4 vs 6 vs 8 speed transmissions

[High Five H2]

So it seems that the newest thing in fuel economy is more and more gears. I would have thought that 6 speeds is enough, but GM just put out an 8 speed and is working on a 10 speed. What's everyone's opinions on these? They're getting really good mileage, but the article says the 8 speed with the newer 6.2L, the L86 accelerates slightly slower than the older L92 with the 6 speed. Why would that be? Are more gears better for performance? I would think so. Some camaro guys are swapping to a 4l80 from the 6l, but I think it's for strength, not performance. They're making built 6l80's now so that should be an issue.

For what it's worth, I'm interested in an engine swap for my 3, but mostly for a better transmission.

http://www.caranddriver.com/reviews/2015-chevrolet-silverado-1500-4x4-62l-v-8-8-speed-test-reviews

14 silverado - 5.4 sec 0-60, 14.1 1/4 mile
15 silverado - 5.7 0-60, 14.3 1/4 miles

both of those are super fast for a truck, though. it's crazy what they can do with a big heavy truck these days.

 

[abearden]

Shorter gears make the necessary RPM range smaller, keeping the engine much closer to its most efficient RPM at all times. Slightly slower acceleration is probably due to switching gears and different ratios.

 

[High Five H2]

i figured maybe they hadn't tweaked the programming for the 8 speed yet.

 

[LagunaH1]

Some car manufacturers use continuously variable transmissions, programmed to simulate an 8 speed.

Funny... in theory the CVT is the best compromise one could come up with, but many car buyers WANT the experience of the transmission shifting.

 

[RamRod]

My GF's car has the CVT and it's surprisingly "zippy" for a little 4 cylinder shoe box on wheels


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[poncho1965]

Reliability is an issue for me. If CVT's prove it I'll be on board. Honda puts them in the Accord, I guess that's a vote of confidence.

 

[LagunaH1]

A coworker of mine has run one of these in a Nissan for many years and AFAIK never had an issue

 

[skeptic]

CVTs have a reputation for being weak. This doesn't mean unreliable, just that they can't handle high torque/hp. I don't know how true this is, just it's reputation.

Back to the original topic - Jeep has a 9-spd out now as well. Personally, I think a 6-spd should be enough. Maybe not optimal for squeezing out that last 1 or 2 mpg, but also less parts, stronger for the same physical size, more reliable.

 

[06 H3]

I have only dealt with small CVT systems in rhinos, buggies and other small non street legal toys and they burn belts when hot they seem to be inferior when racing against a similarly powered toys that had a typical manual 5 speed.

With all that said those CVTs probably have less then half the R&D then the CVTs that go in cars.

 

[abearden]

Any CVT will be weaker than a similar standard transmission just due to physics, for the same reason IFS is weaker than a solid axle. Solid gears are stronger than any CVT design. CVTs will probably get "strong enough" with enough R&D, but they're not there yet.

 

[4speedfunk]

Most drag racers prefer power glides....(two speed). There is only one shift. Maybe the drop in ET that the Destroyer is talking about, really is due to the extra shifting.