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L18: 5-speed swap: 80-83 280Z Close Ratio 3.062 1st / 0.745 5th: Thoughts?


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Shallower 1st (3.0 -v- 3.5) and 2nd

But much higher (numerically lower) 5th (.75 -v-.85)

 

I've got OS 205/75r14's which have a 10% speedometer error and have no issues whatsoever with the L18 pulling out in 1st.  Pulling out in 2nd is too tall.  The 3.062 is "1/3rd the distance to the goal" which might be an issue.

 

But the wide 5th would be TOTALLY AWESOME at 80 mph on the Interstate.

 

Has anyone put this transmission in an L18 or L16?  Did you like it?

 

And are there any installation issues using a Z-car trans.  I'm pretty sure my L18 is long tail housing 4-speed so it should bolt up to the block and the drive shaft should be correct.

 

Some people say there is an issue with the trans cross menter/mount?

 

And finally issues with the shifter location - someone told me to get a L20B 5-speed from a 620/720.

 

I'd really like that .75 instead of a .85 5th.

 

Opinions/Suggestions?

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If you use your truck for commuting this won't be a problem just a slightly longer slip of the clutch to get going. The 3.592 first gear helps a small L18 hauling a load up hill from a stop. If you use for hauling with, I would avoid it.

 

Many have put this transmission behind L16, but mostly 2,100 pound 510s or similar cars. Your 620 is about 400-500 pounds more.

 

People say lots of things and don't forget the '73 had a shorter transmission that yours. This is a total drop in with no mods or problems. Use your clutch throw out bearing sleeve but get a new bearing. The zx will have the wrong speedometer pinion sleeve in it for your differential gearing. You can modify your 4 speed pinion for use in it but now is a good time to get the proper gear to get rid of your 10% speedo error.

 

Shifter will be in the same location.

 

A 720 transmission will also work but only the '80 2wd will fit your truck as perfectly as the zx. It will also not have the big over drive.

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The later zx 5 speed is intended for a much larger, powerful, torquey engine. At 4K in 4th gear it can handle a 1,000 RPM drop into 5th at highway speeds and cruise.

 

 

 

Wind resistance increases with the square of the velocity. If you only need 10 hp to push through the air at 40 MPH you will need 80 HP to go 80 MPH or double the speed. Four times the work done in half the time is 80 HP. This is why going very fast is not easy or cheap.

 

 

 

You would be revving 4,500 at 80 MPH with your current set up. With the zx 5 speed this drops to 3,500 RPMs. Now, no doubt you are making much less power at 3,500 than 4,500 RPM. So will it be enough??? Also will your foot be mashed into the secondary to maintain this speed???

 

The intent of the over drive is to lower cruise speed RPMs and (just maybe) save a little gas. It's not intended to go faster.

 

 

BTW you over size tires are the equivalent of changing from your 4.375 to a 4.19 differential

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L leans to the right. Z leans to the left.

 

With a Z series trans, your shifter will be in the passengers knees.

 

Doesn't this apply to Nap-Z motors, not Z car chassis?

 

Admittedly, I know more about the late model 720's and D21's than I do about the older true Datsun stuff, so I could;d be way off.

 

Apologies if this is veering too far off OP's topic.

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It does. The Z series and the KA series have the same identical engine tilt. Well he did say Z series trans. No-where in the world is the Z car called a Z series, actually S30 is even more accurate because in japan the same car is called a Fairlady or Fairlady Z

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Shallower 1st (3.0 -v- 3.5) and 2nd

But much higher (numerically lower) 5th (.75 -v-.85)

 

I've got OS 205/75r14's which have a 10% speedometer error and have no issues whatsoever with the L18 pulling out in 1st.  Pulling out in 2nd is too tall.  The 3.062 is "1/3rd the distance to the goal" which might be an issue.

 

But the wide 5th would be TOTALLY AWESOME at 80 mph on the Interstate.

 

Has anyone put this transmission in an L18 or L16?  Did you like it?

