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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 9:06 am) |
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Replying to: wwest (Jul 04, 2009 2:23 pm)
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one of my pet peeves too. Seems to be more prevelant with 4 cyl cars though. I assume it is to avoid downshifting on hilss, although some people have speculated it was so cruise control could be used? On my Accord, at 60 IIRC the 5 speed is turning ~2400, but the AT is loafing at 2000 (might be slightly off, but I think the spread is right). 75 form me is about 2900 rpm, and I think the AT is 2500 or less. Now, I have to imagine the AT downshifts at the slightest provocation, since the 4 cyl is a tad gutless below 2500 (for sure below 2K). What people forget though is that the MT would not be shifting up and down constantly (hunting gears) like the AT. If you were pulling an upgrade at 55-60 with a decent load in the car, just leave it in 4th for a little extra oomph. I get pretty good highway mileage for a 3,200+ pound sedan, but I have to imagine a 6th gear for loafing at 75 would really help make it better.
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Replying to: stickguy (Jul 05, 2009 6:18 am) Here are some examples for a 04Civic VP ..."Displacement (cc): 1668 Horsepower  rpm (SAE net): 115 6100 Torque (lb.-ft. rpm): 110 4500 Bore and Stroke (mm): 75 x 94.4 Compression Ratio: 9.5:1 Valve Train: 16-Valve SOHC Multi-Point Fuel Injection Front-Wheel Drive Transmission 5-Speed Manual Transmission Gear Ratios 1st: 3.462 2nd: 1.870 3rd: 1.241 4th: 0.970 5th: 0.711 Reverse: 3.231 Final Drive: 4.111 4-Speed Automatic Transmission Gear Ratios 1st: 2.722 2nd: 1.516 3rd: 0.975 4th: 0.674 Reverse: 1.955 Final Drive: 4.067 So for example given the above information AND the knowledge that parasitic drag is app 11% for a M/T vs 20% for a A/T, the VARIABLES would indicate better mpg for the M/T (despite lower gearing -less mpg) . In fact it is 1-2 mpg better than the A/T. By the same token, IF the M/T had the A/T's GEARING, and knowing that "In fact it is 1-2 mpg better than the A/T", the mpg would increase 1-2 mpg ABOVE that !! So mpg can increase a min of 2 mpg to 4 mpg !!!! One question would be, would the M/T transmission owner be happy with the (higher gearing of the ) A/T LIKE (NOW) sluggish performance ?? This can be done vice versa also (A/T with M/T GEARING) The question would then be are you happy with the much increased performance with the MINUS- 2 to 4 mpg? |
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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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