TrailRecon drops the Diesel

[beaups]

I know I'm going to do a bad job of explaining this so hopefully someone can help me out here. Increasing tire size without changing gearing moves the torque points that the factory programs in for stock tire sizes. These are ballpark and not exact number but a stock vehicle might be turning 1728 RPMs at 70 mph. A Jeep on 37s would be turning 1538 RPMs. But as the load increases that low RPM is going to lug the engine and make it downshift to 7th gear which jumps RPMs to 1971 RPMs to maintain that speed. But now assume you have an extra 2500 lbs behind you. Then it might further shift down to 6th gear which puts the RPMs at 2404 or even 5th gear which jumps the RPMs to 3149. That's going to increase the demand on the engine and increase the temps.

Now assume the same vehicle with 37s is geared to 4.10. 8th gear at 70 mph is 1691 RPMs and 7th is 2166. It's closer to the proper torque band. 4.56 gears would be 1881 RPMs in 8th and 2409 in 7th. With that gearing I doubt there is a need for the transmission to hunt down to 6th or 5th gear. Proper gearing keeps the vehicle in the proper torque band and the ultimately the RPMs and temps down. I hope that makes sense.

I got my numbers by using the gear ratio calculator on Grimmjeeper.com.

2166 rpm is "closer to the proper torque band" for the diesel? Assuming your math is correct, an entirely usable RPM range is available for all 3 scenarios you provided, with the availability of lower RPMs with the stock gear set. I'm not saying regearing would necessarily make things worse (even though that is a possibility), but it is definitely not going to help make it better. This is a close-ratio 8 speed automatic; you aren't going to jump in a single gear from an engine speed that is too low to one that is too high.

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[Chainringtattoo]

2166 rpm is "closer to the proper torque band" for the diesel? Assuming your math is correct, an entirely usable RPM range is available for all 3 scenarios you provided, with the availability of lower RPMs with the stock gear set. I'm not saying regearing would necessarily make things worse (even though that is a possibility), but it is definitely not going to help make it better. This is a close-ratio 8 speed automatic; you aren't going to jump in a single gear from an engine speed that is too low to one that is too high.

You're assuming the gear ratios in the 8HP75 transmission are symmetrical. They are not. The lower the gear the more spaced out they are. So if that stock geared Wrangler on 37s pulling a trailer up long incline is doing so in 6th year and has to jump to 5th that's not as close a ratio as a regeared vehicle having to jump from 8th to 7th. The correctly regeared vehicle will ultimately be pulling the same load at the same speed using less engine speed.

 

[Hercules]

Sure he might have issues… but keep in mind he’s got a financial incentive to always be swapping out for new things. A new 392 or 4xe (which it look like he just bought, or at least did a review on) will surely drive additional sponsorship deals and YouTube views.

Not to mention he was loaded up with weight and towing a trailer over the rockies

 

[gato]

That might have helped considerably as it probably had him down in 5th or 6th gear with all that weight and RPMs too high.

As far as the engine goes, it can not tell the difference between being in a higher gear with a (numerically) higher diff ratio or a lower gear with a (numerically) lower diff ratio.

It's amazing how often this simple fact is missed. On a closely spaced multi-speed (8, 9, 10) auto transmission, with a decent gear spread, other than first gear, regearing has little to no real significance in performance, fuel economy or engine temps.

 

[Jgeiken]

I guess he never had a jk? 240 was everyday temp on any climb in CO, I remember having 235* coolant when the air temp was -5* by myself headed to work over the divide On I70.

He started his channel with a Jk. Still has it.

 

[WhereRU_A-A-Ron]

I was a pretty big fan of his channel but I’ve found it less and less relatable over the last year or so.

He reminds me of my 8 year old son who’s constantly wanting the next best nerf gun, Lego set, Fortnite character, etc. Never satisfied with what he has - always wanting more. Not surprised in the least that he sold the diesel.

To each his own. More power to him.

 

[Chainringtattoo]

As far as the engine goes, it can not tell the difference between being in a higher gear with a (numerically) higher diff ratio or a lower gear with a (numerically) lower diff ratio.

It's amazing how often this simple fact is missed. On a closely spaced multi-speed (8, 9, 10) auto transmission, with a decent gear spread, other than first gear, regearing has little to no real significance in performance, fuel economy or engine temps.

That makes absolutely no sense. Gear ratios have always been well thought out by manufacturers for maximum performance and economy.

 

[BullMoose1776]

It's a V.M. Motori diesel that's been in production a while. And they've been making diesels for a long time.

Just because Fiat bought them out doesn't make it a Fiat.

I stand corrected. I just wish it would have been a Cummins.

 

[grimmjeeper]

I stand corrected. I just wish it would have been a Cummins.

Cummins did some work on their ISF 2.8 to be in a vehicle in the US. I'm not sure which but it didn't work out. But the R2.8 crate engine came out of that work. I've looked into swapping one into a project vehicle.

 

[BeachPilot74]

DEF OverConsumption and Overheating when built up, weighed down and towing a ton

who cares.. lol Kinda tired of that channel anyway.

 

[DanW]

Cummins did some work on their ISF 2.8 to be in a vehicle in the US. I'm not sure which but it didn't work out. But the R2.8 crate engine came out of that work. I've looked into swapping one into a project vehicle.

I'd love to have a YJ with that engine. What a hoot that would be!

 

[BullMoose1776]

Cummins did some work on their ISF 2.8 to be in a vehicle in the US. I'm not sure which but it didn't work out. But the R2.8 crate engine came out of that work. I've looked into swapping one into a project vehicle.

I like that 2.8! Thinking about it in a CJ.

 

[grimmjeeper]

That makes absolutely no sense. Gear ratios have always been well thought out by manufacturers for maximum performance and economy.

Economy yes. Performance no.

Axle gears are determined by the engine and transmission and how well it does in the EPA test loop.

Once in a while, they'll offer an option like 4.10s in the Rubicon but that's pretty rare in most vehicles.

Thing is, pulling a load up a hill the engine needs to operate at a particular RPM to get the job done. The computer will select the transmission gear to put the engine at that RPM. So if you change axle gears, the computer will change which transmission gear it selects to compensate.

 

[grimmjeeper]

I like that 2.8! Thinking about it in a CJ.

I'd love it if they came out with the 3.8 ISF (same family) as the R3.8. I'd put one in an older truck in a heartbeat.

 

[OllieChristopher]

Economy yes. Performance no.

Axle gears are determined by the engine and transmission and how well it does in the EPA test loop.

Once in a while, they'll offer an option like 4.10s in the Rubicon but that's pretty rare in most vehicles.

Thing is, pulling a load up a hill the engine needs to operate at a particular RPM to get the job done. The computer will select the transmission gear to put the engine at that RPM. So if you change axle gears, the computer will change which transmission gear it selects to compensate.

My 2005 GMC is a prime example of the EPA insanity. Base 1500 with 4.3 V6. The stock gearing was 3.25. It could not pull a hill in 5th gear empty. I now am running 265/70-17 tires and 3.73 with TruTrac. Boy what a difference and the fuel economy went up over 3mpg.

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