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Old 09-18-2012, 06:37 PM   #1
toddalin
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Default Confusion in Tuning the Holley Accelerator Pump Cam

When you look through Holley literature and videos regarding tuning the accelerator (squirter) pump cam, most say to use Position 1 (smaller squirt later) for heavy cars and Position 2 (bigger squirt earlier) for a light car.

Then they show a bunch of pump cams with two and even three holes for the pink cam. (Both of my Holleys have pink cams though white is supposed to be stock.)
Click the image to open in full size.

And of course the Holley carb is labeled for Position 1 and Position 2
Click the image to open in full size.

So when literature note to use "Position 2" do they mean Position 2 on the carb, Position 2 on the pump cam, or does Position 2 of the carb ALWAYS get used with Position 2 of the pump cam (because it needn't be so)?

And where would Position 3 of the pink cam go? On Position 2 of the carb?

I've not seen anyplace on the 'net that is specific in this respect to "the definition of Position" and how to properly tune this.


Thanks guys.

Last edited by toddalin; 09-18-2012 at 06:40 PM.
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Old 09-18-2012, 07:33 PM   #2
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It depends on how you want the squirters to work.

The cam basically just revolves around the shaft, the adjustment holes let you fine tune the curve of the cam for your needs.

Early squirt would be position 1, later squirt pos 2.

I think if you play with it a little you will find what works best for you.
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Old 09-18-2012, 08:08 PM   #3
65tripleblack
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Hope this helps:

http://www.youtube.com/watch?v=k-Nx5HEzvlY

Pos 1 on cam should be aligned and screwed into carb hole #1.

Pos 2 and 3 on cam should be aligned and screwed into carb hole #2.
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Old 09-18-2012, 08:47 PM   #4
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Quote:
Originally Posted by toddalin View Post
When you look through Holley literature and videos regarding tuning the accelerator (squirter) pump cam, most say to use Position 1 (smaller squirt later) for heavy cars and Position 2 (bigger squirt earlier) for a light car.

Then they show a bunch of pump cams with two and even three holes for the pink cam. (Both of my Holleys have pink cams though white is supposed to be stock.)



And where would Position 3 of the pink cam go? On Position 2 of the carb?

I've not seen anyplace on the 'net that is specific in this respect to "the definition of Position" and how to properly tune this.


Thanks guys.
Before you go into the plethora of pump cam selections, just what is the symptom that the vehicle has that you are trying to fix?
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Old 09-18-2012, 09:07 PM   #5
toddalin
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Quote:
Originally Posted by 65tripleblack View Post
Hope this helps:

http://www.youtube.com/watch?v=k-Nx5HEzvlY

Pos 1 on cam should be aligned and screwed into carb hole #1.

Pos 2 and 3 on cam should be aligned and screwed into carb hole #2.

Like all the other videos, it is not explicit that you use the same cam and carb hole number, though that is what they appear to do. (Never says it in words.)

I did some testing and measurement on a 650 dp and found that if carb hole 2 and cam hole 3 provide 2.25cc and carb hole 1 and cam hole 1 provide 1.8cc for the pink cam per their literature values, carb hole 2 and cam hole 2 provides ~0.5cc per shot. This is considerably leaner, but I may give it a shot. This is based solely on my measurements with feeler gauges and my calculations. I've not seen anyone document carb hole 2 with cam hole 2 anywhere before.

Alternatively, if I don't like that, it is easy enough to "polish" a bit of lift out of the cams to reduce the pump shot.

Last edited by toddalin; 09-18-2012 at 09:13 PM.
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Old 09-18-2012, 09:16 PM   #6
toddalin
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Quote:
Originally Posted by joebobbilly View Post
Before you go into the plethora of pump cam selections, just what is the symptom that the vehicle has that you are trying to fix?
A rich bog associated with the pump shot.

I've already reduced the squirters from 25/28 to 21/21 with good results. But that's as small as squirters go, so I want to lean the pump shot with the cam.
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Old 09-18-2012, 10:56 PM   #7
DucatiDon
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You may be fighting the squirter ramp. If it is indeed a rich bog, try a more gradual cam (I usually have had the best luck with the pink one)
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Old 09-19-2012, 12:39 AM   #8
toddalin
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Originally Posted by DucatiDon View Post
You may be fighting the squirter ramp. If it is indeed a rich bog, try a more gradual cam (I usually have had the best luck with the pink one)
Already has the pink cam in there.

Note the bog. Pretty evident.
Click the image to open in full size.

But is it lean or rich? Pretty evident that it's rich and from the pump shot in this next run. Note the A/F dips all the way to 10:1 at the point of bog. This is almost 3 points below the following average, which is very good!
Click the image to open in full size.

