Questions about a naps Z20S?

[Spades]

Ok, so, I found a freshly rebuilt naps 2.0 motor and good transmission installed in a 1980 510 wagon...so, I now have my drivetrain for my '72 wagon I am in the process of restoring. Now I have questions!

 

so, this motor is the old 4 plug design of the 2.0 liter motor, so I have some questions about the head on it. everything is freshly rebuilt, including the head, so my question is, how far can the head be ported? I know that the 8 plug designs had breathing issues, and that there was only so far you can go with that design. I do know that the 8 plug design burns the fuel more completely and is a better enginered design, but that a standard L20B motor has more room for porting and higher RPM horsepower.

 

so, my question is, are the 4 plug naps heads as difficult to port? how much of a edge would a L20B head have over it? I am on a bit of a budget, so, the fact that the head on it is fresh, means that if the horsepower gains of a differant head would have to be significant for me to spend the money to buy a l20b head and go through it.

 

If I was to add a pair of side draft carbs, a mild camshaft, header, exhaust, ignition, and a few other minor mods, what gains would I have with a ported napsz20s head verses a ported l20b with the same mods? are we talking like 5hp differance or are we talking like 30hp+?

 

also, is what I have heard correct? are weber side drafts complete junk? do they just fall out of tune, or are they impossible to ever tune right like I have heard? big price differance between webers and mikunis, and I wanna know if its worth waiting a few months to save up enough cash to buy the mikunis. if its a matter of just needing tuned more often, I am fine with that, but if the suckers never run right ever no matter how often they are dinked with, I will wait till I have money for the mikunis.

 

thanks in advance for the help!

[datsunaholic]

The 4-plug NAPS-Z head is absolutely identical to the 8-plug NAPS-Z head, except they didn't machine out the other 4 spark plug holes. Porting issues are exactly the same.

[Spades]

nice...so, the question now, does anyone know what kind of power I could expect from the stock head ported with the modifications listed? from what I have found hunting on the internet all evening, it seems most people with mild naps z motors are running between 300 and 400 cfm carburetors.from what i have read, it seems like side drafts are more for racing aplications, requiring alot more tuning and are set up for higher RPM set ups.

 

I haven't ever messed with carburetors much myself, only fuel injection. my dad is a pro at it, but I know very little even after a evening of trying to learn from reading through dozens of forums.

 

I am good at fabricating, and I have a friend who is a engineer and offered to design a intake manifold for me. one of my ideas was to buy a holly 390 cfm 4 barrel and change the primary jet size and also replace the powervalve to a lower one to increase my around town gas milage, and still have good WOT responce when the vacuum operated secondaries kicked in.

 

with the naps z head ported as far as it can be, and as big of a cam as i can stuff in it, and any other bolt on's i can source, would 390cfm be overkill? i noticed most bolt on weber kits for the z20s are 300 CFM...is 390cfm overkill even with a lower hg power valve and smaller jets?

 

anyone know what HP would be? I know stock its like a sad 88hp or something. any input would be great!

 

EDIT: I was browsing around and found this little tidbit on The Dime Quarterly website, not sure if its true or not, havent checked it out yet.

quote: The engine tilt is not the same as the L-series tilt, so if you use a NAPS-Z transmission it is necessary to fit Z-series engine mounts to maintain the proper transmission shift lever tilt.

 

by z series engine mounts do they mean the naps-z mounts off the 80 station wagon or z-car mounts(280,ect)? I know thats a stupid question but i had to ask it.

Edited August 22, 2009 by Spades

[datzenmike]

The Z20S and the L20B are basically the same motor below the head. It should be said here that while the L series head was designed with some racing in mind the NAPS was more towards lower pollution and so all of it's drawbacks do not present themselves at normal driving speeds, say below 4-5K RPMs. (keep this in mind) The head, at very high RPMs, is where power and performance is made and also efficiency and mileage. The more fuel and air you can get into a motor, and the faster you can do it, the more power it will make. This doesn't happen by itself and the motor has to work hard to draw in air and anything that reduces this ability will rob it of power.

