Will the corvette be the first GM car to have some form of variable valve timing? The corvette is supposed to be America's sportcar yet it still doesn't have variable valve timing or DOHC. I know the ZR1 which costed about $80,000 was a bit expensive but shouldn't our dear freinds at chevrolet be able to create build a motor that uses a proven technology? Even lame Honda is able to sell complete cars with it for hardly nothing. Why doesn't the corvette have it?

I think the nissan 300zx and the toyota supra have had it since the early 90's even volkswagon has there own version now.

I asked my dad what it was an he didn't really even have a clue, and he is a avid shadetree mechanic. Is the new corvette going to be geared for people who don't care about using new technologies?

I vote YES.

 

The trailblazer already has variable valve timeing, so no, it won't be the first. I'm not certain whether or not it'll get it at all.

Scott

 

GM Powertrain has talked to the press about a LS type V8 with two in-block cams. (See Hot Rod, October or November of last year.) The only reason to have such an architecture is to have independently variable inlet and exhaust valve timing or just independent inlet valve timing, which is the most useful for both developing a flat torque curve and controlling emissions.

Variable timing on a single cam engine is only marginally useful - thus, the independent inlet and exhaust cams.

Duke

 

I am happy to tell you that the ZR1 made great use of its own variation of variable valve timing (remember, developed 15 years ago now), The second ignition key, the so called power key allowed the computer to activate the second set of 8 injectors and intake valves, only when it determined that the conditions were right, which included the rpm being high enough. That is why the LT5 even by todays standards had such impressive low end performance (300 pound/foot at only 1000 rpm, but with a 7200 rpm redline!) in addition to its obviously good top end.

The Northstar in the new Cadillac has variable valve timing, I would assume accomplished by a more sophisticated means.

This is also one of the readons that the LT5 had such an excellent performance on the EPA tests, certainly for its time, and even today. Just about the only complaint I can see in the older LT5 method is that because of the mechanical method of activating the second intake and injector per cylinder, it is a rather sharp increase. There is no "smooth" or polite way, it just comes on. Presumably with more advanced control technology today, the variation is more seamless, but not signifigantly different in its effct, or effectiveness.

Another reason not to forget the ZR1, even as new hot cars come along. it was truly a technology statement for GM. In fact that was its purpose.

Regards,

 

HONDA was the first on the market with VTEC in 1989 with the NSX. and held the patent for 10 years. that is why everyone introduced it to the market in 2001. the version in the ZR1 was a totally different style of vvt and that is why it was not affected by honda's design. VTEC is much more complex then what was in the ZR1. i will try to look for the site that has an excellent insight on the workings of VTEC if you are interested. honda's newest version i-VTEC can do the changeover at any rpm. my type-r hit it at 6200 rpm and you could feel the difference. the Northstar version is much like how VTEC works, in fact, almost every company has the same style of vvt. porsche has variocam and that was similiar to the ZR1 (i think).


[Modified by texnteg, 9:47 AM 10/10/2002]

 

VTEC is more than variable cam timing. Variable cam timing simply alters the cam indexing. VTEC has two cam lobes, one for low speed operation and another for high speed operation.

Patents are valid and enforceable for 17 years.

Duke

 

The reason you see it on smaller engines (like the Honda) is because they suffer from a lack of torque. They NEED a different cam at low RPM to generate torque. I don't think there is a need at present for Corvette. Of course once they switch to electronically actuated valves this whole debate is pointless... :cool:


[Modified by Sanctuary, 11:20 PM 10/10/2002]

 

Excerpted from my reply on another thread...

quote:
--------------------------------------------------------------------------------
"An engine’s level of technology is defined by much more than its valvetrain, and efficiency levels of new-tech pushrod engines come very close to those of OHC."
--------------------------------------------------------------------------------

The above is a recent quote from a GM representative on building world-class powertrains, from "The Car Connection".

The comment, in my view, encapsulates precisely GM's philosophy on powerplant design, which is cutting-edge in my view. The fact is, Chevy/GM can design and build any motor they want. Historically, they have built every configuration of piston engine imaginable, including multivalves, diesels, flat sixes, turbos, blowers, V-12s etc. They have vene built rotary engines, gas turbines, and jet engines.

