408 Cam on the way
Edit
So I did some measuring of things.
Piston to deck stats:
Step up is 0.020 above deck.
Piston rim is 0.070 below deck.
Dish is 0.150 below deck.
I figured out KB uses the step up portion as the compression height by measuring from the pin hole, adding half the pin diameter.
Pin hole to rim ranged 0.868 to 0.880. Half the pin is 0.492. Step up is 0.090 above the rim.
0.880 + 0.492 +0.090 = 1.462. The spec is 1.465
Oddly every piston had one side around 0.010 higher than the other. Not sure if that's by design.
I had to scratch my head a little to decide how to do the CC. I decided to start with the step up reference point at zero deck.
CC of the cylinders with piston 0.5" down from there is 131 cc.
Using the formula to get 1" of cylinder volume (d/2)squared x 51.48
(4.030/2) squared x 51.48 =209
Divide by 2 for volume of a half inch is 104.5.
131 - 104.5 =26.5 This is my total dish volume below the step up.
Spec is 25 cc. I think its worth doing to have the SCR nailed down.
I ran the calculation with a 0.070 gasket because KB calls for a minimum 0.040 clearance from piston to head. I'm fairly sure I read that cometic makes a 0.070. At 0.020 this gives me 0.050. I'll for sure be checking all 4 corners.
So much for quench. Had I known about this quirky piston design I'd have found something else. Too much faith in the machinist who picked it out I suppose. Since I've used one for mock up I doubt I can return them.
If I can't find at least a 0.060 gasket I'll be asking for a piston exchange anyway, or the machinist can shave them a little at his cost. Then we may have an issue of the balance.
Edit
So I did some measuring of things.
Piston to deck stats:
Step up is 0.020 above deck.
Piston rim is 0.070 below deck.
Dish is 0.150 below deck.
I figured out KB uses the step up portion as the compression height by measuring from the pin hole, adding half the pin diameter.
Pin hole to rim ranged 0.868 to 0.880. Half the pin is 0.492. Step up is 0.090 above the rim.
0.880 + 0.492 +0.090 = 1.462. The spec is 1.465
Oddly every piston had one side around 0.010 higher than the other. Not sure if that's by design.
I had to scratch my head a little to decide how to do the CC. I decided to start with the step up reference point at zero deck.
CC of the cylinders with piston 0.5" down from there is 131 cc.
Using the formula to get 1" of cylinder volume (d/2)squared x 51.48
(4.030/2) squared x 51.48 =209
Divide by 2 for volume of a half inch is 104.5.
131 - 104.5 =26.5 This is my total dish volume below the step up.
Spec is 25 cc. I think its worth doing to have the SCR nailed down.
I ran the calculation with a 0.070 gasket because KB calls for a minimum 0.040 clearance from piston to head. I'm fairly sure I read that cometic makes a 0.070. At 0.020 this gives me 0.050. I'll for sure be checking all 4 corners.
So much for quench. Had I known about this quirky piston design I'd have found something else. Too much faith in the machinist who picked it out I suppose. Since I've used one for mock up I doubt I can return them.
If I can't find at least a 0.060 gasket I'll be asking for a piston exchange anyway, or the machinist can shave them a little at his cost. Then we may have an issue of the balance.
