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Finally getting back to the 545 in the drag car. Installed the crank and pistons in 4 corners and measured how far in the hole they are. All measurements are at .023" but one (is .020" but was probably user error).
Pistons are Probe forged dish (for SCJ), crank is 4.5" Lunati forged, and rods are 6.8" Lunati 4340. Heads are FMS SCJ (no porting or valve work yet). No cam yet, but as I recall SCJ's can't take more than .700" lift.
Have Felpro .041" head gaskets, so thinking I need .020" off the top. Am I on the right track?
 

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Following.... I just checked my D9TE block w factory replacement pistons and got about the same results, so I'm curious on this one...
 

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I would have the block squared not decked. Take it don't to .010" deck clearance. With the gasket thickness that'll still give you .051" for piston/rod expansion.
 

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Guess it depends on what final static CR you want.
I wouldn't go more than 0.020.
 

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Not much squish area on those Probe pistons.
The flats on the piston should mirror the flats on the head to optimize the quench... heart shaped for SCJ. Then... mill out the valley to achieve the desired compression ratio.

Regardless of off the shelf or custom pistons, the quench should run 0.035 to 0.060 max. Any more is like running D2 heads and the comp ratio should be lowered accordingly to prevent detonation.

I shoot for zero deck and use head gaskets to set the quench (0.042 - 0.048). I also measure the piston with a dial indicator at the center line (front and rear) to prevent errors with piston rock.
 

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Not much squish area on those Probe pistons.
The flats on the piston should mirror the flats on the head to optimize the quench... heart shaped for SCJ. Then... mill out the valley to achieve the desired compression ratio.

Regardless of off the shelf or custom pistons, the quench should run 0.035 to 0.060 max. Any more is like running D2 heads and the comp ratio should be lowered accordingly to prevent detonation.

I shoot for zero deck and use head gaskets to set the quench (0.042 - 0.048). I also measure the piston with a dial indicator at the center line (front and rear) to prevent errors with piston rock.
I didn't deck my 545, I just had it cleaned up and squared, I am using the clegg billet 4.5 crank the 6.8 rod H beams, and 65 cc aluminum head mahle pistons, sce gaskets and a DH blower intake 871 no issues
 

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Discussion Starter · #7 ·
Trying to get in to a decent machine shop to get it squared and decked. Good news is it gave me time to verify piston clearance and it's where I want it at .0048. Need to get going on the C6 now....
 

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Not much squish area on those Probe pistons.
There is plenty squish pad relative to the piston crown's dish with the SCJ chamber shape in this particular combination. In fact, even a round dish would suffice (the D-shape is not mandatory for induced mixture motion).

The flats on the piston should mirror the flats on the head to optimize the quench... heart shaped for SCJ.
That's exactly what this piston crown does. It has dual quench pads specifically because the aluminum SCJ head has a more centrally located combustion chamber (compared to the original iron SCJ head), not to mention the more centrally located spark plug, etc.
 

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There is plenty squish pad relative to the piston crown's dish with the SCJ chamber shape in this particular combination. In fact, even a round dish would suffice (the D-shape is not mandatory for induced mixture motion).

That's exactly what this piston crown does. It has dual quench pads specifically because the aluminum SCJ head has a more centrally located combustion chamber (compared to the original iron SCJ head), not to mention the more centrally located spark plug, etc.

In my many conversations with Randy at RaceTec he stated that a .375" quench pad is more than enough when the chamber is more centered over the bore. Mirror dish or round seem to show little difference.

IE SCJ, AFR, P51 etc.

My dyno work has verified this over the years.







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