 

And are there any installation issues using a Z-car trans.  I'm pretty sure my L18 is long tail housing 4-speed so it should bolt up to the block and the drive shaft should be correct.

 

Some people say there is an issue with the trans cross menter/mount?

 

And finally issues with the shifter location - someone told me to get a L20B 5-speed from a 620/720.

 

I'd really like that .75 instead of a .85 5th.

 

Opinions/Suggestions?

I think some one miss read the original Title and first post.  Z-car to me is a 240, 260, 280 Z car as stated in the title.  Could even interrupt as 300,350, & 370

 

Now if he would have said Z truck I would think of the NAPS Z Engine series.

 

Mike and Flat are correct in their statements.

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My question, about Flats post not the OP's, seems to have completely been misunderstood.  I did indeed read and fully understand the original post and what chassis he was referring to.

 

What I was asking was based on what I've heard about the use of Nap-Z trans and L series motors and there being a tilt issue.  I wasn't sure if there was an altogether different tilt issue with the use of the trans pulled from a Z-car chassis.

 

This is also based on what I understood as being the L-series 6 cyl, that I understood as being in the Z-cars, having the same bellhousing as an L-series 4 cyl. 

 

Again, as I stated, I'm not as familiar with the older Datsun cars, so I was merely asking to gain knowledge.

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Yeah. But I misread.

 

I saw Z. Overlooked -car.

I also saw asking about 720.

 

 

Buyer beware. The 720 only offered the L20B in one year of the 720.

So...if you go asking around for a 720s transmission, you may end up with what you were not expecting.

 

But...but...the 71B bell from the L trans can be swapped to a Z-series 71B trans.

 

So...in a way...I was soooooo on point.

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But...but...the 71B bell from the L trans can be swapped to a Z-series 71B trans.

 

 

This...this right here is some of the kind of knowledge I was looking to gain.  Mostly because it lets me know the 3 extra transmissions I have might actually be worth something to someone before I just scrap them.

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If I'm not mistaken, the 1980 720 2x4 and 4x4 used the exact same transmission.  The transfer case was separated by a short driveshaft.  

 

As for the steep overdrive, I can tell you from experience that my "built" MGB with about 100 hp at the wheels and 1850 lb curb weight did not make enough power to comfortably use the .74 ratio.  I doubt a much heavier truck with 100 hp at the flywheel would like it much either.  Big overdrives like that would be good on a 6 cylinder or even V8 conversion.  

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All '80s 720 trucks used the L series transmission because... L series engine. This excludes the Diesel engine option.  There were no L4 engines after '81.

 

The two wheel drive transmission is the one you want (if at all) as the 4x4 transmission only comes in 4 speed (that year) and does not have the speedometer pinion machined out. The speedometer drive is from the transfer case on them.

 

Both 2 and 4x4 use the same internal wide ratios with a 3.592 first gear. This transmission is the same as the '79 truck ratios as both trucks us 4.11 or lower numbers and need the extra gearing to get rolling from a stop carrying loads.

 

All 4 or 5 speed fourth gears are the same one to one.

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I could definitely pull the Big OD:  there is a summit on Rte 30 just East of Ligonier that is a massive grade - usually you get stuck behind someone terrified of the grade and there is no hope of passing because most cars don't have the big HP to do that.  But my L18 620 made the grade at 50 mph in 4th - although it was floored in a few sections maybe totaling a mile at most.  So on the PA Turnpike, that 0.746 would be perfect, even with the taller 205/75r14's.

 

But I have been paying attention to the various really steep pullouts I have to make locally - I kinda like the low I have right now.

 

I'm undecided about tires:  either tallest I can get if I have to drive in the snow, or the shortest for handling.  If I go short, the Big OD would be OK.  Tall, I'm just not so sure.  I don't really plan to haul anything more than a 1/2 of chip stone maybe a couple more times in my lifetime and other than that, no big loads.  I think I could deal with big loads if I had to with the Close Ratio trans.  HaHa:  if faced with an unexpected big haul job, maybe I could have some really short "hauling tires."

