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Discussion Starter · #1 ·
Alright, I really want to run the TH475 trans due to simplicity and durability. The dilemma here is no O/D. I calculated at 70mph my engine would be turning 2950 RPMS, and that's not claculating T/C slip (someone told me the diesel converter is really tight though). I'm just getting opinions on this, I wont be running my truck at 70mph to often, but I'm mainly concerned with killing this 4bt?
 

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is this going in the durango with the 53s???
 

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I'd think turning those RPM's in a durango on 53's and rockwells would be a requirement just to push it that fast. Just the axles and tires weigh more than a small truck!
 

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Discussion Starter · #5 ·
I'd think turning those RPM's in a durango on 53's and rockwells would be a requirement just to push it that fast. Just the axles and tires weigh more than a small truck!
In all honesty, it's pretty strung out gearing wise (which is obviously why I'm gonna be facing such high RPMs). I plan on 250hp/500lbft, given the gearing and how the power comes off idle I think it will be ample for my needs.

I guess in contrast I'm wondering how much of a hassle it will be on this little engine. It wont be a regular basis, only during times when I'm driving to a trail or etc. Another thing I was curious about was RPMs effecting MPG, are diesels effected severely by RPM like gassers are?
 

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I run rockwells with 46s, and have sold sets of 49s and 53s. The 4bt will work great on the trail with all of the low end grunt, but the only thing that is keeping me from swaping out my supercharged 302 is that your not always able to "crawl" up everything, and you sometimes need wheel speed. right now I can flog it and spin my tires more than twice as fast as could if I was running the diesel even with the 3200rpm spring. And if you havent drove with that big of a tire before, and hydraulic steering you wont want to go 70mph LOL ;) MY2C
 

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Even with the gov spring it will be screaming.. I would change the gearing if possible first... I've "heard" that sustained high rpms are one of the few things that prematurely kill these, not sure if thats true though...
 

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With 4.88's and the NV4500, on the highway for me (only 65ishmph) she's screaming. 80% throttle. Time for me to go 3.73.

1st gear 4Low is insane though.
-Scotty
 

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Discussion Starter · #9 ·
And if you havent drove with that big of a tire before, and hydraulic steering you wont want to go 70mph LOL ;) MY2C
My tires are internally balanced, and steering is setup by Performance Offroad Systems. I feel 100% more comfortable cruising in this thing down the highway than I ever did on 39's with mechanical steering. I do regularly rotate my tires and check for alignment though.
 

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Discussion Starter · #10 ·
The 4bt will work great on the trail with all of the low end grunt, but the only thing that is keeping me from swaping out my supercharged 302 is that your not always able to "crawl" up everything, and you sometimes need wheel speed.
Believe it or not, I like this concept, and since the diesel is so slow revving it will possibly save my drivetrain more. I bet with a HY35 it would help get things turning over faster than stock, otherwise if I need wheelspeed I'll shift to 2nd. :grinpimp:
 

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I guess in contrast I'm wondering how much of a hassle it will be on this little engine. It wont be a regular basis, only during times when I'm driving to a trail or etc. Another thing I was curious about was RPMs effecting MPG, are diesels effected severely by RPM like gassers are?
Higher RPMs do drop off your mileage somewhat like a gas engine but their are a lot of other variables that also play an effect. The diesel engine tuned correctly will still be a better mileage performer than any gas engine you have in it. I'm not sure how conserned you actually are about mileage with rockwell axles and 53" tires though?
 

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My experience is at freeway speeds over 2200 rpms is massive drop in mileage. From mid 20s to high teens up to 2300-2400 rpms. For what its worth... This is with 4.10's, NV4500 .73 overdrive, and 35" tires on a FJ55 Land Cruiser station wagon...
 
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