I’m new to diesels and I was talking to someone else who had a diesel and he said that every diesel engine has a certain RPM sweet spot where the power is optimum. If your RPM drops too low you waste fuel and lose power so you should down shift.
We only talked for a few minutes and I didn’t get the details.
We are in the process of adding pillar gauges for EGT, Boost, and Trans Temp.
Does anyone know exactly what this person was talking about? How do I determine what the range of this “sweet spot” is so I know when to up shift and downshift.
Like my sig says, we have an F-350, 7.3L, with a 410 rear end.
'02 F350 7.3PSD CC LB DRW, Reese 20K Hitch, Brake Smart, AirLift, C-betr mirrors,
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there was a long debate on this subject a couple weeks ago. Use the search function above for optimal towing best economy while towing,, things like that, it should come up.
Personally, and I really got flamed for this but personally I look at the torque curve for a motor and try to keep it in or near the middle of the torque curve. To me that offers the best combination of economy and power on demand.
When I am at 2100 RPM to 2300 RPM I feel the truck pulling effortlessly. It is not lugging or laboring and is very responsive. It feels like it will pull any grade without slowing down. Like the above posts mention it depends on the truck, roads, conditions, ect., but when you find the RPM that "feels" good for your truck you will know it. I do not think this is the most economical RPM but it seems the most efficient for pulling. It feels like you can just hang the RPM needle there and never have to add more throttle to pull any grade without losing momentum.
For my GM 6.5 TD it was about 2500-2600 rpms, for my NA 7.3, about 2600-2700. My dmax is in this range too, 2500-2800. Your 7.3 is probably in this rpm range to when pulling a hill under load. If cruising down a freeway at 60 mph and level, then 1600-2000 rpms is nice for my three motors I have run etc.
I personally when pulling hills try to keep the rpms tween peak torque rpm and the pke HP rpm. Example, if pk torque is 1600, pk HP is 3600, then I like to be about 2600 rpms plus or minus 100-200 rpms when going up a hill. THis is of course, assuming you are below about 2000 rpms in the next higher gear and holding, or going slower yet.
Marty
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92 Navistar dump truck, 7.3L 7 sp, 4.33 gears with a Detroit no spin
00 Chev C2500, V5700, 4L80E, 4.10, base truck, no options!
92 Red-e-haul 12K equipment trailer
3 Single axle utility trailers
According to several diesel techs the "sweet spot" is a term for the most efficient use of fuel for an engine and for the 7.3 is roughly 600 degrees of EGT. I tried to run my old 7.3 as close to 600 as I could when cruising. My current 6.0 runs a little hotter and seems happy around 700. Keeping the engine at or above the torque curve is a good idea as well. Keep an eye on your gauges, especially the EGT and you'll soon get a feel for when the engine is loafing and when it begins to work. Be sure your EGT probe is installed pre-turbo for the most accurate readings. Enjoy!
On flat surfaces, I set the cruise control on our PSD to 60 MPG and the RPM's usually stay around 1800. We set "tow/haul" and let the truck "do it's thing". This is also where we get the best fuel mileage.
Bearnkat wrote: On flat surfaces, I set the cruise control on our PSD to 60 MPG and the RPM's usually stay around 1800. We set "tow/haul" and let the truck "do it's thing". This is also where we get the best fuel mileage.
Sure wish we had that 60 MPG setting on our diesel E350! Sure would save a hella lotta money!
There is no sweet spot rpm, because load requirements are changing constantly, requiring a different HP requirement. The only way to offset the HP requirements of a grade while maintaining speed, for example, is to increase rpm, as torque remains fairly constant across the rpm range.
A stiff headwind with a high drag load has the same effect. If suddenly you have 30 mph headwind, you either have to slow while maintaining the same torque, or drop a gear to higher rpm to meet the higher HP requirements.
The sweetspot rpm, does not exist, but rather is in constant flux.
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