They chose the Gen III SB pushrod engine for their ultimate sports car because it was the only engine which allowed the Corvette team to achieve the performance and packaging goals for the C5. That kind of thinking is why the Corvette Z06 outperforms cars costing twice as much, and faces no direct competition in its price range from a performance perspective. It is not only world-class, but a benchmark by which other car manufacturers try to set standards.

Today's powerplant winners are those which are most effective in enabling the vehicle to achieve its performance goals (form follows function). While traditionalists may focus primarily on the "neato" factor of the motor alone (LT-5 fans), today's powerplants are inseparable from the total package - peripherals and electronics. And it so happens that one of the best today - the LS-6 - is a pushrod design. This engine produces tremendous power output for its physical size (smaller than many V-6 engines) and weight (300lb bare), is reliable, and has excellent fuel economy and low emissions. These attributes make the LS-6 is one of the most technologically advanced powerplants today.

By contrast, the LT-5 weighs close to 500lb bare, and the "tiny" 1.3L Twin Turbo Rotary engine in the RX-7 (long a favorite of the hi-tech crowd) weighs 320lb and produces 255HP.

The S54 I-6 engine in the new BMW M3 makes an interesting contrast: it has all the requisite ooh-ah stuff (super-high specific output, F1-type piston speeds, continuously variable exhaust and intake cams, and 333HP from only 3.2L NA) that makes it the darling of the tech crowd. What they forget to mention, is that the S54 is also a gas guzzler, it is heavy ( nearly 400lb bare and the M3 is therefore heavy at 3,400lb), and it does not make enough Hp or torque to make the M3 truly competitive. To make matters worse, there are now over 200 documented catastrophic engine failures to date, on less than 3,000 cars produced. It may look cool and hi-tech, but it has yielded an inefficient, and therefore low-tech solution. It is a loser, multivalves and all.

Corvette drivers have nothing to apologize for from a technological perspective. The C5 is one of the very best cars out there, period. The C6 will continue this evolution and raise the bar even higher, and pushrods may well be the best solution again.


[Modified by TTRotary, 5:21 PM 10/10/2002]

 

Very :cool: :cheers:

One thing I'd love to see (eventually) is a totally ceramic small-block. That would rock! :smash:

 

Excellent post!

GM Powertrain is doing some very good work!

Their new Ecotec 2.2 liter inline four for small cars in all world markets is an example - DOHC chain drive four-valves per cylinder, all aluminum using lost foam casting process, main bearing girdle with stuctural oil pan, dual counterrotating balance shafts to eliminate the second order vertical shaking force, 307 lbs dressed weight, 100K mile platinum spark plug, 10:1 CR, but it runs on regular 87 PON fuel, currently rated at 150 lb-ft and 140 HP (varies somewhat with application) with an eighty percent torque bandwidth from 1500 to 6000. Versions built in Europe are available in smaller displacements down to 1.6L. Upgradeable for future technologies including variable valve timing and direct injection.

And this engine is for their LOW END CARS!!! In the US it meets LEV standards, and in the J-cars, fuel consumption is reduced about ten percent from prior engine offerings based on EPA ratings. It is also being used as the base engine across the entire Saturn line.

The LS-series V-8 with its small package volume, light weight, high and broad torque bandwidth, and low specific fuel consumption is still the ideal architecture for a high performance sports car.

You did make a mistake on the LS' weight. Fully dressed, which includes all the accesories and flywheel it is close to 500 lbs (lighter than the LT5). I found a dressed weight figure on a GM web site, but I cant' recall the specific site or page.

Duke





[Modified by SWCDuke, 1:41 PM 10/10/2002]

 

ok, thanks...yes, VTEC is variable valve timing and electronic cam control.
i wrote that at a very early hour and was not functioning. i thought patents were only for 10 years. maybe not... i do know honda introduced the technology to the public in 1989, and the NSX took 4 years to develop. so i guess 17 is about right.

and it is not smaller cars, it is smaller power plants where torque is minimal. this is because of european and asian mandates on engine sizes per class. if the US adopted this method. you would see much more technology in smaller domestic motors.


[Modified by texnteg, 3:00 PM 10/10/2002]

 

You know I meant engines, not cars :D

Anyway, you can thank Opel for the Ecotec. And yes they do seem like neat little sewing machines ;)