sharpgt

Excuse me if this has been asked before, but why does the M7 transmission have 3 overdrive ratios? Wouldn't a 6 speed be more efficient from a mechanical standpoint, easier to shift and still meet fuel mileage goals?
Thanks

RC000E

It wouldn't be there...if it didn't need to be there.

The EPA test to validate fuel mileage is a test engineers know well. AFM, CAGS, overdrive gears with a motor making a lot of torque...all games engineers have played to make the car do well on certification, which then meets the standards GM needs across the model lineup. In terms of drivetrain losses on chassis dyno's, versus the engine documented output, there is no indication the transmissions are "inefficient" in any way. There are essentially 2 overdrive gears, not 3. 5th is very much still a "performance" gear, with 6th and 7th being your cruise/mpg options.

Doubt this will get voted on but...you never know I guess.

sharpgt

I'm not certain that 5th is really a "peformance gear". With the GM hotshoe running full tilt at VIR in the Z06 i think he hit 5th once and that is a track with very long straights. I just am wondering if 7 gears is what the marketing guys felt the car needed compete with Porsche 911 which also has 7 speeds but a lot less torque. But it may be an EPA/gas mileage thing even though in the real world 6 gears would acccomplish the same mileage.

grcor

They did not need a 7th speeds. All they needed to do was make 6th taller to maximize gas mileage for the EPA. The 7th speed might be for marketing BS, but unfortunately it just adds more weight to an already over weight car which hurts performance and gas mileage. Very sad.

Iconic

My Stingray isn't yet built, but if we can agree that 5th gear is about the same aprox RPM as my C6 GS, then 5th is a performance gear on the fastest tracks. I have used 5th at Talladega and Daytona. My GS would hit the rev limiter at 150 mph, but the car needed that one more gear to go faster.

At Sebring, Road America, and PBIR I have never got higher than 4th although I have hit well into the 140s at those tracks. I also agree with thread consensus on both not needing 7th gear, and why GM had to build them with a 7th gear.

RC000E

Long tracks like Monticello, with a 3/4 mile back straight that you can enter at 50mph definitely uses 5th gear. It's a usable performance gear.


Foolishness...your opinion lacks depth.

If you did a tall 6th, the transition from 5th to 6th would garbage, or you'd have to turn 5th into a semi overdrive gear. 6th is a midspeed highway gear...55mph type highways where 7th would be lugging too hard and couldn't climb hills, or 5th would be tach'ing enough to kill mpg.

You really think the GM engineers just stick things in there that don't need to be there? 7spds and 8spds are being revealed across the market in new vehicles...and it's not because of marketing...it's because they all need to meet the same universal standard.

An "already overweight car" compared to what...it's former self 20 years ago that wouldn't pass standards today? In current standards the car weighs less than the majority of sports cars out there...lighter than lambo's, Ferrari's, Mustangs, Camaro's...you name it.



I've talked to plenty of GM drivetrain and random engineers...they are well aware these cars would be better with CAGS and drive by wire, etc...but what are you gonna do when your hands are tied?

grcor

In a 6 speed transmission 5th gear is already an overdrive gear, so a taller 6th gear is not a big deal. 6th gear is not a performance gear, it is a highway gear so the transition can be steeper without being a problem.

Yes they do stick things in that do not need to be there. Z06 with seat heaters. Driving a car with Max Performance Summer tires in freezing weather makes no sense. Cylinder deactivation which adds 55.5 (35 engine parts +5.5 exhaust +15 steel toque torque) pounds should not be there. Its the wrong approach to increase gas mileage in a sports car. Name any other sports car in the world that uses cylinder deactivation.

We are talking manual transmissions and I do not know of any 8 speed manuals. So name any sports car that has a 8 speed manual transmission (excluding dual clutch transmissions).

The C7 Z06 gained 350 pounds compared to the C6 Z06 at the same time the ATS and CTS lost hundreds of pounds. I could see the C7 Z06 gain 50 to 100 pound for new standards and upgrades that people have been asking for, but 350 pounds is an embarrassment.