 

A good head design will have intake and exhaust ports that are as straight as possible without sharp bends. In this respect the L head is superior to the NAPS design. The L intake ports are high on the head and travel downward at a steep angle turning slightly at the valve to enter the cylinder. The NAPS intake ports are low on the head just above the block surface and bend sharply at the valve. Because air's inertia increases at high speed it has trouble making this sharp bend and the smooth flow will separate from the inner turn wall and begin to tumble. In effect becoming turbulent and blocking proper flow. Now this was never a consideration for the NAPS Z motor that was designed for low RPM operation and resultant low pollution.

 

A good head will have valve springs that are stiff enough to keep the the valve and rocker arms against the cam lobes at high RPMs and not allow them to 'float'. I've heard that the NAPS springs are weak but by spec they are just a hair stiffer, however the valves are about 1cm longer and so would be heavier than the L series. Again valve float in a NAPS isn't a concern for a motor built for below 4,500 RPM operation. There is no significant difference in L or Z series valve head diameters. Assuming both motors use a 1.5 to 1 rocker ratio the Z engine has a 0.423" lift vs. the L's 0.413" lift. I would say that valve train wise both are comparable. This is not to say they work the same.

 

The L head has intake and exhaust ports on the driver's side. Because of the steeper angle of the intake ports the valves are aligned with a slight tilt also to the driver's side. The Z head is a cross flow design with intake on one side and exhaust on the driver's side. The cam is in the center with intakes on the right and exhaust on the left side. The combustion chamber is very close to the ideal HEMI design and both rows of valves well tilted over from the vertical. This will help with the aforementioned sharp bend in the ports. This sharp bend may have been intentional to induce turbulence entering the cylinder to promote better burning efficiency and lower emissions. Cylinder turbulence will also reduce pre ignition. Again, port turbulence is fine at low RPM but is a restriction at higher. No amount of lift increase will cause an L head's valves to touch, however the Z head valves sit across and slightly to the side of each other and too much lift and/or increased cam overlap can easily cause them to touch, a decided disadvantage at any RPM.

 

NAPS single or dual plugs. Single works just fine but the dual plug design allows much more EGR to be used with this motor with resultant lower emissions. So what is good about dual plugs? Two points of ignition means the fuel burns up faster which allows less ignition advance, (3-5degrees for the NAPS and 10-12 Degrees with L series) cooler combustion chamber, less chance of pre ignition. Oh yeah, the shorter burn time means less oxides of nitrogen are produced and generally dual plugs get very slightly better mileage too.

 

I would imagine the stock NAPS Z20S and the L20B are comparable in performance at lower speeds until the flow advantages of the L exceed the flow limitations of the Z somewhere around 4-5K RPMs. This said, there is more potential for more power in the L design and much of any improvements to the Z series head will just be playing catch up to the L20B. There is more performance equipment for the L head too.

 

I would say the NAPS Z head with 'semi-HEMI" combustion chambers, cross flow and dual plug is superior if it wasn't for the poor air flow at higher RPM's. Too bad these innovations were not included on the L design.

 

There is one thing that can help level the playing field.... a turbo. It is much easier to install on a cross flow design head as there is more room for it on the exhaust side. Because the boost has to be piped to the passenger side this is perfect for the installation of an inter cooler. Because the turbo forces air into the motor it doesn't struggle to inhale. Poor breathing is less of a problem. Now the 'HEMI' head with dual plugs is a plus.

 

 

 

For your '72 'goon use the Z20S motor, motor mounts and the Z transmission from the '80 'goon and engine 'tilt' will not be a problem.

 

A 390 cfm is a bit big. If bigger meant more hp we'd all be running Holly 750 double pumpers. Assuming the mixture is right a larger CFM carb has less restriction and so there is a slight increase in power because the engine works less to breath at higher RPMs. Around town they tend to 'fall on their face' if pushed. A stock or 32/36 Weber is fine.

Edited August 22, 2009 by datzenmike

[Spades]

Thank you for the clarification sir! that info has been very benificial, and now I have some more questions though...

