I just got the head off my slant, and the deck height is approximately .195, though this is a rough estimate, as I can't find my digital calipers. Still, it's close enough to realize it's going to take a whale of a grind job on my cylinder head to get the compression up to anything useful.

This engine has been rebuilt before... Do aftermarket pistons have even lower CR than stock?

Many aftermarket pistons are 'decompressed' if memory serves it's only about .010" though. The last unmolested 225 I measured had the pistons .187" below deck.

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Joshua

This is typical on a stock engine / Piston/ Rod combination.


There are a few ways to change this. - Use 198 Length rods in a 225 Block or Mill~ .100" off both the block and head (check you Piston to Valve clearance!) With stock 225 pistons / rods.


Greg

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http://www.youtube.com/hyperpack

Key here is OR. and ALWAYS MEASURE your block and head. If the motor has been rebuilt before it most likely has some cut off the head to "clean it up".
If you cut more than about .150 total off your head and deck you will NEED new pushrods. Smith Brothers has them fairly cheap.
My 02.
Frank

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Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered

When I rebuilt Linda's engine, the deck on the pistons dropped them down the hole quite a bit. About 20 if I remember right.
The pistons in it were 30's, the new ones 60's. (It was a mess. I think somebody tried to run it with some sort of additive. Tore it all to hell when the goop plugged the ring lands up.)

Anyway, yes, the compression height needs to drop down to keep the compression in check when the bore is increased.

CJ

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Part of Tyrde-Browne Racing

Well...sort of good news. Apparently, I had been going off the radius'd edge of the piston for my height measurement and I now have a far more accurate... Tada! .175 instead of .190 It's not huge, but it helps