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1983 Gran Sport camper?


distributorguy

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It seems all the motorhomes typically have sketchy frame extensions, so watch for that. The rear axle is typically a full floating version of the c200. The engine is no different than a normal 720 from what i understand, not even a cam change.

 

That's about all i know of them.

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I'm more of a 620 guy, but a 720 Gran Sport camper conversion just popped up locally.  Cheap.  Anyone familiar with them?  

Equally curious about it because I just did my daily "Nissan 720 Datsun 720 Datsun Truck pickup" search on craigslist.

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Its a Z24, 5 speed setup.  No idea what gears.  Old tires, bad exhaust, runs ok (meaning passable but not good).  The camper's shitter is missing, which I consider to be a benefit.  

I'm mostly interested in the transmission.  

 

On the Z24, the 2nd set of plugs has nothing to do with the engine right?  It burns in the exhaust manifold???

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On the Z24, the 2nd set of plugs has nothing to do with the engine right?  It burns in the exhaust manifold???

I believe so. I remember reading somewhere that the second set of plugs do not fire under heavy acceleration conditions.  A quick google search gave me this, quoting Mike here

 

They fire together at the same time from the factory. Who told you different?

 

Later Z24s had a cut out to switch to single plug when accelerating under heavy load. Your dizzy would have a 3 wire harness and a single extra 4th WHITE wire with it's own plug. If you unplug this WHITE wire it stays on dual plug operation all the time.

 

 

Notice the extra WHITE wire with it's own plug?

Z244wiredistributorcalisingleordualplugf

 
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If a true camper conversion a Cab/Chassis truck is sent for conversion. This is a HD truck minus the box. There's no mention of year so all had H-190 and probably dual tires however the floating axle was only on the Nov '82 and on with the new Z24 engine. All earlier Cab/Chassis were 4 speeds, all Z24 engine ones were 5 speed.
 
This could be home made for all I know. If it says Grand Sport this is solely the name on the camper. There was never a 'Grand Sport' 720.... Nissan only made the trucks.
 
 

 

 


Its a Z24, 5 speed setup.  No idea what gears.  Old tires, bad exhaust, runs ok (meaning passable but not good).  The camper's shitter is missing, which I consider to be a benefit.  
I'm mostly interested in the transmission.  
 
On the Z24, the 2nd set of plugs has nothing to do with the engine right?  It burns in the exhaust manifold???

Dual plugs fire together. On later years the exhaust side can be turned off simply to reduce engine noise under full throttle loads. (what ever that is) Perhaps the two flame fronts colliding in the combustion chamber? Probably sounds like a diesel's clack clack clack.?? Two plugs allow shortening of the ignition advance and there is less time for oxides of nitrogen to form at peak cylinder pressures/temperatures. Dual plugs allow better ignition of leaner mixtures and more EGR to be added at part throttle. When the engine operates in single plug mode the ignition module automatically advances the timing to correct for the now longer burn time.

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The truck is a late 83 with Z24 and 5 speed.  Its definitely a factory job - somewhere.  I'm guessing it was built somewhere up here - MN or WI.  

 

https://minneapolis.craigslist.org/hnp/cto/d/1983-nissan-camper-rv/6293846137.html

 

 

The Z24 distributor has the same bad advance curve as most Nissan/Hitachi truck distributors.  I've rebuilt a few.  My recommendation has been to eliminate the 2nd plug function and run it with a good primary advance curve.  Its not as if they have domed pistons and the flame front can't travel.  Although they should have domed pistons to raise the compression.  I can't believe this engine makes less power than a stock L20b, despite having a cross-flow head.  Overthinking, bad planning, and emissions requirements = more problems.  

 

This thing would look cool with a regular bed and big old fenders on it.  

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I'm saying Nissan made the truck, minus the box. Conversion companies put the camper parts on. It possible the dealer might order one for a customer and send it out.like the 620 4x4. There will be a plaque somewhere with the builder, date,GVW etc on it.

 

I disagree. For what it was designed for, low emissions and low speed grunt to pull a heavy truck up to highway speeds, it's perfect.... Nissan did not design in much room for improvement with these goals in mind. There is no 'problem', only when looking for performance increases there's a problem.  

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I'm saying the Z24 would make a lot more power with a simpler design - minus all the emissions controls and dual spark.  There's also a KC pickup for sale cheap with an extra engine and trans.  I'm guessing an overlap of the hp/tq curve would show the Z24 has significantly more "power under the curve" from idle to 3500 rpm than a L20b, so are "peak" numbers artificially low???  Or are the head's port designs that bad???  Or the carb is a joke, or ???

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That it would! Even an L20B head for 400xcc less of an engine will do the trick.

 

I found ratings of 130 torque at 2,800 for the Z24. Wow that totally is getting up near the KA but 2,800? Grunt. But it falls off in power over 4K. Yes the head is terrible but on an engine that only has to 'perform' up to and at highway speed it doesn't matter much. Both ports are low on the head and bend suddenly at the seat. That's something that can't be ported out. Look at an L20B and the air falls down hill into the chamber. All Z24s perk up with a Weber which says a lot about the restrictive Hitachi on it. The cross flow and dual plugs would be great for a turbo.

