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Old 07-11-2013, 10:04 AM   #1
C7s
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Default Why didn't Chevy Revise Gear Ratios on 7sp?

I just realized after the fuel economy numbers came out that on the new 7sp manual, chevy left the ratios exactly the same except added the 7th gear. Why wouldn't they revise 1-6 to make them closer and lower now that they have an extra gear? 7th should now be the highway fuel econ gear and 1-6 performance gearing. Did they explain it at all at the bash or 60th anniversary or any other time?
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Old 07-11-2013, 10:12 AM   #2
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I asked the exact same question. I'm confused why they didn't do a close ratio set 2nd through 5th for the road course and then use 6th and 7th for highway fuel economy.
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Old 07-11-2013, 10:13 AM   #3
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I believe the Z51 is closer ratio.

If they close up the ratios too much its a PITA to drive, always shifting.

The big advantage of a torque laden motor is the lack of need to shift.
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Old 07-11-2013, 10:16 AM   #4
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You can always skip gears when driving on the street. I go 1st to 3rd to 5th in my car often. That said, maybe the LT1's mid range torque is so substantial they didn't want to shorten the gearing any further.
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Old 07-11-2013, 10:23 AM   #5
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Quote:
Originally Posted by NoOne View Post
I believe the Z51 is closer ratio.

If they close up the ratios too much its a PITA to drive, always shifting.

The big advantage of a torque laden motor is the lack of need to shift.
Absolutely - To the OP - have you driven a "contemporary" Corvette? With the torque you don't need anything closer. This car is manufactured to meet the needs of multiple customers - street, cruise, track / road course, etc. It's a darn good "compromise" if you ask me.
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Old 07-11-2013, 10:27 AM   #6
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I've wondered the same thing.

I already skip gears all the time in normal driving, and the C6 is turning like 1500 rpm in 6th at "regular" highway speeds. When are you going to hit 7th gear at all? So far I'm not understanding the point there. I figured they would lower 1-6.
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Old 07-11-2013, 10:52 AM   #7
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While there could have been more revision, you still have to ask why?

Performance gearing is available. With the Z51 package. Its a closer gear ratio that makes for lots of fun between 2nd-3rd-4th.. which is where you spend the vast majority of time driving. 5th is for great mpg in the city. 6th is for great mpg on the hwy. 7th is just a natural extension of 6th.. and should make crusing at 80mph a 30 MPG joy.

What I like about 7th more than anything.. is that it puts reverse in its natural place. I've always hated cars where you need to shift up or left for reverse. Reverse should be the last selection on the right side.
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Old 07-11-2013, 11:10 AM   #8
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If you are not concerned with MPGs, then you only need 1-4; you need a lot of open road to really use anything beyond 4th gear.
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Old 07-11-2013, 11:19 AM   #9
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Exactly, I just think it was a missed opportunity for improvement since they redesigned trans for 7th gear. Also, 7th gear added weight!
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Old 07-11-2013, 11:27 AM   #10
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My point is, according to the numbers, there is no point in having a 7th gear as it will never be used at legal speeds on US roads. With the information available today, it appears that it would only be viable as a gas mileage gear at near triple digit speeds. Useful on the autobahn maybe, or if you have a highway where you feel comfortable cruising at extra-legal speeds for extended periods of time.

Or, the intent could be that you turn ~1k rpm on the highway at normal speeds. Maybe the LT1 has that much torque.
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Old 07-11-2013, 11:27 AM   #11
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Quote:
Originally Posted by NoOne View Post
I believe the Z51 is closer ratio.

If they close up the ratios too much its a PITA to drive, always shifting.

The big advantage of a torque laden motor is the lack of need to shift.
Quote:
Originally Posted by mksz51 View Post
Absolutely - To the OP - have you driven a "contemporary" Corvette? With the torque you don't need anything closer. This car is manufactured to meet the needs of multiple customers - street, cruise, track / road course, etc. It's a darn good "compromise" if you ask me.
That uh... sounds like more of an excuse then anything. It doesn't "need" 475 hp either, but I suspect neither of you would be complaining to much.

As stated, with the torque available you speak of, 1-3, 3-5 shifts are possible. I mean, lets be real, your argument is completely negated by the fact that it wants you to shift from 1-4 anyway.

The car really should have been made with the z51 gears standard, but with the .42 instead of .48 7th gear. However, obviously the transmissions were based closely off the t56/tr6060 design, I assume for simplicity and cost reasons. Adding a wider spread 7th gear(.42) to the z51 spec gears might have caused added redesign. Of course, you could argue with only 1 transmission costs could have gone down(and z51 option could still be the same price and no one would have batted an eye since its a great bargain).
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Old 07-11-2013, 11:38 AM   #12
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Quote:
Originally Posted by ny32182 View Post
My point is, according to the numbers, there is no point in having a 7th gear as it will never be used at legal speeds on US roads. With the information available today, it appears that it would only be viable as a gas mileage gear at near triple digit speeds. Useful on the autobahn maybe, or if you have a highway where you feel comfortable cruising at extra-legal speeds for extended periods of time.

