I built a custom SBC. The pistons have a .060" dish, WITHOUT a valve relief. I know I need to use a clay mock-up to determine piston to valve clearance. My question is, how much clearance between the piston and valve is SAFE?

Thanks,
dave w

 

Minimum piston to valve clearance:

Intakes .100"
Exhaust .125"

 

Thanks Stephen 87 IROC

My piston to valve clearance is real close! I'm less than 0.080"! Maybe only 0.070". I'm not good at measuring clay ... soft stuff.

I think I will use a much milder camshaft ... I don't have any other affordable options?

Based on the picture I have attached ... let me know if you agree weather or not, I found the closest contact point?

Thanks,
dave w

 

Based on the attached picture which measures about 7.15" in dia. on my screen and the clearance point is about .14 then scaling that down I come up with about .081 clearance. If the engine hasn't been balanced then you can still have the pistons clearanced, I've even seen guys use a cutter that fit's in the valve stem and do it themselves and not rebalance. It's up to you.

 

Are you checking clearance with a head gasket installed? Are you using solid lifters?

Lift and duration are not usually the factors in piston to valve clearance. It's the valve timing. During the duration, the valves open and close at specific degrees. You can have a cam with more lift and duration but still allow more piston to valve clearance than what you have. You can have 5 different cams with the same lift and duration and if the valves open and close at different points, all 5 cams will act differently.

You can also play with degreeing the cam to change the clearance. If you retard the cam, you will gain some clearance on the intake and lose some on the exhaust. Advancing the cam is the opposite.

Depending who you ask, a minimum clearance can also be .080" on the intake and .100" on the exhaust.

 

yep agree. i ran .070" PTV on the intake with supers stock hemis spinning 9400 rpms. .100" is a good number for exhaust.

 

Solid lifters? - Yes
Head gasket? - No, but I am using .045 shims ... same as the compressed gasket thickness.

Current cam is a real mild .423 / .423, but I only measured .410 / .403 with the stock rocker arms. If I was to use roller tip rocker arms, my measurements would be more accurate?

I think I will be OK with a .390 / .410 and some roller tip 1.52 rocker arms. I'll need to measure again, but I should be around +0.080 ~ -0.100.

I don't know if anyone noticed, but the bore is 3.540 / stroke is 3.10 so this 4.0 liter SBC V8 engine is really for Mileage, not Performance. Kind of cool using 6.00 rods. I have Weiand Stealth intake, with a 4.3 V6 TBI.

Say bye, bye 2.8 V6 say hello 240 cubic inch V8.

dave w