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Author Topic:   holley 4412 help
dode
Member
posted June 01, 2003 03:59 PM
I just picked up a 4412 and have no idea where to even start for our combination. We run 9:1 compression with Crane WG-1064 .480/.510 lift cam. We run stock cast iron intake and exhaust and run up to about 6000 rpms on a 1/2 mile track. Where should I start for jets, accelerator pump, etc. Right now it has #75 jets in it with no power valve. I have no idea what accelerator pump it has. How do you id those? Thanks.

John

#28
Member
posted June 01, 2003 04:50 PM
i may be mistaken but all 4412's have the 50cc accelerator pump.


KPLugnut
Member
posted June 01, 2003 08:05 PM
If the air bleeds are stock size, 74jet and a 4.5 power valve will get you in the ballpark to start.
Set up the idle circuit so that the butterflies are exposing about .025-.030" of the idle transfer slot is exposed underneath the carb, you'll probably need about a .100" or so bypass hole drilled in the butterflies, and the idle screws should start out about 1 1/2 turns out from lightly seated. Fine tune the circuit using a vacuum guage that is reading full manifold vacuum and adjust each one so that you get a peak vacuum reading.
Now, all this assumes that you're running about 6-7lbs of fuel pressure at idle and the float level is set to just a hair below the sight plug hole so it just trickles out when you rock the car a little.
Also, set the accelerator pump up so there is zero play in the pump arm, and use the wide brown/reddish cam that comes with the 50cc pump. The carb should not hesitate off the corners this way and also feed the motor reasonably well.
As for the accelerator pump squirter, the stock size will be a .028" size (the # is stamped on the front between the two holes). Start at that size and either try one down or one up in size depending on the specific needs of your application.

Hope this helps,
KPLugnut


dode
Member
posted June 03, 2003 08:46 AM
Ok...one more question...where is accererator pump squirter? I have it all apart and don't see anything, and I don't see anything called that on the rebuild kit diagram either. Also, right now there is like a yellow colored cam on the accelerator pump. I don't have a red one, but I am working on getting one. Is there a big difference between the two? If so, what is it? Thanks.

John

KPLugnut
Member
posted June 03, 2003 10:01 AM
The pump squirter is located in the throat of the carb and is held in by a Phillips head skrew . Remove the skrew , and it comes right out. It has two nozzles or holes in it and the orifice size is usually stamped on the front face between the 2 orifices.
The old 4412's came with narrow yellow-ish or tan pump cams which roughly were about the same profile as the new wide brown or reddish cams that builders use.
The thing to watch for is excessive wear on the cam's profile surface as well as wear on the arm itself.
Hope that helps,
KP

[This message has been edited by KPLugnut (edited June 03, 2003).]

3xracing
Member
posted June 13, 2003 02:08 PM
I'm wondering how KP can make a recommendation on the power valve with out knowing how much vacuum the engine makes.....
Power valve tuning is the key to making a 4412 perform, and to just throw a number out there is kinda reckless. well not really reckless, but knowing the engines vacuum at idle is key.
Measure the engines vacuum at idle, divide it by 2, and subtract 1. That should be the power valve used is oval dirt racing....ex. If your engine measures 8 lbs. of vacuum at idle, then take that divided by 2 = 4. Subtract 1 = 3. Use a 3.0 valve. If you feel the need to put in a plug... Go up 5-7 jet sizes.


KPLugnut
Member
posted June 13, 2003 09:50 PM
With over 20 years of carb/engine/cam experience, I've basically just developed a working knowledge of the vacuum pulled by many of the cam combo's used in racing at these levels.
Also, having built hundreds of 2bbls and as many 4bbls (or more) exactly for these same applications, and when comparing notes from each, one starts to see trends and things that are consistant from carb to carb and cam to cam, engine to engine.
I'd hardly call what I do reckless....I'm just stating basic baseline starting points to get guys in the ballpark.
And the formula above for power valves is not what most engine builders use, btw. It is generally done (in non-restrictor type carb classes) by choosing a PV 2 points less than the idle vacuum reading....so an 8"Hg vacuum reading will wind up with a 6.5 PV, 6"Hg gets a 4.5, etc....This is not gospel, it's just general rules of thumb...many racers find their specific needs to be something OTHER than this, and NOBODY (IMHO) should be blocking off power valves. That is a crutch that ruins the overall performance of the carb. It will only run right then when jetted for WOT or for anytime the PV wouldn't otherwise be operating, and one would be very surprised to see how often a PV circuit actually comes into play with a 2bbl carb motor...