 

first off, was the stock carb a 32/36 on the 80s napz station wagons? I havent even had the air cleaner off to check.

 

in the future, I want to add some modifications, so the question in my mind, is do I want to keep the head that I have. What I want out of this engine is 140-160 horsepower at the crank. that doesnt seem like alot, but considering this engine is like 80 or 90 horsepower, thats a big jump. will I need a differant head to hit 140hp?

 

if I can hit 140hp on a naps z head, should I look around for a 8 plug model? will the added fuel economy and maybe a bit more hp be worth it? do the z20, z22, and z24 heads interchange? I know a l20b head is a bit of work to fit onto a naps block, so I am only considering such a project if the naps will never make 140hp on its own.

 

if i can make 140hp, even if it only rev's to 5,000rpm...it will be enough for me. the main question I have right now, is if that goal is attainable.

again, my plans are for a custom built intake manifold, a good carburetor, a header and exhaust, ignition upgrades, camshaft, ported and shaved head, and the freshly rebuilt and tuned up naps z20. will that make 140hp or is the naps head just not able to flow enough to hit those numbers?

 

thanks again for the help so far!

 

EDIT: by the way, I was asking about the 4bbl because I would be able to change the power valve and primaries, and supposedly the secondaries on that carb open on vacuum, so I was hoping around town with the lower hg power valve and the smaller primaries, that it would get better milage and drivability around town and more HP at WOT at higher rpms...they offer alot of selection on jet size and power valves for that holly carb, which is why i noticed on various forums that alot of 4cyl and slant six owners were running them.

Edited August 23, 2009 by Spades

[datzenmike]

All L and Z motors used the Hitach carb.

 

Expecting to get over 50% increase in power out of an L20B would be a daunting task. Do do so would require more air and gas and extreme RPMs. So much would extra be needed just to assure that it stayed alive at the the RPMs needed to do this. 150 hp from a Z20 motor would be darn near impossible without a turbo. (I doubt that even with a turbo it would make 140 hp at 5K!) It simply does not have the potential of the L head. An L head swap would get you the closest but still a lot of work. You would end up with a race engine that would be barely drive-able for stop and go street use and need aviation fuel. There are other larger 4 cylinder motors that produce almost that power. The KA24E or DE would also fit to your NAPS tranny.

 

To answer your question about the Z20/22/24 heads, yes they will interchange. The Z20/22 heads are virtually the same and both have round intake ports. The Z24 has larger square intake ports with slightly rounded corners. The round Z20/22 intake will bolt up but the larger Z24 intake would be a better gasket match.

 

Here are my Z24 (top) and Z20 (bottom) heads:

 

http://i138.photobucket.com/albums/q251/datzenmike/L%20Z%20Heads%20and%20Motors/00770026.jpg[/img]"]

 

Fitting an L head onto a Z20 engine isn't that much work. No mods are needed really. Just get an old L20B motor and swap all the timing gear, chain, chain guides, tensioner in fact everything forward of the front of the block and slap on an L head of your choice. Basically you are turning a Z20 into an L20B. All the L parts will fit on the Z20 block.

[Spades]

well, that answers pretty much all the questions I had! so, to make serious horsepower I would need boost...

 

do the naps have any potential for holding boost? if they do, are there smaller carburetors out there designed to have boost pressure passing through them? can these motors handle small amounts of boost? say 5psi?

 

since I am on a budget, I will be keeping the naps motor for a while, one thing I might do if a naps motor can handle a small amount of boost, I may see if I can find a 8 plug naps z24 head, port, polish, and shave it, then add a the rest of the mods I was planning, and then eventually add a intercooled turbo.

 

do you think with minor mods and a z24 8 plug ported head I could at least hit the 110 or 120hp mark? and perhaps with small amounts of boost later hit the desired 150hp range?

 

basically, I am trying to decide if I want to put any goodies on the naps motor, or if I should leave it bone stock and build a L20B head to stick on it...if the naps can eventually make 140-150hp with work, I will buy parts for it as time and money permits, if not, i will wait to buy the cam, header,ect.

 

your thoughts?

