Volvo B18D compression ratios.
 

I was wondering if anyone has data on B18 compression ratios. The information I would like is the head thickness for various compression ratios up to 11:1.
I am fully aware that combustion chamber volume is the true way to establish CR but I have a couple of heads, that when measured with a micrometer are significantly different in thickness. I presume one has been skimmed. As I am in the process of building an engine for my 544 I would like it to be tuned for fast road ( as they say!). I already have a D cam and followers and a set of KD needles for carbs. A 10:1 ratio sounds about right for this set up. If anyone has an approximate head thickness dimension for this CR I would be very grateful. Thank you in advance.

Here you will find the specs for the B18B Type 1, 2 and 3.

https://volvo1800pictures.com/docume...1800_1800S.pdf

Head thickness is on page 03-5

I believe the B18 A and D both used an 88mm head thickness with different gaskets for the slight variations in CR.

The 86.2 mm thickness of the type 2 & 3 head with the correct gasket should yield a 10:1 CR according to the 'specs'. Of course, how Volvo determined that CR is up for question. If it was calculated assuming the pistons flush with the deck your actual compression ration will be lower because if any B18 / B20 has pistons flush with the cylinder deck it is probably by accident. Check your assembled engine and you will likely find that the pistons all sit below the cylinder deck at TDC and all of them by different amounts (at least on my B20E). I don't know where the variation is - piston height or con rod centers or crank throws. As a result you will have different compression ratios on each cylinder and excessive quench zones which may turn your 10:1 CR into a bit of a pinger unless you retard the ignition. You might be able to minimize the variation between cylinders my mixing and matching pistons, con rods and crank throws. The pistons will still all be below the cylinder deck; but, there distance below may be more consistent.

You can partially fix the problem by decking the block so that the highest piston sits flush. This will give you a better quench zone and will help with balancing the CR between cylinders. To get it perfect, you need to deck the block to the lowest piston height and then mill the tops of the other pistons so that they no longer sit proud. At that point your piston, con rod and crank throw are paired so don't go mixing and matching during reassembly.

Head info

B18A (1) 1962-1964, head height 88.0 mm, compr. 8,5 : 1
B18A (2) 1965-1968, head height 88.0 mm, compr. 8,7 : 1

B18B (1) 1961-1963, head height 87.0 mm, compr. 9,5 : 1
B18B (2) 1964-1966, head height 86.2 mm, compr. 10,0 : 1
B18B (3) 1967-1968, head height 86.2 mm, compr. 10,0 : 1

B18D (1) 1961-1963, head height 88.0 mm, compr. 8,5 : 1
B18D (2) 1964-1966, head height 88.0 mm, compr. 8,7 : 1
B18D (3) 1967-19.., head height 88.0 mm, compr. 8,7 : 1

I hope this helps

Thanks for that information - Perfect👍