JMHO, your results may vary.

Dayton Umholtz, owner
Kinetic Performance


RACER35
Member
posted June 14, 2003 01:27 AM
Guru I ain't, but I think I've got a decent handle on the PV thing. This is the way I get it:
The power valve is normally open-increasing the jet size at idle or when the motor is really pulling a boatload of vacume.(like coming off the corner) The motor needs a rich fuel mixture to make touque. Now get out of the corner and head down the straight and your motor needs to lean out to really make horsepower. At that point the vacume drops and the power valve closes and the carb leans out. It was suggested to me to install a vacume guage in the cocpit so that I could tune the power valve to actual racing conditions.


Earl Parker II
Member
posted June 14, 2003 09:29 AM
Eljojo,

Turn it around 180 degrees and you'll have it exactly right. The power valve is closed at idle or when you close the throttle at the end of the straight. Under these conditions the manifold vacuum is high (or, more correctly, the manifold pressure is low). As you open the throttle manifold vacuum falls (conversely, manifold pressure rises). When manifold vacuum falls to a given point, the power valve will open, supplying the extra fuel required for WOT operation.

The opening point in inches of vacuum is stamped on each valve- an 8 and a 5 indicates a power valve that opens at 8.5 in. of manifold vacuum. This means that, as you open the throttle, when the manifold vacuum drops to 8.5 inches the valve will open. If you have a 4.5 inch valve installed, the manifold vacuum will have to drop to 4.5 inches before the valve will open. Therefore, the higher the number, the earlier in the acceleration cycle the valve will open and vice-versa.

KPLugnut is exactly right- you generally want to install a power valve that opens at 1.5 to 2.0 inches lower than whatever manifold vacuum you have at idle. You don't want the valve to be open at idle but you want it to open fairly quickly after you begin to apply the throttle. In general, racing engines seem to perform better when the power valve opens pretty early.

For a more in depth discussion of power valves you can to http://www.parkercarburetion.com/faq.html and scroll down the 'Carburetion' section. The top two items deal with power valve form and function. If you want to save the articles to your computer, just click on 'Save' when the dialog box opens.

------------------
Earl Parker II
www.parkercarburetion.com
704.482.7588


Eljojo
Member
posted June 14, 2003 06:47 PM
Thanks Earl! I appreciate you turvying my topsey..I've been that way all my life...seems like to me I should be getting younger every day!


dode
Member
posted June 20, 2003 08:50 AM
Ok, been sick and I finally got around to doing some playing last night. Vacuum measured between 10 and 11. Is my 4.5 power valve going to cause any problems? It seems to run great up to about 5000 rpms in the driveway. It sounds MUCH smoother than it ever did with the quadrajet. I know the racetrack is much different conditions, but at least this makes me feel better.

John

3xracing
Member
posted June 20, 2003 11:58 AM
Dode,
The power valve won't be affected by revving the engine in the driveway because free-revving the engine doesn't cause a big enough vaccum drop.
But personally, I think if you're pulling 11lb. of vaccum, you're real close with a 4.5. i know other's disagree with me, but just my $.02.


Earl Parker II
Member
posted June 23, 2003 12:03 AM
I'd go with an 8.5, at least to start, and experiment from there if you'd like.

------------------
Earl Parker II
www.parkercarburetion.com
704.482.7588


waltonjr1
Member
posted June 23, 2003 06:56 PM
I know what happens when a power valve goes out in a rodchester carb,the engine starts popping at about 5,200rpm.Is this because its not opening and its starving for fuel at the end of the strait.This drove me crazy for three weeks until someone suggested i change the powervalve.I was told this is caused when the engine backfires.Im now running a 4412 in a 358 that pulls 16" at 1,000 does mean my powervalve should around 13.0 sounds a little high.


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DEANJR#22


Earl Parker II
Member
posted June 23, 2003 10:45 PM
It wouldn't be too high (open too early) but the earliest opening point you can get is a 10.5. I'd recommend starting with one of those.

------------------
Earl Parker II
www.parkercarburetion.com
704.482.7588


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