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NM 521


Oilspot

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So to answer my own question.... My truck, with no front bump stops, the distance between the bottom of the front fender and the ground being 24", on 195/70r14 tires  gives me a fairly smooth ride without the lower arm slamming into the frame. I can't fly over train tracks or anything of the sorts but I'm used to that from driving lowered/ slammed crap most of my life.   

This is the truck with that 24" front measurement, 4" blocks in the rear with no mods to the rear springs. 

vJpf0bb.jpg

A bit to much rake so it'll only get more travel if i raise the front a bit to level it out some.  

I figure this info may help somebody in the future!?!?

 

 

 

A quick question on h190 gearing/ third members. She's pretty spinny on the stock 4.375 (which from what Ive read is stock in the 521's). I can't imagine going any considerable distance on the highway!!! Does anybody have any experience with running different rear end gearing combos? Ie. Does a 4.11 make a noticable difference, is a 3.889 to short for a daily driver with a L16? 

And does any body have a complete third member with a lower gearing they wanna sell???

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1 hour ago, Oilspot said:

A quick question on h190 gearing/ third members. She's pretty spinny on the stock 4.375 (which from what Ive read is stock in the 521's). I can't imagine going any considerable distance on the highway!!! Does anybody have any experience with running different rear end gearing combos? Ie. Does a 4.11 make a noticable difference, is a 3.889 to short for a daily driver with a L16? 

And does any body have a complete third member with a lower gearing they wanna sell???

You'd be better off doing a 5spd swap ... someone here sells a mount and you just shorten the drive shaft.

Yes there are 2 hard to find transmissions that dont need a shorter driveshaft but they are hard to find... any long tail 71b 5spd is what you want....

I am sure some will comment on the gears....

I daily my 521 as much as the weather allows and the 5spd was the best upgrade I have done...

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Ahh ok, well I did a 5 speed swap and my truck is still spinny on the freeway.  Meaning at 70 its around 3800-4k RPMS which I was it wasn't.   So wouldn't be inline with what @Oilspot is saying about replacing the 3rd member?  Because I swapped from a 4 to a 5 and it didn't make all that much difference at speed on the freeway.  

Edited by d.p
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There are different overdrive ratios between the 5 speeds. The most sought after is the ZX box with the barely noticeable overdrive, but for a truck, any wide ratio 5 speed will do the trick.

 

It may be personal preference, and also have something to do with where I live, but I don't mind having a deeper diff ratio. These small motors can run all day long at 4000 rpms. They don't care at all.

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Slow day at work, so I'm getting paid to figure out how third member swaps would work out 🤣

i49rcdP.jpg

 

Cruising 75 at 4k!?!?  Does the l16 put down enough power to pull light grades, fight headwinds etc. Or do I play it safe and settle for a 4mph increase and cruise 71 at 4k?????

 

 

 

 

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2 hours ago, d.p said:

Ahh ok, well I did a 5 speed swap and my truck is still spinny on the freeway.  Meaning at 70 its around 3800-4k RPMS which I was it wasn't.   So wouldn't be inline with what @Oilspot is saying about replacing the 3rd member?  Because I swapped from a 4 to a 5 and it didn't make all that much difference at speed on the freeway.  

I still dont get that.... I saw a good rpm drop from 4th to 5th....

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The '80-'83 zx non turbo OD has a 24.5% reduction in RPMs which will sort of work in a light 2,200 pound 510 with L16 and maybe 70 hp. All other Datsuns (other than the 1200) are much heavier. Nothing is free. All engines have to lift the vehicle weight vertically through any incline. If the RPMs are such that it's not making enough torque for this at the highway speed you are going, you will have to down shift. In addition to inclines, on a flat surface wind resistance (drag) is the limiting factor in top end speed. Drag increases 4 times for every doubling of speed. If your L16 produces 15 hp to go 40 MPH it will have to make 60 hp to go 80. There are more than a few vehicles that will go faster in 4th than in 5th.

