HZJ73 at altitude, gearing options- what would you do?

[MyCruiserisaHogBeast]

Just acquired a 1997 HZJ73, it's awesome. It's on 35s. I live at 6000 feet. I am going to move quickly on some gearing options, I've been prepared for this. I drove it 1200 miles home, going from sea level east through the rockies, and I just took it up into the mountains to take my daughter Skiing. I don't mind it being "not fast" but my suspicions are confirmed by my first little trip upward: the NA 1HZ has enough oomph to push me around, but really struggles above altitude, and the separation between 2nd and 3rd gear makes mountain road pulls difficult. I did like the fact that this thing does cruise well and is comfortable on flatfish ground. I don't want to be locked into turboing is just yet, want to see if I can just keep the 1HZ going as the Toyota gods intended.

So, my choices are: 4:1 T case gears with 10% under drive (true 7.7%), or 3:1 t case gears with 4.88 diffs. I want a lower low range, and lower is better, but the difference between 4:1 and 4.88s+3:1 isn't significant enough for me to sweat. Anyone got any thoughts? I don't want to commit to the 4:1s with under drive and figure out I don't have enough gear reduction for the day to day, but I don't want to do 3:1s with 4.88s and fine that my 1st gear is so low as to be dysfunctional and wish I had gone with a higher total gear set. 4.56 gears don't seem to be worth the investment. Also if I can avoid regearing, that's a plus.

 

[mjw4]

A turbo/intercooler with a boost compensator would be the optimal choice for counteracting altitude, but if you don't want to do that at this time you can look into a high altitude compensator, (if i remeber correctly it can be modified into sudo-boost compensator). @JDM Journeys installed one, so maybe he can chime in.

Not an expert in this, but the transfer case gearing may be the more robust option. As far as I know the lower you go with your differential gearing the weaker it becomes, not sure if that logic also applies to the transfer gears though.

 

[RHINO]

i live in a small community in the Mtns., so i am constantly up and down grades at state hiway speeds, not much interstate unless i travel so my gearing was based on that.

i'm on 255/85's and did 4:88, no tcase reduction. its darn close to being back to stock gearing and as intended, 1st is a granny first that i use as needed on and off road. its still a slower rig but downshifting to 4th holds my speed on the steeper grades where staying in 5th is doable everywhere else, and thats fine for me.

If it were me I'd chuck 5:29's in and be done with it, but thats me, not you.

Sounds like you want a lower low range regardless, so why not drop in the preferred tcase gears and feel it out for a bit. If you decide a little lower yet still 4:56 or 4:88 WOULD be that option.

 

[RHINO]

Not an expert in this, but the transfer case gearing may be the more robust option. As far as I know the lower you go with your differential gearing the weaker it becomes, not sure if that logic also applies to the transfer gears though.

4:10 has always been considered the strongest gearset, when you go lower the ring gear gets thinner, and when you go higher the pinion gets smaller,,, but were talking about measurable differences and extremes in application that will NEVER come into play for most of us.

 

[JDM Journeys]

A turbo/intercooler with a boost compensator would be the optimal choice for counteracting altitude, but if you don't want to do that at this time you can look into a high altitude compensator, (if i remeber correctly it can be modified into sudo-boost compensator). @JDM Journeys installed one, so maybe he can chime in.

Not an expert in this, but the transfer case gearing may be the more robust option. As far as I know the lower you go with your differential gearing the weaker it becomes, not sure if that logic also applies to the transfer gears though.

The very first thing I'd do (if you haven't already) is put in an EGT gauge. You may be surprised what altitude does to your fuel mixture. In my case the higher I went, the worse the black smoke got and of course this resulted in higher EGT's. I began with new injectors and then I put an altitude compensator on top of my early (91) pump, but I don't feel like it made a dramatic difference. Yours being a 97, there's a possibility it came with one? In the FSM there is some info about altitude and what an alt compensator does at a particular level (in meters). If I had my time back I may not have bothered. Opening up the exhaust and then adding a turbo/intercooler after getting everything else running as good as it could was ultimately the right choice for me, living in the Rockies.

But knowing your EGT's would for sure be step 1, in my opinion.

 

[Bogan]

Any NA engine is gonna be super anemic at elevation. We live at 7200' and NA diesels are a dragggggg... IIRC, the 1HZ has an altitude compensator for the fuel pump.

