250 Compression ratio

[Anonymous]

Tomorrow, I am planning on dropping off a D5 head to get it freshened up. New valves, springs, open up the manifold opening for a 350cfm Holley and for some milling. The head will be added to a stock 250 engine. I'm not looking to build a racer, just a good dependable running comuter engine. I want the compression to be around 9.0:1. Can anyone tell me what the compression ratio is for a 76 250cid engine?
Thanks,
Ken

 

[CZLN6]

Howdy ken:

The stock OEM Cr for a '75 250 is rated at 8:1. They typically have 62 cc chambers.

The down side is that you will be replacing the stock OEM .025" steel shim head gasket with a composite type. Depending on brand they will measure from .045" to .055" thick.

IF you were to mill the head .050" and used a FelPro gasket the new CR will be aproximately 8.6:1. That's assuming a typical .150" deck height and a standard bore. If the deck height is different, let's refigure.

Same assumptions but milling .070" will yeild a CR of 9:1. That's also assuming that the chamber volumes are now 48ccs. Be sure to meaure before reassembly.

Also be sure to use hardened washers under the head bolts on reassembly.

Adios, David

 

[Anonymous]

Thanks David,
Hardened washers? Where so I get these?
Thanks,
Ken

 

[Anonymous]

"so" should be "do"

 

[CZLN6]

Howdy Back Ken:

Sorry I missed your reply question. I used a set of hardened washers for a Chevy 250 six.

You can buy new from Mr. Gasket, part # 87, from most Autozone type stores, or Pioneer #S-1018 from NAPA.

How's your head rebuild coming?

Adios, David