 

Calculating engine RPMs is all well and good but a reduction it RPMs also reduces engine power and power is what pushes you through 80 MPH wind.  At 67.3 MPH with a 4.375 axle at 4000 RPMs... if you install a 3.889 your RPMs at that 67.3 MPH has reduced to 3,555. That's a significant loss. Will an L16 pull 4k @ 75 MPH... probably. Will it be sluggish at all other speeds and getting there? definitely.

 

A 24.5% RPM drop @ 4k is 980 RPM. Insane amount. OK for a 2.8 liter 6 cylinder car.

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33 minutes ago, datzenmike said:

The '80-'83 zx non turbo OD has a 24.5% reduction in RPMs which will sort of work in a light 2,200 pound 510 with L16 and maybe 70 hp. All other Datsuns (other than the 1200) are much heavier. Nothing is free. All engines have to lift the vehicle weight vertically through any incline. If the RPMs are such that it's not making enough torque for this at the highway speed you are going, you will have to down shift. In addition to inclines, on a flat surface wind resistance (drag) is the limiting factor in top end speed. Drag increases 4 times for every doubling of speed. If your L16 produces 15 hp to go 40 MPH it will have to make 60 hp to go 80. There are more than a few vehicles that will go faster in 4th than in 5th.

 

Calculating engine RPMs is all well and good but a reduction it RPMs also reduces engine power and power is what pushes you through 80 MPH wind.  At 67.3 MPH with a 4.375 axle at 4000 RPMs... if you install a 3.889 your RPMs at that 67.3 MPH has reduced to 3,555. That's a significant loss. Will an L16 pull 4k @ 75 MPH... probably. Will it be sluggish at all other speeds and getting there? definitely.

 

A 24.5% RPM drop @ 4k is 980 RPM. Insane amount. OK for a 2.8 liter 6 cylinder car.

Lots of good food for thought sir!!!!

 

Would you happen to have any info like torque/ HP curves for the l16? 

 

Im still pretty new to this Datsun thing so stoffrrgen saying a L16 will sing along at 4k all day long was new info for me! 

Edited by Oilspot
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23 hours ago, Oilspot said:

A quick question on h190 gearing/ third members. She's pretty spinny on the stock 4.375 (which from what Ive read is stock in the 521's). I can't imagine going any considerable distance on the highway!!! Does anybody have any experience with running different rear end gearing combos? Ie. Does a 4.11 make a noticable difference, is a 3.889 to short for a daily driver with a L16? 

 

 

A 3.90 with those tires will be spinning 4000rpm at 75mph with a 4spd. 

 

5 hours ago, d.p said:

Because I swapped from a 4 to a 5 and it didn't make all that much difference at speed on the freeway.  

 

The higher your third member ratio, the less difference a 5spd makes. 

 

4 hours ago, Oilspot said:

Slow day at work, so I'm getting paid to figure out how third member swaps would work out 🤣

Cruising 75 at 4k!?!?  Does the l16 put down enough power to pull light grades, fight headwinds etc.

 

An L16 is just starting to get good at 4000rpms. They will steady cruise at 4500-5000 for quite a while. Especially if you get a set of SUs. A 32/36 will do it though. In my experience, changing the rear ratio will do more than a 5spd swap with an L16.

 

Usually I don't go 5spd swap unless I'm putting in an L20b at the same time. As the L20b will NOT pull those 4500rpm freeway runs nearly as well as an L16. Without cam and headwork, an L20b is much happier at 3500ish. 

 

3 hours ago, Oilspot said:

Im still pretty new to this Datsun thing so stoffrrgen saying a L16 will sing along at 4k all day long was new info for me! 

 

It's true, for sure. Stranger still, they seem to get quieter once you get past 4500 also. 

 

This car was L16/4spd/3.90 gears/23" tall tires, and would cruise 75mph all day, with occasional blasts up to 90mph. With your tires being around 24.75" tall, you should be turning lower RPMs than I was (with a 3.89/3.90). Math says a 4.11 would have you about where I was. 

 

Have you already done an EI distributor/coil and cranked up the advance some? If not, you need to. It's do 12 degrees initial on pump gas pretty easily. That really wakes up an L16 too. 

