None of the four stock motors I've taken apart had any piston wedges or eyebrows cut into them.  Two 2.4s, flat tops.  One 2.8 with dished pistons the other a ZX with flat tops.  None had any unless the dished ones would be considered because they are deeper?

39 minutes ago, sweatybetty said:

did stock pistons have a valve relief? i measured the lift at the valve and came up with .433 which is what my haynes manual says is factory lift. id like to jump up closer to .500 but am worried about valve-piston interference. do you think these would work with a higher lift cam? 

Yes.....the 1973 low compression 240Z's came with fly cut Pistons......and yes you can go up to .500 lift (Isky Stage III is .490 lift) as long as the L24 block is over bored .030 inches or more.

More importantly I would measure deck height of Pistons . Unless they are waaayyyy out of the top of the block I would go with what ever cam you want. I'd say with reliefs you could go 550+


Sent from my iPhone using Classic Zcar Club

thank you guys. from what i can measure, the bore is .7mm over and the pistons were even at the top of the block. am i right in thinking the over-bore is to keep the valves from hitting the cylinder wall? ive read that can be fixed with a little grinding.

im still thinking that  bigger valves and a little head work might help get a few more horsepower out this block, even if it is only a 24. i have the webers and a header, so if i can get it to breathe................

If you have the low compression E88 head, I'd dump it for an early E88 or E31 head. The 73 heads are low performance. If your car is a 72 with the original motor, you should be running an early (good) E88 head. Get steel seats (L28) installed and L28 valves and a higher lift cam and you'll get a nice boost in performance

i have an E31 head. i dont think that this is the original block, though. my car is an early 72 and i have a E31 block.

Edited September 5, 20168 yr by sweatybetty

Awesome....steel (L28) seats, valves and a nice Stage III cam and you'll be all set! BTW, when you install a higher lift cam in the L24 head, you'll need to install low profile valve seals to keep the bottom of the valve spring retainers from beating against a stock (taller) valve seal. Your block has already been over bored .75 mm (.030 inches), so you should be all set there.

thats what ive been thinking

I thought this was the L28 block. I took a 73 block apart and the Pistons had reliefs like this.
How big are the rod bolts- 8 or 9 mm?


Sent from my iPhone using Classic Zcar Club

Here's mine from an automatic '73. It has the bigger cap bolts but no reliefs?  It was an early version I guess, it had the good E88, it's on my car now until I get my E31 put together. 

3 hours ago, Diseazd said:

Yes.....the 1973 low compression 240Z's came with fly cut Pistons.....

I did not know that.  More learning.

sb did say L28 block but it's all looking like low CR L24.  Reading back looks like he meant that he took the L24 head off to use onthe L28 but changed his mind about the L28 since the L24 was in good shape.  Diseazd seems to know what's going on.  Collecting the facts, it looks like a rebuilt, ovebored low CR, 1973 L24 with an E31 head.  Maybe it could have just been left together and run?  Surprise.

 

 

Here's mine from an automatic '73. It has the bigger cap bolts but no reliefs?  It was an early version I guess, it had the good E88, it's on my car now until I get my E31 put together. 

Stroker rods!!!



Sent from my iPhone using Classic Zcar Club