Best RPM for MPG -- Cummins 8.3 ISC Engine

[Oonrahnjay]

     I'd like to ask info on the RPM for best fuel economy for a 2003 MY Cummins 8.3 ISC engine, 315 Hp.  Cummins literature on line shows 1500 RPM for later 8.3s with high pressure common rail and exhaust aftertreatment (which my engine doesn't have).  There are other places on them Innerwebs where people have posted that 1500 is the right number for early 200? 8.3s but I don't know if they're really knowledgeable or just WAIGs.
     Anybody have a thought on 1500 RPM?

Thanks,  Bruce H,  southeastern NC

[TomC]

Since I sold 8.3 for Freightliner, the way Cummins wants them geared-if it has the electronic fuel injection pump with lines, then 1,800rpm is cruise speed. If it is common rail fuel injection 15-1,800rpm is used. 315hp is usually 1,000lb/ft torque. The 8.3 is a rugged engine-more so than the 8.9 liter. Just look at the horsepower difference between the ISC and ISL with Cummins marine engines. 8.3/8.9 can have Jake brakes also. 8.3 highest horsepower was 350hp at 1,000lb/ft torque-about the same as an 6V-92TA. Good Luck, TomC

[luvrbus]

The ones I been around like 1500 to 1700 rpm in the RV's for best fuel mileage after 1700 or 1800 rpm they become a 5 mpg engine.

I have never saw Jake's on the RV engine not saying Jakes are not possible but the ones I seen they used the VG turbo for braking.I would prefer the Jakes myself,a friend has a 2010 model it is rated at 380 hp has no Jakes 6 to 7 mpg in a 42 ft RV @ 1500 rpm 5 to 6 @ 1800 rpm

[TomC]

ISB (6.7 liter), ISC (8.3 liter), ISL (8.9 liter) are all available with turbo brake. Just an easy programming that spins up the turbo during braking to create more compression pressure. Better than nothing.
Both the ISC and ISL are available with Interbrake by Cummins (like a Jake Brake). Excellent engine braking. Good Luck, TomC

[Oonrahnjay]

     Thank you all for your helpful, kind, and knowledgeable comments.  Please continue with your thoughts and experiences.  Best wishes,   Bruce H