Quote:
Originally Posted by ShuttlePilot
I'm on the same page as JoeH, and others. Based on the conversation so far my final answer would be 4:10. But as was mentioned I say run what you have first and see what happens. Sounds like the gears are already stuck in the axles and if your not cracking them open for any other reason it won't mater much to have to change now or later. Operative part is your not opening up the diffs for any other reason before install.
I only have experience with my van but in it's current trim my 6.0 likes to live between 2200 and 2500 RPM. Which is where it is most of the time with 4:10's. I'm still on the SMB size of 285's on 16's. I've thought about at the next set of tires going to next size up on 17 rims but I'm content with things for now. Calm weather on highway I'm somewhere around 15-16mpg. Town only driving it's a lot less than that. IDK, I really haven't kept track, but it's way better than the 10mpg I've done in other vehicles.
Just a couple more thoughts about possible issues with being to high geared. On my van the key to getting better millage is speed, further above 70 I go the more fuel, and torque converter locked. When I say above 70 the physics really mean air speed as in 30mph headwind plus ground speed kills millage and gearing is part of that. I could also see a potential killer of millage could be not only gear hunting between 4 and OD but the converter constantly locking/unlocking. I keep a lazy eye on my TQ indicator to keep it locked as much as possible by throttle control and manually dropping out of OD when pulling a mountain. When I'm not in town my TQ is locked all the time for millage, heat and longevity of everything.
Another thing that I rely on at times that the my current gearing provides is the scenario of going 70 (ish) and I need to go to full military power for a mile to get away from some "situation" I can hold the throttle open and the trans won't down shift because I'm already above the max shift RPM for OD.
Lastly, pulling 4th gear on large climbs is something to think about in the gear equation. I hear your planning to be light weight but too high of 4th gear on some climbs could be just a tad to high to keep the turbo breathing and be forced to, God forbid, drop to 3rd. Kind of normal for me to see 3rd on a big climb (Vail Pass) pulling a trailer but I would hate to be trapped between 3rd and 4th gear empty every time.
Anyway just some of my thoughts on what could happen being too high geared with a van like ours. But truethfully, I don't really know for sure. Try the 3:73s and report back.
"One live test is worth a thousand expert opinions" - Vernher Von Braun.
- Eric
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Very valid points, but since i'm stuck with the gearing might as well try it and report back.... but with the speed of the build, it will be while before i do
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