 

 

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4 hours ago, Oilspot said:

Slow day at work, so I'm getting paid to figure out how third member swaps would work out 🤣

 

FYI, this is a really good spreadsheet you can plug all your numbers into to predict RPMs at a given speed. 

 

http://www.grimmjeeper.com/gears.html

 

Using that to play around with different diff ratios and trans ratios will give you a lot of good info. Just know your looking for 3500-5000 as the sweet spot for the freeway. 

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8 minutes ago, datsunfreak said:

 

A 3.90 with those tires will be spinning 4000rpm at 75mph with a 4spd. 

 

 

The higher your third member ratio, the less difference a 5spd makes. 

 

 

An L16 is just starting to get good at 4000rpms. They will steady cruise at 4500-5000 for quite a while. Especially if you get a set of SUs. A 32/36 will do it though. In my experience, changing the rear ratio will do more than a 5spd swap with an L16.

 

Usually I don't go 5spd swap unless I'm putting in an L20b at the same time. As the L20b will NOT pull those 4500rpm freeway runs nearly as well as an L16. Without cam and headwork, an L20b is much happier at 3500ish. 

 

 

It's true, for sure. Stranger still, they seem to get quieter once you get past 4500 also. 

 

This car was L16/4spd/3.90 gears/23" tall tires, and would cruise 75mph all day, with occasional blasts up to 90mph. With your tires being around 24.75" tall, you should be turning lower RPMs than I was (with a 3.89/3.90). Math says a 4.11 would have you about where I was. 

 

Have you already done an EI distribu

 

 

So if a L16 can run 5k for substantial amounts of time, I can run 84mph with fully stock setup and not sweat it?!?!?

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1 hour ago, datsunfreak said:

 

A 3.90 with those tires will be spinning 4000rpm at 75mph with a 4spd. 

 

The driveshaft will be spinning almost 4k. Wheels divide by 3.889

 

1 hour ago, datsunfreak said:

 

 

The higher your third member ratio, the less difference a 5spd makes. 

 

Depends what 'difference' refers to. You go faster or slower in all gears depending on the differential ratio.

 

1 hour ago, datsunfreak said:

 

An L16 is just starting to get good at 4000rpms. They will steady cruise at 4500-5000 for quite a while. Especially if you get a set of SUs. A 32/36 will do it though. In my experience, changing the rear ratio will do more than a 5spd swap with an L16.

 

Usually I don't go 5spd swap unless I'm putting in an L20b at the same time. As the L20b will NOT pull those 4500rpm freeway runs nearly as well as an L16. Without cam and headwork, an L20b is much happier at 3500ish. 

 

 

 

An engine's 'redline' is the point above which the piston speed exceeds 4,000 feet per minute. Near this point the steel in the rods reaches it's limit and begins to stretch and the bearings will fail. Below this point, if in good shape with lots of oil and coolant, an engine will survive indefinitely. I would not test this out and leave for racers but a stock engine will survive much higher revs than you will ever subject it to. The 'redline' for an L16 is 8,250 because of the 73.7mm shorter stroke. The longer 86mm L20B is limited to 7,000. Z22/92mm... 6,500 and the Z24/96mm stroke.... 6,250 RPMs

 

My stock L20B 710 tach is yellow above 6,500 and red above 7,000. Agree the L20B is held back by the stock carburetors and intake. Mine would run out of steam at about 3,500 and it was a long wait to get to 5k. I have motorcycle carbs on it now, basically side drafts and it buzzes easily and quickly to 6k in first. It caught me by surprise the first time. I don't drive it like that.

 

L20B...... 93-95 HP

L18......... 83

L16......... 73................. all HP numbers are when these engines have a good day.

 

My 710 says 110 HP but this is when Gross HP numbers were used. This was changed to Net which is more realistic. Ninety + seems... about right

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gawdamn!!!! 8250 redline!?!?!?

so I figure with 15 coats of wax, she'll slice through the air like a samurai sword (overcoming the aforementioned drag coefficient). On the right day, with no wind, and smooth level surface..... my calculations figure......

