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Z24 crank in a L20B


docbainey

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Medium block 2.4 Liter.

Stuff a Z24 crank and pistons into NAPS-Z or L20B block bored to 89mm by cutting down crank counterweights and clearance grinding block as per Ben Pila. This gives you a 2389cc L-series motor that doesnt require using defective (crack prone) Z24 block, fabricating timing cover, lengthening timing chain or modification to close hood. Z24 piston tops will need to be milled down slightly. Fedral-Mogul 33.8mm pin height pistons might not need milling? Click HERE for Bens write-up of necessary modifications.

Compression ratio with Z24 pistons and open chambered head is 10.25:1 before pistons milled.

parts: : modified Z22 block, modified Z24 crank, modified Z24 pistons, Z22S/ L20B rods

s/2+r+p: 227.7

piston deck height: 0.45 (above deck)

 

 

Stroker 2.3 Liter

Stuff a Z24 crank into a modified Z20/Z22/L20B block by cutting down counterweights as above.

No piston modification or block boring needed for 2283cc L series.

see http://hobbslaw.niss...om/custom2.html for an example

Russ noted that his deck height measured -1.77mm with the Z22E pistons that he first tried using, he eventually used milled Z22S pistons to achieve a higher compression ratio.

Parts: Z24 crank, Z22E pistons, Z22S/ L20B rods in a Z22 block or +2mm bored Z20/L20B block.

s/2+r+p= 96/2+145.9+32.1= 226.0 mm

piston deck height: -1.45mm below deck

 

In the Jason Gray topic they talk about stuffing a Z24 crank in a L20B but none of the links work. It mentioned about cutting the counter weights down. I was wondering how that affected the balance. And I guess a Z24 crank has the same basic dimensions as a L20B? Journal diameters and big end rod thicknes? Flywheel & timing sprockets & such? Does this really drop in?

 

Thanx!

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The throws and the rod caps will hit the L20B block. The throws can be turned down on a lathe but it takes multiple passes so you don't snap the cutting edge off. The block can be clearance ground so the rods clear.

 

There's a reason the Z24 block is two cm taller than the L20B. The stroke is much longer and needs a longer rod (165mm). Running a shorter rod (145.9mm) places the piston lower in the cylinder when the rod and crank form a 90 degree angle. This pulls the piston sideways in the bore and increases side loading friction. Yes it can be done... has been done, but not for a serious street motor that lasts.

 

 

 

Much easier:

L20B or Z22 block bore to 89mm. Fit KA24E pistons on L20B rods and bolt to a Z22 crank. Fit L20B oil pan, all timing gear and cover from an L20B plus an L head and you have a 2.3 liter LZ engine with 9.8 compression.

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Much easier:

L20B or Z22 block bore to 89mm. Fit KA24E pistons on L20B rods and bolt to a Z22 crank. Fit L20B oil pan, all timing gear and cover from an L20B plus an L head and you have a 2.3 liter LZ engine with 9.8 compression.

 

 

Take Mikes advice. I would not use a medium block 2.4 for street use either.

I am building a LZ 2.3 right now. I used an L20 block because I have 4 of them laying around. Since mine is 1/4 mile use only, I filled it with block filler to keep the cylinders from distorting. When I took it to two machine shops to have it bored, The first shop wanted $360.00 to bore and hone. The second wanted 250.00 to 300.00. So I took it home and bored it myself on my Bridgeport, leaving .010 for honing. It took ten plus hours to whittle it out, but turned out great.

 

What I learned from this is, to use a L20 block you will spend more money in machine work than the cost of a Z22 block, And end up with a thin walled block. Unless you get your machine work for free, use a Z22 block.

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As I've stated before in my KAZ24 build thread, there's nothing wrong with the Z24 block. All L series tend to crack at the head bolt holes, usually from over-torquing of the head bolts. Weld them up, good to go for another 200k. Just sayin'

 

But yes, sticking the Z24 crank in a 20b block isn't worth the 8mm more of crank stroke or whatever. Just use a Z22 crank, then you're up 6mm.

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There's a reason the Z24 block is two cm taller than the L20B. The stroke is much longer and needs a longer rod (165mm). Running a shorter rod (145.9mm) places the piston lower in the cylinder when the rod and crank form a 90 degree angle. This pulls the piston sideways in the bore and increases side loading friction.

 

Sorry Mike, but "pulling" is a bad choice of words. On the compression/combustion stroke cylinder pressure is forcing the piston into the outside wall~ the rest of the time the piston's pretty much just "along for the ride". In a low rod/stroke ratio motor this produces more side thrust in the cylinder wall opposite crankshaft rotation. The reason a long stroke motor needs a longer rod is for longevity. Reducing piston sideloading is paramount to a long-lived engine design. Look at nearly any over-the-road diesel (the ultimate in longevity) and you'll see rod/stroke ratios in excess of 2/1 and more. The greater the rod/stroke ratio the less internal friction, and more force is transferred thru the drivetrain for power to the pavement.

 

Peace~

Scott

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Sorry Mike, but "pulling" is a bad choice of words. On the compression/combustion stroke cylinder pressure is forcing the piston into the outside wall~ the rest of the time the piston's pretty much just "along for the ride". In a low rod/stroke ratio motor this produces more side thrust in the cylinder wall opposite crankshaft rotation. The reason a long stroke motor needs a longer rod is for longevity. Reducing piston sideloading is paramount to a long-lived engine design. Look at nearly any over-the-road diesel (the ultimate in longevity) and you'll see rod/stroke ratios in excess of 2/1 and more. The greater the rod/stroke ratio the less internal friction, and more force is transferred thru the drivetrain for power to the pavement.

 

Peace~

Scott

 

Yes. The longer the better but that's not practical in a car.

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I'm not sure if rod ratio is the issue here. A medium block lz24 has a rod ratio of 1.51, if I remember right. Most Honda's have a rod ratio thats about the same. I hate FWD's more that anyone, but Honda's go 200k easy. I think the issue is pulling the piston skirt out of the bottom of the cylinder with the increased stroke. If we could find a shorter piston that stayed in the cylinder at BDC, It might work out. Rod ratio is a very sensitive subject with some. Argument's always seem to start.

 

IMO, If you are doing any driving with sustained rpm's, stay with a higher ratio. Longer rod = slower piston speed= less demand on head flow= HIGH rpm.

 

Short rod = high piston speed=more demand on head flow= low rpm. Yes side load creates heat and wear. You just have to decide for yourself if it's worth the added CC's (It is for me)

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