psy4s

OK, OK Now what?
I have used three programs to estimate compression, and have three numbers. I want to keep my 383 at 11-1 or under 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



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...alculator.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

psy4s

I did run the cranking compression Calculator
http://www.not2fast.com/turbo/compre...pressure.shtml
and it shows with my cam I am actually getting actually 10.5 while running if it is 11-1, and 9.2 if I am running 9.7, and if this is correct, I could even do ok with pump gas High Test if running what looks like 11-1.

vetteoz

iTrader: (13)

Dynamic Compression ratio ( DCR ) not static compression ( CR ) is the determining factor and that is determined as much by whatever cam you choose to run.
Long duration cams bleed off cyl pressure so effective CR ( DCR ) becomes lower
You need to know what cam you are going to run before deciding final CR of a build.

Read
http://www.kennedysdynotune.com/Dyna...ion%20Tech.htm
and
http://members.uia.net/pkelley2/DynamicCR.html
for a better understanding of how it affect your engine

Download and install this calculator ( the most accurate around )
http://cochise.uia.net/pkelley2/dcrvb6.zip

Does static CR and if you enter your cam specs gives DCR

Guest

Based upon the data you posted, they're right. That should be just fine with high octane fuel and aluminum heads. DCR is a better way to run the ragged edge of as much compression as you can, but can be risky bumping the limit.

Whats the cam you were planning on?

psy4s

lift @valve
IN 0.492
EX 0.509
OPEN
BTDC 1 DEG
BBDC 48 DEG
CLOSE
ABDC 33 DEG
BTDC 6 DEG
CENTERLINE
LOBE SEP 112 DEG
INTAKE CENTER LINE 107 DEG