Holley Power Valve

[William G.]

Happy Holidays to everyone. Best wishes to all in 2017.

I'm presently in a state of disagreement with a supplier of Holley rebuild kits (Allstate, by name). I recently ordered a repair/rebuild kit from them and we disagree on the correct power valve for a List 3367 carburetor (300 and 350 hp 1966 327). When I received their kit it included an 8.5" power valve. As I was convinced the correct valve for this application is a 6.0" or 6.5" I purchased, locally, a 6.5" valve and sent a letter to Allstate saying that I wasn't happy with their service. The other day I received a call from Allstate and the gentleman I spoke with was very nice and he politely explained to me that Holley has ALWAYS specified an 8.5" valve for this application. I would expect that these two engines would run rather rich using an 8.5" and that this valve would be better suited to say an L76 (List 2818). I told the Allstate gentleman that the NCRS Forum experts (Duke Williams, etal) would, unless I was very much mistaken, not concur with his belief that an 8.5" would be right for a hydraulic lifter cam application. But................there seems to be one theory that the valve should be sized 1/2 of idle intake vacuum and with that viewpoint and given that my 300 hp engine pulls 19 inches at idle (even though it could use a rebuild) and that (perhaps) the 1964 L76 would (based on the 1/2 rule) use the 6.5" or even a 5.5" valve, perhaps he's right..............? Do I owe Allstate an apology or is his Holley chart very dated and a 6.5" valve has been deemed proper for 40 years or so. My letter to Allstate wasn't exactly nasty but then I didn't pay them any complements, either.

Perhaps when we order repair kits we should be careful and specify the power valve we want? It seems rather senseless to order a kit and then find that the most expensive component in that kit is not correct for the engine.


Bill

[Joe L.]

Re: Holley Power Valve

Happy Holidays to everyone. Best wishes to all in 2017.

I'm presently in a state of disagreement with a supplier of Holley rebuild kits (Allstate, by name). I recently ordered a repair/rebuild kit from them and we disagree on the correct power valve for a List 3367 carburetor (300 and 350 hp 1966 327). When I received their kit it included an 8.5" power valve. As I was convinced the correct valve for this application is a 6.0" or 6.5" I purchased, locally, a 6.5" valve and sent a letter to Allstate saying that I wasn't happy with their service. The other day I received a call from Allstate and the gentleman I spoke with was very nice and he politely explained to me that Holley has ALWAYS specified an 8.5" valve for this application. I would expect that these two engines would run rather rich using an 8.5" and that this valve would be better suited to say an L76 (List 2818). I told the Allstate gentleman that the NCRS Forum experts (Duke Williams, etal) would, unless I was very much mistaken, not concur with his belief that an 8.5" would be right for a hydraulic lifter cam application. But................there seems to be one theory that the valve should be sized 1/2 of idle intake vacuum and with that viewpoint and given that my 300 hp engine pulls 19 inches at idle (even though it could use a rebuild) and that (perhaps) the 1964 L76 would (based on the 1/2 rule) use the 6.5" or even a 5.5" valve, perhaps he's right..............? Do I owe Allstate an apology or is his Holley chart very dated and a 6.5" valve has been deemed proper for 40 years or so. My letter to Allstate wasn't exactly nasty but then I didn't pay them any complements, either.

Perhaps when we order repair kits we should be careful and specify the power valve we want? It seems rather senseless to order a kit and then find that the most expensive component in that kit is not correct for the engine.


Bill

Bill-------


According to GM and Holley, the carburetor GM #3884505 also known as Holley List 3367, uses power valve GM #3852470 also known as Holley 25R-219-65 or Holley 125-65. These are 6.5" valves.

[Timothy B.]

Re: Holley Power Valve

William,

Keep in mind the correct method to select the power valve opening vacuum number is to drive the car at cruise RPM's between 2500 and 4000 and note the lowest vacuum reading. Level road, slight load cruise RPM's is what you are after and select a valve that opens at approx. 2" vacuum less than that lowest reading. This will allow the engine to run off the main circuit (main jets) and when you accelerate and the vacuum drops the valve opens right away to allow extra fuel.

The opening point of 8.5 is fine for your 300hp engine, keep in mind it's the power valve channel restriction holes that regulate the amount of fuel allowed to flow to the main well not the opening point of the valve. You could probably use a 10.5" valve and be fine. Holley specs the 6.5 because it's safe and will seldom allow extra fuel when cruising the hood..

Merry Christmas.

[Gene M.]

Re: Holley Power Valve

Just for a point of interest, I installed a 5.5 p/v and did not notice any real difference. Fuel consumed may be a bit better on the L79. Summit has these at reasonable prices. They appear to offer a wider vacuum rating than was offered back in the day.

[Timothy B.]

Re: Holley Power Valve

Gene,

You probably didn't notice any difference because the carburetor main circuits are usually rich, these carburetors are generic to 300 & 350hp engines and the camshaft timing is completely different between the two. If you lean the main jet to keep the plugs clean the power valve opening point becomes noticeable because under load that extra fuel at the right vacuum level is very important. The area you reduce the jet size can be added to the power valve channel restriction holes to restore the original engineered WOT calibration.

I enjoy reading/learning and trying different combos on my 3810 Holley and the engine responds very well to a leaner tuning but it's a learning curve.

