napz engine

[720s]

looking to upgrade my truck to pull a bit more what parts should I install maybe cams ?

 

so far i have

flow master 40 series straight pipe

32/36 weber

msd ignition

center force clutch

headers

holley electric fuel pump

[datsunaholic]

Pretty good there- you've bought a bunch of stuff that doesn't actually increase horsepower.  The Weber might have helped driveability; a Weber 38 would have probably been more noticeable.  The Z24 isn't one that takes to mods very well, there are design limitations to the head that simply don't lend well to normal mods, like porting, bigger valves, higher lift cams.  There once was an "RV"cam that helped with lower-end torque but killed top end, what mods you made are more optimal for top end and kill the bottom end.  The headers and high-flow exhaust would let it breathe a bit more (at high RPMs, the stock stuff was good for 4K RPMs) if it wasn't strangled by the stock intake and valves.  Plus what kind of MSD ignition?  Does it actually fire both sets of plugs?   Or was it just a pair of MSD coils using the stock ignition module?  The NAPS-Z used dual plugs to reduce emissions by halving the ignition advance, but also means you can't advance it very much. changing it to a single-plug operation requires a LOT more advance, but the flamefront is far from optimal.

[flatcat19]

Headers? As in 2?

[datzenmike]

The NAPS engine is perfect for what it was designed. Very good low speed torque and low emissions. To that end there is no need to make power above 4K on an engine driven at 3K on the highway nor is there need to provide allowances for improving the top end performance. In all engines it's the head that makes power and the block strength that keeps it all together. The NAPS head does not breath that well above 4K... because it doesn't need to. It also can't be made to breath well because of it's design. Larger diameter valves and increased valve lift will cause the valves to touch. 

 

However.... there are several things that lend the NAPS to a turbo application.

 

Cross flow design with hot exhaust ports far away from the intake ports. Turbo on one side and intake on the other. Keeps the plumbing simple and easy and lends itself to an inter cooler.

 

Hemi style combustion chamber. The most efficient there is

 

Dual spark plugs. Shorten the burn time allowing much less ignition advance and chance of detonation.

[Rjawm]

Pretty sure the part you are looking for is called a KA24E.

[datzenmike]

You've probably covered everything with a 32/36 and a low restriction exhaust. The stock ignition and exhaust manifold is more than enough for up to 5K.

 

An '85 720 had deplorable differential gearing and at best 3.889 for the 5 speed and 3.70 for the auto. Lower RPMs give slightly better mileage in every gear but not so great acceleration, so going to a 4.11 or a 4.375 will rev the engine higher at the same speed. This means the engine is making better power at the same speed than the old differential. It's also very cheap, maybe $100 or less for the diff. Does not add any extra strain to the engine/clutch/transmission or drive shaft either. Best $100 you will spend on it.

[datsunaholic]

What Mike said- a 4.11 would probably be best.  Besides, how fast can you GO in Hawaii?  Let alone Maui?   But lots of hills.  Rear gear change would make it more peppy.  Probably have to source a diff from the 48, though.  I didn't see very many Datsuns on Oahu when I was there... and that was in '95 (saw 2- one was crushed and rusted away in the bushes of Sacred Falls State Park, the other was on fire on base at Pearl).

[720inOlyWa]

That is funny, Doug. On fire? Oh man.  

 

I hesitate to comment along with such august and well informed experts except to note that it takes all kinds in Ratsun land. I read this thread and though it was funny that my desire was the opposite: I don‘t need it to be breathing harder or quicker- I could use a sixth gear!

 

Recently, I test towed a 950 pound drag weight boat trailer with my relatively freshly rebuilt napz engine and driveline. Yes, I do need air shocks, or something to support the bumper a bit, but otherwise, I could hardly feel it back there. The Fudgecicle ran that right up the hills like a bitch. I was thrilled. It was a big affirmation for my eventual plans for this tuck: to tow my 18' skiff all over everywhere and back. The trailer wiring set up is wonky right now, and will need sorting, but the truck is well up to the task. For this kind of load oriented light truck use, I find this combination- in dead stock form- executes well beyond initial expectations. I started out wondering, but now, I am a big fan.

[datzenmike]

If towing or carrying a heavy load use 4th gear. 

 

If passing  or climbing a grade always use 4th or even 3rd as necessary.

 

Fifth should be used for highways cruising or light load, not to hard accelerate in.

[720inOlyWa]

...and I do. Works just fine!

[720s]

alright thanks for the help

[720s]

yeah Hawaii has a lot of speed limits but I like to just cruise & once & a while open it up

[asid99]

Yeah, with a straight pipe you will actually be loosing power, but maybe because of the webber you broke about even. The back pressure from a tuned exhaust usually helps widen your powerband. Have fun doing valve adjustments regularly, because all my friends with straight pipes (no matter the car) are ALWAYS tinkering with valves

[Lockleaf]

Yeah, with a straight pipe you will actually be loosing power, but maybe because of the webber you broke about even. The back pressure from a tuned exhaust usually helps widen your powerband.

I'm sorry, but this is all entirely incorrect. Back pressure is only a measurement of resistance to flow. It is not a performance modifier. Two things about exhaust (post header and collecter) affect power, exhaust velocity and scavenging. These are controlled by selecting a proper exhaust tube diameter and components.

 

When straight piping (which actually is the highest flow option) only pipe diameter is changeable. It needs to be large enough to allow the air out rapidly, but small enough to maintain high exhaust velocity.

 

If using mufflers or resonators etc, you want to select components that flow as close to the cfm of your piping as possible, but because they create turbulence, they are always creating loss.

 

Here's an excellent primer in actual performance exhaust theory.

 

http://www.nsxprime.com/nsx-faq/exhaust-theory/

 

Want more? Read everything written by David Vizard. He's an engine performance research scientist with tons of empirical evidence to back his claims.

[asid99]

I'm sorry, but this is all entirely incorrect. Back pressure is only a measurement of resistance to flow. It is not a performance modifier. Two things about exhaust (post header and collecter) affect power, exhaust velocity and scavenging. These are controlled by selecting a proper exhaust tube diameter and components.

 

When straight piping (which actually is the highest flow option) only pipe diameter is changeable. It needs to be large enough to allow the air out rapidly, but small enough to maintain high exhaust velocity.

 

If using mufflers or resonators etc, you want to select components that flow as close to the cfm of your piping as possible, but because they create turbulence, they are always creating loss.

 

Here's an excellent primer in actual performance exhaust theory.

 

http://www.nsxprime.com/nsx-faq/exhaust-theory/

 

Want more? Read everything written by David Vizard. He's an engine performance research scientist with tons of empirical evidence to back his claims.

I didn't mean to say that it lost power, but that it limits the powerband. Restricting and expanding the flow and travel length of exhaust, you can control the powerband. Racing teams have used this method since way-back-when. My dad's old laydown gokart in garage actually has this, and it is astonishing. You pull the paddle behind the steering wheel once you feel like you are topping out, and you expand the powerband and can go further. I don't really care what that man you linked me to says, I've literally experienced it myself, and it is crazy. Ride an old endurokart if you can find them, they were on most of them back in the day. This would also probably be the easiest way to experience it.

[datsunaholic]

But aren't most old kart motors 2-stroke?  Some 2-stroke engines benefit greatly to having expansion chamber exhausts, since those engines have no "intake" or "exhaust" strokes and rely on the exhaust velocity to do proper scavenging.  The expansion chambers are really only optimal at certain RPM/Load levels, so having a modifyable chamber would change the power band.

[flatcat19]