[hotrod937]

I'm building a 385 sbc with a .576 lift Mechanical roller cam and 155#/420# springs. The heads are huge Dart 230cc that are ported with a vic Jr. air gap that has a higher rise than the normal vic jr. (so my T/A's shaker lines up)

I've got a Holley 850 and was told I may need to change my power valve with the cam I'm running. I plan on getting a Holley book and doing a rebuild myself. What power valve change do I need and what jets should I start with on the dyno?

[red65novawagon]

You really need to know the vacuum level @ idle first before you can really go anywhere with it. I would use the secondary throttle adjustment to get the idle air initially set this will help get air into the engine without having to expose the idle transfer slots on the primary side which would affect the power valve function too but you'll have to do this with the carb off the manifold.

[454C10]

what duration is the cam???

get it running first. check the vacuum at idle and during highway driving and during lite throttle driving around town.

With bigger cams, I typically run a pv at 1/2 the idle vacuum, but make sure the pv doesn't come on while just driving down the highway.

you will get better throttle response if the PV is a little bigger, but mpg will go down.

A 4.5 or 5.0 normally does the job with bigger cams.

a cam like yours will need lot of initial ignition timing. 20 to 25 degrees.

[hotrod937]

Thanks guys. I'll start with a 4150 rebuild kit and ask 'em for some extra power valves and jets.

[cobalt327]

Originally Posted by hotrod937

Thanks guys. I'll start with a 4150 rebuild kit and ask 'em for some extra power valves and jets.

Unless this is a once-in-a lifetime deal, consider Holley #8081 jet assortment kit. It's a $52 hit from Comp Prod. but is far cheaper than buying individually.

PV's are $6 a pop, pays to buy them as you need them as they will stiffen w/age.

[hotrod937]

Yea I should have ordered the jet kit when I had 'em on the phone today.