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390 valve lift: what is "safe"?
First off, I do not know alot about the FE's. I have a 1967 390 out of a Fairlane GT that was rebuilt awhile ago, maintaining the stock pistons and heads. I plan to add a new oil pump, and a few basics such as carb, intake, cam, etc.. I have been looking through some speed shop catalogs, and some of the valve lifts I see seem pretty steep- i.e. .57, .60, etc..
Id like to go pretty radical with the cam as without power brakes, vacuum is not as much as a concern. I know the pistons, thickness of the head gaskets, what type of heads and if they have been milled, etc. play a major role- but at what valve lift should I start being concerned. Any help or suggestions would be greatly appreciated. Thanks, Greg |
Greg,
The '67 390GT used the same cam as in the 428CJ. .481 int .490 exh lift |
Thanks for the response, and I will take note of the info as I am trying to find out as much as possible about the engine, particularly heads, etc. Basically all I know about the engine is that they were supposed to be a somewhat conservative 335 HP.
I am concerned about valve lift on aftermarket cams. For comparison, I had a 73' 351C, and went with a cam with .563" intake and .534" exhaust, the advertised duration was 294*, but I have no idea what the duration was at .5 valve lift to compare it with whats available now. I was also advised by the builder who did the machine work that .563/.534 was "getting up there"- but thats for a Cleveland with the 2 bbl heads I was running. I am wondering at what numbers do I need to really start paying attention to valve / piston clearance. Again, thanks for any help. Greg |
From my experience, the cam manufacturers usually set the cams up so they'll fit. From my experience, the time when things get tight on an FE is on the intake, as the intake is opening faster than the piston is going down. I've only run Comp cams, and it appears they design the cam so that it'll have enough clearance. You should definitely check both intake & exhaust valve-to-piston clearance whenever you change a cam, but from what I've seen you won't have a problem. I haven't seen an exhaust valve come anywhere near the piston to bother actually measuring the clay. My current cam has a .675 lift (solid roller).
Dan |
Measure it with the clay. The intake can hit. The exhaust can hit. They both can hit. I've been down that road a long time ago.
Max lift is never the issue. Its duration. At max lift the piston is way down in the cylinder. Normally you tag a valve 8-10 degrees before or after TDC. More duration brings the parts closer together at that point. Too close and your credit card implodes... The rest of your engine is stock? Get a mild hydraulic and call it a day. Something in the 230 @ .050 range will sound "rumpity" enough, and mid .500s in lift is safe with stock parts Barry R Survival Motorsports |
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