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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 5 (permalink) Old 05-25-2005, 07:27 PM Thread Starter
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Safe engine RPMs

I just bought a 94 5 spd powerstroke with 4.10 gears and 235 size tires. It is low geared as can be i think the rpms were around 2500 at 70 mph and 2800 at 80. Is 2800 rpms safe rpm to hold steady on a diesel like this if not what is. Sorry for the dumb questions but ive mostly owned gas trucks(1 6.9L diesel 4-5 yrs ago with no tach). and im not real familiar with the newer diesels.
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post #2 of 5 (permalink) Old 05-25-2005, 07:38 PM
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Re: Safe engine RPMs


Shouldn't be a problem. Your rpms are high because of the 4.10s in the rear...my 97 with 3.73 gears is at 2000rpm at just over 70mph. If it bothers you could always go with bigger tires to compensate.

I believe you could hold these trucks at "redline" on the tach all day long and not have a problem. My thinking is that redline on the tach is a "fuel injection limit" and not a mechanical limit of the engine. If possible I would think a powerstroke engine could spin at least 5,000 rpms without a problem...but getting the fueling for that rpm would be a problem.

An apples to oranges example is our TDI engine. It's "redline" on the tach is only 4500 rpms and won't rev beyond 5000 rpms...however...the internals are almost identical to a 2.0L vw gasser engine which redlines at almost 7000rpms.

It is a question of fueling.

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post #3 of 5 (permalink) Old 05-25-2005, 08:17 PM Thread Starter
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Re: Safe engine RPMs

Thnx for the info i know about gears i was planning on 33s or 35s depending on money during the summer. or 3.73 gears but thats going to be even more expensive. But you say holding almost 3000 on them isnt a problem.
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post #4 of 5 (permalink) Old 05-25-2005, 09:59 PM
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Re: Safe engine RPMs

My understanding of our engine is that the original IH engine was governed at 2600 rpm. At 75 mph with your setup (same as mine) you'll be at the original red line, before Ford moved it up to 3200 rpm. These engines have large pistons, long rods which put a lot of pressure on the main bearings, etc. It's my opinion that if you intend to get 400k miles out of the truck, try to stay at or below 2600 for extended periods. get larger tires to improve your gear ratio if you need to drive at those speeds.

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post #5 of 5 (permalink) Old 05-25-2005, 10:17 PM
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Re: Safe engine RPMs

[ QUOTE ]
Thnx for the info i know about gears i was planning on 33s or 35s depending on money during the summer. or 3.73 gears but thats going to be even more expensive. But you say holding almost 3000 on them isnt a problem.

[/ QUOTE ]

I've got a 4.10 & 235s and although I never drive over 75 mph, I never had a problem with high rpms. Changing your rear gear ratio will be a bit pricy, but the savings in better fuel ecomomy will eventually pay off in the long run. Those with a 3.55 claim the best mpgs (19-20).

http://www.drivetrain.com/Fordtrkratio_posidata.html

Knowing what I know today, I should have put 3.55s on years ago.

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