Anybody tried it? I know the truck KA24 pistons are the same bore and pin fitting as Z24 pistons, but the compression height worries me. They are both dished, but the dish in a KA24 piston is much shallower. In a stock KA24E they are 9.5:1, and that is with a much more open head design. Anyone know what sort of compression they would give in a Z24?

Stock ka24e's are not 9.5:1, that's the DE.

Most ka24e's are 8.6:1 stock (2.2cc dish I think but not sure). The higher comp early E pistons are flat tops with no dish.

Early ka24e's had 9.1:1 comp

Some people put E pistons in a DE to net 11.1:1 with the lower comp pistons, and 11.6:1 with the early high comps.

I think z24 pistons have a 15cc dish, but I'm not 100% sure. z24 comp is 8.3:1 stock

Rods are the same length and are reportedly interchangable in sets (with pistons). IDK what the specs are exactly.

Truck versions of ka24's (E and DE) have press fit piston pins. 240sx versions of ka24's (E and DE) have fully floating pins.
Modified by seang at 4:06 PM 12/16/2009

the way i've been looking at this is simple... don't do it unless you're doing an actual/i] build... the pins aren't direct swap from what i remember as sean siad above... but you can make them work pretty easy (relatively speaking)

but as i mentioned... if you're going to do it... do it right (headwork, cam etc) otherwise it'll just be a mess IMO

I do know that the truck ka pistons use the same pin as the Z24, so that is even easier that 'making it work'. If it is only 8.6:1 with the KA head, it actually might not be bad with the Z24 head on it (less than 10:1). I might just give this a shot.

The reason I'm wondering is that I've got a warmed-over Z24 in a 84 4x4 that needs a bottom-end rebuild anyway. It's got a 32/36 and header on it, was well as having the ignition rigged so both coils fire throughout the power range. Since the 32/36 DGEV gives me a lot more flexibility on jetting, I was looking into higher compression with the Z24 setup, since I have some Z block specific bolt-ons and I prefer the earlier torque curve of the Z24 in a 4x4. Also, I've always thought you couldn't do much head work on the Z24 because of the water passages right next to the intake ports; is is really worth a minor P&P?

I cut and pasted this from another forum (the 510 realm.com)...

"Nissan designed the NAPS for low pollution. The engines were never built no expected to rev much above 4K, they will of course but they are already running out of breath. They are a great motor for what they were intended and that was to run in a certain RPM range, so valve springs are only stiff enough for that. The port runners are low on the head with a sharp bend into the cylinder which again flows plenty of air... at low RPMs. Valve lift is limited by valve size and position but again breaths fine at lower speeds. Valves are longer and heavier than the L valves but won't float in the RPM range designed for.

You can mess some with valve timing events and lift but beware there is a limit where the valves will touch each other. Porting the runners can help but can't fix the design, and the Z head will never equal the L head for flow. Port flow will always be the limiting factor with the Z engine. More cam and carb won't fix it altogether, you can only maximize the flow limit built into it with some porting.

Trick 2.2 NAPS blocks with L heads on them and multi carb or EFI make between 130- 140 hp. With Z head and a 50 shot of N02 expect 165 - 180 hp realistically.

Another snippet from 510realm.com I find interesting...

"There are many misconceptions about the dual plug system on the NAPS. Both plugs are fired together producing two flame fronts that reduce the burn time. Think of lighting both ends of a candle. The shorter burn time means that the engine will run with less ignition advance. Your dual plug Z22 has a static timing of around 3-5 degrees BTDC while the single plug L20B is 12 degrees BTDC. "

---------------------------------------------------------------------------------------------

A few things about ignitions...

"First of all electricity, ALWAYS TAKES THE SHORTEST ROUTE TO GROUND. It wont divide down two wires, one wire and plug will always present an easier path to ground and it will take it. Also a 100K volt coil will never fire a plug with 100K volts. The voltage from a coil starts at zero and rises up (very quickly) like driving up a hill. When the voltage reaches a point where it can jump the plug gap to ground, it will. At that point the arc is a direct short to ground and the voltage cannot rise any higher. A idling engine needs barely 8-10K volts to fire the plug. At full throttle, the full cylinder offers more resistance to firing and the voltage needed may increase to around 20K volts. Higher compression or turbo engines will need maybe 25-30K volts to fire their plugs. Normally aspirated engines will run just fine on the stock Nissan Electronic Ignition systems. Aftermarket coil makers love to advertise sexy big voltage numbers, but the truth is you only need and use about 20K of those volts. Your Z22's stock EI distributor and dual coils will be enough for what you have, and then some, given you actually replace the cap and rotor with new ones."

