I just went from a 285 to a 315 on my truck. Planning on doing a gear swap, I have 3.55 with a 5 sp now. Just wondering what kind of rpm's you guys are running with 4.11s on the highway. I don't do too much towing I have a 5k travel trailer that I pull. My question is should I go with a 4.56 or 4.11 with the 35" tires? also my temps are at 1200 pulling the slightest grade right now, 5th gear is out of the question unless it's a flat ground. Not sure what my timing is at would bumping it up some help with the temps?

 

Something sounds off about those temps. Timing should help, but you might want to check the accuracy of the pyro. To answer your actual question I would not go below 4.10s. I just went the other way with my '99 and am very happy with the change. We have 285 BFG's on the 97 and it is fine off road. I might try some 35" Pro Comp xterrains tomorrow to see if they fit.

Randy

 

I'm thinking of going back to a 285 myself, looking at 1500k just to change the gearing, when I could spend that on a new turbo if I keep the 285s. I was just wondering if anyone else was running 35" with 3.55s and what kinds of temps they had. It's not bad empty, just towing with this setup is not fun. I live around 7k ft. elevation too.

 

My 95 has 305/70s on it and I wouldnt even think about going to 4.10s. I am still spinning right at 2K RPM at 70 MPH (according to speedo which may be off). I havent pulled a loaded trailor yet but it hauled the empty trailer (2000 LB) better than my 2004.5. It had no idea at all that it was back there. Even when lug shifting off the stop lights where RPM was only around 1300 RPM after the shift. My truck is stock other than being straight piped and I have no problems running in fifth. I cant tell you what my EGTs are as I am waiting to sell my GMC so I can get gauges and do some mods. Retiming the pump should help the temps along with a less restrictive exhaust and a better flowing air filter. Your tems definatly sound a little warm for running empty so I would do some investigating. Good luck.

 

What type of tires? I may know of a home for them.

I haven't had the 97 to Flag yet and I didn't have the gauges when I took a 35' TT to Show Low. I know our 180 HP 550 TQ recon at 12000# had no issue up the B-line or to Prescott. But it is completely stock. We'll be in Flag in the middle of OCT. I could let you know then.

Randy

P.S. I have a good D-80 4.10LSD carrier and gear set.

 

What RPMs are turning? And what were the temps before the tire change? Could be the RPMs are a little low. Need more boost.

 

Hey new river the tires are 315X75R16 BFG Muds, I don't think it's a boost issue so much, but just out of it's gear range. It does good empty 19.5 mpg avg. the rpms are around 1800 in 5th gear at 60 I can make close to 30 psi. I had a 100# plate in and changed that to a #6 which didn't really help much, I'm leaning towards a new turbo right now.
The temps when pulling hang around 11.5 to 12 just with the slightest grade or a head wind. Before the tires I could clmb anything without going to 4th and temps would run 10 to 11

 

Keep in mind it will run cooler at a higher RPM even with the same or less boost. If the road is strait run it up a couple of hundred RPM and see what your temps do. Also did you have your speedo recaled after the tires? Our 7 with just 285 BFG is off about 4 MPH @ 71. 3 @ 60. It will make a difference in your RPM.

Randy

 

I had the same questions. My wifes 98 with 285's and 3.55's usually runs empty at about 680 degree's, 8 psi of boost at 75 at 1900 rpms with a max of 1100 degrees when I punch it. The speedo was off about 5mph going from the original 245's to the 285's. My 02 has the 315's and they look so much better. I also have 3.55's but have some 4.10's at the house that I bought off e-bay. I pull mostly with that truck. Cruising at 2000 with the sixer puts me at about 80. after some calculations I figured I would be right at stock with the 265's and 3.55's compared to the 35's and 4.10's. That puts me right at 72 mph at 2000 r's. That is where it needs to be. Another option that I looked at was just putting in an underdrive. More expensive but more options for empty and towing, plus it is so much cooler to talk about with buddies. I am doing the gears because I am putting an arb air locker in the rear and a eaton electric locker in the front. It all depends on what you do. If you tow alot, do the swap, if you dont, run what you have. 1100 dollars or more is alot of fuel. Plus just bump up the power a little. With 4.10's though, it will be easier on the clutch and tranny.