LZ22S Pistons

[dat260]

Hi guys

Would the LZ22S piston be a good alternative for my L28 crank/240 rods combo? Piston specs: 87mm bore, 35mm pin height and 9.33cc dish = 8.3:1 same as a stock L28 but with a different rod/stroke ratio, also good for pump gas. It will be approx .5mm below deck, does it matter? Also, if I shave the piston flat would I increase or decrease compression? I'am thinking it might increase but since its below deck, thats were I get confused.

Cheers, Ari

[mperdue]

If you shave the piston and deck the block the same amount you will increase compression (effectively reducing the dish on the piston). If you just shave the piston you will lower compression because you will be increasing the combustion chamber size.

Compression is (VCC+VD)/VCC where CC and D are combustion chamber and displacement volumes. An example CC=1 and D=8, compression is (8+1)/1 = 9. Say you increase the CC to 1.2 (by shaving pistons for example). Then compression is (8+1.2)/1.2 = 7.67. Displacement won't change no matter what you change with the pistons, deck, head etc (EDIT unless of course you change the pistom diameter which will affect displacement ).

[dat260]

Thanks Mperdu. I was looking into this replacement thinking it would be a low cost alternative compare to ArizonaZ pistons which are designed for my crank/rod combo.

Cheers, Ari

[dat260]

Here is another approach. How about L28 dished pistons. According to Lengine program if I combine this piston with the L28crank/240rod combo the deck would end up being 2.730 above deck. Now, here is the approach. If I shave the piston let say 2.7 I would end up with the factory deck height, it would be like a raised pin height by 2.7, no? As for the compression it would depend, if buy shaving I end up flat or dished. Mperdue what do you think, would it work or I got it wrong?

Ari

[ZSaint]

Are you talking taking 2.7mm off the top of your piston? If you are, you will be in trouble with too thin a piston. You will warp a ring land or burn a piston from the intense heat generated. I put a set of Z22S pistons in my 2995 block. With the additional stroke, the piston bowl was machined flat for zero clearance. The engine shop was concerned about the material being a bit too thin above the top ring. You will have a much more serious problem removing that much material.

[dat260]

Are you talking taking 2.7mm off the top of your piston? If you are, you will be in trouble with too thin a piston. You will warp a ring land or burn a piston from the intense heat generated. I put a set of Z22S pistons in my 2995 block. With the additional stroke, the piston bowl was machined flat for zero clearance. The engine shop was concerned about the material being a bit too thin above the top ring. You will have a much more serious problem removing that much material.

Hi ZSaint,

I was thinking of just shaving the edge of the piston, almost making it flat. What crank and con/rod are you using? I have a stock L28 crank with 240 con/rod.

Cheers, Ari

[ZSaint]

No problem as long as you do not turbo it. You need all of the piston material to cool the ring land. With NA, you will not have a problem. That is all my machinist did and I have had no problems.

[240ZMan]

I hope I'm not hijacking the thread with this question: Why are you using 240 con rods? What is the advantage in an L28 over the stock con rods?

[dat260]

Hi 240Z

Here is a link that will give you an explanation about this modification.

http://forums.hybridz.org/showthread.php?t=100032

[NZeder]

I hope I'm not hijacking the thread with this question: Why are you using 240 con rods? What is the advantage in an L28 over the stock con rods?

If you have a copy of "How to Hotrod and Race Your Datsun" there is a section in the book that explains the rod/stroke ratio and how changing this alters piston speed at different points in the stroke. I can't recall which but I think increasing the rod length increases the piston speed at the top and bottom of the stroke. Were as a short rod will (not only increase the angle/pressure on the side of piston) but will slow the piston down in the top and bottom of the stroke but increase the speed in the midle of the stroke = usually equals more torque. With the increase of piston speed at the top it makes getting the valve timing correct and also results in usually a small duration.

So this is why a 3.1 stroker (LD28 crank/L24 Rods = 1.60 rod/stroke ratio) produce so much torque and why you can have high duration cams.

The L24 engine has a 1.80 Rod/Stroke ratio and these are said to rev better than the L26/L28 with their 1.65 ratio. So by using the L28 crank with a L24 rod you get a 1.68 (closer to the ideal 1.75 for a short stroke engine which the L Series are ie bore is bigger than the stroke or over square? I think that is right - I am not a mechanic just a computer guy who is keen to learn more about Zed/Engine = not a computer )

I hope this info is of some use and if I have any of this incorrect please correct me so I can learn more