1967 427-390 Holley Power Valve

[Jeff B.]

I need to replace the power valve on my 67 427-390 4-spd with original Holley 3811 carb. Have seen many Hg sizes available. Does anyone know what size the factory size is. The guy at the parts store says 6.5.
Thanks for any replies.

[Donald A.]

Re: 1967 427-390 Holley Power Valve

Original factory may or may not work depending on your engine, updates, cam, compression etc. Rule-of-thumb that has been around a while is to check your hot engine idle vacuum and then divide that by half, that will get you very close to a good setup. For example, my idle is 14 so I use the 65 power valve

[Robert B.]

Re: 1967 427-390 Holley Power Valve

If your engine is stock, a 6.5 should work well. I am using that power valve in my 427/390 with good success. If it's modified, then you'll need to measure vacuum as Don has suggested. What has happened to require a new power valve?

Bob

[Richard F.]

Re: 1967 427-390 Holley Power Valve

Backfire thru the carb will do it in a heartbeat.

[Jim T.]

Re: 1967 427-390 Holley Power Valve

I have used the 6.5 in my 68 327/350 with my Holley 650 spreadbore installed in 1974. I have also used a lower number, I believe I have a 5.5 in it now and works great, drove it yesterday.

[Robert B.]

Re: 1967 427-390 Holley Power Valve

Backfire thru the carb will do it in a heartbeat.

Sure will - I had that happen on a Route 66 trip several years ago. It made the rest of the trip pretty lousy. After that, I installed the Holley power valve check ball kit - no more power valve problems!
Bob