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a littel history for the audience. take one stock 454 add 12to1 speed pro pistons, 840 rec port heads, 600 lift cam, turn to 6000 against the chip and you get multipel bent valves, broke inner springs and cam lobes nocked off , now we all know how stupid i am can you help me figuer out how much cam i can get away with. new set up the same 12 to 1 pistons but since the aforemention heads are preaty much used up, let's put a set of 320 dart heads with 230 in and 188 ex valves in. before i buy a cam i'm trying to deside how much before it hits. the clearance between the piston dome and ex valve at top dead center is only 372 thous what gives?? thanks gary b

You sure about that Gary? .250 is a quarter of an inch!!!! You've got almost 3/8 of an inch valve clearance with 12 to ones? How deep are the valve reliefs?

i'm chasing this one. but the culprit i think is going to turn out being the dome on the piston and not the cam at all. i put the dart heads on yesterday and the dome actualy hit the ridge between the valves. used clay on top of the pistons at the valve and it was papper thin to being tore on others when turned over by hand. there is little pocket on the piston maybe 125 thousand. originialy i took the springs off buped it to top dead center droped the valves to the piston and measured the distance back to the seat. there speed pro forged pistons if that helps.

Sounds like you need some piston dome massaging huh. You can also use the light spring method also. Are you degreeing this cam?

2 degrees positive cam timming, priced the local machine shop to deepen the pockets and take a littel off the top and at 50 a piston i think ebay is where they would go other than giving this headache to some one else. what makes it worse i've got two sets of these bast////.. thanks i guess a lesson learned is never free... gary b

Am I understanding this right? $50.00 a piston to flycut the valve pockets? I'd check with another machine shop.

jeeez i admit that it has been a long time since i built a race motor.. this problem along with Heather's deal ?? maybe i'm missing some facts ??
Lippy mentioned valve timing allready.. i remember looking for .040 p/v clearence on a L-88 chev deal.... as Rock mentioned $50 per sounds outragous to me ? just been working on stock drivers for the last25 years so......

What rods are you using? Wrong length maybe?? Is it a stroked crank? Are the pistons supposed to be stock pin height?

Something doesn't add up.

Have to agree with Randy, something doesn't add up here. .300 thousanths clearance and the valves hit? better go back and check the cam. Your using up a lot of clearance there.
Art

eagle stock stroke crank. stock dimple rods, pistons 30 over 12 to 1 speed pro pistons, cam measuers 678 solid lift, suposed to be 574 some where a mix up. still i would think it should clear. gary b