OK found them.  H2716 are NA 1973 240z 1mm over pistons, H2711 are stock NA 1973 240z pistons.

 

http://datnissparts.com/x-1973-240z-l24-oe-oversize-cast-pistons-1-0mm-040-84-0mm-12010-h2716-set-of-6-also-fits-l26-l16/

Edited August 31, 20204 yr by 240260280

Wow!! That's awesome! . . . how can you tell they are oversized and not H2711? Are there advantages / disadvantages to this design change. Sounds like it was more emissions friendly. . . . Compression didn't change but a better burn?  Thanks again. . . 

You will need to measure the diameter of the piston. 83mm is stock.

21 hours ago, HS30-H said:

 

AMPCO was/is a majority Nissan-owned affiliate company, making parts for use on Nissan vehicles.

Whilst the H2716 'Pop-up' pistons were not OEM on any S30-series Z, they were supplied by Nissan as a service replacement part on Nissan L-series engines. They are not 'aftermarket' or custom.

I’ve been trying to get info on these pistons for a while. I built an L24 engine with 1mm oversized Nissan pistons (with these valve reliefs) some time back and noticed these pistons were about .7mm above deck. I had installed the early E88 Head. They were no problem and worked fine, but my guess is with the stock gasket, they were close to being “too close” to the early head. They worked fine, no contact issues even at high rpm, but I see where 240260280 shows the service bulletin from Nissan saying they were “NOT interchangeable with the earlier cars”. I would imagine if too much metal was taken to “true” the block, there could be a contact issue. Any experience with these pistons being used with the early heads, and if someone was concerned with these pistons being too close, would having a machine shop shave the piston top say .5mm solve the problem? In other words, how much could you machine off of these pistons without affecting the piston?

These are NOS (new old stock) 240z  original L24 pistons, they have no indents..    these are 1 mm oversize

Later on i red that they also fit L26 blocks..

(New pistonset.. in stock still. just 30+ years of dust and some lube on them..)  I also have a 1973 complete engine, so i could measure the diff. between those orig. and 1973 pistons, there should be a difference of 0.7 mm! 

 

7 minutes ago, Diseazd said:

I’ve been trying to get info on these pistons for a while. I built an L24 engine with 1mm oversized Nissan pistons (with these valve reliefs) some time back and noticed these pistons were about .7mm above deck. I had installed the early E88 Head. They were no problem and worked fine, but my guess is with the stock gasket, they were close to being “too close” to the early head. They worked fine, no contact issues even at high rpm, but I see where 240260280 shows the service bulletin from Nissan saying they were “NOT interchangeable with the earlier cars”. I would imagine if too much metal was taken to “true” the block, there could be a contact issue. Any experience with these pistons being used with the early heads, and if someone was concerned with these pistons being too close, would having a machine shop shave the piston top say .5mm solve the problem? In other words, how much could you machine off of these pistons without affecting the piston?

We posted at the same time.. both talking about the 0.7 mm diff..  haha..

I once put a E30  (No not E31)  A E30 head on my L24.. That gives you some compression hahaha long time ago but i remember the starter had trouble starting it!   Did'nt drive very well.. few days later i blew the gasket out haha.. still learning hey...

5 minutes ago, dutchzcarguy said:

These are NOS (new old stock) 240z  original L24 pistons, they have no indents..    these are 1 mm oversize

Later on i red that they also fit L26 blocks..

(New pistonset.. in stock still. just 30+ years of dust and some lube on them..)  I also have a 1973 complete engine, so i could measure the diff. between those orig. and 1973 pistons, there should be a difference of 0.7 mm! 

 

No need to measure, 240260280’s post shows these pistons are .7mm taller, and I’ve seen that when I used these later pop up pistons. When you order replacement pistons from Nissan, this is what you get.....or got (not sure if still available). With allowable clearance varying from builder to builder ( most want 1 to 1.5 mm clearance), is .8mm clearance enough? It was in my build, but some may argue it’s not. My question is how much can be shaved off the top of the piston to reach a comfort zone of clearance in the early engines? 

1 hour ago, Diseazd said:

My question is how much can be shaved off the top of the piston to reach a comfort zone of clearance in the early engines? 

You'll have to measure, and make your own decision. Once you start modifying factory parts, that's the deal...

Agreed.....good advice.....I would leave that up to a good machine shop. The pistons have been no problem with .8mm (.032 inches) of clearance with a stock head gasket in the early L24. 

I recall seeing different top surfaces on L28 pistons but not L24.  The stock fly cuts are new to me.

 

Edited September 1, 20204 yr by 240260280

I have 0.58 mm clearance in my engine. I originally had 0.56 mm and a piston just kissed the head.

On 8/29/2020 at 7:00 PM, ToolBoy said:

Hello to all. . .  I just received an L24 engine a few days ago that I was intending to use for backup parts but I'm thinking it might be a better engine than the L26 that's currently still in my series 1 car.

. Previous owner raced Z's in the midwest 15 years ago and he's now getting rid of some stuff. He couldn't say much for sure about this engine so I took my chances and the price was right. Any info is appreciated. Thanks in advance.

If it's a race engine it's good odds that it's high compression.  The guy used the pistons to raise CR instead of shaving the head maybe.  So, if you want to use it you might have to use high octane race fuel, or "detune" it to avoid detonation.  Retarded timing, run it rich, cam timing, etc.  Doesn't really look like a drop it in and go engine.  Measure and calculate combustion chamber volume to start.

Or, since you have it apart, just buy pistons that will give you the CR you want for a street engine.