1st Generation Dodge Cummins 89-93 Discussion of 12 Valve 5.9 Liter Dodge Cummins Diesels with Rotary Injection Pumps

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Old 01-13-2013, 10:55 AM
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its very annoying to be cruisin down the highway basically floored at 75mph. So I was wondering what I could do to get my top speed up so I could actually be able to driveon the highway. I have the 3 speed automatic transmission.
 
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Old 01-13-2013, 11:02 AM
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Originally Posted by Cow tipper
its very annoying to be cruisin down the highway basically floored at 75mph. So I was wondering what I could do to get my top speed up so I could actually be able to driveon the highway. I have the 3 speed automatic transmission.
not really sure why you would max out at 75 mph , i can get up to 75 going up a slight hill on the highway and my truck is almost all stock , maybe there is something wrong there but im not sure
 
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Old 01-13-2013, 11:05 AM
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Well, a couple of questions. WHat is your gear ratio? 2wd or 4wd? Any Intake mods? Exhaust mods? Your 3 speed auto can only do so much. What kind of RPMs are you hitting at 75 mph? What is your tire size? ........Brain fart.......
 
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Old 01-13-2013, 11:16 AM
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pretty sure gear ratio is 3:08 its 4x4. Has a K&N intake filter, the exhaust is straight back but is still stock, and im hitting around 2500 rpm at that time. I can hit 90 if im really trying to torture my truck.

---AutoMerged DoublePost---

tires are 31 inch
 

Last edited by Cow tipper; 01-13-2013 at 11:16 AM. Reason: Automerged Doublepost
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Old 01-13-2013, 11:25 AM
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While not knowing the rolling radius of those tyres, 3:08 gears with direct drive will give you somewhere close to those speeds at 2500 rpm
 
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Old 01-13-2013, 11:30 AM
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so what are you suggesting I do?
 
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Old 01-13-2013, 11:32 AM
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Overdrive gears are about the only way you will get the engine rpm down.
Your maxxed out on final drive ratio.
Being a 4X it may take some doing, different transmission with over drive is required.
Sorry for the good news
 
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Old 01-13-2013, 11:33 AM
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thanks man
 
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Old 01-13-2013, 11:34 AM
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x2. If ya wanna bring down the RPMs and increase speed, Look into an overdrive unit and split the gears. You will essentially end up with a 6 speed trans. Lower RPMs at 75 will also net you much better MPGs. Even better if you slow it down some. The good Lord gave us multi-lane highways and streets so others can pass if they think youre too slow.........
 
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Old 01-13-2013, 11:41 AM
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If you have enough driveline length you maybe able to squeeze an overdrive unit behind the trans but being 4x4 you will only be able to use it in high range 2 WD drive.
Sounds more like an overdrive setup out of a later model would be the easiest.
 


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