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'80 720 L20B


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1 hour ago, datzenmike said:

They are for 1mm over size L18 pistons. Replacement pistons would always have the same dish to keep the compression ratio similar.


I wound up actually finding a Z22 crank/block that I'll build the big bore with.  I think the Wiseco K586M89AP pistons are my best shot with the closed chamber head.  If my math is correct it should put about 9.7 compression.


I'll keep the L20 and turbo it at a later date.

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I tried one of those on line calculators and it was terrible.... besides being in inches. Asked too many questions about cam timing and degrees. Yes your cam does intimately affect your compression but all I want is something that compares apples to apples. I assume that a builder will know that the actual compression varies with engine speed/volumetric efficiency and the cam he selects. That's their problem.


I work with cc's and mm's

1/ Combustion chamber volume

2/ Crushed gasket volume (I use 1.2mm)

3/ Volume above (negative) or below the deck (positive) the piston rises to at TDC

4/ Bore and stroke cylinder volume

5/ Piston dish volume


Add 1/ through 5/ and divide by 1/

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I think the Z22 block bored out to 89mm and using stock Z24 dished pistons is the way to go with a closed chamber head, 8.9 to 1 compression ratio and it will run fine on 92 pump gas, it has torque and freeway rpms with a stock L20b cam, been driving mine for 8 or 9 years now, I did have to do a head gasket recently, but I run regular gas and had it timed at 0 degrees until I re-curved the distributor, it's timed about 7 degrees BTDC now, if I had been using 92 I likely would have had to do nothing to the distributor.

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Yes you can use the Z22 rods, that is what I did on both my LZ23 builds, I use Z22 block/crank/rods, I use stock dished Z24 pistons, and I used my custom closed chamber head(basically a 219 head), my compression ratio is 8.9 to 1, and I use my truck as a truck and I tow a trailer behind it also, it has a shitload of torque(stock L20b cam), on the freeway it is  alright towing the trailer, but empty and no trailer it really goes.

There is some more involved, you need to make sure the block is not cracked around the center head bolt hole and the water jacket on the passenger side as I recall, and you have to drill some coolant holes in the Z22 block for the L head, you also use all the rest of your L block stuffI(oil pan/engine mount hardware/timing chain cover/head) to install the Z22 block in your 720, basically it is an L block without any of the Z block stuff on it.

This link below of my LZ22 build shows the cracks I am talking about, I used the block anyway as these were not very big cracks and i have never had an issue because of them, but I was taking a risk, the link also shows the coolant holes I had to drill in the block, I don't know if you can see the photos(may be blurred) unless you have the photolame fix(extension) that is available, sorry but this is when Photobucket was still a good photo hosting site.



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Right. Just sand the edges with emery cloth or a file to make sure.


I sand all the bearing saddle edges (in the block and on the caps) to knock off the sharp edges anyway. This ensures that when installing the bearing shell, you don't put a scratch in the backside, which can cause bearing clearance issues.

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