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High Elevation Gear Ratio - 33's - 6-Speed (NSG370)

Rickyd

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Joined
Jan 2, 2020
Messages
61
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PNW
Dig around here long enough and you'll see that I too rarely leave anything alone, particularly engines - though the stroker engines I play with have a few more cylinders...


Strokers are fun, though a stroker 4.0L still leaves much to be desired IMO. When 4.2 cranks were cheap and easy to find, every town had a good machinist, and local tuners who worked on the JTEC were common, it made more sense. For me nowadays, it's a lot of time, money and work for a whopping 230hp and 315 ft lbs.
Yep its no v8. Its what the 4.0l should have been from the get go.But for smog reasons i went with one and don't regret it. Even using forged pistons,edelbrock head and a custom cam wasn't unreasonable.especially if you subtract the cost of rebuilding a 4.0l.
 

Zorba

"The Veiled Male"
Supporting Member
Joined
Apr 2, 2020
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7,899
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Merritt Island, Fl
^ very much this!!

Hell back in the Golden Days of Granny Gear transmissions, the L gear was ~5.xx to 6.xx in some cases (the old Muncie 465 was 6.55:1). More importantly, 1st (actual first, not L) was a very streetable 3.58:1. The NGS's 2.62:1 2nd gear is not appropriate for starting from a stop in about 99.5% of driving situations.
And my beloved SM420 clocked in at over 7:1 - something like 7.05:1 or somesuch. I think the new Bronco transmission has gotten it right - its an SM-465-ish 6.5xx:1 as I recall.
 
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PowderFactory

PowderFactory

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Joined
May 5, 2022
Messages
6
Location
Silver Plume, CO - elev 9100’
Thanks so much for your help, and I really appreciate everyone’s comments! I know the 4.0 is not the most powerful engine, but have been driving them in my XJ and TJ for 25 years, and never really “needed” a regear to keep safe highway speeds in CO until got my LJ with 285’s about 6 months back. I really like my lift height, and may be able to fit 34’s with some highline fenders in the future, but wasn’t really planning on 35’s at any point. Sounds like 34’s may put me in between ratios (4:56/4:88) otherwise my gear selection would be much easier (4:56 for 33’s, 4:88 for 35’s) Yes, gearing is expensive! That’s why I’ve been obsessing about it for months, since I only want to do it once! While living at high elevation with hilly terrain all around seems to play a role in my decision, I don’t want to be overgeared to the point where I can no longer go 80 comfortably (I get that I will have peak HP at 4500rpm, but driving over 3500rpm for extended periods really sounds loud and feels inefficient on the highway). Would be nice to keep it in 5th going 60-75, and have 6th gear still be effective and comfortable for 75-85. I get that the automatics need much deeper gears than manuals, but most of the advise I have received shows 4:56 for 33’s (either with the 5 speed or 6 speed). Looking over the gear ratio calculator, the 6 speed seems to need one step higher gears to be at the same rpms (3000) at 75mph (4:88 in AX-15 5speed = 4:56 in NSG370 6 speed). While I’m leaning towards 4:88 (with the logic that they will accommodate larger tires In the future), I’m worried that 3700 rpm at 85 might not work well for me.
 

JMT

The Jeep Guy
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Thanks so much for your help, and I really appreciate everyone’s comments! I know the 4.0 is not the most powerful engine, but have been driving them in my XJ and TJ for 25 years, and never really “needed” a regear to keep safe highway speeds in CO until got my LJ with 285’s about 6 months back. I really like my lift height, and may be able to fit 34’s with some highline fenders in the future, but wasn’t really planning on 35’s at any point. Sounds like 34’s may put me in between ratios (4:56/4:88) otherwise my gear selection would be much easier (4:56 for 33’s, 4:88 for 35’s) Yes, gearing is expensive! That’s why I’ve been obsessing about it for months, since I only want to do it once! While living at high elevation with hilly terrain all around seems to play a role in my decision, I don’t want to be overgeared to the point where I can no longer go 80 comfortably (I get that I will have peak HP at 4500rpm, but driving over 3500rpm for extended periods really sounds loud and feels inefficient on the highway). Would be nice to keep it in 5th going 60-75, and have 6th gear still be effective and comfortable for 75-85. I get that the automatics need much deeper gears than manuals, but most of the advise I have received shows 4:56 for 33’s (either with the 5 speed or 6 speed). Looking over the gear ratio calculator, the 6 speed seems to need one step higher gears to be at the same rpms (3000) at 75mph (4:88 in AX-15 5speed = 4:56 in NSG370 6 speed). While I’m leaning towards 4:88 (with the logic that they will accommodate larger tires In the future), I’m worried that 3700 rpm at 85 might not work well for me.
The 6-speed has always been an odd duck for gearing. You’re experiencing it! It’s hard bc you want to only do it once. Final tire size is the biggest factor. When I re-geared I was firm on 33’s as final tire choice. Now I’m on 35’s.
 
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