[datzenmike]

A normally aspirated engine will need to rev reliably to quite high RPM to pull in enough gas/air to achieve 140 hp. A turbo at 5 PSI will in theory cram about 30% more fuel/air in at the same RPMs. If you are making about 100hp at 5.5K in your Z20 then a 5 PSI boost will add (in theory) 30% more hp making 130 hp.

An advantage to a turbo is that a 'racing cam' is not needed nor desirable. A high overlap cam (time when both valves are open) will allow the turbo to push gas/air right through the motor and out the exhaust. A definite waste.

 

Most engines will handle 5 PSI boost. 7-8 PSI and you still could get by on stock eutectic pistons any higher and forged ones should be used. On any turbo motor HEAT is a killer. The extra 30% means 30% (at least) more heat that must be gotten rid of through the cooling system. Maybe a bigger rad. Heat breaks down the oil. Maybe an oil cooler and high volume oil pump from a KA motor. Heat will increase the chance of pre-ignition which will pound the brittle stock pistons to pieces. Some form of ignition retard or water/alcohol injection may be needed to reduce this and keep the motor alive. A good quality head gasket and head bolts to contain the extra compression.

 

As stated before the NAPS and the L20B are basically the same below the head, so yes the NAPS will handle 5 PSI of turbo boost. Same as the L20B and more if properly prepared. With a blow through system the stock carb or a 32/36 (don't go smaller) is fine if contained in a sealed metal box with the turbo output pressure fed into it. An electric fuel pump with an output pressure set by the boost pressure will prevent the carb from running out and the 5 PSI pushing the gas back into the tank.

 

Keith Law on 'The 510 Realm' has a blow through L20B (HEAVILY) modded for longevity that makes 250 Rear wheel hp but this is the exception.

 

 

110 hp is .......... possible.

[HRH]

I'll sell you a rebuilt Z20S, but you have to take the entire 1981 720 4x4 with it as well. I detest Z heads, as Datzenmike can attest to!

 

But it IS possible to build a 9000 rpm L20B with not that much effort. However it does require exceptionally stiff valve springs, and .120 off the head. No, that's no a typo. It would make a crapton more hp than the Z, and would be a lot more fun.

 

My Datsun guru built that engine in a previous race car. He said the hard part was finding a machinist who would agree to shave that much off. Max allowable is supposed to be .060 for an L head.

 

I'd build an L for the 510. However, for an off road machine, a Z head works great as it does have nice low rpm characteristics.

[izzo]

ill take the z motor, give you 150 for it :D

[Spades]

another thing that will help me decide if I want to keep this naps Z 4 plug head...

 

are there any manufacturers that make a high performance coil and spark plug wires? been snooping around the internet, and while you can get coils and wires other than OEM grade stuff for the z22, z24 and newer stuff, the 1980 z20s with the 4 wires seems to not have much in the way of upgrades. all I found so far was OEM grade replacements.

 

anyone know of anything? if I can't even get a decent coil for it, that gives me a good idea of the lack of performance parts out there for this head and makes me lean towards a z24 or l20b head even more.

[izzo]

i bet you could get away with a hardbody coil, or something off an m30.

 

I heard that the Z24 dual coils, sometimes it runs like crap if you replace both with something else, but if you just do 1 it works ok with a performance boost.

 

ill have to try and find the thread so dont quote me

[Spades]

yeah, I am sure there is something out there that would be better than the stock, the question is what,lol.

 

unfortunately for me, this is my first datsun, so my knowlege of nissan electrical systems is very litte...before I go swapping random coils into it, I would love to hear from one of the forum gurus who may be able to tell me what modifications could be available to this engine.

 

if there are a few go fast goodies and the possibility of a low boost intercooled turbo available, I will keep the engine and head, and toss parts at it as I have money.

[izzo]

well mines just the l20b, but it runs just 4 plugs like yours. so it should be fine. I just ran a hardbody coil and it improved some. Yello620 put an M30 i believe in his, and other people run different stuff as well. they are super cheap and about a 5 minute install really if you get one from a JY

 

could run an accell coil but i think thats a waste of money