Thread 'High altitude compensator 1HZ retrofit?'

May 8, 2021

Boosting the 1hz has its champions and detractors, but there is no denying that in stock form it suffers as the air density decreases.

Without diving into turbo debates, I'm wondering about high altitude compensation.

In some markets it came from the factory with an HAC on the injection pump. Has anyone here added one to a rig that didn't originally come with it? Did you see any real world difference as your altitude increased? Was it worth the effort/expense?

• JDM Journeys
• 1hz
• Replies: 62
• Forum: 70-Series Tech

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[bj70bc]

turbo, and 10% OD gears, you will be much happier all the time

 

[rick_d]

"want to see if I can just keep the 1HZ going as the Toyota gods intended."
The Toyota NA gods hate us. The HZ is a rotten under-powered truck for US highways as was the 2F/3F. Toyota NA does not want to sell you shiat so you will be ordering stuff from Kurt, Georg, and offshore.

"I live at 6000 feet. I am going to move quickly on some gearing options//Also if I can avoid regearing"
w 35's 4.11's or 4.30's are best option. You will still need to get to highway speed. Driving 60 mph on a road where traffic is 75+ is dangerous.

"I don't mind it being "not fast" "
You will. Or you will only log 3,000 miles per year for 5 years then sell at a loss.

"NA 1HZ has enough oomph to push me around, but really struggles above altitude"
Yeah, it is an HZ designed for 1500 feet or under operation.

"the separation between 2nd and 3rd gear makes mountain road pulls difficult"
W H55 gear box you are stuck.

"I don't want to be locked into turboing"
Then repower with HD or FTE (FT's too rare)

I have a 79 series which is a long pickup. Snow, altitude (9,000'), long hauls above 80 MPH are common for me. I just spent a week in 4 corners driving from Tucson up to Flag at 7K and Mx Hat (455 miles one way) then back, then to Cloudcroft (370 miles) at 9K and back.
the narrowness of the truck and the fact I don't baby it allow me to get to camps I need to, haul crap I don't want, and building materials I need.
I have 1992 HDT, H152, std H1A, 3.9:1 w 255/85/16 which after logging a decade with 4.11's puts the engine into a better power band for a long truck.

Personally I would ask bottombracket his thoughts. hdt w 4.3:1's and R151. He is a lowlander but daily drives truck (74 series).

The HZ, B series (all), H/2H, 2F/3F, and other smaller 4's are not fit for todays driving on US routes. I drove a 22RE for a decade but speeds were 55 MPH restricted and could limp up hills but also did better than 20 mpg.

If you want to sit in the right lane buy a Mog or a Pinz.

 

[Chamba]

Having owned numerous diesel land cruisers, I can tell you that I agree with most of the above. Once you've turcharged this engine, you'll actually want the lower gearing because it will be good to keep it in a lower rpm band.

With a good turbocharge at a healthy boost of about 7-12 psi this engine will love to be about twenty two hundred r p m.

As for the jump between first and second 3.73 gears can help that quite a bit, but having a good turbocharger may mean that you always start in second except on the steepest inclines.

That engine lends itself really well to a good turbo charge system- especially at altitude. I Wouldn't touch the gears a bit until it's turbocharged and you find out exactly what that engine's capable of.

 

[TreadingLight]

I've put almost 200k km on my hzj75, driving cross country multiple times a year. I can keep up with traffic at 70-75 mph but prefer to cruise a little slower. I don't need to go 80 and while I wouldn't mind more power, the 1hz is just fine if you drive it like it was intended. Mountain passes in the RH lane are slower but still no big deal.

I've also met more than one global traveller in the states in hzj75 troopys who don't go over 55. Not because they can't go faster but because 55 is just fine if that's where you want to be.

Anyhow, I disagree entirely with @rick_d. Buy a pinz if you want one, not because some people think Toyotas should all be 300hp.

To the OP, an EGT gauge, turbo, and an intercooler would safely replace all the missing oxygen at elevation. Boost wouldn't be the limiting factor, fueling would be. This is my plan to cut black smoke and lower temps when I'm in the Sierras.

The Toyota NA gods hate us.

I agree with this part but for totally different reasons. While the rest of the world got the 70 series we got turds like the 62 and the 80 and the 250.