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Old 04-15-2012, 09:40 PM
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Holley 950HP Carb issue that I have never seen before...input?

Hello everyone,

Well I saw something I have never seen at work and I wanted some input. Motor is a pump gas 540. It has a Holley 950 hp carb. Well the primary and secondary jets were the same (77's). Now both primary and secondary metering blocks have a power valve, but there is no number listed on the side of them, there is what appears to be a one but it looks like the casting. The only thing I see is on top where is says c765. The only time I ever heard of squaring the jets is on a carb with no power valves and a blower carb.

Now my question is why is the jetting done this way? And what the hell vacuum does this power valve open up at?

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Old 04-15-2012, 09:57 PM
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Quote:
Originally Posted by oldschool101
Hello everyone,

Well I saw something I have never seen at work and I wanted some input. Motor is a pump gas 540. It has a Holley 950 hp carb. Well the primary and secondary jets were the same (77's). Now both primary and secondary metering blocks have a power valve, but there is no number listed on the side of them, there is what appears to be a one but it looks like the casting. The only thing I see is on top where is says c765. The only time I ever heard of squaring the jets is on a carb with no power valves and a blower carb.

Now my question is why is the jetting done this way? And what the hell vacuum does this power valve open up at?
If there's a PV front and rear, there's no need for a large split front to rear, you might expect to see maybe 2 numbers higher on the secondary side- depending on what the combo needs. On a carb w/o a rear PV there should be a large split- 7 or more numbers, depending.

As for the PVs having no numbers, I'm guessing they're some sort of generic, i.e. not a Holley PV. Most of these are 65. You can check the vacuum w/a hand held vacuum pump like a Mityvac. Mine came w/a suction cup that works to test them.
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Old 04-16-2012, 05:06 AM
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Yes the 950 hp comes square jetted. Mine had 79's in it from Holley with 6.5 PV's ft and rr and holes in the butterflies. Mine was very rich on the idle and transition circuits and lean at WOT. It took a bit of work to get a decent fuel curve which included installing replaceable IFR's, tslot jets and PVCR's as well as blocking off the middle e holes. I also replaced the butterflies as my engine didn't need the bypass air.

Last edited by TommyK; 04-16-2012 at 05:24 AM.
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Old 04-16-2012, 05:17 AM
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Thanks for that info, TommyK- baseline jetting and whatnot is sometimes hard to come by; I'm sure this will help someone down the line, especially if the title of this thread could be changed to add "Holley 950 HP" so it will show up during a search for info on that carb..
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Old 04-16-2012, 07:29 AM
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Quote:
Originally Posted by oldschool101
Hello everyone,

Well I saw something I have never seen at work and I wanted some input. Motor is a pump gas 540. It has a Holley 950 hp carb. Well the primary and secondary jets were the same (77's). Now both primary and secondary metering blocks have a power valve, but there is no number listed on the side of them, there is what appears to be a one but it looks like the casting. The only thing I see is on top where is says c765. The only time I ever heard of squaring the jets is on a carb with no power valves and a blower carb.

Now my question is why is the jetting done this way? And what the hell vacuum does this power valve open up at?

The numbers on the PV can be hard to read. They are stamped on the steel piece that retains the diaphragm. I believe yours are 6.5 as noted by the "c765" you found.
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Old 04-16-2012, 07:48 AM
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↑X2 I thought the same thing. The numbers are sometimes on the edge of the pot metal "hex".


Last edited by cobalt327; 04-16-2012 at 07:57 AM.
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Old 04-16-2012, 09:40 PM
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Thanks to everyone for the info. Cobalt 327 that is where the numbers were on my power valves. From one of my holley books it described the number being on the side of the hex. So when I didnt see it there I said hmm. YOu guys really know your stuff, I love this site! Now all in all is the Holley 950hp a good drag race carb?
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Old 04-16-2012, 10:37 PM
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Quote:
Originally Posted by oldschool101
Thanks to everyone for the info. Cobalt 327 that is where the numbers were on my power valves. From one of my holley books it described the number being on the side of the hex. So when I didnt see it there I said hmm. YOu guys really know your stuff, I love this site! Now all in all is the Holley 950hp a good drag race carb?
For the most part they're not bad for an "entry level" race-type carb. They don't actually flow 950 cfm, but then several of BG's carbs didn't flow their numbers, either (some more, actually). Then there's the question of how the flow is measured- wet or dry, and at what depression. The Holley 950 HP is thought to flow in the low to mid 800 cfm range. But of course most everyone is going to think a "950" carb flows 950 cfm.

Bottom line (sort of, anyway) is if the Holley 950 HP is tuned correctly, it works OK. It has a good amount of tunability and in the right hands it'll get the job done for a reasonable price. Tuned one for a 455 Pontiac that had Edelbrock heads and a fairly stout solid lifter cam (248 degrees @ 0,.050" lift), it needed some smaller secondary bleeds, jetting was close as I remember, PV was only in the front. Had real good response and overall was satisfactory.

IIRC the 950 HP has a mixture of a 850 base plate and a modified 750 body, forget where I heard that. When I was using it, I had thought it flowed 950 and was a little surprised it responded the way it did. After finding out the difference in the real flow to the advertised flow, I was less surprised!
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