Long Shot--What's My RPM?--1HZ

[Aidan Klimenko]

Hey, y'all! This is a long shot, but I've been curious about what my RPM's are in my tachometerless Troopy and thought I'd throw this out there to see if anyone is running anything similar and either has a instrument cluster with a tach or has added one themselves. Listening to the engine has been just fine, but I've always been curious just what the numbers are.

My setup:
78 Series HZJ78L (probably irrelevant)
R151F Transmission
4.11 R&P
265 75 16 tires (but moving to 255 85 16 next week)

I don't run it over 100km/hr as it seems to howl. Happy at 90 km/hr.

Any insight would be cool!

Thanks.

 

[AirheadNut]

You should be turning about 2300rpm at 100km/h with your current tires. I’ve found this calculator to be very helpful: Gearing Analyzer with Shift Tracer - https://www.blocklayer.com/rpm-gear

 

[Aidan Klimenko]

Hey thanks this is a great resource. I had seen that online calculators existed but hadn't realized they had such a wide library of pre-loaded gearbox ratios!

The previous owners of my truck never took it over 100 kph, so in the 5 years I've owned it, I haven't either. Looks like I might be able to go a bit faster.

Thanks.

 

[Gun Runner 5]

There’s little doubt that Kermit drives a diesel 70 Series.

 

[Aidan Klimenko]

Does anyone know what the factory ring and pinion options were for the 2002 78 series 1HZ? A while back I did the "turn driveshaft with truck on jacks" test and thought it was 4.11 but am seeing a few posts about 4.3 being factory?

Looks like the difference between the two isn't huge, but for the sake of trying to nail this RPM equation, knowing what's in there would be great.

Thanks

 

[JuanJ]

Hello,

Most 70 Series trucks have a 4.11:1 gear ratio.

The parts catalog mentions one option for post-1999 trucks, namely 4.11:1. Other options are open differential or locked differential.





Juan

 

[Aidan Klimenko]

Thanks Juan, that’s great. Thanks for the info.

 

[svsisu]

TinyTach makes a nice, small digital tachometer that is easy to install. They are 24 volt compatible and the transducer clamps around one of the injections lines. For a 1Hz you would want to substitute the 6 mm transducer for the 4.5 mm.

Diesel Tiny-Tach | Design Technology, Inc., Home of Tiny-Tach

Diesel Tiny-Tach. An hour-meter for diesel engines.

www.tinytach.com

 

[Aidan Klimenko]

Great! I just emailed them about swapping for a 4.5mm. This looks great. Just wish it were an analog dial!

Thanks.

 

[svsisu]

Great! I just emailed them about swapping for a 4.5mm. This looks great. Just wish it were an analog dial!

Thanks.

I hear you on an analog dial, but it does fit in with the overall vibe of these trucks. There are other options out there, but for the price and ease of install it's hard to beat, and it's also easily removable. I find I rarely look at it now, but it was great for figuring out what the engine was turning at different speeds etc.

 

[Aidan Klimenko]

100% agree. This will be great. Thanks again.