Low RPM load limits? Lugging?
 

What load limits do you use when you are at low rpms? I find that below 1500 rpm, operating at too high a load makes the engine sound and feel rough, which I assume is nearing the lugging point.

idle-1300: 40% load(sometimes a little more)

1300-1400: 50% load

1500-infinity and beyond: No limits

Below 1500 is probably always too low for flooring it for any purpose at all. But above that, in a naturally aspirated and relatively low-power engine that is also in good working order, there is not much chance of damage. ECUs will adjust timing and AFR as needed to avoid pre-detonation. Nonetheless, 1500 is my absolute bottom for relatively high load (75%, which is a long way from WOT). But generally I am at 1700 or higher as I accelerate. Been doing this for years all the time and have 248,000 miles on the original engine now. ;)

Great video here: https://www.youtube.com/watch?v=soJe...ature=youtu.be

In my Insight, the engine feels fine wide open down to maybe 1200rpm. At those low revs, even barely touching the pedal is enough to give it 100% load, because it needs so little air.

Edit: Recently passed 220k and it still runs like a brand new engine.

Drive by wire throttle won't let you do anything that's bad for the engine, IMO.

For my 8L engine build I would like to cruse along at 70mph turning 1,400rpm. If the engine doesn't like that I will have to change rear end gears.

Not nearing . It is the indicator of lugging. Roughness is lugging beyond what the computer is able to maintain smooth operation.

Number of cylinders and/or displacement count, imo.

My 3 cylinder Geo isn't much good under 2000rpm at heavy load, whereas my wife's V6 happily chuggs down the the highway at 1500rpm. My Miata (read: DOHC/high-revving) is a turd below about 2500 rpm.

That guy does such great tutorials. My head feels funny, did I just learned something?!!

Have I missed something here? All the BSFC graphs I see seem to show that the engine is less efficient at low RPM & higher load.

Here's mine:

https://i.imgur.com/aijThJR.jpg

High load = good. Low load = bad.

You're rarely going to be working in the optimal range/load -- you don't need the 50+ hp being generated to cruise along at normal speeds -- so the next best thing you can do is to run at the lowest RPM that will give you a decent load (~80%, above which most engines tend to run rich).

The more energy the engine can create per stroke (without running rich), the more efficient it is going to be. If you're making 10hp @ 1500 rpm, you're a lot more efficient than making it at 3000.