This is in my other thread, but i thought it might be worth it's own post because it's not specifically about the heads persay.

So, Phil, your idea sounds like what i was thinking, and yeah, basically i'll probably end up saving my whole 74 engine for rebuilding at a later date. But for later this summer, I've also got a 75 motor that i'll clean up and get decked probably and stick the cleaner head on it with an 030 gasket and a new D cam and what not and call it good for now. That should be enough of an increase in power and efficency over my current setup of a 71 b20b with 42mm intake valves and what i suppose is a C cam that seems to stop pulling above 5k rpms... Not fun... So, a tighter squishing D cam engine with 44mm intake valves and my lightweight 8bolt flywheel and i should be having some more fun i think.

So, should i have this cleaner head resurfaced before i install it though? I think if I go this route(the one above) all I have to do is have my block decked however much i find i need to by looking at how far the pistons come up in the 75 block as is, and the head resurfaced and then get a new cam and lifters and associated stuff and a new timing gear setup of my choice... Thoughts?
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new sig in progress...

I have some input that seems to fit here - but then I ALWAYS have input, don't I?

My Dad and I raced PV544's back in the late 1960's through the mid 1970's. Our engines were a large part of our success. We always used the B20, and shaved the heads as well as decked the blocks. Compression ended up in the 14:1 range.

In fact we blew the porcelain center out of more than one spark plug!

In addition to a hot cam, we added much larger valves and used the Weber carburetor. As I recall, VW valves were perfect for the setup, but I don't recall the specifics.

The problem we had to overcome was the high compression continually blowing out the head gasket. In the end we machined a groove into the top of the block around each cylinder and installed a copper O-ring along under the head gasket. We never lost a head gasket after that, even though we had to carry an extra set of spark plugs!

While a 14:1 compression ratio is far too high to use with the crappy commercial gasoline we get today, the O-ring would be a good idea if you start having problems with head gaskets. If I were blueprinting a B20 I'd have it done as part of the build.

Also, the Carter H6SU's were better for performance, but took too much
'fiddling' to keep them in tune. Thus the swap to the single Weber carb.

I congatulate you on your racing success and on the development that went into your engines, but I must suggest that much has been learned about what makes power in the past 30 years -- and that applies to archaic things like B20s as well.

The reason for decking the block is not so much to raise compression as to improve combustion efficiency. There's also a lot that can be done with the shape of the combustion chamber in that regard, and also to transfer the burn energy more efficienty to the pistons. There's a tradeoff in the shape between efficiency and flow which we try to balance, and port volume versus flow velocity -- smaller ports that don't look remarkable on a flow bench, may actually result in more power and torque in actual practice.

It's now possible to have a fully streetable B20 (runs happily on 92-octane unleaded) that outpowers full-on race motors from the '70s...

Kyle,

I wouldn't deck a block without doing a blueprinting job on it, because tight squish requires that the bearing clearances are accurate and the rods are all straight and the same length, etc. In stock, used form, we see piston heights vary a lot.

It's not the decking that costs, but all the other work that makes the motor precise enough to run tight squish without danger of a piston hitting the head.

So for now, I say if you have a solid block, leave it along, shave the good head about .040" (assuming it's close to stock thickness now -- check!), use a .030" head gasket and call it good.

All right, Phil, here's a question I've been wanting to ask for a long time, but didn't dare to for fear of exposing my ignorance. But what the hell, it's the last day of the year, so let's live dangerously. When you guys refer to "blueprinting" what do you mean? For a while I thought it had something to do with revealing hidden fractures in metal parts, but now I'm beginning to think it means measuring engine components to assure they are within the designed specs and then rectifying them. Am I getting warmer?
Bob S.

You're close, Bob. Blueprinting means machining an engine very accurately, and to specific dimensions.

For instance, the factory specs for certain bearing clearances might be .0015" - .0030", and as long as each bearing falls within that range it's considered accurate enough. On a blueprinted motor, we might specify .0028" for those, and the clearance for each bearing in the set will be machined to precisely that. Similar improvements in precision apply to setting endplay, parallelism and perpendicularity throughout the motor.

In factory motors the rods may vary a few thousandths in length. That's no big deal with the large piston-to-head clearance found in stock motors, but we're trying to reduce it to essentially zero at peak RPM and operating temperature. Any variance in piston height relative to the block deck can obviously be disastrous in this scenario. Many machine shops are not equipped to correct this.

After all that, everything gets balanced by removing metal. Like reciprocating parts all weigh the same, and rotating parts don't have a heavy or light side (there's more to it, but you get the idea).

The result is a motor that's vibration-free, runs with reduced friction and stress, and is uniformly strong. I'd say blueprinting and balancing adds $500-$800 to the cost of an "average" rebuild so it's generally done only to motors that will be receiving expensive performance mods, but any motor will benefit.

Thank you, Professor, that was indeed a lucid explanation. Almost makes me feel I should retrieve that B-20 block from the scrap pile where I dumped it, mate it with the B head I still have, and have the whole job done for the fun and beauty of it.
May good fortune pursue you relentlessly in this new year.
Bob

I agree. The pistons were essentially flush with the deck on my '75. That's pretty much my plan, .040" off the head and replace the externally leaky .030" HG that's already in place. Then get the SU's rebuilt, which may or may not happen this summer. And after that, just drive the damn thing and be happy with it. Yeah, right.....
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Andrew - B20 dreaming of turbo