For the purpose of the O/P the 8.5 power valve on his engine will be fine, just take note to use the correct gasket and tighten to the torque of 100 in. lbs which is tighter than most other fasteners on the Holley. Vacuum from a 300hp engine will find fuel and air from any gasket or modular surface that's not flat and create a internal leak to drive you crazy.

[William F.]

Re: Holley Power Valve

Yes, but to answer original post , Holley specifies the 6.5 power valve. William Gist, Don't fool with Allstate, etc. Order a genuine Holley kit.

[Gerard F.]

Re: Holley Power Valve

Bill,

Hate to disagree, but I think Allstate gave you the correct size power valve (85) for an original 3367.

They may be recommending a 125-65 now but my Holley Illustrated Parts & Specs catalog 36-51-7 (circa 2002-2004) shows a 25R-591A-85AS power valve assembly for a 3367. Additionally the catalog shows using the #2 pump cam position for a 3367, which would give it a richer shot on acceleration.

Attached is a comparison chart for my 3810 which I prepared from the catalog when I was looking for equivalent parts on other carburetors.


Perhaps my catalog is wrong, or the spec was later changed.

[Gene M.]

Re: Holley Power Valve

Gene,

You probably didn't notice any difference because the carburetor main circuits are usually rich, these carburetors are generic to 300 & 350hp engines and the camshaft timing is completely different between the two. If you lean the main jet to keep the plugs clean the power valve opening point becomes noticeable because under load that extra fuel at the right vacuum level is very important. The area you reduce the jet size can be added to the power valve channel restriction holes to restore the original engineered WOT calibration.

I enjoy reading/learning and trying different combos on my 3810 Holley and the engine responds very well to a leaner tuning but it's a learning curve.

For the purpose of the O/P the 8.5 power valve on his engine will be fine, just take note to use the correct gasket and tighten to the torque of 100 in. lbs which is tighter than most other fasteners on the Holley. Vacuum from a 300hp engine will find fuel and air from any gasket or modular surface that's not flat and create a internal leak to drive you crazy.

No jetting changes, just the 5.5 p/v. Have not had any issues with plugs. Running AC 44 with solid core Packard 440, good Mallory points, timing at 14 degrees, and dwell at 31. But most important NO CORN JUICE. I have over the years played with leaner jetting but always reverted back to originals. If memory is working the stock #65 primary jets are in there now.

couple nice you tubes on p/v

https://www.youtube.com/watch?v=6vKlAnKdcB4&feature=related

https://www.youtube.com/watch?v=WfjkeC3dPSI

[Joe L.]

Re: Holley Power Valve

Bill,

Hate to disagree, but I think Allstate gave you the correct size power valve (85) for an original 3367.

They may be recommending a 125-65 now but my Holley Illustrated Parts & Specs catalog 36-51-7 (circa 2002-2004) shows a 25R-591A-85AS power valve assembly for a 3367. Additionally the catalog shows using the #2 pump cam position for a 3367, which would give it a richer shot on acceleration.

Attached is a comparison chart for my 3810 which I prepared from the catalog when I was looking for equivalent parts on other carburetors.


Perhaps my catalog is wrong, or the spec was later changed.

Jerry------


The GM information I provided above came out of a 1966-70 editions of the Chevrolet P&A Catalog.

[Jack M.]

Re: Holley Power Valve

I've found these two websites quite handy for Holley Carb Parts info: Table 1 and Table 2

In addition, I've also compiled the info into a handy spreadsheet: CLICK HERE
(NOTE: There are two tabs/sheets containing Table-1 and Table-2 on the bottom-left of the Excel file.)

[William F.]

Re: Holley Power Valve

My 2003 HOLLEY master catalog lists 125-65 for 3367 as well as 3810 and 2818 carbs. Instead of this back and forth, why doesn't someone call Holley tech support and get their answer as to whether they have changed recommendations.

[Jack M.]

Re: Holley Power Valve

Or you can go directly to Holley Carb's Rebuild Kit Selector: CLICK HERE
They have a link for a parts spreadsheet... I reformatted it a little: CLICK HERE

[Jack M.]

Re: Holley Power Valve

BTW- All the sources I've noted (including Holley) refer to part 125-65 as the proper Power Valve for the 3367 carb.

[Gerard F.]

Re: Holley Power Valve

Jack,

Attached is an excerpt from my source, the Holley Illustrated Parts and Specs manual 36-51-7 which I purchased from Holley in 2004.

I have highlighted the power valve specs for the 3367 and various other carbs (part#83). This manual has some 350 pages of original specs on every Holley carb produced and the drawings in it are the basis of every carb kit that is presently produced. As I indicated above, the Holley power valve part number for a 3367 as originally spec'ed was 25R-591A-85AS according to this book.

The spec may have been later changed to the 125-65 by Holley and GM. I believe the change may have been made in 67 as most of the 67 4160 carbs went to the 65 power valve. I also note that there were many 65-66 4160 carbs which used the 85 power valve.

Maybe the change had to do with the onset of emissions controls. Or maybe it didn't work well with the high performance cars with low vacuum at idle. But for a car doing 19 vacuum at idle, an 85 or 8.5 should do well.

[Timothy B.]

Re: Holley Power Valve

Jerry, if there was a change to the #65 P/V my thinking is that it protected engines with sporty cams that make low vacuum. This would insure the valve did not open during cruise RPM's.

I had to delete my last sentence because I didn't have enough coffee yet.