Hi guys, I've been browsing through the great BrickBoard a bit, but couldn't find what I'm looking for:

I've got a B18A with a nice head, hardened seats and mildly ported exhaust ports, but cilinders are worn, and the engine starts to consume some oil.
I also have a B20 block with rather good pistons but no head.

Can I put the B18A head on the B20 block (using a B20 gasket)? I know it 'fits' but how would such a setup run?

There would be a larger quench area since the actual CC is smaller, but I can't imagine that would be good for flow. Any thoughts, anybody tried?

Thanks in advance, cheers Ben
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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

My main question would be... what year B20? If its a later one with metric bolts, them metric bolts might not fit through the smaller holes in the head... or maybe they will... maybe its the other way around.

Past that, I'd say go ahead and give it a try... but I'm not gonna say it'll work well... or at all for that matter...

-Matt
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-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC

Check out this article: http://www.vclassics.com/archive/badmotor.htm

Go ahead drop the damn head on already. I put a b18 head on a .o3o over b2o block with a weber and headers in a 122 estate and flogged it for 12yrs. It did diesel a bit, though, but it ran like a raped ape.

What kinda horsepower did this bastard/hybrid engine produce? 60? 70 maybe?

Yeah - an engine like that will run and you can suffer through driving it. Won't run all that well compared to a stock engine. Probably make real good torque, but only across a real narrow rev range (say, 3000-4000), have fewer horsepower than any stock engine Volvo built between 1955 and 1988, have more problems than any stock engine, be more prone to fouling plugs, less economical and more likely to clog the combustion chambers with carbon than a stock motor. Dieseling is a sign that something isn't right. Makes more sense to correct it than ignore it.

Good motor: B18.
Good motor: B20.
Bad motor: B18 head on B20 block.
Bad motor: B20 block on B18 head.

All of 'em will run. If you think a mismatched engine will run well, you clearly haven't experienced a well built one.

skeptic

If you think a mismatched engine will run well, you clearly haven't experienced a well built one.

Perfectly said! And too many people haven't.

If you think a mismatched engine will run well, you clearly haven't experienced a well built one.

The gentleman who began this thread was talking about materials on hand- b18 head, b20 block. If price is no object, then by all means spring for the latest and most expensive parts; it's pretty obvious that those will work the best. However, having worked on Volvos professionally for 25+ years (often for individuals for whom price WAS an issue), I can say that the b18 head will work fine on the b20 block.

The gentleman who began this thread was talking about materials on hand- b18 head, b20 block. If price is no object, then by all means spring for the latest and most expensive parts; it's pretty obvious that those will work the best.

Yup, that's indeed the case here. I think we all know that a B18 head suits a B18 block the best, and the B20 head realy belongs to the B20 block. But that does not mean that interchanging parts can't be done. (although I would never fit a B20 head onto a B18)

Even though it might not be the best setup you could think off; the B18 head on the B20 might still be a better engine then the B18 as it is at current (with it's worn pistons & cilinders).

Anyway, I'll see what I decide on. If I do go ahead, I'll post the results, hopefully it runs like a raped ape aswell ;) LOL...

Thanks and cheers, Ben
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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

This job is a quick one- 2 to 3 hours. Also, I didn't use a thick head gasket. I used a stock B20 gasket. Compression ran 190 each cyl. It's simple- do it.

I guess this quote would aply to me then:

"Because the B18 head and B18 combustion chambers were carefully engineered to match the B18 bore. The shape of combustion chambers is critical in controlling burn characteristics, resisting detonation and pinging while translating the chemical energy in the fuel into kinetic energy in the pistons (we're talking "squish" and "quench" here). What had changed?

A major factor in determining compression ratio is the area of cylinder wall swept by the pistons on each stroke. The swept area rises steeply with an increase in piston diameter -- long story short, the big bore pistons jam an increased volume of gas into the old combustion chambers. The B18 big bore kits therefore come with thick head gaskets (.080" vs. .050") to keep the compression within reasonable limits, effectively increasing the volume of the chambers by making them taller. This results in chambers not only too narrow for the bore, but also too far away from the pistons."

But, yes, I am aware of that. But since the head is an A-head it has low compression. With the petrol here in europe (or LPG which has octane number > 100) High compression would be no prob (better even). I do guess that the burn characteristics and gas flow might be a problem though.

What if I would just cut the edges of the CC on an angle (where they normally match the bore)?? Like so: (blue is B18 bore, green is B20 bore, red bying the new CC shape)



Would that work? (Btw, would that also work for a B20 head on a big bore B20 block?)





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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

Yes, that's the idea, and you'll find that the straight surface on the side opposite the spark plug will naturally move back a few mm as well. Cut it all back the same amount, so it remains straight -- not a figure-8 shape.

Pic below is of chambers taken out to 93mm and using 46/38.5mm valves, so the straight side has shortened a lot... but it's still straight. (Sorry it's blurry, best I've got.)

However, you'll still have the smaller intake valves and ports of the B18 head. Wouldn't it be easier to recondition a B20 head, assuming such things are not rare where you are?

Well then it would be not quite like what I had drawn. It would be like this then:



But then, would it be ok if I cut the walls of the CC on an angle instead of straight? (just easier to make it like that) Like I've drawn in the first sketch.

--
P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

I think the walls should start out pretty much vertical, and radius down to horizontal like they originally did. I'm not expert enough to tell you what would happen if they slanted, though.

The slanting would be fine on all sides but the quench areas (you want tumble there). Insofar as the shape is concerned, a "figure-8" is considered the best chamber shape for two-valve heads with a spark plug in the middle. Of course, realities of construction make that nearly impossible. If there is enough meat in the head without going into the water jacket you will be OK... There may not be that kinda metal to work with.

More likely, you will end up making is less angled and more "dished" in an attempt to get more volume so your static CR isn't astronomical.

Mike!

Insofar as the shape is concerned, a "figure-8" is considered the best chamber shape for two-valve heads with a spark plug in the middle.

That seems to be the common wisdom about that, but not everyone would agree. The guru I use says 8 is a fine shape if you don't mind reduced VE and how the combustion pressure transfers less efficiently to a *round* piston (his emphasis).

This is about the point where it gets beyond my current understanding of the theory, but I have yet to find anything the guy has told me that didn't produce the results he said it would. Come take a ride behind the motor with the head I showed in the pic, and you won't be surprised -- you'll be shocked.