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Direct injection theory

NAPZ24 to DIRECT in jection  

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  1. 1. Do you think it would feasible to convert the NAPZ dual spark to a single spark Direct injection setup?

    • Do Eet!
    • Not possible
    • Not worth it
    • Rabbit chili would be a better use for your time, plus its delicious.

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Some one on NICO asked if they could just make both spark go at the same time or if you could just do away with the hard to reach intake side plugs and just have the exhaust side for spark.


The latter had me thinking if you had only exhaust side spark like the KA24e then couldn't the other port be converted to direct injection. I am pretty sure the z24 is also a HEMI so it seems like it could be a sweet option for a more efficient fuel system and added power.


I don't know all that much about Direct injection and how thats timed...if it is even different at all than a traditional fuel rail.


I'd like to hear any thoughts from more capable minds. To me it seems like it wouldn't take much to rip a system out of a new four banger and mount it up. From the look of the pic on howstuffworks it looks a lot like a normal fuel rail.

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Not real sure about the head design factor, but one of the biggest things for the direct injection is the fuel pumps. VWs have 3, my old Mazdaspeed 6 had two. Basically the standard fuel pump in the tank running the standard 45psi, then another on the block ran off of the cam that pushes it up around 1400-1600 psi. That's how my mazda ran. I miss my mazda.

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yeah, nissan direct injection is around 2000 psi, the pumps for direct injection are usually, cam gear, or chain drive, etc. Not too familiar with naps heads, but I'm realtivly certain that the flame front would not be anywhere close to correct without massive head work

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Yes, the L series has a cam driven fuel pump. its actually a worm gear iirc that is bolted on the end of the cam. Cam spins, worm gear rotates pumping the lever on the fuel pump.


IIRC the naps head does have that. I can't remember what the cam looked like on the naps, but maybe you could put an L series worm gear on there? Waiting for Datzenmike or sealik to chime in.

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front of motor and you can see the casting front left side


side shot and you can see the casting up front to the right side.


top view



Not sure if I have a shot of just the cam, but I do have a motor sitting on the floor of the garage to play with.

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im retarded, dunno what i was thinking about the cam....



Anyways, the end of your cam has the sprocket. the fuel pump gear thing would go on the outside of it. find one off an L20, put it on there and then do some measurements to be sure the fuel pump level would line up with it. -- BEFORE you cut out the casting.

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when i say L20, i really meant any L series, l16 or 18 would do too


Looking at other GDI setups. it seems turboing makes air delivery way better, and with the long stroke, it should push lots of exhaust through a turbo. I have that hx35 holset around. A twinscroll manifold would push it quickly.


I feel as if I am trying to figure out how to make my z24 a Direct inject turbo diesel without running diesel. luckily the head seems to be an okay design for it. I am reading fuel ratios like 40:1 so I am sure building up a forged bottom end would be needed as well. I guess I should blow one up NA first. I am guessing the ECU will be the most difficult part.

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There was a magazine article on this a while back, can't remember which magazine, but basically it won't work unless you want to dump a shitload into it. The management alone to monitor the fuel and ignition timing is just not possible for any aftermarket systems at current. A GDI motor is VERY different from a regular one. I'll bet if you had $10-$20,000 you could make it work, but probably not worth it for a Z24 motor. I am glad that you're thinking out of the box though. +100 for ADD!! ;)


And on that note, have you made your rabbit chili yet? Rabbit is delicious.

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And on that note, have you made your rabbit chili yet? Rabbit is delicious.


No... I plan on raising meat rabbits soon though, so hopefully this time next year I will have it sorted out and in the crock pot. :)


Yeah reading more and more it seems unless I am a programming god with a motorhead on my shoulders, I doubt I would get it running.

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okay so cam driven. Didn't earlier datsuns have cam driven mechanical fuel pumps? I think the napz head still has the casting for that but its not drilled out or whatever. Or am I wrong on that?


The Z22 ran a mechanical or electric fuel pump....covered with a removable plate on the latter years running the electric pump

The Z24 has the same 'opening'...but it's plugged


It has a dual row chain cam sprocket. not sure how many motors were dual row.


All Ls and Zs use the same cam sprocket (double row), crank gear and tensioner ...only difference is the length of chains and guides

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Sealik, do you know if the internal casting in the head is any different or does the shizz need to mount to the outside and be the right length?



I'll check...but I assume if one was to cut that whole out on the Z24...the mechanical pump should work...maybe :D

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The mechanical fuel pump on L-engines does not use the camshaft eccentric to push the fuel into the carburetor. When the eccentric moves the lever on the fuel pump, all it does is pull a spring loaded diaphragm, and that draws fuel in to the fuel pump. The spring loaded diaphragm pushes fuel in the fuel line up the needle and seat in the carburetor. If the carburetor does not want any fuel, the diaphragm just does not move, in spite of the camshaft turning. When the carburetor wants some fuel, the spring in the fuel pump pushes the diaphragm, and the next time the camshaft eccentric moves the lever on the pump, the pump draws in more fuel.

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The "probable" solution would be to have a piston with a "pocket" like the Honda CVCC engine that faces the surviving spark plug to concentrate the initial relatively lean fuel/air mixture and after ignition, injecting the rest of the fuel. Classically this would be a "semi Diesel" ignition. Ignition before top dead center with continued injection and fuel burning beyond top dead center. Much power and a very hot exhaust. The ignition diagram is almost square, not a diagonal slice. It is a hybrid between the classic Diesel and spark ignition combustion cycle diagram.

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Direct injection theory is totally different than carb or efi. Direct injection can run insane air fuel ration like 40 to one. In a normal car this wouldn't even come close to igniting. In a direct injection motor the design of the combustion chamber/piston top and injector position are such that a mere whisper of fuel is injected in a tiny swirling cloud around the spark plug with ordinary air around it. Think of a jelly filled doughnut. This tiny cloud of proper fuel and air mix will ignite and heat energy (work) can be extracted. I'm not even sure if there is a throttle plate on these motors. Because the fuel is a fine mist around the plug all you do when stepping on the gas is inject more fuel. I think the direct injection motors have high compression too. This is because most of the heat energy is concentrated in the center of the combustion chamber with an insulating sphere of ordinary air around it. The combustion chamber walls are cooler and detonation very unlikely.


On an ordinary EFI the fuel is injected into the intake port in the head at any or all times because it doesn't matter. All you need is the gas and air to mix and be ready. The intake valve opens and sucks in a homogenized mix of gas and air. The DI motor needs the injection at a precise time that varies like ignition advance. Too soon and the precise mixture will dilute in the surrounding air in the combustion chamber and won't burn. So many variables for the computer to adjust for.

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