>I know some of you out there know some about this so I thought I'd ask
>clarification on a few questions I have. I have an L20b sitting in the
>garage right now striped down to the block. I'm doing a total rebuild.
>Right now I'm debating weather I should bore it out 2mm and put a z22s
>crank, rods, and pistons in or leave it as is. My calculations seem to
>bring the compression ratio pretty high though with the first option (around
>9.5-9.8:1). I have a u67 casting head that I'm putting on. Does anyone
>know if this is right? This is going to be a street driver. Also does
>anyone know where I could get a crank from a z22? Every parts store I've
>tried can't get one and I don't really want to have to tromp through junk
>yards to try and find one. I may have to wait till it warms up to get one.
I'm pretty sure the U-67 head can be found with both small and large
chambers. You may want to have yours cced to be sure. Obviously stuffing
the increased swept area created by a 2mm overbore and the longer Z-22
stroke is going to pump up the CR a bit. A couple of folks on the 510
list have really good sites with various block/head info and specs. Take
a look at Jason Gray's site <http://home.att.net/~jason510/>. There are
some good links off of the Dime Quarterly site
<http://dimequarterly.tierranet.com/>, too.
A couple of head issues to keep in mind. Chamber design can be as
important (if not more so) in controlling detonation as greater chamber
volume, so while a larger open chamber can contribute to detonation a
smaller well designed chamber can actually help prevent it. You can
moderate a higher static CR with a a longer duration and overlap on the
cam, but that usually reduces low end grunt which is one of the main
reasons to build the bigger motor in the first place, IMHO.
The best source (down here) for the Z-22 bits are engine rebuilders and
JYs. I'm sure dealers can order the parts, but they'll probably be very
expensive compared to these other places. I'll be looking for a fairly
clean JY Z-22 for the internals. I can't offer any idea on prices, but
I'd guess under $200 for a complete good short block, whereas I'd expect
the dealers to want at least that much for a crank.
There are potential problems with the Z-22 piston which are low pressure
castings and don't like frequent or sustained trips above about 5K. That
may not be a problem in a daily driver. Custom forged pistons run about
$120/each, but going that route might allow reducing pin height enough to
use longer rods and reduce rod angularity. You might want to start with a
Z-20 rather than the L-20b as the Z-20 will (supposedly) take a larger
overbore than the L-20b.
If you're going to rebuild the L-20b anyway it seems to me that using at
least the Z-22 crank, rods and pistons to go to an L-22 is a no brainer
for me. The only added costs are to get the Z-22 parts. Low costs for
relatively big gains, usable all the time.
Feeding one of these things is another issue and I've probably rambled
too much this time.
FWIW,
Ron
Ronnie Day
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ron510@mac.com
ronday@home.com
ronnie_day@acd.org
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Dallas/Ft. Worth
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'71 510 2-dr (Prepared Class Autocrosser)
'73 510 2-dr (Street Toy)
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