Combustion Ration on a 1679

[Snoopy1971]

Hi all. I had a hole in a piston face (see one of my previous threads for a pic), so I did a top end rebuild to maximize the biggest displacement size I could get without have to split or do any machining to the case. I used a top end rebuild kit from AA … 88mm thick-walled pistons, cylinders, and new heads bored out to accept the cylinders.

So I have a ’68, which has an H case that started life as a 1493. Somebody somewhere along the line bumped up the pistons to make it a 1585 dual port, and now the 88mm pistons bump it up to a 1679. I have stock 69mm connecting rods and I will assume I still have the stock cam etc, as I didn’t split the case. Valves on the heads are stock 35.5/32 size. Single 34Pict-3 carb.

What is an acceptable combustion ratio?

I measured my deck heights to be:

#1 - .049"
#2 - .051"
#3 - .049"
#4 - .053"


I measured my combustion chambers to be 48 cc (even though the guy at AA told me on the phone that they are 60cc.

So using these numbers in one if the online engine calculators (CB Performance, Jbugs etc), gives combustion ratios in the 8.5-8.6 range.

Is this acceptable or is it too high?

Also, I have always just used 87 octane gas, would I need to bump that up to 91 or 93 or leave it?
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1968 Bug

[67rustavenger]

My 1679 has 8.8:1 compression ratio, semi hemi heads, the heads came with the car when I bought it back in 2015.

I refreshed the engine two years ago, new bearings pistons and cylinders and had a local fella regrind the valves and seats.

I run 87 octane in it all the time. Never had an issue with it running hot or a lack of power.
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I have learned over the years.
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GFY's Xevin and VW_Jimbo!
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[NJ John]

8.5-8.6 is totally acceptable.
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1973 standard, yellow, lowered, 3” narrowed front, 1600 blo-thru turbo w/single dell 15.4@86, so far
11.41 et buggy. Long gone
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[Snoopy1971]

Great, thanks everyone!!
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1968 Bug