Or, the intent could be that you turn ~1k rpm on the highway at normal speeds. Maybe the LT1 has that much torque.
Guys it's not some GIGANTIC step down from 6th.

With 285/35/19 rear wheels, .42 7th, and 3.46 rear, that means:

60-1089rpms
65-1180rpms
70-1271rpms
75-1361rpms

So 65 is almost 1200rpms. That can be done cruising down the road. Plus, whatever speed(s) the EPA test at, obviously they were high enough for the C7 to gain a noticeable advantage over the c6. The fact these speeds can be done in 4 cylinder mode(albeit that is a honkin 3.1L 4 cylinder) is more impressive.

Now can you actually pass anyone in 7th? That's a bit debatable...
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Old 07-11-2013, 11:48 AM   #13
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I keep saying it is nothing but marketing...trying to keep up with the Europeans and their low torque, small displacement, narrow power band engines which benefit from more ratios. I am now ready for the Porsche fan boys to attack. ha ha
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Old 07-11-2013, 11:52 AM   #14
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Quote:
Originally Posted by ChucksZ06 View Post
I keep saying it is nothing but marketing...trying to keep up with the Europeans and their low torque, small displacement, narrow power band engines which benefit from more ratios. I am now ready for the Porsche fan boys to attack. ha ha
I strongly suspect this is the right answer.

Add another gear for a ~150rpm difference at 70mph? It can't be saving that much gas. Better mileage is coming from other factors.
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Old 07-11-2013, 12:06 PM   #15
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So why did GM add the 5th, 6th and 7th gears....
Fleet MPGs/gas guzzler tax. I love the optimal performance achieved in these cars while avoiding an additional tax.
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Old 07-11-2013, 12:15 PM   #16
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GM has other factors to consider while building cars. The most notable is CAFE. For each 0.1 MPG they fall under the standard they have to pay a fine of $5.50 on every car sold. GM builds millions of vehicles so this isn't exactly chump change. I don't know if it is brand specific (i.e. Chevy) or GM total but regardless the fine could really add up.

So... add the 7th gear for even a half a mile per gallon it could make or break the average. If memory serves they are trying to raise it to near 40 MPG on average in just a few years.

I personally don't mind the gearing. In my C4's I liked having the 6th gear but when I needed to downshift it was too big a change for normal driving. Driving through hills or just passing all I needed was a bit more RPM not what I got out of 5th gear so I'd end up shifting a lot between 5th and 6th at certain highway speeds or certain conditions. My guess is with the 7 speed I'd just leave it in 6th in those conditions.
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Old 07-11-2013, 02:59 PM   #17
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Quote:
Originally Posted by travisnd View Post
I asked the exact same question. I'm confused why they didn't do a close ratio set 2nd through 5th for the road course and then use 6th and 7th for highway fuel economy.
There was a speed-in-gear chart last fall. The Z51 box drops RPM's from 6500 down to 4500 through the first five gears. GM had to target that engine speed as the best place to begin acceleration in the next gear after a redline shift. Once they did that, GM calculated the ratios for the Z51 box.

It will be interesting to see what ratios the new hi-po version gearbox gets, when they announce it at the 2014 Detroit auto show. Stronger engine, maybe higher redline, may allow different ratios for the "Z06" box.
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Old 07-11-2013, 04:50 PM   #18
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Quote:
Originally Posted by ny32182 View Post
My point is, according to the numbers, there is no point in having a 7th gear as it will never be used at legal speeds on US roads. With the information available today, it appears that it would only be viable as a gas mileage gear at near triple digit speeds. Useful on the autobahn maybe, or if you have a highway where you feel comfortable cruising at extra-legal speeds for extended periods of time.

Or, the intent could be that you turn ~1k rpm on the highway at normal speeds. Maybe the LT1 has that much torque.
I turn ~1krpm all the time on the street in my little LS1 (5th around 30mph, 6th around 40-45), and can actually accelerate pretty good as long as it isn't too steep, if it starts to lug, I downshift to 5th.

The intent is absolutely to turn 1krpm on the highway with the LT1.

I agree it would have been nice to shorten up or make closer the 2-5 gears, but it is possible that with so much torque, the extra time to shift actually makes you end up slower. Plus if you have so much torque you can spin the tires easily, gearing for more doesn't really help.
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Old 07-11-2013, 05:05 PM   #19
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At least 6th should have been revised. I have the 'Z51' tranny on my '12 GS, and even though it has closer ratios than the base car, 6th is almost too tall already at 83 mph at 2K rpm. Leaving the ratios the same and just adding 7th was pretty stupid IMO. Since the biggest jump is from 5th to 6th, at least 6th should have been made closer, and 7th just a hair taller than the current 6th. But the GS has some weird ratios, to be honest, so a full revision would have been warranted, especially when the damn car lasts 9 or more years.
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Old 07-11-2013, 05:05 PM   #20
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There are other considerations too.

Drive by noise at speed tests from the government.

The vehicle can only make so much sound at a given speed. Since you cannot drive past the mic at 25mph in 7th gear there are considerations given to that also.

Some mid 2000 Jeeps had horrible gear ratio choices 100 percent driven by that rule.
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