Yea but your not a company driver, you can buy a late model truck and make it whatever you want. I built what I wanted and was tens of thousands cheaper than new. I searched for something as close to what I wanted as I could find and changed the rest. However you need to start with something built in this decade, with parts that are still available. Odd ball parts increase downtime and costs.
My point of bringing up the ISL vs the ISC is you were worried about transmission ratios. Don’t ever replace HP with gears.
Na you can keep your little truck, it’s a market I don’t understand but to each their own. You could buy one of those California single axle hay hauler semis. The look of medium duty without all the downfalls. You can get a real engine and driveline.
I wasn't trying to imply I was replacing HP for gears.. I was pointing out known issues with gear splits/shift points that happen at common road speeds.. I've had this problem with company trucks when I was a company driver along as being an O/O
25-30% jump in a gear shift creates a problem.. more so if it happens at speeds above 50.. rolling heavy or high sail scream the engine in the lower gear or lug the crap out of it in the higher gear..
Take 3.58 gears 36" tires 55mph in 4th (direct drive) is ~1800rpm.. 5th is usually .75-.70 for Allison 3000.. puts 55mph at 1300-1400rpm.. truck gets slowed down for whatever hills, traffic, Sunday driver.. now the truck is hunting between 4th locked, unlocked 5th and locked up 5th gear.. and results it throws mpg out the window..been there done that..
It's exact problem I had with the 1000series in my 07 Chevy.. had a 30% jump between 4/5 shift.. I band-aid the problem by moving the shift point to left to happen at 45mph by putting shorter gears in the diff at cost to be able to run 75 and up out west..
On a 13spd with 3.58
12th is .86 1600@55
13th is .73 1400@55
With 13sp I can run longer legs in the diff and slow driveshaft speeds down. Like 3.21-3.31
One doesnt have this problem
Attached is the graph for a 450/1250 L9 rated at 1250 at 1400-1500rpm..
6th gear on a 3000rds is .65:1(wrong on previous post)
3.90 puts 4/5 shift around 45-50 and 70 1650
3.73 puts 4/5 shift around 50-55 and 70 1590
3.58 puts 4/5 shift around 55-60 and 70 1500
One Has to wind out 4th gear to 1800-1900rpm to catch 5th gear above 1400rpm or you just slow back down and downshift back into 4th with the Allison..
With the Allison its a 500-600rpm drop on 4/5 shift pending 5th ratio option... on a 13sp it's 250rpm drop from 11/12(direct to 1st OD) and I'm running lower gear to ~1700 vs ~1900 with the Allison, to catch next gear by 1400rpm
To me less time spent below/above peak TQ the more efficient the setup will be..
While back I ran across a guy with a M2-106 ISL9/3000 with 3.90 gears 255/70/22.5 tires with 350hp.. 5th gear was too steep to run up jelico grade at 50k which forced him to play elephant races at ~40-45mph.. best tank mpg he was low 7mpg.. avg mid 6
worse tank mpg I got was 6.9mpg, best was 11.2mpg avg mid 9mpg with a worn out mechanical 8.3.. got less that 8k on the rebuild before I parked the truck. I was avg high 9s with it..
I'm assuming you've seen rpm to speed charts for transmissions? This basically all I'm doing.
Those day cab single axle truck out of CA would be nice starting point