Instead of me copying and pasting a s***load of informations, I'll just post the link to the results I got when I Googled "porting a naps-z head"...http://www.google.com/search?h...=&oq=

[QUOTE=seang]

"There are many misconceptions about the dual plug system on the NAPS. Both plugs are fired together producing two flame fronts that reduce the burn time. Think of lighting both ends of a candle. The shorter burn time means that the engine will run with less ignition advance. Your dual plug Z22 has a static timing of around 3-5 degrees BTDC while the single plug L20B is 12 degrees BTDC. "

Check out the distributor cover. The rotor is 180 degrees to each other but the lugs on the cap are not. This is to allow one plug to fire before the other, allowing the flame front to ignite and then to completely burn out the rest of the combustible mixture. This is also the reason this engine works well with the timing so close to and after TDC.

The primary plug fires 10 degrees before the secondary plug, yes. It's for emissions more than performance. You can get more advance with one plug. How much more I do not know.

Early naps-z used a single plug with the same combustion chamber shape as the dual plug. Later on they went dual to meet ever stricter emissions laws, and in that respect, it was a role model.

--------------------------------------------------------------------------------------------[copied from SAE webiste]

Nissan Naps-Z Engine Realizes Better Fuel Economy and Low NoDx EmissionDocument Number: 810010

Date Published: February 1981

Author(s): Masanori Harada - Nissan Motor Co., Ltd. (Yokosuka, Japan) Tadashi Kadota - Nissan Motor Co., Ltd. (Yokosuka, Japan) Yos***aka Sugiyama - Nissan Motor Co., Ltd. (Yokosuka, Japan)

Abstract: Nissan Motor Co., Ltd. has succeeded in developing a highly reliable, simple-mechanism engine that can be used with a carburetor system, a fuel injection system or an LPG system. During the 1980 certification programs conducted in the United States and Japan, this engine was unrivaled in its low emissions and excellent fuel economy.

Such high fuel efficiency is realized by the adoption of a fast-burn combustion system. Fast-burn combustion is made possible by the development of a high-speed swirl system and a two-point ignition system. Furthermore, an EGR system with a VVT valve has also been developed to afford precise control over the EGR, which is what optimizes the performance characteristics of this engine. Uniform EGR distribution is realized through improvements made in the intake manifold.

Because of its low emission levels and high fuel efficiency, this engine is expected to find wide utilization in meeting the stringent requirements for energy conservation and environmental protection.


Modified by seang at 5:33 PM 12/17/2009

Cool. Its easy to get as much as 50 degrees advance from the distributor by adding weight to the weights and adjusting the tension in the springs. The head is poor when it comes to the production of power due to the ports. They are too long and the sharp bends does not allow the high velocity needed at high rpm to pass or keep the levels of swirl for efficiency, but I think you already know that.

Yeah, the Z heads are pretty much known to be poor for performance. The L series head is good for the Z20-Z22, and the KA head for the Z24. However, for what I'm looking at with a 4x4 setup, I don't really mind the lack of revving; I'm just looking to do basics to up the power without going crazy. If I wanted significantly more power I would swap in a KA24 (but again, would need new bolt-ons, would have to figure out fueling, etc).

So... back to the original topic, KA24 dished truck pistons in a Z24 longblock...

You do mean new ka24e pistons, right? I saw a set of 4 on Ebay (8.6:1, with rings) for less than 80 dollars new. That's cheap, and they are NPR pistons with good feedback on the website. They can be had in common oversizes.

Yep. Even new from retailers like Summit they're only $140 or so, so it seems like a pretty easy way to bump compression if the shortblock needs rebuilt anyway. I just have trouble believing somebody hasn't tried it. I know the Z series are the black sheep of the Nissan 4-cyl blocks (designed for emission/no serious performance potential), but being that cheap I would have thought somebody with basic bolt-ons would have tried it.

Seems I'm not the first one to wonder. Check this outhttp://4wheeldrive.about.com/o...0.htm

Let's see if this guy answers email questions...

Mmmmmm 9.5:1/9.6:1 using stock KA truck pistons in a Z24. Since I've got a DGV to dump fuel and a header/open exhaust, I'm going to have to try this now. Will probably be a couple months still though, since I'm not pulling the engine out of the 4WD until winter is done.
Modified by mdjett at 12:40 PM 1/1/2010