Series 60 DDEC 4 cruised at 1300rpm it is possible ?

with a 13 speed and under 80k should be fine, 13th on flats and if you need a little extra umph run it in 12th

 

When on relatively flat ground with no wind to fight, 1300 rpm cruising is not too bad. Anything other than that, you want to be 1400 or more. I regularly cruise around the same area as you, running 70K or more, and mine does a stellar job in the 1425 to 1475 range, and still pull off averages of high 6's in the winter, and high 7's in the summer, even with the winds. When things are really good, flat and no wind, can easily get into mid to high 8 mpg territory frequently.

I have to side with Detroit's hp/torque/economy charts when it comes to the DDEC IV. They recommend speccing 1400 at 60 mph for economy, 1500 at 60mph for performance. Mine has 2.64 rears, and I run the 18 speed in direct 16th, which sits me on 1400 rpm at 61 mph or 1500 rpm at 66 mph. This is the same as anyone with a standard 10 or 13 running in the top hole with 3.55 rears. I will do the bulk of my cruise time at 1425 rpm / 62 mph. Once in a while, I will step it up, but generally never run over 1500 for normal cruising. Nice thing with the 3.55 rear, I can drop a gear and work the two lanes around Iowa with a gross load at 55-60 mph and it puts me in the prime performance curve, 1500-1600 rpm, of the engine to work those hilly two lane areas and still not take it in the wallet on fuel economy.

Keep in mind, that RPM's below 1400 on the Detroit 60, and EGT's will really climb when working a load. There is no real benefit to running that low when pulling anything heavy. You are fighting a combination of exhaust flow and rotational inertia of the engine at the lower RPM's, and the exhaust temps are going to rise up pretty quickly. That is why, when working the engine, I will stay on the high side of the 1400-1500 rpm range. It keeps the EGT's 900F or lower, even on a scorching hot day and a really tough pull. Once the RPM's drop below 1400, you can watch the pyrometer start to climb pretty fast.

 

The engine is not designed to run 1300 at cruise. I find myself sometimes at 1300 when empty, but like Cowpie says, it will be far from optimal. I have 3.36 and run around 1425 in 13th at 70mph which is optimal for me.

 

I am running 22.5 LP. Wide based on the drives.

If you want a better grip in how the road speed vs rpm plays out with various rears, trans gears, tires, etc, I have a spreadsheet that you can have, where you can plug in rear ratios, tire rotations per mile, etc and see things side by side and for various gears all at the same time. Sometimes it is more visual and clear when you can look at the differences side by side and compare. Just send me a PM with your email, and I will forward it to you. Tried to put in up in this post, but system doesn't allow Excel spreadsheets for some reason. Anyone else want a copy, just PM me with your email and I'll get it to you.

 

interesting info. I did not know lower rpm's on a hard pull raises e.g.t's. I have no pyro or boos gauge so I don't know what my truck is doing concerning these factors. on my truck, for sure below 1300 r.p.m's is lugging the motor. I have a friend who has a newer detroit a 06' with a 515 h.p. & he says his book suggests upshifting at 1100. there is no way I could shift that low with my ddec 3

 

Boost gauge is a great reference to have for economy. Drive by it using only as much boost/throttle as necessary to maintain steady momentum. You may be footing it at 25 psi and not even realize it. Then just barely, almost imperceptible back out of that throttle, and see that all you needed to maintain that exact same momentum was 15 psi. That saves fuel. It's "driving with an eggshell between your foot and the throttle". In slight hills driving by the boost gauge and right footing the throttle will net better mpg's than using the cruise control. Cruise control will practically peg your boost on small hills when really it's not necessary to fuel that much making it over the rises.

 

I would think higher rpm's would create higher engine temp creating higher e.g.t temp.

 

Higher rpms moves more air, creating lower temps. When you're lugging the engine, the turbo isn't spooling fast enough to get rid of the heat.