 

 

138 MPH!!!!! 

Son of a bitch!!!!!

 

I'm gonna need a helmet for this for sure!!!!! 

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2 hours ago, Stoffregen Motorsports said:

8250? I think not. Besides that, you're not making any power with a stock L motor anywhere past 6000K.

Well shit! 

I've gotta see if I can cancel my order for that 10k monster tach before they ship it. 😊

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3 hours ago, Stoffregen Motorsports said:

8250? I think not. Besides that, you're not making any power with a stock L motor anywhere past 6000K.

 

Stroke in inches X 8,250 RPMs / 6 .... must equal less than 4,000 ft/min. In this case 3,987 RPMs... close enough. This is the average piston speed, keep in mind that it's stopped at TDC and BDC and is accelerating and decelerating violently in between. Maximum piston speeds are when the rod and the crankshaft throw are at 90 degrees to each other. Very roughly at 70-80 degrees BTDC and ATDC.

 

 

You can go to a higher red line with special rod fasteners, stronger lighter rods, lighter forged pistons but for stock internals stay lower than 8,250 (that should be easily done) to be safe. Oh absolutely, the stock cam, carburetion and intake is for highway speeds. Not much pull above 4k.     

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So to take this discussion on a hard 90degree turn.....

 

Anybody have a trashed stock 521 bench seat laying around? I've got three broken springs in mine and am looking for a donar seat to replace them with.

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2 hours ago, Oilspot said:

So to take this discussion on a hard 90degree turn.....

 

Anybody have a trashed stock 521 bench seat laying around? I've got three broken springs in mine and am looking for a donar seat to replace them with.


That’s Ratsun for you. 

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On 1/27/2022 at 5:35 PM, datsunfreak said:

 

A 3.90 with those tires will be spinning 4000rpm at 75mph with a 4spd. 

 

 

The higher your third member ratio, the less difference a 5spd makes. 

 

 

An L16 is just starting to get good at 4000rpms. They will steady cruise at 4500-5000 for quite a while. Especially if you get a set of SUs. A 32/36 will do it though. In my experience, changing the rear ratio will do more than a 5spd swap with an L16.

 

Usually I don't go 5spd swap unless I'm putting in an L20b at the same time. As the L20b will NOT pull those 4500rpm freeway runs nearly as well as an L16. Without cam and headwork, an L20b is much happier at 3500ish. 

 


my man I have a built L20b with dual Mikunis and 280zx 5 speed in my truck. And it cruises in the freeway at 70 right around 4k RPMs.  My expectation was that dropping a 5 speed in would decrease the amount of RPMS at speed vs my old 32/36d l16 and stock 4 but it hasn’t. My truck is faster and has an additional gear but RPMs on the freeway are roughly the same just different gears. 

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Whats the final drive on the 5 speed you've got. The stock 4 speed is 1:1, I'm gonna guess the 5th in your box is pretty close to that. 

what trans did you put in there?

 

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All 4 and 5 speeds are 1:1 in 4th.

 

2 hours ago, d.p said:


my man I have... 280zx 5 speed in my truck. And it cruises in the freeway at 70 right around 4k RPMs.  My expectation was that dropping a 5 speed in would decrease the amount of RPMS at speed vs my old 32/36d l16 and stock 4 but it hasn’t. My truck is faster and has an additional gear but RPMs on the freeway are roughly the same just different gears. 

 

If you indeed have an '80-'83 280zx the over drive is either 22.7% for the '80 or 24.5% for the '81-'83. This is 227 or 245 per 1000 RPM drop.

 

So at 70 MPH your RPMs in 5th would be 908 or 980 lower or 3,092 or 3,020... again it would depend on the year of the zx 5 speed. You would most definitely notice loosing 1/4 of your RPMs.

 

There is one more year of zx 5 speed, and that is the mid ratio of '79. It has a 13.6% OD (about half the other two) and this amounts to a 544 RPM drop, a lot less noticeable. This transmission is also used in the late 280z, 620, 720, 810 and Maxima.

 

 

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