Firstgens.com

OK, OK Now what?

I have used three programs to estimate compression, and have three numbers. I want to keep my 383 under 11-1 so I can run pump gas. My pistons are MAHLE

MAHLE forged pistons flat tops SBC-425030F05. +

Bore 4.030

Stroke 3.750

Rod 5.7

Comp Height 1.425

Weight Grams 458

Dome Volume -5cc

In their listing it says,

BORE 4.030

STROKE 3.73

ROD 5.7

DOME VOLUME 64CC/76CC 11.3/9.9

PART# SBC-425030F05

My Rods are Eagle H-Beam 5.7



Most heads for SBC are 64cc-65cc chambers but for safety sake I thought I would go with AFR #1038 with 72cc chambers. I do want over 10-1 compression and now I have more questions than answers. I do want to run High Grade pump gas. Any ideas as to how to proceed. I dont have the heads yet,



I ask the guys at an engine shop and they told me I would only have 10.5 with 64cc heads, so I stated running programs.

http://www.rbracing-rsr.com/compstaticcalc.html

said I would only have 10.6-1 with 64cc and 9.75-1 at 72cc

http://www.race-cars.net/calculators/co ... lator.html

said I would have 11.1-1 compression with 64cc and 10.1 with 72cc

http://www.csgnetwork.com/compcalc.html

said it will be 10.5-1 and 9.73 at 72cc



Engine cylinder Bore 4.030

Stroke Length 3.75

Head Gasket Bore 4.2

Compresses Head Gasket Thickness 0.41

Combustion Chamber Volume In CCs 64

Piston Dome Volume Negative for dished -5

Piston Deck Clearance .020

If the piston to deck is .020 the compression will be 10.38 with 65cc heads & a 39 thou gasket
The new AFR heads are 65 & 75 not 72cc

Also if you email or PM me I may be able to save you a buck or two on the AFR heads

I use Pat Kelley's DCR calculator, which figures Dynamic Compression Ratio taking the camshaft into account.

I'll get it posted in the document downloads section later, might make for some lively discussion.