Measuring Deck height, Compression, and pushrod questions

[Rustang Racer]

I'm gonna be pulling the head of my '77 250 next week to install a Clifford 264H cam. While the head is off I want to measure the deck height so I'll know what size the combustion chambers need to be on my other head that I'm working on for later. So how do I measure the deck height? Is it from the top of the piston to the deck or from the piston ring to the deck?

Also, I will be switching from non adjustable rockers (1977 250) to adjustable rockers (1965 200). Will the pushrods from the 77 250 work with the adjustable rockers when installed on the 250?

One more thing. What parameters should I use in the falcon six Performance Compression Calculator for the 250? I used:
Bore 3.68
Stroke 3.92
CC 62
Head Gasket Thickness .05

Doing this I got a 9.3:1 Compression ratio. That seems too high. I thought it would be more like 8.7:1. What did I do wrong? Do 250's have a bigger dish in the pistons than 200's?

 

[addo]

You get bigger numbers than a 200 because of the extra stroke. I don't have DD2K or any similar, but these programs may be able to give you a dynamic CR with your nominated cam. It would be interesting.

Adam.

 

[Does10s]

You will need to get new pushrods. They need to have a cup in one end and a ball at the other. www.fordsixparts.com sells them.
Later,
Will

 

[mugsy]

Deck height is measured from the top or flat surface of the block to the top of the piston. I am familiar with the 200 because I own one, those pistons has a dish in the center. The height is measured to the "ring" around the piston parimeter, not to the bottom of the "dish".

As for your calculation, also include the deck height, this can change the compression ratio quickly and significantly. I have seen stock type motor with the piston "down in the hole" from 0.010 to 0.030. On my "stock rebuilt" motor one piston was over 0.060 below the deck.

Mugsy

 

[CZLN6]

Howdy John and All:

FoMoCo compensated CR for the longer stroke 250s you increasing deck height. My '72 250 measured .150" down. I've heard of numbers from .120" to .150". Add to that an aftermarket composite head gasket and kiss your quench good-bye. You can deal with this design short coming when you rebuild you block.

Nugsy and Will have you covered on the Pushrods and How-to measure deck height. Just make sure your piston is at top dead center and that you are measuring a clean piston top area, just above the pin. It you measure the sides, piston rock will give you a false reading.

Be sure to clean up the piston tops while you have the head off. You might want to CC you head while you have it off, just to know for sure, what the volume is.

Adios, David