RC000E

Could you consider possibly pouring half as much effort into all this jabber to possibly reading a book? So you've got it all figured out...crazy all those engineers couldn't come up with your simple little principles and equations. Dont' you find that strange?


Interior adds weight...the buyer demographics spoke...it's what they want...simple. The old guys write checks, and the old guys want seat warmers...period.

The 7th speed is necessary, get over it. Go do research on the EPA testing procedure for mileage standards. IT WOULDN'T BE THERE if it didn't need to BE THERE.

Cylinder deactivation is part of the architecture. No other manufacturers use it, because no other manufacturers make the torque an LT makes. This goes to spreading the cost across the lineup. You want a Corvette that matches Porsche at 40k less dollars, they need to use the entire lineup to spread cost. This is reality...reality of building these cars affordably...this isn't la la land.

Instead of spouting off what they should've done, how about you answer WHY THEY DID IT. If you're smart enough to fix the car so simply, then bestow upon us your reasoning as to why its all there. Love to hear it...proceed.

sharpgt

Mercedes had cylinder deactivation and Audi just reintroduced it.

grcor

I do not see any Sports Cars that are currently being made or coming in the future from Mercedes or Audi that have cylinder deactivation. What models are you referring to, remember they have to be sports cars.

grcor

The 7 speed transmission is not necessary. There a lots of cars currently being sold with 6 speed transmissions. Just because someone in Chevrolet decided that the C7 manual would be 7 speed does not mean that it was the correct decision or the only way to get it done. That 7th speed added 11 pounds to already over weight car

Is this the best you can come up with? If you did a simple check you would find a number of sports cars that make more torque than the LT1 (Viper, Aventador, 488 GTB, Catifornia T, F12 Berlinetta, FF, 650S, 675LT, GT-R, 911 Turbo) . Some even make more torque than the LT4 (SL65). None of them have cylinder deactivation. Your comment about spreading cost across the lineup is nonsense. Read the thread on this forum where C7 Z06 owners are saying that the engine rarely goes into ECO mode and that it is “wasted technology”. All the money that was wasted in engineering/development/testing cylinder deactivation could have been used to solve the overheating issues. https://www.corvetteforum.com/forums...s-v8-mode.html

RC000E

You guys are killing me. Let me tell you, I work off of actual knowledge, not with a google screen set up beside. I've been in the automotive industry my whole life...you know how many people I see come and go like you...know it all from the recliner.

You're talking about peak torque numbers, exotics...get your head out of your ***. Can't you think more broad versus so focused. You're talking about marquee brands, you're talking about cars who can't spread the development cost over a very broad spectrum. Your comparisons are apples and oranges....hell apples and donuts. I can't invest more than an absolute MINIMUM of brain activity responding to you because the time is simply so wasteful.

These systems are available for TESTING PURPOSES, to validate the car via govt mandated and lineup mandated standards. I've spoken with these engineers AT LENGTH...have you??? No...guaranteed not. All car companies have employed multiple forms of fuel savings "technologies", most of which aggravate the owners of the cars. I have BMW's that have **** slow throttle response, Sti's have sport sharp and intelligent modes that make them suck...this is REALITY. You want to get away from it, buy non federally certified automobiles...simple. My friend owns Superlite Cars, he'll sell you a Z06 annihilator for 65k. You can put a plate on it, drive it daily then go to thunderhill and win the unlimited category...this exists.

You guys wear me out.

Again, how about you educate us all and instead of telling us why it shouldn't be there, tell us why it is. Why would a company, in business selling cars 100 years, invest countless hours and millions of dollars to put invalidated technologies on engines if they served absolutely no purpose. Do you even take a moment to listen to how absurd you sound? These engineers don't want to put CAGS on a car, nor do they want to put an eco mode there. Thank them for the fact you can deactivate all this so easily.

