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C7 Engineering Challenge

 
Old 10-26-2008, 08:18 AM
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I Bin Therbefor
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Assumptions, if the statements coming from GM about the C7 being exciting to drive by maintaining or bettering the current power to weight ratio are true, it's fairly straight forward to do some basic calculations on the power and weight of the C7. I've taken as a starting point the new 5.5lt high tech V-5 being developed for ALMS GT2 racing in 2010. My numbers for the current C6 came from the DEC08 issue of Car and Driver. The task is to maintain a weight to power ratio of 7.5lbs/hp while keeping the economics under control..
The first pass results in a C7 of 387hp at 2904 lbs from a 5.5lt V-8 engine. A weight loss of 370lbs. Not an easy challenge. The most obvious approach would be to build all Corvettes on an aluminum chassis that was optimized for aluminum, not the current compromise design which is required because both aluminum and steel chassis are built on the same line. Such an optimized design can accomodate a Targa roof and still drop roughly 100 lbs. We're still left with 270lbs which must be eliminated. The next step would be to look for other weight saving use of aluminum, other light alloys and possibly high strength steel. I don't have the least idea how much this can help but I do know that GM is looking at friction welding to joint light alloys with steel, so there is the potential for using the proper alloys for weight loss and still not breaking the assembly budget. There would also be some weight loss from eliminating the more complex methods of joining the materials presently in use.
If the 5.5lt high tech V8 is to use DFI, we can raise the power output to 400 and actually get better economy over a non DFI engine, that would let us build a 3000lb car which would leave us with 170lbs to eliminate. Still not an easy task.
So it seems that a combination of engine technologies and some weight loss would enable the C7 to maintain the prsent day excitement and still improve the gas milage. The easiest approach seems to be to utilize some of the already developed engine technologies that GM has demonistrated on the experimental push rod V8s in the slightly smaller displacement of 5.5lts. Specifically DFI and VVT. Accompanied by some materials substitutions to reduce weight. This approach would apply to the entire GM line of vehicles, so some of ther engineering costs would be spread across the entire line. Lest I forget, there are gains to be had from improvements in the transmissions also.

Last edited by I Bin Therbefor; 10-26-2008 at 08:31 AM.
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Old 10-26-2008, 06:03 PM
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Originally Posted by I Bin Therbefor View Post
Assumptions, if the statements coming from GM about the C7 being exciting to drive by maintaining or bettering the current power to weight ratio are true, it's fairly straight forward to do some basic calculations on the power and weight of the C7. I've taken as a starting point the new 5.5lt high tech V-5 being developed for ALMS GT2 racing in 2010. My numbers for the current C6 came from the DEC08 issue of Car and Driver. The task is to maintain a weight to power ratio of 7.5lbs/hp while keeping the economics under control..
The first pass results in a C7 of 387hp at 2904 lbs from a 5.5lt V-8 engine. A weight loss of 370lbs. Not an easy challenge. The most obvious approach would be to build all Corvettes on an aluminum chassis that was optimized for aluminum, not the current compromise design which is required because both aluminum and steel chassis are built on the same line. Such an optimized design can accomodate a Targa roof and still drop roughly 100 lbs. We're still left with 270lbs which must be eliminated. The next step would be to look for other weight saving use of aluminum, other light alloys and possibly high strength steel. I don't have the least idea how much this can help but I do know that GM is looking at friction welding to joint light alloys with steel, so there is the potential for using the proper alloys for weight loss and still not breaking the assembly budget. There would also be some weight loss from eliminating the more complex methods of joining the materials presently in use.
If the 5.5lt high tech V8 is to use DFI, we can raise the power output to 400 and actually get better economy over a non DFI engine, that would let us build a 3000lb car which would leave us with 170lbs to eliminate. Still not an easy task.
So it seems that a combination of engine technologies and some weight loss would enable the C7 to maintain the prsent day excitement and still improve the gas milage. The easiest approach seems to be to utilize some of the already developed engine technologies that GM has demonistrated on the experimental push rod V8s in the slightly smaller displacement of 5.5lts. Specifically DFI and VVT. Accompanied by some materials substitutions to reduce weight. This approach would apply to the entire GM line of vehicles, so some of ther engineering costs would be spread across the entire line. Lest I forget, there are gains to be had from improvements in the transmissions also.
Downsizing can reduce weight, too.
GM
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Old 10-26-2008, 07:25 PM
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Gearhead Jim
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Problem is, all of this development work takes money, and GM ain't got any.
They can muddle along with the current C6 or a slightly warmed over version they could call a C6.5, for maybe another 10 years. After that, the CAFE requirements are gonna start killing them unless everybody WANTS to buy Cobalts.
GM needs to start making money before any serious work starts on the C7, and that's not going to happen very soon.
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Old 10-26-2008, 10:37 PM
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Originally Posted by Gearhead Jim View Post
GM needs to start making money before any serious work starts on the C7, and that's not going to happen very soon.
You might be surprised at how little money it can take to redesign the Corvette. The C5 was designed with as a little as $250M, total. That may seem like a lot to you and me, but it's chump change to GM, even in their current hurting situation.

Weight can be lost by the use of Al for the chassis, carbon fiber for the body, etc. But the costs are the concern. Another thing they can (and will) focus on in order to cut fuel consumption is aero. The C6 is currently pretty slippery at a .28 Cd. If they could drop that by a hundredth, it could help fuel economy significantly.

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Old 10-27-2008, 01:42 AM
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Maybe they spent $250 million on design, but does that including all the tooling and plant configuration costs?
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Old 10-27-2008, 08:45 AM
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Originally Posted by proexpert View Post
Maybe they spent $250 million on design, but does that including all the tooling and plant configuration costs?
I'm pretty sure it did. Check All Corvettes are Red for confirmation of that (it's been a long time since I've read it). The Corvette has pretty much always been designed/built on a relatively shoe-string budget. That's what makes the thing so damned wonderful.

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Old 10-27-2008, 08:56 AM
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DFI also contributes in another way. Because the air/fuel mixture is cooler the compression ratio could be raised to 12.5 to 1 which makes more power. Bucket seats are another area that could be engineered to reduce weight.
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Old 02-13-2009, 12:02 PM
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Personally, I think GM should stop investing in so many rebadged Trucks, SUVs, and CUVs, and show commitment to world class cars and technology. How about "Professional Grade" cars.

Yes GM has some made improvements (like the Malibu, 2L-Turbo, CobaltSS, Solstice/Sky, Magnetic shocks, Supercharged LS9) but the competition is relentless. Advanced AWD, Twin Turbos, DSG Transmissions, true Hybrid "cars" on 2nd/3rd gen, rev-matching, and much more.

Honestly, the Corvette is already falling behind technologically compared to the Germans and Japanese its just that the chassis, weight, and powerplant are so good it still continues to perform (amazing platform). Great car! But come on GM, invest in core technologies and competencies and build great "cars". ..and market them properly and build brand equity. Be persistent. The best thing GM has going for it is the Corvette!
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Old 02-18-2009, 11:56 PM
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The key phrase here is "by maintaining the current horsepower to weight ratio". This statement, if directly from GM is dead give away. First, stop thinking V8. Start thinking V6 and forced induction. The Solstice, as it sits, is what 2900 lbs? GM cutting Pontiac and Saturn? The Solstice and Sky already being built in Bowling Green? I think I have an idea what the C7 is going to be like.
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