Sons first car. 521

[521aiden]

On 2/17/2022 at 6:45 AM, d.p said:

Do you already have 280zx flat top cams?  They have been NLA for sometime now and almost impossible to find.  

no i don’t have flat tops yet. i plan on buying them from someone who has some already but what i’m missing is a few gaskets pistons rings and some head and block work but not going to pull the trigger on pistons till i know what size i’ll need 

[d.p]

IMHO bore out an L20b block to 86mm and good luck finding 86mm 280zx flat tops to match.  If I could do mine over again I would have gotten flat tops.  But used what I had (dished). 

[datzenmike]

Find an '80-'82 A10 HL510 Z20S or the '80-'81 S110 200sx Z20E engine and ...

 

A/ rebuild it, preferably with 1mm oversize Z20 pistons and rings. Put your favorite L head on it and the timing cover, guides and chain from an L20B, or...

 

B/ get the 152.5mm rods out of it. Maybe you can still buy them new? Buy new 86mm (1 mm oversize) Z20 pistons and rings and bore your L20B 1 mm oversize to match. 

 

L20B and Z20 engines are the same block and use the same crankshaft so Z20 rods and pistons will swap into an L20B block. What you want are the Z20 pistons which are flattops. They have a shorter pin height than the L20B piston so the Z20 rods are longer to compensate. The smaller combustion chamber, better breathing L head makes a 10.11 compression 1997cc long rod L20B

 

Z28 flattops, if available, will be the same minus the long rods.

[521aiden]

2 hours ago, datzenmike said:

Find an '80-'82 A10 HL510 Z20S or the '80-'81 S110 200sx Z20E engine and ...

 

A/ rebuild it, preferably with 1mm oversize Z20 pistons and rings. Put your favorite L head on it and the timing cover, guides and chain from an L20B, or...

 

B/ get the 152.5mm rods out of it. Maybe you can still buy them new? Buy new 86mm (1 mm oversize) Z20 pistons and rings and bore your L20B 1 mm oversize to match. 

 

L20B and Z20 engines are the same block and use the same crankshaft so Z20 rods and pistons will swap into an L20B block. What you want are the Z20 pistons which are flattops. They have a shorter pin height than the L20B piston so the Z20 rods are longer to compensate. The smaller combustion chamber, better breathing L head makes a 10.11 compression 1997cc long rod L20B

 

Z28 flattops, if available, will be the same minus the long rods.

i have a z20 block l20 crank z20rods and i believe l20b pistons. the motor i have now was built by the previous owner and i was 15 when we assembled it so i don’t exactly know the bore or piston that’s in it. i’ve seen that the 280zx pistons were similar size and should work for the application im running a u67 now and i plan on atleast a port and polish and possibly some bigger valves. i have access to some good deals from Schneider so i’ll be using them. the biggest dilemma i have now is one availability of pistons, and two i don’t know my current cylinder bore and i won’t know until i mic it and see how much i’ll need to take off. i think most of what you recommended is done but besides availability is there a reason a z20 piston is better than a 280zx piston. also if i were to go big valve where’s a good place to get them from i haven’t seen much but i also haven’t looked into it much. thanks for the help.

-aiden

[521aiden]

i didn’t see the last comment about being the same besides the long rods. will 280zx pistons fit on a z20 rod or are they too tall/ different wrist pin?

[datzenmike]

They are both flattops, maybe the Z20 will be easier to find than the 280zx. Z20 pistons allow you to use longer rods. Theoretically there is a high RPM benefit to increased rod/stroke ratios.

 

L20B or L28 pistons from a 280zx will not work with Z20 rods. They are longer and would push the piston up into the head. All L series pin heights, the distance from the center of the pin to the top of the piston, are 38.1mm. The Z20 pin height is 31.75mm.

 

 

Stock L20B bore is 85mm so it needs to be enlarged to 86mm to fit 86mm 280zx pistons. A used block will need to be over bored so might as well go to the largest... 1mm or 86mm same as the 280zx pistons.

 

 

This is a Z20 piston. It has small eyebrows cut for valve clearance but for all intents and purposes it's a flattop.

[521aiden]

3 hours ago, datzenmike said:

They are both flattops, maybe the Z20 will be easier to find than the 280zx. Z20 pistons allow you to use longer rods. Theoretically there is a high RPM benefit to increased rod/stroke ratios.

 

L20B or L28 pistons from a 280zx will not work with Z20 rods. They are longer and would push the piston up into the head. All L series pin heights, the distance from the center of the pin to the top of the piston, are 38.1mm. The Z20 pin height is 31.75mm.

 

 

Stock L20B bore is 85mm so it needs to be enlarged to 86mm to fit 86mm 280zx pistons. A used block will need to be over bored so might as well go to the largest... 1mm or 86mm same as the 280zx pistons.

 

 

This is a Z20 piston. It has small eyebrows cut for valve clearance but for all intents and purposes it's a flattop.

okay thank you i’ve been looking into parts and what’s out there. there isn’t much for pistons of any type but if i have l20b rods i might make the swap to z rods and if i have z rods i’ll be on the lookout for forged pistons. I appreciate all the info 

[datzenmike]

Find hypereutectic Z20 pistons in some over size, good enough for street. The Z20 was used in the 720 into '86 so try looking for pistons for a 720 engine. If those are unavailable then custom forged with 31.75mm pin height in some over size.