i updated post #9.

added 4.88's and 5.13's just for fun.

take note that i changed the spreadsheet a bit to make it a little bit more usefull. I highlighted between 65mph and 75mph as i figgure that is where most of your towing will be. I also changed the max engine speed to a more realistic 3500rpm. I can't immagine spinning more than 3000rpm all day long, especially in a diesel, so keep that in mind when you are looking at the RPM columns.

something else to take notice of is the fact that you would have to drop below 50mph before the trans can downshift from 3rd to 2nd when running 4.56's. Maybe that don't matter to you, but it kind of stood out to me.

5.13's ... don't know who would want those ... but hey, rock crawling is fun too

 

The gears will not affect the speedo. The VSS still reads the same tone ring. The tires are what changes the speedo. He will want to have the truck reflashed at the dealer or use an aftermarket device to correct the speedo. Most tuners on the market will not be able to correct the speedo.

Yes they make headers for the 7.3l. They really do not do much until you get up in the high power range with far more boost than stock. With a tune and exhaust you do not need to install headers. If it were me I would go with the 4.56 gears due to the extra rolling resistance of the large tires and extra wind resistance of the lifted truck.

 

You're going to have to explain that one further ....

Perhaps there is something different about the SD's that make this statement true, but it is certainly not for every vehicle I have ever owned or driven.

your speedometer reads off a tone ring, just as you say, and is calibrated such that a certain number of clicks means the vehicle travels a certain distance, based on the computer assuming a tire size and gear ratio (which is programmed by the factory).

if you increase the tire size, the speedometer will be off by the same percentage as the change in tire size. if you add the same percentage of gear as you increased in tire size, then the speedometer will read correctly again. the only location i can see for which this would not be true is a tone ring at the wheel, which would be unaffected by a change in gear ratio, but would be affected only by a change in tire diameter.

in fact, air pressure alone can make a difference, depending on the accuracy of the measurements. At work, we use DMI's, which read off the VSS, but do so such that they are accurate to less that 1foot per 1000. (usually less than 1 foot per 2000). i have calibrated my meter such that it is repeatably accurate to 0 foot in 2000ft, then changed the air pressure a couple PSI, and the meter is no longer accurate. being off as much as a couple feet depending on how much you change the air pressure.

maybe i'm missing something, but unless the SD's part from the norm, and read vehicle speed off the ABS wheel sensors, your statement cannot be true. If it is reading from the tail of the transmission or transfer case, the VSS would be affected by any change to the overall gear ratio, which includes axle ratio and wheel diameter.

 

The VSS takes the reading from the ring gear of the rear differential. That makes one revolution each time your wheel makes one revolution. While tire size does affect it, the ring and pinion ratio do not.

 

after i posted that i thought about taking a reading off the ring gear, which would make my assumptions false as well.

I learned something today

 

Well this is great..so I was taking it to M&M in sicklerville, NJ.. So as luck would have it the front drive shaft U Joint took a crap on me.....so I got it towed to the shop...and yes that sucked...I found out that I have a Dana 50 upfront and a 10" in the back...so he is checking with the manifactor that he uses on the noise level. He said that manufacture said that with 37" tires and with 456 it would turn around 2100 rpm at 70 mph and it would be like putting 410 on it for stock tires...the 488 would be like 435 or 456 and turn 1900 rpm around 70 mph...if not he will replace them at no cost. I also am replacing the auto hubs..since they were engaged when they were suppose to be in 2 wheel drive. Will get the name of the gears and hubs both made by the same company..they are manuel lockers..

This guy Mike is the guy all the rock climbers and big trucks go to in jersey and the outlining areas. He also is doing some other things just because he doesn't like the way it is set up..a good guy had a blast talking to him...he does mud bogs all over the country..has a big *** truck in his garage...over 800 hp very impressive

 

2100rpm@70mpg does not sound too bad to me. It is up to you though. You would not want to go 4.88 gears with the 7.3l, well at least if you do any highway driving with it.

 

Ok just got back from looking at my truck over at M&M in Sicklerville, NJ.. Mike had the gears in and was just waiting for me to get there with the new manual locking hubs. This guy did some crazy stuff to my truck.. fixed some problems that he found while under the truck. The front drive shaft didnt have the correct clearance and the price was good. To say that he fixed stuff is an understatement........he went thru everyting....

 

Right on. Nice to hear there are still quality shops out there taking care of folks without screwing them in the process.

 

Always like to see owners share their experience with reputable shop. Thank you.

 

Ok the shop I took the truck too put in what the gear manufactor suggested. Well, after he installed them the manufactor called and said that was a gas motor rigt...nope diesel...they told him that the 488's are the wrong answer. They shipped him the 410's and paid for the installation. Now I need to look at a new exhaust system from the turbo back. The mechanic looked at it and found that the exhaust is about 2" to small for the turbo and is choking it. Any suggestions on a good system would be helpful