ams@philabs.UUCP (Ali Shaik) (02/12/86)
I thought one of the virtues of 5 speed transmissions was that one could obtain better MPG, as compared to 4 speeds (the reason being the engine runs at a slower and perhaps more efficient speed while in 5th). This is not true specifically in the case of the Toyota Tercel. The quoted MPG for the 4 speed is significantly higher than that of the 5 speed, in the manufacturers brochure. (Note that the engine size is 1.5 litres for both of them: in some cars, the 4 speed version, being the el-cheapo, has the smaller engine and consequent higher MPG). What then are the virtues of 5 speed vs. 4 speed? Ali Shaik (..ihnp4!philabs!ams ) "25 years experience writing disclaimers for the self-employed"
mberns@ut-ngp.UUCP (Mark Bernstein) (02/13/86)
** I wonder if the issue here is the gearing - the relation between the transmission and rear end ratios. To balance things out in terms of performance and economy, don't mfrs. play with rear end gear ratios? I bet there's a difference here between the 4 spd and 5 spd car you mention. One thing I've noticed (having one car with a 5-spd and another with a 4 spd) is that there's a trade off... you might get an "overdrive" effect, slower rpms at top gear, with the 5 speed, BUT at the expense of pulling power. You get a shortened power curve in the lower gears. I'm *constantly* shifting around in my 5 spd when in the lower gears - the car just runs out of steam, and quickly; to keep the engine rpms in a comfortable section of the power curve I've got to downshift - and then, earlier than I'd like, I run out of rpms and have to upshift. Especially in any kind of curvy, hilly terrain, such as that west of Austin. I guess the "closer" gearing ratios in the 5 speed account for this. My four speed can stay comfortably in a higher gear under a wider variety of conditions. And all this, I have a feeling, is *not* a direct function of size and hp of the engine, etc. The 5 speed is an Accord (1.8 liter), while the 4 spd is a Volvo (a 2.1 l, but *much* heavier). Perhaps the best compromise would be a car with a true 4 speed (in terms of ratios, etc.), with a separate, switch-on/off overdrive. I think that recent Volvo 4 spds have this feature - an "electric" overdrive activated by a slide switch on the gearshift knob (but not my 1980, alas! - my engine is doing anything BUT loafing in 4th at highway speeds). I'm sure many other cars have something like this. Has anyone had experience experience with these? Do they "feel" like 5 speeds or something different? mb
srk@teddy.UUCP (02/14/86)
In article <2956@ut-ngp.UUCP> mberns@ut-ngp.UUCP (Mark Bernstein) writes: >... I'm >*constantly* shifting around in my 5 spd when in the lower gears - the >car just runs out of steam, and quickly; to keep the engine rpms in a >comfortable section of the power curve I've got to downshift - and >then, earlier than I'd like, I run out of rpms and have to upshift. >Especially in any kind of curvy, hilly terrain, such as that west of >Austin. I guess the "closer" gearing ratios in the 5 speed account >for this. My four speed can stay comfortably in a higher gear under a >wider variety of conditions. And all this, I have a feeling, is >*not* a direct function of size and hp of the engine, etc. The 5 speed is an >Accord (1.8 liter), while the 4 spd is a Volvo (a 2.1 l, but *much* >heavier). All other things being equal, a car with close ratio gearing should require LESS frequent shifting than one with wider ratios. This is because you should have a better chance of finding a gear well suited to the average load. However, the key word here is "require". It may be FUN to shift more frequently with the close ratio gearing since as conditions change you can find a gear close by that is a good match. This may be the reason why you actually shift more frequently with the five speed. :-) The other point is that all other things are probably not equal - in that an engine with a narrow torque curve will require more frequent shifts than one with a broad curve. I have heard that the Honda engine is a "high-reving" engine, and perhaps your instincts are telling you to upshift before you actually need to, which (in effect) would narrow the torque curve and cause more frequent shifts. But I am only guessing here - I'll leave it to the Honda owners to comment on this. -- Stephen Klein ...!decvax!genrad!panda!srk
2212msr@whuts.UUCP (ROBIN) (02/17/86)
> Perhaps the best compromise would be a car with a true 4 speed (in > terms of ratios, etc.), with a separate, switch-on/off overdrive. I think > that recent Volvo 4 spds have this feature - an "electric" overdrive > activated by a slide switch on the gearshift knob (but not my 1980, alas! - > my engine is doing anything BUT loafing in 4th at highway speeds). > I'm sure many other cars have something like this. Has anyone had > experience experience with these? Do they "feel" like 5 speeds or > something different? > > mb Having Volvos with both 4speed and 4speed + OD of the same years I can attest to the fact that the OD vesion drives no differently, i.e. no extra rowing around of gear shiftiing. Just more relaxed 'high' speed cruising and better gas milage. My '85 has 4+OD, but unfortunately has a much lower numerical ear axle ratio and it doesn't cruise worth a d*mn in OD if there are hills at anything over about 70. It's not unusual to find onesaelf in 3rd at 80 to maintain speed up stiff hills on interstates. I much prefer the 4speed+OD to the typical Japanese 5 speed for just the reasons you mentioned. Max Robin email:whuxg!2212msr
bruce@dciem.UUCP (Bruce Ferguson) (02/21/86)
Volvos have had the electric overdrive available since at least 1967 on most models, and standard on up-market models since 1970 (or so) . I have a 1971 142E with OD and the standard (for this model) 4.31 final drive ratio. This makes for pretty speedy progress through the gears, and it would be revving far higher than appropriate for cruising if it did not have the OD . The OD has a ratio of 0.79 to one, so when engaged, the final ratio "appears" to be about 3.44 to one. The non-OD Volvos of this era had 4.10 to one ratios, eventually falling to about 3.77 with more recent years. I believe the early gearboxes (M41's) also had longer indirect gear ratios, making them more of a "close-ratio" box (its all a matter of degree). My 142E definitely gets better hwy mileage than other 140's without OD, but I suggest it is largely due to the fuel injection , rather than the OD. If my diff ever blows up , (162,000MI now) I will replace it with a 4.10 to one unit, 'cause I think it has the torque to twist it. With the OD engaged that will yield an effective overall ratio of about 3.24 to one, for less noise and wear. I think the main reason for Volvo doing this , (using separate OD's) is to avoid designing, and tooling a new (5 spd) transmission. The Overdive units are made by Laycock , in England (HORRORS!) Guess what is the only part of my Volvo that has ever leaked oil (no prizes)