Can too low an RPM on a Series 60 hurt MPG?

belfert · August 04, 2013, 03:12:05 PM

My bus has a Series 60 engine and a B500 transmission. The original configuration had 6th gear on the transmission locked out. With 6th gear locked out and running in 5th gear I would be running about 1,550 RPM at 65 to 66 MPH. This year I had 6th gear enabled and when in 6th gear the engine turns around 1,400 RPM. I was hoping for better mileage, but it seems like mileage was the same or worse. We got something like 6 MPG this trip when the norm for the same trip is more like 7 MPG. Now, it was much warmer than typical for this trip and we ran the generator 24x7 while on the road with two or three A/C units running all the time. We are doing the exact same trip in late September so maybe that will be a better MPG test with less generator usage.

Does the Series 60 get worse mileage turning slower RPMs? Is it possible the engine is working harder even though it is turning slower?

bevans6 · August 04, 2013, 03:22:59 PM

The bus takes a certain amount of horsepower to go a certain speed. It takes a certain amount of fuel to create that horsepower. If you use the fuel at 1400 rpm or 1550 rpm, you still use the fuel. I have often found that running at a higher speed lets the engine develop the horsepower at a lower amount of throttle and be possibly more efficient.

Brian

belfert · August 04, 2013, 04:22:37 PM

I may be misunderstanding things, but isn't overdrive supposed to improve mileage? Shouldn't it take less HP to move the vehicle forward in that case?

I know a lot of people claim their cars get better highway mileage at say 70 MPH than at 60 or 65 MPH even though at 60 MPH they should already be in the highest gear with an automatic. In theory it seems like a vehicle should get the highest possible MPG running at the minimum speed required to shift into the highest gear and running consistently at that speed. Aero drag is less at lower speeds of course.

Zeroclearance · August 04, 2013, 05:28:24 PM

Brian, I get between 7.2 to 7.8 mpg.. And this is usually without the generator running. I have more HP than you and weight more. I am usually in 6th gear 99% of the time.

So, my question for you is? Have you adjusted your intake and exhaust valves AND injectors?? Are you getting full boost and steady boost? Have you checked your compressor wheel for damage?

If you have done all of the above, I would bet that your Genset ate the fuel difference.

belfert · August 04, 2013, 06:05:54 PM

Quote from: Zeroclearance on August 04, 2013, 05:28:24 PM
Brian, I get between 7.2 to 7.8 mpg.. And this is usually without the generator running. I have more HP than you and weight more. I am usually in 6th gear 99% of the time.

Your bus most likely came from the factory with 6th gear enabled. My 6th gear was not enabled from the factory. I have 4.10 gearing and that is supposedly why the manufacturer didn't enable 6th gear. I have been told the likely reason they didn't enable 6th gear is because the RPMs would drop too low for the B500. The B500 is smart enough to downshift to 5th if the RPMs get too low. Maybe they didn't want it hunting at 55 to 60 MPH. Right now, my B500 shifts to 6th about 61 or 62 MPH and will hold 6th at least down to 60 MPH.

I had the valves and the Jakes adjusted around 35,000 miles ago when I first got the bus. I don't recall if the injectors were done or not. I haven't looked at the compressor wheel, but the turbo boost seems correct for an 11.1L Series 60. The 11.1L runs a fairly low boost from what I have been told and that matches what I see.

luvrbus · August 04, 2013, 06:20:07 PM

What is your 11.2 series 60 a 350/370 hp ?

Zeroclearance · August 04, 2013, 06:33:41 PM

My point is.. You might not have enough power/torque to maintain the overdrive (6th).. Boost (air) with fuel will give your the peak torque at 1450 plus or minus... You might need to reprogram your ECU and replace your turbocharger for more output.. If you have the early engine without the proper head bolts, rod bolts>> you might be limited.

Clifford might remember the HP limit and boost limit if you have a early engine.

belfert · August 04, 2013, 07:01:36 PM

It is 325/350. I would certainly be willing to manually downshift to 5th if I would get better MPG. The other option would be to reprogram the WTEC back to original program.

Could a Detroit dealer tell me if my engine has the updates or not?

Zeroclearance · August 04, 2013, 09:13:22 PM

I'm pretty sure that you can go up to 430HP WITH a ECU reprogram and turbocharger change.. Maybe 450HP.. I wouldn't push it past that if you have a early engine.

I don't think that you have enough power with 330/350HP to run in 6th..