OK, so I needed to decrease the pump shot. I changed from 25/28 to 21/21 squirters and note the bog last Saturday on the dyno pull. Still there and rich, but much decreased.

Note that it is now only 2 points (rather than almost 3) below the following average, though the whole chart has been moved up 1.1 to 1.2 points, most possibly due to A/F meter calibration as documented by others at the dyno run with on-board A/F readouts.

SOP confirms that the bog has substantially lessened wit hthe smaller squirters. But there are no squirters smaller than 21s so I now need to decrease the volume of the pump shot.

Click the image to open in full size.
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Old 09-19-2012, 02:19 AM   #9
DucatiDon
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Double pumper or Vac secondaries? Ill assume vac.
Can you get the secondary throttle plates to open sooner, getting more air in, = more lean?
softer secondary spring?
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Old 09-19-2012, 12:59 PM   #10
toddalin
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Originally Posted by DucatiDon View Post
Double pumper or Vac secondaries? Ill assume vac.
Can you get the secondary throttle plates to open sooner, getting more air in, = more lean?
softer secondary spring?
Double Pumper.
Click the image to open in full size.
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Old 09-19-2012, 01:47 PM   #11
65 vette dude
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Make sure that the accelerator pump arm is resting against the cam, and the slightest movement of the throttle rod back, moves the pump arm, and fuel dribbles out of the squirter. I had a stumble with the red cam. & I at first went back toward the blue and white cam, and the stumble got much worse. I then went the other way with the orange cam, and the stumble was much better......but still there. I then tried the green cam, and the stumble was completely gone. This was on a 2818 single pumper. One thing is for sure......I don't think there is any sure fire formula on what cam to use.....its trial and error, until you find the right one. By the way, I 'm in hole #1.
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Old 09-19-2012, 01:51 PM   #12
PAmotorman
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Default cc volume of holley pump cams

the volume stated is for 10 shots of the squirter. sorry i guess i can't attach anything to this post.
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Old 09-19-2012, 01:57 PM   #13
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That dip at about 2300 has nothing to do with your carb, I don't know if you have headers, or not, but with the same EFI modified Vic Jr manifold,a nd the same 1.62" headers on both a 327 L-79 motor and my new 427 SB, the same dip was there at about 2300. Totally different cams, heads, everything, except the intake and exhaust,and obviously, i don't have a carb.

The tuner was able to tune it out by richening up the AFR in that 2300 RPM range.

It appears to be some sort of reversion, as the addition of an H pipe behind the collectors helped it go away some, plus added ~150 lt-lb of rear wheel Tq in the 1500-2400 RPM range.



EFI is real easy to reprogram on the dyno, carbs and mechanical ign curves, not so much.



Doug

Last edited by AZDoug; 09-19-2012 at 02:38 PM.
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Old 09-19-2012, 02:20 PM   #14
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Here are couple dyno runs, before and after H-pipe, notice how the AFR goes way lean in the 2300 range before H-pipe, the car wanted gobs more fuel, after H-pip, the dip was gone,and AFR was much better.



Doug

Click the image to open in full size.

Click the image to open in full size.
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Old 09-19-2012, 02:43 PM   #15
toddalin
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Part of the problem is that there is what I preceive as conflicting data on the internet about the cams.

For example, this shows the volume in ccs for 10 strokes with a 50cc pump, rather than the stock 30cc pump that I use. So for a single stroke, all of these values must be reduced ((30/50)/10).

Regardless, the pink cam shows the highest volumes other than the brown cam. These same values are included in the Holley Carburetor Manual.
Click the image to open in full size.

Now this is where I find the data conflicting...

For a pump cam to create a bigger shot, it MUST push the internal piston FURTHER into the bore to displace a larger volume of fuel. It doesn't matter what the ramp profile looks like, only how far the plunger plunges.

For example, if I push on a "floating roof" on a cylinder with a hole that is filled with a fluid, the volume that comes out doesn't matter how fast or slow I push, only how far.

If in fact the cylinder were continually filling during the push, then the speed and ramp profile would make a difference. But that's not how it works. You fill the volume when the pedal is released and push it out when the pedal is depressed.

So, if the pink cam has the greatest volume (other than the brown), it should also have the largest lift. My thought was to move down to the orange cam as per the chart above with the impression that it should have less lift because it has less volume.

Now look at this chart. It clearly shows that the blue, orange, and green cams all have more lift than the pink cam. So, I'm conflicted because if in fact they do have more lift, they should also have more volume. If that is the case, using an orange cam would be a step in the wrong direction.

Seems like the only way that I can know what I will/should have relative to what I have now is to polish down a pink cam's ramp by about 0.01". According to my measurements and calculations, an inch of lift at the arm is worth about 37.5cc and this would reduce the pump shot from the published 1.8cc to about 1.4cc using Position 1.

Click the image to open in full size.

