B18A to B18B - how much to skim off head?

[warninglight]

My 196 Amazon has a B18A with 36VN carb in it. I've just removed it to do a few jobs, and want to upgrade it to B18B spec, which I understand is a cam, a head skim, twin HS6 and a better exhaust.

From what I can find online, the B18A has either 8.5:1 or 8.7:1 CR, and the B18B (or the most powerful one at least!) has a CR of 10:1

Does anyone have any info on how much material needs to be skimmed from my A head to get to, or close to, 10:1? As far as I can see, head gasket changes can alter it on the B20, but I can only see one gasket available for the B18.

Thanks!

[Ron Kwas]

wl;

Your understanding of what it would take to improve performance is correct...Heights of the Cyl head for various Comp Ratios should be listed in the shop manuals...I'd recommend going by that. I'd measure to see what you presently have and see how that corresponds to numbers in the book (it may have been previously shaved, and if that's the case, this needs to be taken into account). I wouln't go higher than 10:1.

Head Gasket thickness affects CR of course...ideally, you should measure volume of Comb Chamber, add vol of HG (squished! if necessary, measure and use thickness of old one.) and Displaced Volume, and run the calculations for CR.

Good Hunting!

PS; I see in you have a Laplander...a somewhat exclusive club...if you are interested in making contact with LL owners here, let me know and I'll coordinate contacts (I just recently helped another stateside owner do an Alt conversion on one).

[warninglight]

Thanks for the reply, Ron.

After a second look at my workshop manual, I found that I had the B18B engine chapter in the back, so it looks like, compared to the Type 1 B18A which I have (or should given the Zenith 36VN carb), it needs 1.8mm skimmed from it. I will of course confirm the measurements as they stand before I hand it over to a machine shop. I could go for slightly less of a skim, but everything else seems to be the same to squeeze 115bhp from it, so why not?

I'd love to get in touch with some Laplander owners in the States. Good information on them in English isn't easy to come by, and I still don't know much about them.

[jimbo1593]

aren't A and B head gaskets different thicknesses?

[c1800]

Lots of reading here, with links to more info.
Many things to consider, including the state of the rest of your engine.
Good luck!

https://www.volvoforums.org.uk/showt...ight=Skim+head

[Clan]

Originally Posted by warninglight

My 196 Amazon has a B18A with 36VN carb in it. I've just removed it to do a few jobs, and want to upgrade it to B18B spec, which I understand is a cam, a head skim, twin HS6 and a better exhaust.

From what I can find online, the B18A has either 8.5:1 or 8.7:1 CR, and the B18B (or the most powerful one at least!) has a CR of 10:1

Does anyone have any info on how much material needs to be skimmed from my A head to get to, or close to, 10:1? As far as I can see, head gasket changes can alter it on the B20, but I can only see one gasket available for the B18.

Thanks!

There were about three different thicknesses of head gasket , the B20 E had the thinnest ! i would go for that one , no B18 had a CR of 10:1 that was reserved for the B20E , with it's fuel injection it had a better control of the fuel mixture so didn't tent to "pink" . You should just put a complete 135 bp B20E engine in and be done with it :-) I would use the Bosch LH Injecton from a 940 , it should work very well .

[northNH]

B18B’s as used with 1800s, Amazons and 140s did have 10:1 CR.

I believe the CR sweet spot with today’s available fuel is ~9.5:1.

And many aftermarket head gasket thickness choices to mull over...

[Clan]

Originally Posted by northNH

B18B’s as used with 1800s, Amazons and 140s did have 10:1 CR.

I believe the CR sweet spot with today’s available fuel is ~9.5:1.

And many aftermarket head gasket thickness choices to mull over...

ahh yes the 108 bhp and 115 bhp versions all the lower versions were 9.5:1 ...

[Vintagewrench]

After having covered 10K plus miles on the road that also included 350 miles of vintage racing on the track w/a B18B in a 1800s over the last two years here is what was learned about running one of these high compression engines on today's available pump gas. The engine is relatively fresh and a compression test yields between 180 to 185 psi on all cylinders.

With the ignition timing set at spec one of these engines will run just OK on today's 93 octane fuel but will operate noticeably better and produce more power with 91 octane gas w/o ethanol and also get better gas mileage. Find some near you @ https://www.pure-gas.org

The best head gasket to use that produces the most HP, smoothness and fuel mileage is a Cometic multi layer steel gasket that is .028 to .035 thick. When rebuilding an engine check the piston to deck height and have the top of the block milled so that the pistons you end up using are flush with the top of the block. This will ensure the squish band https://en.wikipedia.org/wiki/Squish_(piston_engine) in the combustion chamber of this engine will be the correct thickness.

[jimbo1593]

In the UK octane ratings are minimum 95, with "super" unleaded being 97-99 RON.