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How much to deck?

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Post  Slowride June 6th 2022, 10:55 pm

Finally getting back to the 545 in the drag car. Installed the crank and pistons in 4 corners of the D9 truck block 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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Post  dfree383 June 7th 2022, 6:36 am

Measure again if you think it’s user error, sometimes they aren’t equal.
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Post  rmcomprandy June 7th 2022, 10:16 am

Slowride wrote:Finally getting back to the 545 in the drag car. Installed the crank and pistons in 4 corners of the D9 truck block 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?

The original decks are usually not perfectly straight to the crankshaft centerline.

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Post  Dave De June 7th 2022, 7:41 pm

A .003" difference is unlikely especially if its not a corner hole. However, you could have a few parts tolerances on the long side add up together to give it an additional .oo3"
I suggest that you re-measure using a large depth mic base that straddles the center of the cylinder so that piston rock wont influence the measurement. Then swap the .020" in the hole piston and rod with another and remeasure. To have one hole .003 different is most likely from the crank throw, rod length, or the compression height on the piston.

I had a similar build to yours but the block was decked to zero in the hole. The thin head gasket with short stroker pistons lead to minor piston strikes with the head on one bank. This wasnt good, you might want to leave the deck alone or run a thicker head gasket if decked to zero.

My build was a 547 with D9TE block, 4.5" RPM crank, Eagle rods, Diamond pistons and SCJ heads.
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