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You don't get any benefit from dual plugs until compression goes sky high IN ADDITION to 4" or lager diameter piston OR a piston with an obstructive (poorly designed) dome.  Dual spark is either a plan for failure (backup like in a plane or firetruck) or used in HUGE cylinders like the guys at Bonneville running an 11:1 compression 600 cubic inch Hemi engine with 41 psi of boost on top of it.  Too much nitro-methane to burn with one plug - the plug melts away before the run is over.  

 

It sounds like part of the Z24 issue is cam timing.  Advanced for grunt.  You could shift that power curve into the 2000-4500 range for better drivability I'd bet.  

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Hemi designed chambers naturally have poorer emissions for reasons i don't completely comprehend. But as far as all the reading I've ever done, modern Chrysler hemis run dual plug for the exact same reason Nissan did in the z series engines, strictly to improve emissions.

 

Nissan did make a 4 plug z20? head in the 200sx for a couple years.

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It sounds like part of the Z24 issue is cam timing. Advanced for grunt. You could shift that power curve into the 2000-4500 range for better drivability I'd bet.

An interesting thought, one that might bear closer inspection, but doesn't necessarily resolve the fact that head seems to run out of breath completely in that 4500rpm range. But perhaps much of that reputation comes from the cam?

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...and from the carb.  The carb is the end choke point that kills it at 4500.  Remember how the 620 redline is 7000 rpm?  You can't get there until you install a much better carb and manifold.

A low power band is generally 100% cam timing.  

Low hp is cam timing, if it makes good torque.  

Choked performance is from too small a carb, too lean fuel mixture, too much distributor timing, and likely cam timing designed to heat the exhaust for better emissions.  Standard formula 70's emissions tuning to import foreign vehicles.  Federally mandated tuning procedure, present in Japanese, German, and British cars across the board.    

 

All these factors are generally in place when you have a vehicle that is known to eventually crack the cylinder head.  When you push a motor to run borderline hot all the time, inject fresh air into a hot exhaust right near the head, and excessively lean out the fuel mixture with extra ignition advance, cracks happen.  

 

The Z24 head has nearly a hemi chamber.  It should run well at 30 degrees total timing, but the chamber has no squish and its relatively turbulent due to the port designs in the head.  And the ignition trigger starts to regress timing at 4000 rpm, so its a problem above 4500 too.  It can probably all be "undone" with a Weber conversion, distributor recurve, and a new valve cover gasket.  And some porting.  And an adjustable cam gear.  

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Well, other than you saying so, I have never heard of the EI distributor timing retarding above 4K. No one here has ever mentioned or observed this. I did mention the E12-93 module (there may be others, but not the matchbox E12-80) has adjustable retard controled by the EFI on the later 280zx and Maxima. Maybe you saw this in action?  

 

The Z24 and the L20B have the same cam specs of opening closing overlap and lift per FSMs. This is not to say they are on the same tooth just that the cams are essentially the same.

 

The Z24's timing is 5 +-2 degrees. (L20Bs are 12) Mostly from having dual plugs and shorter burn time. I agree this may be somewhat retarded than needed but how to tell? I guess you could add more and more till it pings and see how much you could get away with. The hemi head is fairly detonation resistant to begin with.

 

The carb is too small for it, but running richer does not make it a barn burner either. Larger carbs like a Weber does wake it up.

 

Where do you hear the heads eventually crack? Again no one here complains of it unless running with a blown head gasket which by the way is common, I do agree. It's preventable though.

 

The Z series do not inject air into the exhaust ports, there's no pump. They use the exhaust negative pulses to draw air into the exhaust manifold through a one way reed valve on the air cleaner. 4x4s have two. It's totally passive in design.

 

The '84 Z24 mechanical advance max is 10 @1,900 + 5 static X 2 = 30

 

 

Porting won't hurt but can't totally undo the bad breathing. It will never breath like an L20B and why an L head swap is so successful.

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Well, I guess I see the timing retard because I have the tightest Sun distributor test machines on the planet.  Hotrodded beyond what Sun ever meant them to do.  I can see timing variations of 1/4 degree very clearly, and I see what the pickup coil or the module does, separate of what the amplifier does.  You can't see that without a test rig like I have.  In the vehicle, you see the sum of timing chain slop, gear slop, end float in the distributor, etc...  I can isolate specific distributor traits and minimize them so what you get in the car/truck/boat/tractor/generator/etc... is closer to ideal.  

 

Not that it matters, but so far the best electronic system I've seen is a Mopar pickup module triggering a Chevy HEI module.  Durable and crisp, without as many side effects as using an HEI style or magnetic or optical pickup.  Its basically what MSD uses, only cheap and plentiful.  Easily retrofit into many applications thanks to Rockauto and Google.  You can even upgrade to that sensor in the 1980 Hitachi EI distributor with some effort.  

