Piston / Valve Clearance

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sbh126

sbh126

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I recently replaced my cam with a .550 lift solid roller cam. .587 with my 1.6 rockers. I measured my piston to valve clearance using Comp's checker springs and a feeler gauge and with .020 lash I have .250 clearance on the Intake at 10* ATDC and .266 on the exhaust at 5* BTDC. That was a lot more than I was expecting to see.

What is the suggested piston/valve clearance for big block motors? Given the numbers above it appears like I could run a cam with substantially more lift without issue as long as my springs don't bottom out. Looking at the Comp catalogue it looks like all the higher lift cams have power bands that are much higher than mine and go well into the 6k RPM's. I'm not sure I'm willing to go above 6k.

Is there power to be gained by installing a higher lift cam or will it be counter productive since I wont be spinning fast enough to take advantage of it?
 
everyone assumes lift is the direct factor of piston to valve, when duration is actually a larger factor. When a valve is at max lift, the piston is way down in the cyl. now how long that valve hangs open....thats where things get close.

.080/.110 is the ballpark we use.

onto if adding random lift would increase power. depends on the rest of the build, head flow, etc. plus the more lift, the closer you get to coil bind, and i don't know what you're using for springs.
 
Is there any sure way to know if a cam will clear without installing and measuring it?
 
Nope. Either clay checking....or using a dial indicator and a checking spring. But again....unless this is some ported aluminum headed monster...you probably will benefit zero, or even go backwards with a "bigger" cam.
Do u want power brakes? Street manners? Any drivability whatsoever? What's your converter like? All questions that need answered before swapping out your brand new cam, just bc u haven't yet smashed the valves.

Fyi I make 600 horse with .135 and .190 with almost 800 lift...u probably have a ways to go.
 
johnnymac2k6 said:
Nope. Either clay checking....or using a dial indicator and a checking spring. But again....unless this is some ported aluminum headed monster...you probably will benefit zero, or even go backwards with a "bigger" cam.
Do u want power brakes? Street manners? Any drivability whatsoever? What's your converter like? All questions that need answered before swapping out your brand new cam, just bc u haven't yet smashed the valves.

Fyi I make 600 horse with .135 and .190 with almost 800 lift...u probably have a ways to go.
Click to expand...

bare minimum at all stages of rotation: .080 intake-.100 exhaust
 
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