Last edited by toddalin; 09-19-2012 at 03:02 PM.
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Old 09-19-2012, 02:49 PM   #16
toddalin
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Quote:
Originally Posted by AZDoug View Post
That dip at about 2300 has nothing to do with your carb, I don't know if you have headers, or not, but with the same EFI modified Vic Jr manifold,a nd the same 1.62" headers on both a 327 L-79 motor and my new 427 SB, the same dip was there at about 2300. Totally different cams, heads, everything, except the intake and exhaust,and obviously, i don't have a carb.

The tuner was able to tune it out by richening up the AFR in that 2300 RPM range.

It appears to be some sort of reversion, as the addition of an H pipe behind the collectors helped it go away some, plus added ~150 lt-lb of rear wheel Tq in the 1500-2400 RPM range.



EFI is real easy to reprogram on the dyno, carbs and mechanical ign curves, not so much.



Doug


Yes I have headers and an H-pipe.

While the dip may be due to the pipes, the only place to address it is at the carb. If the run shows rich at this point, then it needs to be leaned out a bit, just like your mechanic addressed yours at the fuel injection by richening it a bit.

But I tend to think that it is more carb oriented because when the operator would "roll the throttle through the squirt" rather than "nail" it, the dip is reduced. And my foot tell me the same thing when I roll, versus nail it on the freeway in OD and get a pump shot.

Last edited by toddalin; 09-19-2012 at 02:59 PM.
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Old 09-19-2012, 02:59 PM   #17
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The chart doesn't seem to have any correlation to the tables, including total lift, even using multiples of different hole positions. I would agree teh orange cam would be the best to try.

Doug
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Old 09-19-2012, 06:05 PM   #18
toddalin
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Quote:
Originally Posted by AZDoug View Post
The chart doesn't seem to have any correlation to the tables, including total lift, even using multiples of different hole positions. I would agree teh orange cam would be the best to try.

Doug

The thing is, I have a blue cam and measured it, and it does have more lift than the pink cam even though it is listed with a lesser volume. So there must be something more here than meets the eye.

Ultimately, I had a few extra pink cams and figured that at least I know where I'm starting from. So I simply used some sandpaper/emery board/1200 grit to remove a bit of the profile. I followed the existing profile but tried to take a bit more toward the bottom for a slower ramp speed. I then copied it onto another.

By my rough estimates, I took them down to about 1.3cc as opposed to 1.8cc per shot in Position 1. I haven't tried measuring Position 2 with the modified cams.

We'll see what happens after I install them. I can always put the unmodified ones back in.
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Old 09-19-2012, 07:08 PM   #19
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Look at the second chart. Many times it is the duration of the shot, not the amount.

http://www.quickfueltechnology.com/I...-41141-100.pdf

Last edited by GCD1962; 09-19-2012 at 07:14 PM.
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Old 09-19-2012, 08:11 PM   #20
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Originally Posted by toddalin View Post

But I tend to think that it is more carb oriented because when the operator would "roll the throttle through the squirt" rather than "nail" it, the dip is reduced. And my foot tell me the same thing when I roll, versus nail it on the freeway in OD and get a pump shot.

Oh lawd this is agonizing. First off, your dyno tuner don't know squat.

It would be nice to know all the particulars, as in, what series carb do you have...the engine hp part says enough about what's underneath it.

I'm guessing a 750HP series 4150 Holley or is it a derivative carb?

Your first problem is too much carb for the motor. This creates a lean condition (I don't give a shiz what the dyno tells you or the o2 sensor either) right off throttle. The reason it doesn't 'bog' (stumble) when you ease into it is because you get enough air velocity going into the carb for a proper metering signal.

I will assume nobody has made the mistake of blocking the power valves.

Put a 31 or 35 squirter in the front of it with 71 jets (in the front)(and put the stock rear squirter back in), make sure you have zero clearance at the pump arms, put the stock (or leave it as be) pump cams back in it, and forget the A/F ratio.

Flat foot the sob off idle and tell me if it 'bogs'.

I went through this same thing with a friend of mine that did the dyno tune deal years ago. Same deal as yours. Didn't want any help...was too proud. Don't blame the guy either, being a mechanical engineer and all.

After about a dozen trips to the drag strip running high 12's, I bet him I could get his car in the 11's in 3 passes or less.

Took off that DP he had, went to changing jets and stuff (and I had to listen to the dyno a/f ratio chatter like a woman side seat driving all the while), slapped it back on. 11.98 first pass. Then I asked about his timing (i thought is was suspect too slow). Wasn't for sure, so I took the cap off and adjusted it according to the rotor (just guessing trying to get close to 40 degrees since he was running pathetic world product heads). 11.80 second pass.

He had had enough help at that point.

But do what you want to do, it makes no difference to me.
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