Power Valve in Holley

[Jim Marshall]

I was rebuilding a Holley/Small Block Ford carburetor with a genuine Holley Marine kit and heeding most of the advice I picked up on this forum (thanks to all). One was matching what existed with what is provided in the kit. This is where I ran into a little snag.

First, those little numbers on the power valve are almost unreadable but I borrowed a magnifier. My old carb setup (since day one) had 8.5 vacuum. There were two power valves provided. The closest was 7.5.

I can pick up a 8.5 from Jegs if it really matters. My question is, does it?

Thanks again.

Jim

 

[Tig]

Re: Power Valve in Holley

Yes it does matter. But it's been so long since I tuned a Holley I had to google this.
http://www.angelfire.com/fl4/pontiacdude428/HolleyInfo2.html
Sounds reasonable from what I can recall and they say you need one in the range of 7.5 to 6.5
You don't want an 8.5

 

[Jim Marshall]

Re: Power Valve in Holley

Thanks for the info. I think it sounds in range. Have you ever used one of the power valve shields listed in the article for backfire protection?

I am using a Edelbrock Performer 289 manifold, having made a custom bracket for the throttle linkage. Would you recommend using their manifold bolts?

Jim

 

[Jim Marshall]

Re: Power Valve in Holley

So basically the 302 came wrong from the factory with the 8.5. I guess the kit guys were smarter than the OEM guys

Jim

 

[Bifflefan]

Re: Power Valve in Holley

The way a power valve works is,
At the lowest vacuum at WOT the power valve opens to cover up the low signal through the venture's. You want the power valve to open just above the lowest reading you get at WOT.
So you hook up a vacuum gauge and get out on the lake, have a buddy watch the gauge and slam her WOT, Say it drops to 6" mercury, so you want to have a 6.5 power valve.
The 8.5 installed at the factory is a generic setting for the most common numbers they could find. It also pretty much negates the chance of ever running to lean at low vacuum.
You can trial and error this also, install the 7.5 and see if you get a flat spot when going from the throttle just cracked to WOT, if so bump it up to an 8 or 8.5 if not you good to go.
I doubt that the 7.5 will affect the motor at all. 8.5 is what we run in race engines as they have little vacuum anyway.
6.5 is the normal factory installed one for most apps.

 

[Jim Marshall]

Re: Power Valve in Holley

I noticed 8.5 was common in Jegs and Summit. This is kind of an oddball engine anyway, direct from Glastron. It has 351 heads, Osco manifolds. It claims 200 hp on the valve cover.

Jim

 

[Tig]

Re: Power Valve in Holley

Power valve shields are new fangled stuff. I do not have one. The PVs were pretty tough and do have a check ball for protection.
I have no experience with their manifold bolts.

Here is a Holly doc on power valves.
http://www.holley.com/data/TechService/Technical/power_valves.pdf
I'm unclear if this is specifically for race engines but they would have you select a PV that is 8.5" divided by two, so 4.25. Next closest going down would be 3.5"

 

[Bifflefan]

Re: Power Valve in Holley

I noticed 8.5 was common in Jegs and Summit. This is kind of an oddball engine anyway, direct from Glastron. It has 351 heads, Osco manifolds. It claims 200 hp on the valve cover.

Jim

Are there spacer type head washers on the head bolts?
302 has smaller head bolts than a 351 and requires special washers with a spacer built onto it the makes up the difference.
My 3.7 has 170 HP.
Doesn't sound that wild to me.

 

[Tig]

Re: Power Valve in Holley

Biff's proceedure sounds good.

 

[Bifflefan]

Re: Power Valve in Holley

Here is a Holly doc on power valves.
http://www.holley.com/data/TechService/Technical/power_valves.pdf
I'm unclear if this is specifically for race engines but they would have you select a PV that is 8.5" divided by two, so 4.25. Next closest going down would be 3.5"

That is interesting reading. I have never heard of this method, and i have read all of the Holley performance stuff i could get my hands on over the years. Including books written by Holley.

 

[Jim Marshall]

Re: Power Valve in Holley

I don't think it really is that wild. It is a 1974 and who knows why they did it. It is an Osco manifold with Glastron cast into it. Part are interesting to find sometimes.

Originally the engine had a cast iron manifold on it with what looked to be standard bolts with no washers. I picked up the Edelbrock cheap and thought why not. It sure weighs a lot less. I saw that Edelbrock makes a special set of bolts including washers.

I bought a brand new crate Ford Explorer 5.0 engine to put into it but there was so many changes I rebuilt the old one. Now it needs a home.

[/IMG]

Jim

 

[zbnutcase]

Re: Power Valve in Holley

Are there spacer type head washers on the head bolts?
302 has smaller head bolts than a 351 and requires special washers with a spacer built onto it the makes up the difference.
My 3.7 has 170 HP.
Doesn't sound that wild to me.

No those 351W heads were factory installed by Ford, and they use a special stepped head bolt with built in washer too. I have a set these heads&bolts on the 302 in my Ranger 4x4 pickup, they came off an 888 Mercruiser.

 

[Jim Marshall]

Re: Power Valve in Holley

About the bolts on the manifold. Hmmmm! Here is a picture. See one tucked under the hose. They look pretty standard to me.

 

[Bifflefan]

Re: Power Valve in Holley

No those 351W heads were factory installed by Ford, and they use a special stepped head bolt with built in washer too. I have a set these heads&bolts on the 302 in my Ranger 4x4 pickup, they came off an 888 Mercruiser.

Well there you go, I learned something today...LOL
I knew they make special bolts for the BOSS, but didnt know they made them for the 351 head on a 302. We always use ARP bolts on our engines.

 

[Jim Marshall]

Re: Power Valve in Holley

Bifflefan,

I have seen those. They look like a good set.

Jim

 

[Jim Marshall]

Re: Power Valve in Holley

My wife thinks I will never get this thing together, but really, I am making progress, learning a lot, too. You know how it goes, if you knew how much work projects would take you would go fishing with someone else.

Jim

 

[Tig]

Re: Power Valve in Holley

Jim, if you happen to have the valve cover off, jot down the casting number on the head. I'm curious.
I'll apologize in advance for the next highjack
zbnut, What tranny do you have in your Ranger? My F47 with a 302 is slated to go on Ranger running gear.

 

[Jim Marshall]

Re: Power Valve in Holley

Tig,

I will try to remember to get it tomorrow.

Jim

 

[Jim Marshall]

Re: Power Valve in Holley

TIG,


All I see is 351 in one spot and WF cast into another.

Jim

 

[Tig]

Re: Power Valve in Holley

I should have mentioned that D0OE or C9OE is what I would expect. Either way, I was just curious. I'm sure it's a good working package.
I found this list of head casting numbers for your reference.
Good luck with your project!