L21 Piston Choice

[510SSS]

I am still trying to get to the bottom of what would be the best pistons to utilize to make a L21 Long Rod. I already have an L20b block, so I am going to use that.

 

I have heard that boring to 89mm to use ka24 pistons can be dangerous. I want the L21 to be able to rev high, and I have read that the thinner piston rings of the Z pistons are part of the reason that this is possible.

 

If i use VG30e pistons, does anyone know if they also have similar thin compression rings? Also, If used would the tops have to be milled down? and if so by how much? I dont mind only boring to 87 or 88mm I just want all of the correct parts because my engine is already at the machine shop.

[datzenmike]

Your combination of long rod and L20B crank limits your piston choice to late Z22E or VG30E pistons. (87mm bore) Both will fit without milling the tops.

 

 

The KA24E or the Z24 (89mm bore) will stick out above the block deck by 2mm. Both the KA and the Z24 pistons have a high ridge around the outside top edge and more than enough material to remove 2mm ... actually you could remove 1.75mm and still be within the 1/3mm above deck recommended by Jason Gray. Probably sandpaper and a sheet of glass would do for this. This will effectively move the top piston ring 'higher' toward the combustion chamber and it will run hotter. Be sure to carefully check the ring end clearancees.

[510SSS]

Ok, Thanks Mike. So if I decide to go with VG30e pistons do I use all the stock specs for ring gap, etc from nissan? or do I have to change them because of the different block?

 

What about the thickness of the ring question, does it effect the ability of the engine to rev up, anyone know the answer to this? Also, anyone know how to calculate what would be the deck height with unmilled vg30e pistons?

[datzenmike]

The piston won't know the difference so set to Nissan ring clearances. You could use used pistons to keep the price down. After all the block has to be bored out to match the piston anyway.

 

I would imagine a thinner ring has less friction against the wall but a thicker one may seal better. For a street motor I would want thicker to last longer.

 

The stock distance from the crank center line to the top of the block on an L20B/Z20/Z22 is 227.45mm. The crank throw + rod length + piston pin height must all total up and be no more than 1/3mm above this or less.

 

42mm (stroke/2) L20B crank

152.5mm Long rods

31.75mm VG30E pin height

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227.25mm not bad. The piston is about 0.2mm below the deck

 

 

For the hell of it this would make a motor that is 2043cc and with an open chamber L head would have a compression of 10.38

[510SSS]

Oh damn that sounds around about right for what im looking for. What about what jason grey said about the 1.5mm rings of the Z22e pistons being less prone to flutter than the L20b 2mm rings? The VG30e piston has a 2mm ring like the L20b so I hope this will not contribute to flutter at high rpm.

[RAT510]

why not just use the Z22E pistons?

[RAT510]

Ok, Thanks Mike. So if I decide to go with VG30e pistons do I use all the stock specs for ring gap, etc from nissan? or do I have to change them because of the different block?

 

What about the thickness of the ring question, does it effect the ability of the engine to rev up, anyone know the answer to this? Also, anyone know how to calculate what would be the deck height with unmilled vg30e pistons?

 

try using the helix design utility to calculate piston rod block combos and deck heights. im building a similar engine for my car so would be interested to see which way you go with this. as far as using the design utility set it up as a z22 block, that gives you the 87mm bore essentially the same as a bored out L20B. most of the dialog boxes can be edited so just put the VG30 piston specs in on top of the Z22E piston specs to give you the figures you looking for.

[510SSS]

I decided to go with the vg30e pistons, I do not have much time, and I need to get the 510 back to daily driver status. I am shooting for 150rwhp and 150 torque so I figured the VG30 piston would be much more willing to handle that considering the amount of power developed by the VG30.

 

I got them in 0.02 oversize so I will have a 87.5mm bore I figured this would be a good compromise between displacement and not having to thin the cylinder walls too excessively. I was going to go with forged Wiseco or JE pistons, however I just dropped $300 on z20e rods, so I figured that cast VG30e pistons were ok because I've read they can handle up to 500hp before one would need forged.

 

I found a set by Beck-Arnley at Rock Auto with rings included for only $135, so I jumped on it. LMK if anyone has had any problems with that this piston rod combo. I think it will work well with the low pin height of the early vg30 piston. Also it has press fit wrist pins just like an L piston so no oiling modification needed like later vg30 pistons.