You guys are the classic folks who would come in my restaurant and tell me why a jack and coke shouldn't cost 5.00. The guys who would come in my shop and say fabrication shouldn't be so expensive when the same part is available on ebay and "looks amazing". The guys who have no global sense of business, no understanding of costs and regulatory measures, just a sense of your own household demands, and a crude sense at that. TRY TO THINK A LITTLE HARDER about the absurd claims your making.

See you at SEMA, I'm sure you won't be there.

grcor

A restaurateur who moonlights as a car designer, fabricator, project manager, videographer, and marketer who knows everything about anything. It all makes perfect sense now.

sharpgt

I think the Z28 comes with a 6 speed and does quite well on the street and track.

Clairvoyantwolf

Porsche, Ferrari, and BMW, among others have gone to some form of forced induction to meet EPA mileage and emission standards. The only real hold outs among new sports cars is the GT350 mustang, which brings to bear "only" 525hp (remember Tadge said they couldn't go much beyond the LS7's power level while still meeting emissions...looks like Ford couldn't either).

The Corvette gets it done with CAGS, which can easily be defeated. A 7th gear for manual transmission cars, which doesn't have to be used. And DOD, which also doesn't have to be used (for manual transmission cars). The trade off is of course weight, cost, and complexity, but far less so than if the team went with forced induction across the line.

You yourself made the same complaint about the Z06 that Porsche, Ferrari, and BMW enthusiasts are now making, that the high reving character of the car is being lost by going to forced induction. I don't know about you, but I'd much rather have the C7 as it is now than with the twin turbo V6 out of the ATS-V. A 7 speed and DOD is a very small price to pay compared to utterly transforming the character of the car.

grcor

It's not forced induction that reduced the LT4 to a maximum 6500 rpm, it was cylinder deactivation. Have you looked at the 488 GTB or 650S/675LT? They have small twin turbo V8's that rev to 8000+. Auto companies are being forced into reducing C02 and the only way to do it is smaller displacement. Then use forced induction to get the power back. I could live with a 7 speed if it where a dual clutch and you can run in automatic mode or use the paddle shifters.

Clairvoyantwolf

The LT4 has the same rev limits as the LS9 and LS3. The LS7 was an outlier (even so the LT4 and LS7 have their peak power at virtually the same rpm, 6,400 rpm vs. 6,300rpm). The addition of DOD to the LT4 vs. the LS9 (and LT1 compared to LS3) comes at no appreciable performance penalty. That is quite different than, for instance, the previous generation M3 that was a NA V8 that made peak power at 8,300 rpm and spun to 8,400 vs. its replacement which is a turbo I6 that makes peak power from 5,500-7,300 rpm and spins to "only" 7,500 rpm.

Ferrari's and McLarens can't be effectively used in comparisons to Corvettes. Those cars cost multiples of even a Z06 and their builders aren't as constrained by practicality and reliability as the Corvette team. The fact that the Z06 must be compared to cars that two to three times its asking price to find its performance peers is a testament to the Corvette team's engineering skill.

My mentioning of Forced Induction was to say that all auto companies have to pull the proverbial rabbit out of the hat to meet the upcoming emissions and fuel economy rules. ...They have been warning of such for years. GM powertrain, for whatever reason, is of the opinion that it's better to make a larger engine smaller with DOD than a smaller engine larger with forced induction. There seems to be some merit to that as I remember a recent Luxury SUV test were the Cadillac Escalade had the highest or close to the highest acceleration numbers and ALSO the best observed fuel economy. Anyway, the corvette team since C4 has pursued the fuel economy strategy of high low rpm torque (that is then extended to higher rpm since it is a sports car) and a very wide ratio transmission. Hence, the C7 has DOD to make the engine "seem" smaller under certain load conditions (I'll note that the C6 was going to have DOD with the LS3, but there was too much NVH), CAGS, and an even wider ratio transmission with the 7th gear.

Once again, very small price to pay compared to, for instance, the BMW M series guys.