Curious about c6 shift points/towing/mpg.

[jayro88]

I replace my IP/Injectors etc and got it all timed correctly on my e250. Now I was working on adjusting my VRV. Originally the previous owner had it turned all the way toward the cab so that it got into 3rd (its a c6) as quickly as possible. He said he did this because he thought it would help with MPG's. I am going to be towing a travel trailer come spring and am adjusting the VRV so that it will hold the lower gear a little longer. So I have 2 questions:

1. Am I thinking correctly about adjusting the VRV to hold a lower gear a little longer for towing? I am thinking it will help get up to speed and keep the engine in it's power band.

2. As far as mileage...while you want to keep the RPM's down I would think that having it shift into 3rd to soon could hurt your mileage. It gets really doggy and causes you to give it more throttle than you would if you had stayed in the previous gear a little longer. Now I know that in the lower gear you will be turning more RPM, but will the extra RPM's use more fuel than the extra throttle in a higher gear?

Thanks

 

[freebird01]

your thinking correctly. albeit i hate the C6 behind an idi with a passion... if that VRV is adjusted to shift too soon the van will feel like an overweight slug... and your right about lugging. these engines were designed to run on the Governor. if you can keep your coolant temps down I found that i got better MPG if it stayed in the powerband even if it meant down shifting and running it at 2800-3000 rpm instead of lugging it down to 1800-2000.

noticed that big time with the 85 RCLB truck i took to the rally last year. but the RPM deal holds true auto or 5 spd

 

[Greg5OH]

that is something I have been wondering about. Say your at 50% "throttle", 2200 rpm in 4th or 1900 in 5th for example. Same load. same grade.

The pump is still pushing out say 50ccs, but Im assuming ebcause higher revs, the engine is consuming it at a higher rate.

 

[jayro88]

your thinking correctly. albeit i hate the C6 behind an idi with a passion... if that VRV is adjusted to shift too soon the van will feel like an overweight slug... and your right about lugging. these engines were designed to run on the Governor. if you can keep your coolant temps down I found that i got better MPG if it stayed in the powerband even if it meant down shifting and running it at 2800-3000 rpm instead of lugging it down to 1800-2000.

noticed that big time with the 85 RCLB truck i took to the rally last year. but the RPM deal holds true auto or 5 spd

Thanks. Took a couple of adjustments but I got the VRV where I want it. Man, it makes a big difference on how the van feels when I drive it. Doesn't feel like pig any more.....or at least less of a pig.

that is something I have been wondering about. Say your at 50% "throttle", 2200 rpm in 4th or 1900 in 5th for example. Same load. same grade.

The pump is still pushing out say 50ccs, but Im assuming ebcause higher revs, the engine is consuming it at a higher rate.

I would say that "In Theory" if the throttle input is exactly the same the engine is going to consume more fuel at a higher RPM. The issue is that in order to maintain speed or accelerate in higher gear that is out of the power band you are going to have to increase your throttle input and for a longer period of time. My question was if the fuel consumed by the increase time/throttle input was more than the increased consumption due to the raised RPM's

 

[Greg5OH]

only way to really answer that is to knwo what the BSFC, is at those rpms in 2nd and 3rd. or at least BMEP and estimate from there.

 

[freebird01]

what happens is when you downshift and spin the motor faster its not working as hard so you potentially can ease off the throttle. however speed is effected but your efficiency goes up. its a balancing act for sure.

i can tell you pulling a 16' 10k equipment trailer (appx 2k lbs) and my samurai (appx 3k lbs) behind my ext cab 4x4 w/ 7.3 banks turbo zf 5spd and 3.55 gears it was very noticeable. if i ran it in 5th and lugged it on the flat 1800-2000rpm it would get worse mileage then if i would downshift to fourth and let is scream 2500-2800 rpm and you can tell the truck wasnt working nearly as hard. was a difference of 10-11mpg vs 12-13mpg.