cam specs
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New User
Joined: Dec 2006
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cam specs
Hi, I was wondering what would be a good size cam to use in my 69 390. I think i would like to have the biggest i can go with without having to change other parts or do a lot of ajusting. The motor has stock heads. I put 10:1 flat top forged pistons and bored .30 over, if that matters.
Post Fiend
Joined: Jan 2003
Posts: 8,600
Likes: 4
From: Iowa
Well, you could change the cam without changing other parts, but it might not be right when you get done!
One, you need to change lifters. I assume you know about this if you're thinking about changing the cam. Lifters and lobes wear into each other, and changing out the cam requires new lifters.
Two, used valves can sometimes get a bit of wear on the stem. If your new cam lifts them higher, the ridge that built up at the top will now be forced into the guide, and that can hurt stems and guides. It would probably start burning oil.
Three, you will probably need new springs. Not only to prevent coil bind, but the more agressive cam will probably need a stiffer spring than stock.
Four, if your motor was originally a hydraulic lifter motor, you probably have a non-adjustable valvetrain. What this means is you cant adjust lifter preload. If you put the heads back on the wrong side, got the pushrods mixed up, etc, preload can be wrong, which can cause problems. The good news is you can easily convert to an adjustable valvetrain. Ask if you have questions.
Five, at about .550" lift, you'll start squishing the stock umbrella valve stem seals with the bottom of the spring retainer, so you'll have to think about that.
Sixth, even if your pistons said 10:1, that's rarely the case, especially in FE's. Head gasket selection has a lot to do with it. Go figure it up here:
http://www.kb-silvolite.com/calc.php?action=comp
I recommend one of the following cams:
Comp 280H
Comp XE274H
Crane 343941
Crane 344341
One, you need to change lifters. I assume you know about this if you're thinking about changing the cam. Lifters and lobes wear into each other, and changing out the cam requires new lifters.
Two, used valves can sometimes get a bit of wear on the stem. If your new cam lifts them higher, the ridge that built up at the top will now be forced into the guide, and that can hurt stems and guides. It would probably start burning oil.
Three, you will probably need new springs. Not only to prevent coil bind, but the more agressive cam will probably need a stiffer spring than stock.
Four, if your motor was originally a hydraulic lifter motor, you probably have a non-adjustable valvetrain. What this means is you cant adjust lifter preload. If you put the heads back on the wrong side, got the pushrods mixed up, etc, preload can be wrong, which can cause problems. The good news is you can easily convert to an adjustable valvetrain. Ask if you have questions.
Five, at about .550" lift, you'll start squishing the stock umbrella valve stem seals with the bottom of the spring retainer, so you'll have to think about that.
Sixth, even if your pistons said 10:1, that's rarely the case, especially in FE's. Head gasket selection has a lot to do with it. Go figure it up here:
http://www.kb-silvolite.com/calc.php?action=comp
I recommend one of the following cams:
Comp 280H
Comp XE274H
Crane 343941
Crane 344341
Post Fiend
Joined: Jan 2003
Posts: 8,600
Likes: 4
From: Iowa
Possibly, if you know what's in the motor. Make sure the springs will work with the cam you select, and make sure there's no interference (like valve to piston, or spring retainer squishing the stem seal, etc. 10 miles wont have been enough to wear the valve stem, so you're ok there. If you keep everything in order, preload *shouldn't* be affected, but you must check anyway.
