'82 720 Z22 w/auto - Smog legal powertrain update?

[wasoncebroken]

Hello folks -

First off, thank you kindly in advance for providing the know-how and guidance for these vehicles.

 

I've recently been gifted with a Datsun 720 kingcab. It's fitted with the Nap-Z 2.2 liter carbureted motor behind a three speed (what appears to be a Borg Warner) automatic transmission. It runs good, however, the three speed makes for a high revver at highway speeds. I've fitted 16 inch Toyota P/U wheels with 205/65 tires and that certainly helped quite a bit but its still not all comfortable cruising at 70+ highway speeds which are so common these days, so here's my question.

 

Ultimately, I'd prefer a complete motor/trans conversion to a later model but want to keep any associated hassles in doing so to an absolute minimum. If, for example, a viable option included a later F.I.'d  2.4 or even V6 Nissan powertrain. I could handle that without issue as long as it was simple and didn't require a month of Sundays rewiring everything. Another thought was installing a later 4 speed auto (it must remain an automatic) with lock-up converter which would lower the revs, increase comfortable highway cruising speeds and fuel mileage simultaneously. Can I just swap in a later trans as a bolt-in?

 

 I'm in California so smog legality is imperative. A decade plus ago I helped a friend convert his '77 chevy luv pickup to a complete buick/olds 231 V6 and as long as ALL smog components (Including cat converter) were in place (and the powerplant was from a later model year) - it was no problem. He still drives it on a daily basis and its accumulated well over 160k miles over the years. In my case - I prefer keeping it Nissan.

 

Again, thank you for your knowledgeable opinions and advice.

 

regards,

Joe

[datzenmike]

Hi Joe and welcome to Nissan.

 

Nissan stopped using the BW automatics in early 71. Yours will be a 3N71B a very tough reliable transmission made by JATCO.

 

The high revving is just an impression brought on by the sound of the engine. It's not particularly high just seems so. As you have a Z22 I'll assume you have an '81 or '82 and both these years used a 4.11 rear end. The standards are equipped with 3.889 rear ends so I suppose the automatic is revving 5% higher. That's 150 RPM at 3,000 RPMs not much at all really. 

 

The '83 on up 3N71B used with the Z24 engine does have a torque converter lock up that will drop the highway cruise 200 to 400 RPMs

 

Now there are practical limits to how low you can run your engine and still be able to cruise at 70 MPH. For one, the engine has to rev in order to make enough power to pull the truck and push into the increasing wind resistance. Too low and you foot goes closer to the floor and either the secondary opens or it down shifts and that's the end of any mileage gain. This doesn't take into account any increase in road grade or days with a head wind. 

 

The later L4N71B is very slightly longer than the 3N71B, I measured about an inch. They were used on early '86-'89 D-21 Hardbodys with Z24i engines. The first three gears are the same but the overdrive is a monster 0.686 4th gear. (remember, this was used with a larger displacement, higher torque Z24 engine)

[Stoffregen Motorsports]

Early vehicles that don't use a computer to control the transmission don't usually run into any hassles when doing a trans swap. So if you find one that works for you, it should not be an issue with your local emissions testing facility. I conform to the mantra that less information is better, so I would never offer up any knowledge of mods that I've made to anyone who could make life difficult for me.

 

As far as motor swaps go, I've said it a million times , buy a whole donor vehicle. You will have all the smog pieces, all the brackets, pumps, pulleys, computers, fuel tank/pump, etc that you will need to do the swap, and you can always sell of the remaining parts to help with the costs of the project. And if you stay within a vehicle platform family, a lot of the parts off the newer donor may be bolt on and in better condition than on the vehicle being swapped. Steering boxes, axles, brakes are all examples of those parts.

 

High mileage Hardbody pickups can be bought for $1000 or less. I would start there.