 

Actually on the tires:  maybe have very tall All Season tires for snow and trips and run the low profiles other wise.  Actually that might be a good solution.

 

But then the Simple Question:  What is bugging me right now?  Obviously High Rpm on the Interstate.  So maybe that should get tahe concern.

 

Oh, but what about that BW T5?  it's a 3.50 / 0.78 5-speed?  That would be ideal

_______________________

 

EDIT:

 

I guess another thing not to loose site of is heavier transmission waste more HP.  So the Z-car trans are heavier since they can take more torque.

 

Maybe a L20B 5-speed is the best compromise.  In fact, it would directly address the Interstate rpm.  (And aren't they 55# and basically UPS-able?)

 

Or maybe the first $100 deal that comes along (!)

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You won't be using the overdrive upgrade. Should be downshifting.

 

 

And with all the different ratios, on paper, the difference is so slight.

 

 

What I am always on the lookout for is the mid-ratio to use with a 4.11 rear end behind an L18/L16.

 

For now though I have doglegs to use until my search is fruitful.

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there are two number that can be used to describe the "power" of an engine.  Peak torque, and peak horsepower.  Peak torque happens at a lower RPM than peak horsepower, horsepower is a function (multiplication) of torque at a certain RPM, times RPM.

At peak horsepower RPM, you actually have less torque that at a lower RPM.

 

If you change the gearing (including the tires) to lower the RPM of the engine, you might get into a situation that you cannot pull the grade you are climbing, without down shifting.

Additionally, if you change the gearing (including the tires) to lower the RPM of the engine, you may not have enough torque at the rear tires to overcome air resistance, and have to again down shift, or open the throttle enough that the carb starts to richen the fuel air ration, to make more power.

 

Another factor to consider is changing the gearing (including the tires) to lower the RPM of the engine will make the truck accelerate slower in any gear.  this means that if you get into a situation where quicker acceleration is needed, you will always have to think ahead enough to again, down shift.

 

There is no problem with a Datsun engine running high RPM.  They are built to do that.  You have a Datsun, not your Grandfather's Oldsmobile.

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I could definitely pull the Big OD:  there is a summit on Rte 30 just East of Ligonier that is a massive grade - usually you get stuck behind someone terrified of the grade and there is no hope of passing because most cars don't have the big HP to do that.  But my L18 620 made the grade at 50 mph in 4th - although it was floored in a few sections maybe totaling a mile at most.

Five speeds do not give you better hill climbing ability. If you were floored in 4th shifting to 5th you will slow down. In fact all your gears will have less power except 4th which remains the same. 

 

 

So on the PA Turnpike, that 0.746 would be perfect, even with the taller 205/75r14's.

 

This is true. Overdrives allow a small RPM drop at highway cruise speeds (although the zx overdrive is a monster 25.5%!!!)  to save a little gas. That's it. You will definitely go faster in 4th than you will in a zx overdrive 5th.

 

 

Oh, but what about that BW T5?  it's a 3.50 / 0.78 5-speed?  That would be ideal

They are physically larger (no room) and longer (need shorter driveshaft) and I doubt the shifter or trans mount is in the correct place.

vs.

The zx 71B 5 speed is totally, a drop in swap.  

 

 

I guess another thing not to loose site of is heavier transmission waste more HP.  So the Z-car trans are heavier since they can take more torque.

 

Maybe a L20B 5-speed is the best compromise.  In fact, it would directly address the Interstate rpm.  (And aren't they 55# and basically UPS-able?)

 

Or maybe the first $100 deal that comes along (!)

You already have a 71B 4 speed. The 71B 5 speed is not any stronger as it a 4 speed with an added overdrive gear. They weigh at most 10 pounds more. 

10 pounds...

 

1.6 US gallons.

House cat

Three month old baby

10 lb bag of sugar/flour/rice

 

Ten pounds is less that the junk you have in your vehicle right now.

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the worst case scenario is you put the trans in and the gearing doesn't work for you then you sell it to someone who can use it 

but with all your statements you will overall be happier with the zx 5 speed untill you try to haul a heavy load 

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