Advice on safe interstate RPMs 65-80 mph - Diesel Forum - TheDieselStop.com
Power Strokes 1994-1997 General Technical discussion of topics related to vehicles powered by the Power Stroke engine in 1994 through 1997 models.

 
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post #1 of 8 (permalink) Old 03-13-2019, 09:05 PM Thread Starter
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Advice on safe interstate RPMs 65-80 mph

Just curious of what you fellas get as far as Rpms and at what speeds you get with your setups and advice on what changes I could make to get mine where I’d like it. My setup is a 94.5 7.3 PSD, single cab long box. It’s 4x4 and has roughly a 7 inch lift with 35s and is backed by a ZF5 close ratio trans. As far as the tag says on the rear it should have a LS 4.10 gear in it. I’m concerned about long hauls in this truck because at say 75-80 mph I’m turning 2600-2700rpm and I’m aware the valve trains in 7.3s aren’t exactly the greatest. I would like to make a trip to the beach in it (6-7 hour drive all interstate driving) is it a bad idea to run it at those RPMs for that much time? I have considered swapping to 3.73s maybe 3.55s as I don’t tow all that much very often but I have pulled up to 10k and will again at some point.
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post #2 of 8 (permalink) Old 03-13-2019, 09:34 PM
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If you wanted to you could just place a brick onto the throttle and let it hit the governor and run it there all day long with no problems.

If I am unloaded I'll run my truck at 80mph all day long and not even give it a second thought. Loaded I'll keep it around 70.

With your 35's have you re-calibrated your speedometer for them?

As for swapping gears if I would do it I'd go to 3:55's. 3:73 is so close to 4:10 that I doubt that you would notice much difference. Also where you tow or haul things could help in your decision. I do most of my driving in Colorado with trips to Utah, Arizona, Wyoming and Idaho so I get into a lot of hills.

96 F250 PS XLT 4X4 long box, 5sp,4.10, manual hubs,pyro+boost guages, Dark Toumaline, add a leaf, Dale's TYMAR, and HX hose, downpipe, coolant filter, Luk clutch
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post #3 of 8 (permalink) Old 03-13-2019, 11:19 PM Thread Starter
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If you wanted to you could just place a brick onto the throttle and let it hit the governor and run it there all day long with no problems.

If I am unloaded I'll run my truck at 80mph all day long and not even give it a second thought. Loaded I'll keep it around 70.

With your 35's have you re-calibrated your speedometer for them?

As for swapping gears if I would do it I'd go to 3:55's. 3:73 is so close to 4:10 that I doubt that you would notice much difference. Also where you tow or haul things could help in your decision. I do most of my driving in Colorado with trips to Utah, Arizona, Wyoming and Idaho so I get into a lot of hills.
I have not calibrated my speedo. I know it’s about 4 or 5 mph off from about 30mph+ according to GPS and speed traps. It may try closer to 10 mph at interstate speeds. All my towing is gonna be done on mostly flat ground with a very minimal inclines. It was my understanding that with a zf5 the gear ratio is reslly gonna be most noticeable in OD/5 that being because of the very close gearing in the trans it self
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post #4 of 8 (permalink) Old 03-13-2019, 11:30 PM
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The trans really has nothing to do with the gearing once you hit 5th gear. I don't have the ratios but all the Zf 5 speeds have close to the same 5th gear ratio.

96 F250 PS XLT 4X4 long box, 5sp,4.10, manual hubs,pyro+boost guages, Dark Toumaline, add a leaf, Dale's TYMAR, and HX hose, downpipe, coolant filter, Luk clutch
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post #5 of 8 (permalink) Old 03-14-2019, 04:46 AM Thread Starter
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The trans really has nothing to do with the gearing once you hit 5th gear. I don't have the ratios but all the Zf 5 speeds have close to the same 5th gear ratio.
well 5th is where I’m gonna get my final drive and where I get my max speed and RPM. My truck will go 95 and absolutely no more. The gearing stops it from going any further, I’m looking for around 2200 rpms at 80mph. I get 2700 rpm at that speed as it sits now. I know the ratios in the trans has nothing to do with the top speed and rpm ratio but a E4OD auto seems to do much better when it comes to highway driving and I would expect that as a ZF5 isn’t designed for it.
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post #6 of 8 (permalink) Old 03-14-2019, 04:48 AM Thread Starter
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The trans really has nothing to do with the gearing once you hit 5th gear. I don't have the ratios but all the Zf 5 speeds have close to the same 5th gear ratio.
well 5th is where I’m gonna get my final drive and where I get my max speed and RPM. My truck will go 95 and absolutely no more. The gearing stops it from going any further, I’m looking for around 2200 rpms at 80mph. I get 2700 rpm at that speed as it sits now. I know the ratios in the trans has nothing to do with the top speed and rpm ratio but a E4OD auto seems to do much better when it comes to highway driving and I would expect that as a ZF5 isn’t designed for it.
I’m just curious if these RPMs are something I should concerned about and if I do regear the rear axle what others recommendations would be.
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post #7 of 8 (permalink) Old 03-14-2019, 09:02 AM
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I wouldn't worry about the RPM's at all. As I mentioned there is a govenor in the PCM that is set at a certain RPM, I think it is 3500 RPM's but I am not sure and you can run it at that point all day long.

As for regearing you have a 4x4 so you would also have to do the front end.

96 F250 PS XLT 4X4 long box, 5sp,4.10, manual hubs,pyro+boost guages, Dark Toumaline, add a leaf, Dale's TYMAR, and HX hose, downpipe, coolant filter, Luk clutch
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post #8 of 8 (permalink) Old 03-14-2019, 11:08 PM Thread Starter
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I wouldn't worry about the RPM's at all. As I mentioned there is a govenor in the PCM that is set at a certain RPM, I think it is 3500 RPM's but I am not sure and you can run it at that point all day long.

As for regearing you have a 4x4 so you would also have to do the front end.
yea I have the front drive shaft removed right now, assuming the front gear ratio isn’t really considered until 4x4 is engaged.
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