My engine builder says that a cam with 540 lift at the valve is too big for a 383 with flat top pistons. Is it true? Cam is 540 on both sides with 1.6 rockers and is 240/246 @ .050.

I'm interested also,I'm thinking of testing with the same.Also depends on what your springs are rated at I would think.

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It'll probably fit, no problem. Doesn't matter that it's a 383; a flat top that comes to the deck, is a flat top that comes to the deck. Could be a 283 or a 434, doesn't matter.

But, the only way to know FOR SURE, is to mock it up and measure it.

Cam timing dramatically affects the clearance. Max valve lift on both valves occurs when the piston is somewhere near halfway down in the bore, so the max lift spec is totally useless for even making an educated guess. What matters is what the valves are doing when the piston is near the top of the stroke; specifically, during the "overlap" period, when the exhaust is just closing, and the intake is just opening. The earlier the intake opens (advancing the cam would make it worse), the more likely it is to have a problem; the later the exhaust closes (retarding the cam, or reducing the lobe separation, will make this worse) the more likely it is to cause trouble.

speedomotive sells a 383 flat top motor with a 555 solid lift flat tappet

That cam should not be an issue with any piston I know of.
Ask your engine builder exactly what total lift has to do with piston to valve clearance?? :D
Duration, lobe separation & where the cam is installed are far more important.
The only reason total lift is important at all is that most higher lift cams open the valves faster so they are off the seat further at overlap.

Originally posted by motown/malibu:
speedomotive sells a 383 flat top motor with a 555 solid lift flat tappet I've been hearing alot of bad things about these guys. I was considering buying from them but now I'm not so sure.

Mike, How will going to a 1.6 rocker affect(if at all)the duration of a cam,say on a comp 292H?
Steev


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I can attest to a UD Hyrdo 284/292Dur@.006, 230/238@.050, 114lsa, 108CI, .565 w/ 1.6 Rockers having PLENTY of clearance on a decked/flat-top 383 with AFR 195 Heads milled down to 66cc, .041 gasket. There was something like 1/2" clearance.

If you have a 540 cam with a 1.5 rocker you have a 576 cam with 1.6 rockers if I did my math right. I don't know what your cam specs are but I'm just guessing why he might be saying that. Maybe he was thinking of your gears, trans, converter, vacuum and intended use. He may also be thinking of your springs yada. You shouldn't have valve piston clearance problems with flat pistons even with that lift though. What size rods are you running?

Originally posted by onebadd66:
Mike, How will going to a 1.6 rocker affect(if at all)the duration of a cam,say on a comp 292H?
Steev


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Can't give you exact numbers but in general it will increase the seat duration by about 8 degrees or so with a hyd cam & the .050 number will go up about 4 or 5 degrees, .100 by a little less & so on & obviously the lift will go up too.
Harold could probably recite you very close numbers but I'd have to measure it smile.gif

With a solid, assuming you readjust your lash the seat numbers will not change but everything else will.
If you don't change the lash the seat numbers will change also.

Im not running a 383 but my 350 has about .033 quench, 268/278@.050 and lift is .562/.570 and i think if i remember right i had .150 of clay on the top of my pistons and i didnt even touch it. You may need to look for a new engine guy!!

Thanx Mike graemlins/thumbsup.gif

Steev

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Originally posted by Nickel333:
Im not running a 383 but my 350 has about .033 quench, 268/278@.050 and lift is .562/.570 and i think if i remember right i had .150 of clay on the top of my pistons and i didnt even touch it. You may need to look for a new engine guy!! Man thats a lot of cam........You must have one stout little 350 graemlins/thumbsup.gif