Cruising RPM

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Mar 15, 2009 | 07:46 PM

HS400

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Cruising RPM

What is the limit that you can safely turn these engines consistantly on the highway? I was towing about 8K and cruising at about 2500 rpm @ 67-68mph. Is 2500-2600 rpm going to kill this engine? 1994 7.3. I would absolutly love to have a 6th gear.

Mar 15, 2009 | 08:06 PM

David85

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From: Campbell River, B.C.

2500 is no problem at all. For a N/A IDI, its actually close to ideal for those conditions. Bit of a waste for running empty, but for heavy towing its a good speed.

Mar 15, 2009 | 08:28 PM

Dave Sponaugle

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From: Nutter Fort, WV

2550 is my normal 70 MPH cruise RPM with no overdrive.

Mar 15, 2009 | 09:00 PM

HS400

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Well thats great news! Mine is a five speed with a 4.10 gear.

Mar 15, 2009 | 09:08 PM

JHoffman93

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From: Westfield, MA

How do you find out what gear ratio is in these trucks? I have a 5 spd 7.3 and it runs closer to 2800 at 70 empty.

Mar 15, 2009 | 09:27 PM

LCAM-01XA

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Quote:

Originally Posted by JHoffman93

How do you find out what gear ratio is in these trucks? I have a 5 spd 7.3 and it runs closer to 2800 at 70 empty.

Your trans have a top gear ratio of 1:0.76 which means to be at 2800 rpms while moving at 70 mph and rolling on stock size tires you gotta have 4.56 rear gears, I use an online calculator for that stuff.

Mar 15, 2009 | 10:02 PM

JHoffman93

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From: Westfield, MA

Another gear related question, where would I find the transmission model number used in my truck? Is it printed somewhere on the truck?

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Mar 15, 2009 | 11:09 PM

LCAM-01XA

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if tis a 5-speed manual, then tis a ZF5, no other models available for those years.

Mar 16, 2009 | 10:57 PM

#10

Dave Sponaugle

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From: Nutter Fort, WV

Could be a 42 or 47 series ZF 5.

The ID plate is on the drivers side in the top 1/3 of the tranny and about even with the shifter for a front to back location.

Probably covered with oil dirt, but take a rag to the flat place about 1.5" tall and 2.5" long.

Transmission number and gear ratios are listed on the plate for all six gears.

What size tires are you running?