You don't have to reset your Allison.. Just drop it into 5th..

TomC · August 04, 2013, 09:19:37 PM

S60's are supposed to be run between 14-1600 for most economical cruise. Best to get an instantaneous MPG readout gauge. Many times running an engine at a lower rpm will make it work harder making for worse mileage.
Except for the new DD engines. They really like to run slow-like around 1100rpm. But then they have common rail fuel injection that has endless timing scenarios-unlike the S60 that is injected with a camshaft. Good Luck, TomC

luvrbus · August 04, 2013, 09:35:02 PM

Your problem and I agree with ZC not enough hp for 6th they do ok set at 400 hp but before I did anything I would have a dealer run your engine numbers most buses than ran the 11.2 it was 375 max

The school here has a couple of D MCI that have the 11.2 (325hp) and B500 when I had 6th gear unlocked their millage went down till we bump the 11.2 to 400 hp that was all that was allowed with their engine number and that bump cost $2500.00 with new turbos done at WW Williams in Phoenix it does raise the torque range from 1300 to 1425 rpm it worked for them they are back to 7.5 to 7.9 mpg with teachers for drivers

belfert · August 05, 2013, 01:13:47 AM

Quote from: luvrbus on August 04, 2013, 09:35:02 PM
Your problem and I agree with ZC not enough hp for 6th they do ok set at 400 hp but before I did anything I would have a dealer run your engine numbers most buses than ran the 11.2 it was 375 max

The school here has a couple of D MCI that have the 11.2 (325hp) and B500 when I had 6th gear unlocked their millage went down till we bump the 11.2 to 400 hp that was all that was allowed with their engine number and that bump cost $2500.00 with new turbos done at WW Williams in Phoenix it does raise the torque range from 1300 to 1425 rpm it worked for them they are back to 7.5 to 7.9 mpg with teachers for drivers

The bus seems to drive just fine in 6th gear. It just seems like MPG is less, but with so much generator run time using the same tank it is hard to know for sure.

I don't know if I would want to try to upgrade the HP of my engine. I would be worried about destroying the engine with more HP. I know that if I had a DDEC IV that the only program for an 11.1L is a 400 HP program. I'm probably best off just manually downshifting to 5th gear and running the engine in 5th gear for best mileage. I suspect it would cost more than $2500 to get the work done at a Detroit dealer today since they are charging $129 an hour.

belfert · August 05, 2013, 01:16:26 AM

Quote from: TomC on August 04, 2013, 09:19:37 PM
S60's are supposed to be run between 14-1600 for most economical cruise. Best to get an instantaneous MPG readout gauge. Many times running an engine at a lower rpm will make it work harder making for worse mileage.

Clifford is saying that some 11.1s have been upgraded to 400 HP and they get better mileage. Wouldn't I still have a problem with my RPM being too low if I had more HP?

B_K · August 05, 2013, 05:40:45 AM

Quote from: belfert on August 05, 2013, 01:16:26 AM
Clifford is saying that some 11.1s have been upgraded to 400 HP and they get better mileage. Wouldn't I still have a problem with my RPM being too low if I had more HP?

NO!

There was a reason they had 6th locked out! If you want to play with 6th you'll need to do as Clifford an other say an up the HP & torque in order to run/maintain it EFFICIENTLY!

If it was simply just a matter of unlocking 6th most or all Dina's would have already been done by previous owners?

BK

belfert · August 05, 2013, 08:58:36 AM

Quote from: B_K on August 05, 2013, 05:40:45 AM
NO!

There was a reason they had 6th locked out! If you want to play with 6th you'll need to do as Clifford an other say an up the HP & torque in order to run/maintain it EFFICIENTLY!

If it was simply just a matter of unlocking 6th most or all Dina's would have already been done by previous owners?

I would bet the biggest reason previous owners didn't do it is because it is hard to do. The local Allison dealer was going to charge me something like $750 to do it, plus they needed a letter from an engineer at the original manufacturer stating it is okay to make the change. Jack Campbell knows an Allison dealer in Florida who will reprogram WTECs for $100. The catch is they need the CIN number from another WTEC that is programmed the way I wanted it. They wouldn't just change parameters in my WTEC. Jack provided the CIN number from his MCI with Series 60 and B500 that has 6th gear enabled.

I figured I couldn't really hurt anything by making the change. I certainly never expected I would get worse mileage. I figured at worse I would get the same MPG as always. I figure it cost me around $300 for the programming change, shipping, and extra fuel used.