rookie ques bout piston2valve clearance


Founding Member
Oct 14, 2000
miami fl
how can i figure out piston to valve clearance before i buy the cam? i dont want to buy an expensive engine combo and have the wrong cam ..pistons..etc...i plan to use afr 185's(58cc)with a 331 stroker figuring about(give or take depending on which piston brand i use) 10.5:1 compression with Comp Cams XE274HR * Advertised duration: 274 intake/282 exhaust* Duration at .050 in.: 224 intake/232 exhaust* Gross valve lift: .555 in. intake/.565 in. exhaust* Lobe separation: 112 degrees
will i be alright? how do i check this?? any help is appreciated...thanks
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Others can give you an idea what their clearance was on a similar combo - if they've measured it. Most haven't. The problem is that a combo with identical components can have significantly different clearances. The only way you'll know your exact clearance is to measure with your cam.

There are some ways you can mitigate the uncertainty, but you'll have to take some measurements. First, you'd need to go ahead and get your heads, and pistons and do a mock up install to take some measurements - no way around that step. You'll need a degree wheel, and a dial indicator and a positive stop (to find actual tdc) - the same equipment you'll need to degree your cam or measure your p to v, so you're gonna need it eventually anyway. Basically, you'll need to remove two valve springs (int/exh for #1 cylinder), and using the degree wheel and dial indicator, measure how much distance there is between the valve being closed, and the valve touching the piston at 5degrees btdc, at tdc and at 5 degrees atdc. If you provide those measurements to any of the custom cam designers out there, for a given rocker ratio they can compare that to the lift at the valve at the same points (-5, 0, +5) -- the difference between that 'drop valve' measurement you made, and the lift of the valve at the same point is a pretty good approximation of your p to v clearance; so they can come up with a cam that should give you the clearance you need. You might be able to get the same info out of the tech lines at some of the cam companies -- but I wouldn't hold my breath. Most of the folks I've talked to are more marketing folks than technical specialists.
thank you guys for your input...i appreciate it greatly...i asked a couple of people i know this same question after assuming they know what they are talking about but today i found out they dont....i guess the only way to measure this is by physically measuring paper work will help me but thats ok b/c thats how you learn i suppose...thanks again :)
Give DSS a call, they have stroker kits in stock that have pistons that will clear your exact combo. I gave them a call, told them what I had, and they had the right pistons on the shelf. Got them in a cpouple days, and no clearance issues at all. Very pleased, especiallt after the tech guy at Summit told me no one makes pistons to clear 2.02 valves in sbf. Dumb@$$.
Haven't had it to the dyno, but I figure it should be good for around 330ish at the rear wheels. I like the combo, as it's gone deep into the 12's with spray on street tires, but I just scored a 351 block from a friend of mine, so I'm off to build a 392 for next year. Car's mad fun as it is, but my friends LS1 is just god aweful fasft, and he's looking into a 427 block now. I can't let him stay ahead of me like that :p.