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Automotive News & Views The Future Of The Manual Transmission
5809 messages, Last post on Dec 03, 2009 at 12:30 PM
You are in the Automotive News & Views Forum. Your Hosts are steve_ & claires
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Replying to: shipo (Jul 04, 2009 7:13 pm) There are two operational parameters of primary interest for these engines. With WOT operation the pumping losses are ZIP but the frictional losses dominnate. Just cruising along at partial throttle, light engine loading, the frictional losses are minimal but the pumping losses dominate. Therefore one of the chief ways to increase "cruising" FE would be to reduce engine RPM. So it doesn't matter so much that a particular engine can produce a nominal level of cruising HP from, say, ~2000 RPM to 3500RPM, what matters is running at the lowest possible RPM and thereby reducing the frictional losses.
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Replying to: wwest (Jul 05, 2009 8:27 am) Max torque comes on  1,750 rpms to 2,250 rpms? One of the best matings would be with a 6 spd manual transmission to stay at an rpm certain or to stay within the narrow range (500 rpms)? In addtion, manual transmission parasitic frictional losses are the lowest at app 11% |
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Replying to: wwest (Jul 05, 2009 8:27 am) The fact is, a well thought out CVT does not offer any real world advantage over a similarly well thought out manual transmission. This is a simple fact of life. |
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Lots of info. I just like to wing it. Looking up all thoughs details gices me a headache! But I think you made the point that taller top gear gearing can increase cruising MPG. And the simple answer to the question about giving up performance? No reason to, if they just added a 6th gear on top of the current box. Even if they just made 5th slightly taller, the only difference would be using 4th slightly longer (shifting up at say 55 instead of 50). Not a biggie either. |
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Replying to: mcdawgg (Jul 04, 2009 9:38 am) I completely agree. My theory is that the automakers don't want you to have to downshift while on the highway going up a hill. I'd welcome it, makes the drive more fun and saves fuel! Twenty years ago, when I started driving, you had to downshift at least a gear or two in almost any 4-cylinder/manual to increase (or sometimes maintain) forward momentum....my old '81 Accord and '85 Civic required frequent shifting to gain any speed! So it seems logical that someone who buys a manual transmission would be okay with a true overdrive 6th gear...even if it meant an occasional shift down to 5th or 4th on hilly roads. And most modern vehicles have enough power so frequent downshifts wouldn't be needed on most cars. Several months ago, I drove a friend's Nissan Versa from Atlanta to Knoxville with the cruise set between 75-80mph. It has a 122hp 1.8L I-4 and 6-speed manual transmission. I never had to downshift to maintain that speed. And the engine was only turning about 3100-3200rpm at 80mph. My Mazda3 runs closer to 4000rpm at 80mph in 5th gear,....it NEEDS another cog!
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Replying to: igozoomzoom (Jul 06, 2009 8:02 pm) The question "here" involves whether or not an MT, well driven, so geared would yield improved FE over a CVT and it simply cannot.
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Replying to: wwest (Jul 07, 2009 8:16 am) i.e., 1. parasitic loss actual/percentage due to CVT transmission 2. dyno runs 3. even hp/torque ratings at the flywheel vs hp/torque ratings at the rear/front wheels. Googling turned up a paper from Pusan University indicating a range of 30-8% (power loss) for a motorcycle, whicl arguably lacks any number of power drains a normal passenger sedan has link title |
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I recal reading a test in one of the car mags (C&D maybe) a couple of years back. They did a test of a Sentra (I think) or Versa, with AT and CVT. Ran them back to back over the same route. ANd no, I don't remember if it was all city, highway (for some reason I think it was), or mix. ANyway, turns out that the slushbox got better mileage than the CVT. I think it was due to the higher parasitic losses in the CVT (just took more out of the engine to keep in turning). |
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Replying to: wwest (Jul 07, 2009 8:16 am) Sorry my friend, like it or not, believe it or not, in the real world, the CVT is incapable of delivering better mileage than a well driven car with a properly thought out manual transmission.
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Replying to: shipo (Jul 07, 2009 6:12 pm)
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