Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Compression Ratio Calculation
View Single Post
  #3 (permalink)  
Old 08-31-2012, 11:59 AM
F-BIRD'88's Avatar
F-BIRD'88 F-BIRD'88 is offline
Yada Yada Yada
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,284
Wiki Edits: 0

Thanks: 5
Thanked 399 Times in 393 Posts
I have built many of these 350 SBC's using the 416 heads with porting and larger valves.
The chambers end up around 61 to 64cc once the chamber wall is relieved for the larger valves.
(1.94x 1.60 best)
(assuming the heads were not shaved)

The only way to determine the exact real CR is to get the real measured head CC chamber volume and the real piston deck clearance @ TDC and the actual gasket thickness. and the piston valve relief volume.

Interactive JavaScript to Calculate Engine's Compression Ratio (CR)

Actual piston deck clearance can range from .055" in the hole @ TDC to 0 decked to a negative
( piston above deck, over decked block)

If it runs on 94 octane gas with 34 to 36deg timing and correct jetting and spark plug heat range don;t worry about it.

The Sunoco/ Petro Can Ultra 94 is pretty good stuff.

You are under 11:1 cr.

Typical head gaskets are 4.166" x .038 to .041"
or 4.10" x .015" stell shim style.
many flat top rebuilder pistons have a modifed pin height 1.54" resulting in a .045" to .055" deck clearance and lower than expected compression ratio.

1.56" is stock.

typical flat top piston valve relief volume is -4cc to -6cc

Running downt he 1/4 mile will tell you how much Horsepower you are making wiht this motor.
MPH and car weight w driver.
This combo should run pretty strong if the 416 heads were ported too.

( I have made well over 400hp with bigger cams and ported 416 heads)
The 224 106LSA .450" lift cam should run pretty good.
Will work best with a 3500 stall and gears for best ET.
Reply With Quote