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6.5L Diesel Engine Discuss the 6.5 GM diesel engine & associated components. Automatic transmission questions & problems belong in the 4L80/85 - 4L60E - 6L90 Transmission Forum


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Old 06-03-2019, 08:14 PM   #1 (permalink)
Bart Sheffield
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RPM difference

Can anyone tell me rpm numbers running a 373 and 342 rear end at 70mph .I have a 410 and it's just to low for me I will not be pulling anything she is just a play toy.. so every day at 3k rpms at 70 just no need for that..thanks

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Old 06-03-2019, 10:18 PM   #2 (permalink)
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From my memory when I had a 3.42 rig I think 2K was around 60. If you are never going to tow and have a 2x4 I would say just go for the 3.42.

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Old 06-03-2019, 11:47 PM   #3 (permalink)
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Yeah that's what I'm thinking yes it 2 wheel drive and guna be bagged and lot of custom things done so the only thing it will ever pull will be a boat and not far at all.. thanks for the info.. so I'm guessing 342 will probably drop me 500 rpms maybe at 70 unlike the 410 70 at 3k rpm that will be ACCEPTED..
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Old 06-04-2019, 12:18 AM   #4 (permalink)
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If you're looking to find out mathematically before doing anything;
Gear Ratio Calculator

Confirmed. trans/ diff/ rpm/mph
4l80 373s [email protected]

Figure for your trans(nv4500 or 4l80)

Just my 2cents...
Advisable to have sustained rpms 2100-2300(depending on setup) and lower. 2500 max but not sustained.
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Old 06-04-2019, 01:22 AM   #5 (permalink)
tnDan
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They made a 3.36 gear for the 10.5" full floater back in the 70s. Only found 1 and was in a ~76 C20 454/th400 truck.

Set the cruise for hours on my old 2000 K3500 6.5TD running 26-2700 rpm. Makes for a LONG day.

Keep an eye on ebay for a gear vendors OD unit, knock RPMs down 22%.
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Old 06-04-2019, 01:29 AM   #6 (permalink)
Bart Sheffield
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Od unit..? I'm new at this lol..
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Old 06-04-2019, 01:36 AM   #7 (permalink)
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Auxiliary overdrive unit, bolts on to the back of the transmission.
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Old 06-04-2019, 06:20 AM   #8 (permalink)
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My 3.42 gets me 2200 at 70
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Old 06-04-2019, 07:11 AM   #9 (permalink)
Bart Sheffield
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Bing... that's what I'm after...thanks
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Old 06-04-2019, 09:31 AM   #10 (permalink)
jnlperformance
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Different transmission(s) = different gear ratios. 3.73, 4.10, 3.42 etc. Will have different top speeds depending on transmission used.

The link I provided gives correct data based on trans, diff, transfer cases... etc... two columns for comparisons.



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Last edited by jnlperformance; 06-04-2019 at 09:32 AM.
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