2006 - 14L Detroit Series 60 Questions

I find my best MPG when I keep the boost <20%... climbing or pulling away from a full stop @ 80k real gently still tops the 20% mark, but it's brief... I actually get better MPG @ 70 mph than I do @ 60... Series 60 likes 1400-1450 rpm for most efficient mpg/burn...

 

Why would you see 5 psi boost at idle? Or is that a DD thing? It would suggest to me a sensor calibration problem.

I also just got a scan gauge, as in yesterday. Haven't had a chance to try it on a load, but just a short local run empty and bobtail. When my right foot's lifted, turbo boost is zero just like the dash gauge shows ('07 C-15).

Edit: After typing that I thought of something. Is it possible you had the jakes on and decelerating when you read your "idle" boost? That would show some boost.

 

I've noticed the same thing getting better MPGs around 68-70. The I try and keep the turbo pressure down as much as possible so using hills to your advantage is best. The higher and longer the turbo boost, the more fuel you burn. Shifting at lower RPMs helps as well.

 

THe VNT runs at idle. I think it's that DD thing. I know I can hear it spool up after about a minute of idling.

My best fuel mileage seems to be around 1400-1425 RPM. I cruise right at 66-67 mph at that speed.

I have no boost gage yet, so I have no clue what it's running.

I know right now after all the work I have done, my mileage if FINALLY averaging high 7's on paper. Currently, my IFTA report for this quarter is showing 8.06 mpg.

 

I had a truck with a boost gauge that was running mid to high 7's but the company took it out to replace it with a right weight gauge and from then on it was getting low to mid 5's. On the last run coming in I averaged 5.3 for the quarter and my driving habits never changed. To this day I'm still wonder how that was possible.

 

I've been experimenting, Horse - I have a DD60, 14L, 515hp. I started with the 62mph that the big carriers force on drivers, Swift, Prime, US, Stevens, you know them. I ran around 6mpg for 10,000 miles, average conditions and loads. I did some internet research and downloaded the power chart for my engine. The torque spec is constant from 1,100 to 1,500, and drops off steeply above that range. Horsepower curve is low at 1,100, climbs to a peak around 1,800 r's. The point where the torque and horsepower curves most closely approach is @ 1,400rpm. So I drove another 10,000 miles at 1,400 rpms wherever possible. Mileage went up to about 7.25 to 7.5 average! My experience mirrors yours, the DD60 runs a sweet spot around 1,400-1,450. Right now, I'm running another 10k at 1,350 rpm. 1,400 is about 67-68mph, which is nice. 1,350 is around 65-66mph, which is just fine with me. If the truck is using less fuel, it's running more efficiently and will last longer. I figure.

On fuel efficiency and consumption, so much depends on loads and roads. 45K in the box will need more fuel than 25K. Mountains will need more than cruising along an interstate highway in Nebraska. On mountains, Horse, what is your experience? You use more going up and less going down, but if you go from Missouri to Denver, it's almost all up. So that matters on fuel. And on how much you're dragging along behind. And wind. And construction. And traffic. And scales. And......

 

My pre-purchase dyno report shows a max boost of 36 psi @1900 rpm. That was under 100% load. As I recall they mentioned that they thought that was a couple of lbs. low, but they didn't think it was an issue since I was getting 81% of rated power to the rear wheels.