1968 Mexican 520

[AbRamGom]

Hello i recently acquired an original 1968 Mexican Datsun 520. It currently has a 1599cc engine and a 4 speed transmission. Any thoughts or ideas on what might be good things to do to it?https://photos.app.goo.gl/C76zYZUWJkq9Kz8fA

[Gluteus Maximus]

Nice Truck!

[datzenmike]

 

 

Mexico engine is J1600.

[Charlie69]

That is a beautiful truck Drive it and enjoy it.

[Juanjoze]

On 11/2/2022 at 6:59 AM, datzenmike said:

 

 

Mexico engine is J1600.

And J1500 too.

[datzenmike]

Could very well be. The J series also came in J18 size.

[zed1]

Very cool. What is your plan

Was this previously equipped with a dual brake master cylinder (red circle)?

Keith

[1001001SOS]

Wow that interior looks amazing! What a cool truck.

[AbRamGom]

On 10/10/2023 at 8:04 AM, zed1 said:

Very cool. What is your plan

Was this previously equipped with a dual brake master cylinder (red circle)?

Keith

I'm not too sure but I believed it was attempted at some point but ended up keeping the single master cylinder. As for my plans for it, I'm thinking of redoing all the wiring and putting a weber 32/36 on it, clean up and paint the engine bay and lower the gearing in the rear from the 4.88 I believe to maybe a 4.10 or something a little smaller

[datzenmike]

The J engine doesn't make a lot of power. It's small displacement so not much low speed torque. It's made to rev. The rear end ratio lowers the overall RPMs in every gear. Lower RPMs = less engine power making highway speeds, into the wind and inclines more of a struggle. I agree 4.875 is a bit much but it's designed for carrying maximum loads. 4.11 id do-able but it may be too much the other way. I wouldn't go lower. Try and find someone who has done this and what they used.

[Stoffregen Motorsports]

Wayno has always suggested the 3.90 swap in his 320s. He seems happy with it.

[datzenmike]

I think you're right and the 3.889 is far more plentiful. Unless the 521 is hundreds of pounds heavier. The 320 is so small it's like you put it on and wear it.

[wayno]

I have 3.90 gears in my NL320 I bought from Mike, but it has a more modern 1980ish E1 engine, it drives fine until about 55/60mph, then I have to start pushing the gas pedal deeper for any more speed, there is not much left after 65mph(level road).

 

As for a 520 with a J16 I do not know what to recommend, 4.37 gears come to mind as they are plentiful.

Edited July 19 by wayno

[datzenmike]

It's the wind resistance, which increases with the square of the speed. If 10 hp to go 50 NPH it takes 80 hp to double the speed. Lowering the differential ratio can easily lower your top speed as the engine is not revved up enough to make it's full rated power. In fact it may go faster in third gear.

[AbRamGom]

Alright so let's say I end up putting the 4.37 gears into it. What would the supposed top speed be? Would it be enough for me to get on the freeway in the slow lane?

[datzenmike]

edited:

 

Does it not go highway speeds now with the 1,600cc engine? Probably will now with the 4.875 just takes a long time to get there. Again this is designed to carry heavy loads and without that there's not as much need for the 4.875 that are in it. The biggest complaint with the stock gearing is the screaming engine but it was designed to be this way to do it's job. You won't hurt it, it just sounds bad.

 

So what's the reason for wanting lower ratio differential? Quieter? mileage?

 

J16???? 1,600cc ??? probably output around 85 NET hp? The 320 is small so not plowing a lot of air out of the way.

[Stoffregen Motorsports]

I'm confused. It has a more modern E1? They stopped building the E1 in the late '60s.

 

[AbRamGom]

6 hours ago, datzenmike said:

edited:

 

Does it not go highway speeds now with the 1,600cc engine? Probably will now with the 4.875 just takes a long time to get there. Again this is designed to carry heavy loads and without that there's not as much need for the 4.875 that are in it. The biggest complaint with the stock gearing is the screaming engine but it was designed to be this way to do it's job. You won't hurt it, it just sounds bad.

 

So what's the reason for wanting lower ratio differential? Quieter? mileage?

 

J16???? 1,600cc ??? probably output around 85 NET hp? The 320 is small so not plowing a lot of air out of the way.

I would like to get a higher mph overall because as of now my top speed is about 55 mph on a straight flat road. As for the noise I don't really care about the noise 

[datzenmike]

A tune up is far cheaper.

 

At 55 you are only revving 3,565 RPMs. With 4.875 ratio you should be capable of well over 4K in 4th and that's 63.5 MPH. 4,500 is 71 MPH. The J15 makes 76 hp so the J16 will make at least that much.

 

There's something wrong with your tune up if you can't go above 55.

Check valve lash.

Check the timing.

Check the fuel filter is not part plugged, just replace it.

Check that the primary is fully open when floored.

Check the secondary is opening and you are not running on the primary only.

[Stoffregen Motorsports]

Maybe more than a simple tune up. Depending on how many miles are on it, it may be time for a rebuild or at least some heavy work, like a valve job.

 

As Mike said, tune up things like plug wires, cap/rotor, spark plugs, etc. Then maybe add in a couple degrees of ignition timing. There is an intake manifold for an MGB that will bolt up to your engine that will take a DGV Weber. That would be a nice upgrade too. A slightly larger exhaust would give you more throttle response and some upper RPM horse power.

 

 

[datzenmike]

2 hours ago, datzenmike said:

 

 

At 55 you are only revving 3,565 RPMs. With 4.875 ratio you should be capable of well over 4K in 4th and that's 63.5 MPH. 4,500 is 71 MPH. The J15 makes 76 hp so the J16 will make at least that much.

 

 

To put a finer point on this.... a 3.889 differential will only be turning 2,764 RPMs at 55 MPH. Now you tell me is your J16 going to be making more power at 3,565 RPMs with a 4.875 or at 2,764 RPMs with a 3.889 at 50?????????

[EDM620]

From the pics it looks like smooth roads where you have or got it. Many mexican roads are cobblestone that beat the crap outta vehicles. Big bonus if the suspension is solid.

[wayno]

7 hours ago, Stoffregen Motorsports said:

I'm confused. It has a more modern E1? They stopped building the E1 in the late '60s.

 

 

I believe Mike said it had a 1980 E1 engine likely from a forklift that came with a spin-on oil filter, I would not swear it was a 1980 as enough time has passed by for me to forget things.