thank you! that is so cool... and the part about the problems with the cadillac 8-6-4 and why it "failed"...
was fascinating. i'd never heard that before, and it makes total sense. they discovered a problem years ago that probably could only be solved by the compute power available today!

thanks!

but the part about it not getting into the C6 because of some exhaust manifolding issues???? c'mon....

 

Not exhaust MANIFOLD, but EXHAUST packaging. And that was only one of the issues. If you've ever spent much time under the floorpan of a Corvette, you'll notice there ain't a lot of real estate under there. Everything is packaged very tightly. The requirements for active exhaust hardware did not allow for packaging under the Vette. Meagher is an engine / powertrain engineer, so he was speaking from the parts of the system that he understands. There were other vehicle related issues that he would not have been called upon to resolve that also needed to be addressed. Those items were not discussed in the quoted interview.

Peace,

Martin

 

Although Shining Arcanine's premise is an interesting one, there are several problematic areas. Fuel economy is not just about engine size and/or aero. It's also a function of weight and tire rolling resistance.

When people decide they want a "luxury car" what are they really saying? Typically they are saying they want a vehicle that is highly refined (quiet and smooth), has a solid, safe feel, quality and durability, has excellent ride and handling characteristics, decent to overwhelming performance and a lot of high tech goodies. So how does all this come together?

Well, as someone has already mentioned, when you put 4 cylinder engines in progressively larger and or heavier cars, they tend to have to work harder and they get noisier (not refined) and hotter and more prone to breakdown (less durable). Since they have to spin at higher rpms, a 4 cylinder in a larger car would be less smooth at highway speeds (again, not something the luxury buyer wants) than the same engine in a lighter car.

So, why not just make the luxury car lighter? Well, there is a lot of work going on in that area, but the requirements for more content (safety equipment like multiple airbags, antilock brake systems, traction control systems, ultrasonic and radar based park assist systems, cameras, alarm systems, you get the picture) add mass. Other than the safety content, you could strip some of that stuff out, but then you wouldn't have a luxury car anymore.

Lastly, tires can not be ignored. There is significant stress in the vehicle development world in striking the right balance between tires that have low rolling resistance (easier to get moving, more difficult to stop), smooth ride (luxury focused) and excellent handling (wide grippy sports car focused tires).

There are a few entry luxury cars that have 4 cylinder engines. BMW 3-series vehicles have had 4 cylinders for years. For US models they are going away from 4 cylinders in favor of Inline 6 engines because the demand for 4 cylinders is low and the performance of the 4 cylinder versions is suffering from all the things I've mentioned above. The Saab 9-5 has a turbo 4 as a base model and it gets pretty decent fuel economy, but it's content is luxury more from a European perspective of luxury than a US perspective.

Someone mentioned that the ability of the Corvette to get decent fuel economy from a 400 hp engine is an indication that 4 cylinders could be made powerful enough to power larger cars. The reality is that the engine in the Corvette is waaay beyond what is required to power the vehicle under normal circumstances, so the engine basically loafs most of the time. The automatic transmission in the Corvette is very efficient and allows the engine to operate in its most efficient ranges. (The same basic transmission is also used in most GM pickups and SUVs.) Most people aren't using anything approaching the 400 hp that's under their right foot. The same vehicle with a 220 hp V8 would probably have less efficient fuel consumption.

Peace,

Martin

 

thank you for the reply, Martin. the reason for my post and the comment you responded to was that i didn't see a connection between exhaust systems and DOD. i thought DOD would be handled in the block or the heads and wouldn't have any impact on the exhaust system, per se.

can you enlighten me some more on how DOD would affect the exhaust packaging? thanks!

and as for my history with GM, my first car was... http://www.plusaf.com/myvette.htm this one... followed, not exactly in order by a 67 Pontiac Tempest Sprint (6 cyl, OHC, Quadrajet 4-barrel carb), 77 Pontiac Lemans with the uneven-fire V6 which took me about three years to engineer out the "stall during warm-up."

been there, had lots of fun. the '77 Lemans cornered flatter than the Corvette (i ordered it with the quick-ratio steering -- about 2.5 turns, lock to lock, and stiff front and rear anti-roll bars, etc.)

back at 'cha..

 

I'd need to have a system engineer provide all the delicate details of what would need to happen in the exhaust system. You are correct in your understanding of the actuation of the DOD system being managed in the cylinder block and cylinder heads. Thing is, all the downstream systems now have to deal with the changes in operating conditions.

The exhaust has to be tuned differently when the vehicle is operating on 4 cylinders as opposed to 8 and has to have the ability to seamlessly switch between the two operating modes. There are also other areas of the car that have to be carefully integrated to optimize noise, handling, and vibration differences that exist between 4 and 8 cylinder operating modes. Meagher was only addressing the exhaust issue because changes required in developing an exhaust system may have driven back to require him to do something different with the exhaust manifold to accomodate vehicle changes.

Peace,

Martin

BTW - Nice Vette (talk about a redundant statement!)

 

thank you, martinjlm! that makes total sense.
i am now more enlightened, and i appreciate that.

and yes, i loved that car. i wish i still owned it...

if it were not for a mis-communication with my ex-wife (note: ex-wife), i might still have owned it!

no such problems with new wife.

 

During a discussion with my brother in law the other day, he pointed out that if everyone drove around Trans Am's instead of SUV's overall US fuel economy would rise significantly


Actually I am all for hybrids with components that act like traditional turbochargers, or superchargers. Ala Accord. My thinking (I'm sure I'm not alone here) If auto manufacturers start hybridizing performance vehicles, it will mean quicker adaptation for other types of cars at a quicker pace.

Wouldn't it be awesome if one day instead of chosing the gas engine size for your car, if instead you were able to chose the electric engine size? ford for instance could offer people the performance package the put in the Mustang, or the standard electrical package they put in the focus

That sort of thing would actually get people excited about the technology. Thats where I see it going very soon.

 

Actually that was what drove my decision. I looked at the ratio of electric to ICE power and choose the affordable vehicle with the largest electric to gas ratio.

Bob Wilson