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how to build a LZ24 engine


Rat720

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Post #2 is for Rat720 for an '81 720 truck. You are posting in his thread and hence the confusion.

 

 

For a car application like yours....

 

I said:

 

A truck oil pan definitely won't fit.

A truck oil pan is deep at the back and a car is deep in the middle with room at the back for the steering linkage to pass.

 

 

IF your L20B is in a car then putting it on a Z series engine should work.

 

 

 

The following L series front cases will convert that Z 5 speed for use on your car but the 720 5 speed came it two different lengths. One 26" long will fit the other 31.5" will need the driveshaft shortened. Both will need the transmission cross member modified.

 

4 or 5 speeds

'75-'78 280z

'79-'82 280zx non turbo

'74-'79 620

'80 2wd 720 not 4x4

810

'81-'84 Maxima

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The length is different again probably around 30" so maybe a driveshaft modification.

 

OK the D21 Hardbody uses a 71C transmission. The 720 and earlier are 71B transmissions. An L series front casefrom a 71B will bolt on but the counter bearing is larger in the 71C. You can simply pull the 62mm one off and us a 56mm from a 71B in place of it and the matching 71B cover plate. The 1st/2nd shift rod is also 16mmon the 71C instead of 14mm on the 71B so the hole for the rod needs to be enlarged and can be done with a Black and Decker hand drill. Now the big problem is the 71C gears are wider and the front counter drive gear will rub the case. Some machining is required by a shop. No way around this. If you go ahead with this I can give you come specifications for the machinist.

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Sounds like I need to find a 720 5 speed....lol.

 

If I still lived in Bakersfield I wouldn't bat an eye on still using the D21 5 speed. But I moved to NorCal in a small town 6 months ago and there are no machine shops that will attempt it. I already tried with having an aluminum blower snout I needed turned on a lathe for another project. They all looked at me like I was from Mars.

 

The source for the Z24 is a small tow yard, but I think he might have a '86 720 2wd too. The engine in the '87 has less than 100k, not sure on the 720.

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Okay, I found a low mileage Z24 and manual transmission in that same tow yard from a '84 2wd 720.

 

Was a 4 speed even offered in '84? I know it's a manual, I can see the stick. I can't tow through the gears because the truck was rolled and the cab roof if caved in.

 

Thanks!!

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The Z24 crank does not fit without cutting the counter weights down and trimming the L block. There's a reason for rod stroke ratios. Short rods on long stroke increase the side loading on the piston near BDC.

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I know the crank counterweights have to have about 1/4" trimmed off and the block needs clearance.

 

As far as the rod to stroke ratio, it's no different than a SBC 383 stroker using a 400 crank (3.76") and 350 rods (5.7") and I have literally built 100's for myself, customers, and friends. Still have one I built in 1996 and its still going.

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