[Jack_K]

I know the cylinder head volumes, the head gasket thickness, and the compression height of the pistons (although I have no idea what that means). I have flat top pistons with two valve reliefs.

I've seen calculators for this but they want deck height. I didn't measure the deck height of the pistons so I don't know that. Can it be determined from the compression distance?

Jack

 

[fauxrs]

I know the cylinder head volumes, the head gasket thickness, and the compression height of the pistons (although I have no idea what that means). I have flat top pistons with two valve reliefs.

I've seen calculators for this but they want deck height. I didn't measure the deck height of the pistons so I don't know that. Can it be determined from the compression distance?

Jack

No Deck height cannot be determined from compression height. The compression height is the distance from the centerline of the wrist pin to the top if the piston, which deck height is the distance from centerline of crank to top of deck - these are unrelated measurements.

The standard deck height for a small block is 9.025 inches, if you had no material taken off the deck then that dimension should be good.

 

[ccc]

what isze engine and what size deads do you have ? with that info we can get you close but more info is needed.a 350 with flat top pistons and 64 cc heads can be between 10.3 to 10.6 depending on the other variables

 

[Jack_K]

what isze engine and what size deads do you have ? with that info we can get you close but more info is needed.a 350 with flat top pistons and 64 cc heads can be between 10.3 to 10.6 depending on the other variables

Yes, I know that. I need to know my piston to deck height and dome volume of the picton. Here it is with both of those set to zero, for lack of knowledge.
http://www.gtsparkplugs.com/CompRatioCalc.html

Nmbr cylinders - 8
Bore - 3.765 (305 .030 over)
Stroke - 3.48
Chamber volume 58 cc
Gasket thickness - .035 to .040
Gasket bore diameter - 4.00??
Piston to deck height - ??
Piston type - flat top
Dome volume - ?

 

[fauxrs]

The standard deck height for a small block is 9.025 inches applies to the 305
If your piston is a flat top, it has no dome and thus no volumn

 

[steelybill]

Without knowing the height of the piston, like proud of the deck, or down in the hole a bit, you will have a close figure, but not exact. But close may be only a tenth off in the calculations, with the volume figures you already have.

 

[ccc]

he will have volumn with the flat tops because of the valve reliefs. the flat top 305 was 9.5 because of the smaller piston area. piston deck height can vary with engine to engine there are too many varieables. it needs to be measured. is it a 2 or 4 valve relief piston ? figure about 5.5 cc s for the reliefs if its a 4 and less for 2. the deck height can be anywhere from .040 to .018. in 40 years of doing small block chevys i have seen them anywhere in that window

 

[steelybill]

Sounds like typical production tolerances !:smileyb:

 

[ccc]

got bad when they started doing the engines south of the border.:dontknow:

 

[Jack_K]

he will have volumn with the flat tops because of the valve reliefs. the flat top 305 was 9.5 because of the smaller piston area. piston deck height can vary with engine to engine there are too many varieables. it needs to be measured. is it a 2 or 4 valve relief piston ? figure about 5.5 cc s for the reliefs if its a 4 and less for 2. the deck height can be anywhere from .040 to .018. in 40 years of doing small block chevys i have seen them anywhere in that window

So it looks like about 10:1 I guess. That would mean 91-93 octane?

 

[ccc]

if you have the stock flat tops with the factory 58 cc heads you are at 9.5 and will run 85 fuel

 

[JJLT1]

with the 9.025 deck,, the +.025 is the normal production tolerance,,that would be an average..
as said,, i saw them from .015 to .032 also.. and is not equal front to back and side to side..

a normal 4 valve relief average volume is +6 cc,, so half that is 3,, could be more or less..
look up the pistons you used, it should be listed..

the gasket thickness/bore should be listed for them also..
.038 is a normal compressed thickness for the thick gaskets..

you can run cheap gas and be gentle on the timming curve or
run the good stuff and add a little more timming..
.
.i got 9.65 cr with these #s

Nmbr cylinders - 8
Bore - 3.765 (305 .030 over)
Stroke - 3.48
Chamber volume 58 cc
Gasket thickness - .038
Gasket bore diameter - 4.00??
Piston to deck height - +.025
Piston type - flat top
Dome volume - +3

 

[Jack_K]

with the 9.025 deck,, the +.025 is the normal production tolerance,,that would be an average..
as said,, i saw them from .015 to .032 also.. and is not equal front to back and side to side..

a normal 4 valve relief average volume is +6 cc,, so half that is 3,, could be more or less..
look up the pistons you used, it should be listed..

the gasket thickness/bore should be listed for them also..
.038 is a normal compressed thickness for the thick gaskets..

you can run cheap gas and be gentle on the timming curve or
run the good stuff and add a little more timming..
.
.i got 9.65 cr with these #s

Nmbr cylinders - 8
Bore - 3.765 (305 .030 over)
Stroke - 3.48
Chamber volume 58 cc
Gasket thickness - .038
Gasket bore diameter - 4.00??
Piston to deck height - +.025
Piston type - flat top
Dome volume - +3

The pistons have 4 valve reliefs so, if I use 6 cc, I get a CR of 9.31. It looks like 9.5 is about right.

Still, it depends on how much they had to surface the deck and heads. I have no idea.

 

[Jack_K]

if you have the stock flat tops with the factory 58 cc heads you are at 9.5 and will run 85 fuel

What's 85 fuel? If E85, I can't find any. If 85 octane, the lowest around here is 87. So 87 is OK?

 

[goodcruiser]

Jack as long as you're under 10.5-1 regular 87 octane should not be a problem.
http://wiki.answers.com/Q/How_do_you_convert_compression_ratio_and_psi