 

As far as cracked heads - I'm referring back to my comment about British, German, Japanese as a whole.  American cars fell into the same routine.  Burned head gaskets are also caused by a lean condition and advanced timing.  A lot of times its just poor maintenance however.  

 

Modern Chrysler Hemi engines run a total of 16 degrees timing!  That's what an efficient combustion chamber should do for you.  My L20b race engine runs at 28 total, and like it enough to pass by 10k rpm with ease.  The Z24 is at 5 degrees at idle because it makes the exhaust gasses hot, which means a clean tailpipe.  Again, Federally mandated laws for "clean emissions" even though it results in high NOx levels.  Bump that to 14, take some timing out of the distributor and torque goes up exponentially so you no longer need to screw up the cam timing.  I bet the difference between an L20b timing chain set and a Z24 timing chain set is the cam timing?  Holes drilled differently?  I've never even worked on a Z24, but that's what I'd expect to see.  

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So your magic machine shows Datsun EI module retarding above 4K, or  just some timing jitter from natural causes of wear and slop. Because, not the same thing. Later Z24i and KA engines use a splined spindle/CAS distributor to eliminate some of this designed in slop.

 

Datsun/Nissan heads are not known for cracking is my point. This is most certainly not known to eventually happen on them. Block cracking is much more prevalent.

 

I'm confident that you can't bump a Z24 to 14 degrees and get away with it ... for long. If it was single plug perhaps.

 

 Cams are the same but how they are timed, I don't know. There may be the three holes for adjusting chain slack from wear, but the Z series do not specify this in the FSMs, in fact there is no notch for a reference point to gauge the wear.

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Well the owner's kid decided he was going to keep the camper, so its off the market.  No longer for sale.  So much for waiting until Saturday.  

 

Mike, thanks for the timing advice, especially since I've rebuilt and recurved in excess of 15000 distributors and have roughly 8000 very happy (repeat) customers.   :confused:

Idle timing is decided by fuel quality.  Even my flathead Ford prefers 14 degrees at idle.  The trick is to adapt the rest of the advance curve to work with the 14 degree idle setting.  Dynamic compression at higher rpms is a different animal.  The engine needs what it needs and the factory never delivered the "best" curve - it delivered an average curve that worked ok and had the cleanest emissions without causing undue damage.  There is a lot of room for improvement.  But DON'T set your timing in a stock distributor to 14 at idle - it could fall flat on its face by 3500 rpm!  

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Most of your advice is for old school points that are.... so '60s  obsolete. No one is going to take them in and mod them like you recommend so that leaves working with them in the real world which is limited to constant replacement and setting the gap. The next logical improvement/upgrade is to eliminate them entirely and replace them with a pointless electronic distributor for more reliability and power. These are things that are well within the ability of any backyard mechanic.

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Mike, that's pure bullshit. Do you also argue that a light switch in your home is not as good as a digital version?  Cars ran beautifully for 100+ years using points.  Why are they now obsolete?  Because someone came up with a band-aid to put into a distributor to make it work differently for 20 years or so?  At least until they figured out how to get rid of the distributor altogether (genius in my opinion).  

 

Keep in mind what a distributor is supposed to do.  Its supposed to pick up a specific degree of crank rotation and trigger the spark.  Anything that alters the distributor's perception of the crank position screws up the state of tune.  A mechanical switch (that needs adjustment every 6000 miles) isn't a bad way to go versus a "digital" switch that's function WILL be corrupted by plug wire noise, alternator fields, and weak grounding.  At least points are predictable.  Mike if you had one of my point distributors, you'd change your mind on your first drive - even though you wouldn't have a clue why.  You, like everyone else, would be dumbfounded once you realize what you've been missing all these years.    

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Evolution moves forward. The EI distributor is the next logical step toward a crank angle sensor and getting rid of them entirely. That 'band-aid' makes your distributor virtually maintenance free. It eliminates point bounce, floating, pitting/wear that degrades the contact surfaces and alters the dwell and timing. In addition, with a running charging supply of 14.3 volts, the EI conducts more power (14.3 to 18 amps) than the points system can handle (that requires a ballast resistor 4.76- 5.5 amps) through a lower impedance coil for more output voltage.

 

Plug wire noise? As only one plug is fired at a time how is it going to change it's own perception of where the crank is or when to fire while it's firing the plug?  Alternator fields? if any detectable are nowhere near the distributor. Weak grounding would be common to a points distributor also. Distributor shaft wear would be less with an EI but mechanical and vacuum advance alterations would be the same on both. So whats the difference? the elimination of points and higher output.

 

I can see a market for rebuilding a worn out distributor, changing the mechanical and vacuum advance curve. Only the purist of the purists would still have points in their '67 Mustang. It's inconceivable that any '55 Chev / Camaro / Challenger / Fairlane is driving around today without taking advantage of an electronic distributor or 'add on' EI box.  

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