Engine speed when driving sedately
10-17-2014, 03:45 AM
#1
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Engine speed when driving sedately
My MT C4S up shift indicator goes on about 1k rpm lower than I'm comfortable with I assume for fuel efficiency. I've tried obeying it's suggestions when just cruising but it keeps engine speed around 1-1.5k. I always thought that was bad for the engine and usually keep it around 2k at the lowest while I'm using the throttle.
I've been thinking that since the PDK is actually better rated for economy and has the same gears, maybe that's how it achieves it, by shifting so early and keeping the engine rpm low. Maybe I'm mistaken and it isn't actually bad and need to reset my threshold.
What are people's experience with non-sport driving (I know, who does that in a 911) both MT and PDK?
I've been thinking that since the PDK is actually better rated for economy and has the same gears, maybe that's how it achieves it, by shifting so early and keeping the engine rpm low. Maybe I'm mistaken and it isn't actually bad and need to reset my threshold.
What are people's experience with non-sport driving (I know, who does that in a 911) both MT and PDK?
10-17-2014, 08:31 AM
#3
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I use the full rev range, once the car is up to temp, every trip out. But if I'm cruising 65-70 mph on the highway I shift into 7th gear and use it's efficiency. Around town, I use the PSE as my shift indicator.
10-17-2014, 09:19 AM
#4
All the low RPM fears go back to a couple of problems- carburetors that ran so rich at low RPM they would over time lead to fouled plugs and carboned up pistons and valves, and pistons and other parts made of weak alloys that couldn't take the impact of ignition at low RPM. These are non-issues today, and have been for many years now.
Still, even with DFI and all, its hard not to imagine there isn't going to be at least some small amount of harmful carbon build-up in an engine that's run at extremely low RPM all the time. Key phrase being, "all the time." As long as driving in a high gear just off idle is something you do only when it makes sense, and there are still plenty of times when you let her rip, then what's to worry about? This is by the way pretty much the way I have driven every car (and motorcycle) I've ever owned.
Still, even with DFI and all, its hard not to imagine there isn't going to be at least some small amount of harmful carbon build-up in an engine that's run at extremely low RPM all the time. Key phrase being, "all the time." As long as driving in a high gear just off idle is something you do only when it makes sense, and there are still plenty of times when you let her rip, then what's to worry about? This is by the way pretty much the way I have driven every car (and motorcycle) I've ever owned.
10-17-2014, 03:34 PM
#5
Drifting
I've always been taught and teach that low RPMs "lug" the engine and isn't good for it. Knocking, bucking, etc. are not pleasant.
I just laugh at the little shift arrow. Right, like I'm doing 1500 RPM and it wants me to upshift. Not.
Anywho, I concur with the OP's suggestion that the better PDK gas mileage is because it shifts much earlier than a typical MT driver would.
That said... maybe next week I'll try my daily commute following the computer's suggestions to see how it affects my MPG.
I just laugh at the little shift arrow. Right, like I'm doing 1500 RPM and it wants me to upshift. Not.
Anywho, I concur with the OP's suggestion that the better PDK gas mileage is because it shifts much earlier than a typical MT driver would.
That said... maybe next week I'll try my daily commute following the computer's suggestions to see how it affects my MPG.
10-17-2014, 04:31 PM
#6
Burning Brakes
If it's not physically lugging your engine, i.e. bucking, knocking, etc, then it's not lugging your engine. My 7MT car with 37K miles on it runs like a champ at all rpms, I choose the appropriate gear for what I'm doing at that moment.
PDK loaner cars I've had (Boxster and Cayenne) were into very high gears at very low speeds and never lugged either. All about the economy and emissions, flooring it in either would shift down several gears.
BTW to the OP, pretty sure you can uncheck the shift indicator via the PCM, one less nanny to obey.
PDK loaner cars I've had (Boxster and Cayenne) were into very high gears at very low speeds and never lugged either. All about the economy and emissions, flooring it in either would shift down several gears.
BTW to the OP, pretty sure you can uncheck the shift indicator via the PCM, one less nanny to obey.
10-18-2014, 12:57 AM
#7
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If it's not physically lugging your engine, i.e. bucking, knocking, etc, then it's not lugging your engine. My 7MT car with 37K miles on it runs like a champ at all rpms, I choose the appropriate gear for what I'm doing at that moment.
PDK loaner cars I've had (Boxster and Cayenne) were into very high gears at very low speeds and never lugged either. All about the economy and emissions, flooring it in either would shift down several gears.
BTW to the OP, pretty sure you can uncheck the shift indicator via the PCM, one less nanny to obey.
PDK loaner cars I've had (Boxster and Cayenne) were into very high gears at very low speeds and never lugged either. All about the economy and emissions, flooring it in either would shift down several gears.
BTW to the OP, pretty sure you can uncheck the shift indicator via the PCM, one less nanny to obey.
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10-18-2014, 10:03 AM
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10-18-2014, 12:31 PM
#10
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This is one of the reasons the PDK works so well - in sport mode, which is what I drive in 99% of the time, the gearbox keeps the engine revs above 2,000 rpm. The GTR doesn't have a gearbox mode that does anything similar and will instead change gear anytime the revs will end up over 1,000rpm. This makes driving in automatic mode in a GTR pretty frustrating as you are always feel as if you need to be a gear or two lower....
10-18-2014, 05:21 PM
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10-19-2014, 09:17 AM
#15
The shift indicator definitely turns off in my 7MT in sport modes.
Right out of the owners manual:
The upshift indicator is only active when "Sport" or "Sport Plus" mode is switched off.
Right out of the owners manual:
The upshift indicator is only active when "Sport" or "Sport Plus" mode is switched off.
Last edited by todd92; 10-19-2014 at 10:50 AM.