Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Bogging/Lugging (How can you tell when you are doing the engine harm?)

SentraSE-R · 02-06-2010, 01:14 PM

I've heard, but can't verify the truthfulness of the claim, that modern engine control computers won't allow you to damage an engine. They supposedly shut the engine down, rather than allow it to run under too much load.

My SE-R's engine/transmission combo is similar to yours, a 2.5L, 170 hp, 6 speed. I use 6th gear from 40-45 mph upwards, on level ground. I have noticed my cruise control will kick me out when I'm going up steep hills at 50 or 55 mph. IIRC, the engine is still on, and I'm left in 6th gear under minimum load, with speed steadily dropping, forcing a downshift.

1200 rpm is probably too low an engine speed for cruising. Your engine's BSFC graph should point you to where you want to be. Usually, your best efficiency is between about 1500 and 2200 rpm for 2 liter class engines. Rather than cruise at 1200 rpm (30 mph in 6th?), I'd use a lower gear to accelerate past that speed, and coast in neutral or EOC through that 1200 rpm dead spot.

The way I'd handle a 30 mph cruise, I'd pulse from 25 mph to 35 mph in 4th gear (about 1500-2000 rpm), shift to neutral (either NICE or EOC), and glide back to 25. I wouldn't risk lugging the engine in 5th or 6th gear at 30 mph. 4th gear gives you more acceleration ability.

You might find this article interesting for ideas on how to wring best mileage out of your 3.

02-06-2010, 01:14 PM	#2 (permalink)
SentraSE-R Pishtaco Join Date: Jun 2009 Location: Bay Area, California Posts: 1,485 Mean Green Toaster Machine - '06 Scion xB Team Toyota 90 day: 48.92 mpg (US) Thanks: 56 Thanked 286 Times in 181 Posts	I've heard, but can't verify the truthfulness of the claim, that modern engine control computers won't allow you to damage an engine. They supposedly shut the engine down, rather than allow it to run under too much load. My SE-R's engine/transmission combo is similar to yours, a 2.5L, 170 hp, 6 speed. I use 6th gear from 40-45 mph upwards, on level ground. I have noticed my cruise control will kick me out when I'm going up steep hills at 50 or 55 mph. IIRC, the engine is still on, and I'm left in 6th gear under minimum load, with speed steadily dropping, forcing a downshift. 1200 rpm is probably too low an engine speed for cruising. Your engine's BSFC graph should point you to where you want to be. Usually, your best efficiency is between about 1500 and 2200 rpm for 2 liter class engines. Rather than cruise at 1200 rpm (30 mph in 6th?), I'd use a lower gear to accelerate past that speed, and coast in neutral or EOC through that 1200 rpm dead spot. The way I'd handle a 30 mph cruise, I'd pulse from 25 mph to 35 mph in 4th gear (about 1500-2000 rpm), shift to neutral (either NICE or EOC), and glide back to 25. I wouldn't risk lugging the engine in 5th or 6th gear at 30 mph. 4th gear gives you more acceleration ability. You might find this article interesting for ideas on how to wring best mileage out of your 3. __________________ Darrell Boycotting Exxon since 1989, BP since 2010 Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin Mean Green Toaster Machine 49.5 mpg avg over 53,000 miles. 176% of '08 EPA Best flat drive 94.5 mpg for 10.1 mi Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg Last edited by SentraSE-R; 02-06-2010 at 01:23 PM..