave. It did run out of shot pretty quick which didnt effect this setup, but might on something like a vacuum secondary 4 barrel that may need a shot to hold on longer.


Interesting subject though. Using two TPS units one could make a great graph of the action.


Jess

Are there only 2 cam choices for the Dominators?
http://www.jegs.com/p/Holley/749195/10002/-1/10313

Yep. You have to enlarge the cut-out for the throttle shaft on the others so they’ll fit, or grind the big yellow ones down to reduce the pump shot. The plastic is tough and grinding with an abrasive stone is the easiest way if you have one small enough to fit in the existing slot for the 3/8” shaft.