Looking for some advice on the thickness of a head gasket for the following:

B18D block bored with 0.040 pistons and a B18B head shaved 0.010, mildly ported.
2" exhaust
K cam
4-2-1 123GT manifold

I had 155 compression on all 4 cylinders with the standard low compression B18D head. Not really sure what to expect with the new head.

Any recommendations on the head gasket?

What is your objective? Do you want to run 87 octane or are you prepared to run higher octane. Was the block decked to establish the correct quench band. This will determine how much static compression the engine will tolerate without detonating. Un decked with a K cam - anything in the order of 10:1 will likely require 92 octane fuel. Decked with a correct quench band and you might do 10.5:1 on 87 octane - or so I have heard people claim.

Measure the clearance volume of the combustion chamber. With that value and your swept volume value you can play with various gasket thicknesses to calculate different compression ratios. There are various CR calculators available on the Web. Cometic makes B20 gaskets in various thicknesses. I don't know whether they make B 18 gaskets. If they don't, then you are constrained to using the original gaskets and may be limited in your CR options.

Thanks for the info.

I'm using 92/93 octane because where I live, few stations provide ethanol free gas unless it's the top grade.

I won't have access to my block to test anything until I remove the old head. But given that I have a pretty mild setup for a B18B head (it was decked 0.010), there must be some general parameters I can work with.

The most common B18B gasket is the .85mm and the most common B20/B18 gasket is the .80mm. Think I'd be safe with either one?

The thin, B18B headgasket is what you need, it will put the quench in the .035"-.045" range where it should be if you have the correct pistons. Don't let anyone tell you it needs to be tighter. You should drop the compression ratio a little with some chamber massage if you don't won't to put high octane in it. (Are you talking about 10% ethanol?)

Thanks for replying. This confirms what I've done so that's great. I purchased the 0.80mm / 0.030" gasket which is pretty widely available.

We have around 10% ethanol for the most part, with potential more to come in the future. I already put higher octane in so it's not too big a deal. Would be nice to put regular gas in but it's not a goal.

Thanks!

I did some back of the envelope chicken scratches while having coffee. The B18B head gives a nominal compression ratio of 10:1. Your 0.040 overbore increase the engines swept volume - easy to calculate. The 0.010 shave decreases clearance volume - not so easy to calculate because of the irregular shape of the combustion chamber; but, I took a guess at a form factor of about 50% of the full bore. I ignored the effect of head gasket variability and assumed that the pistons are flush with the head (which is what Volvo assumes when it provides the compression ratio specs).

If the B18B head has not been messed with, I guesstimate that you will end up with a compression ratio some where around 10.3:1 - 10.4:1. If the block is decked for flush pistons you should live happily with 92 octane fuel, the proposed gasket and no detonation. If the block is not decked, you may have to reduce the ignition advance just a nudge to avoid detonation; but, that is a may not a definite.

The k cam has slightly less overlap than the D cam I use which will result in a slightly higher static compression which may change the tendency to detonate. Only testing will confirm.

Thanks. This really helps me out quite a bit. It's been a journey just to find the right head gasket and then with all these little mods it's been tricky to figure out what the end product will be and the performance level.

What do you think the HP output would be, roughly, compared to an original 90HP B18D?

B18B / 0.040" pistons / K cam / mildly ported and decked
4-2-1 Siamese manifold from a 123GT
Full 2" exhaust
twin SU HS6 with high flow air cleaners

When you consider that the B18B as supplied in the 1968 version of the 144S for the US market provided 115hp with a 10:1 compression ratio, split exhaust manifold (1.75" exhaust pipes) and twin SU's and "C" cam you will probably see something in the 120hp range with the mods you've made. You will have picked just a couple or 3 of cubic inches displacement and your .010" head shave will get you less than a .5 increase in compression ratio.
I originally built a performance B18 for my '68 144S using a later (carbed - Canadian?) head with 44mm intakes, some porting and shaved the head from its very low 8.5:1 (as measured by deck height and compared to specs in a Greenbook) up to over 11:1 by taking .125" off it. I also used a "K" cam. Later I moved the head and cam to a 1969 B20 and figure I have something in the 135-140 hp range. I base that figure on having calculated my speed on the Watkins Glen back straight to be 115mph (over the original 1969 B20's 103mph top speed as measured by Road & Track magazine - which I know to be true as I received a "speeder" at that figure before I moved the parts to the B20 -- pleaded not guilty - reduced to 65mph). The 1971 142E that clocked 115mph as top speed by R&T was rated at 130hp. -- Dave

I'll take 120+HP and a 1/3 increase in power over stock any day!

Thanks for your reply.