Pontiac Solstice Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
51 Posts
For the new Ecotec, variable valve timing helps deliver 90 percent of the torque peak at as low as 2400 rpm. That sort of responsiveness enormously enhances engine response
This is something that the otherwise wonderful Japanese cars don't seem to understand.
 

·
Registered
Joined
·
1,570 Posts
I am very curious about the mechanism of the computer controled variable valve timing. Exactly how does a computer adjust the valve lifter? Does anyone know?
 

·
Premium Member
Joined
·
5,206 Posts
AeroDave said:
I am very curious about the mechanism of the computer controled variable valve timing. Exactly how does a computer adjust the valve lifter? Does anyone know?
AeroDave,

It depends on the type of adjustment, there are two basic types for DOHC motors. I don't know which type the Solstice will have.

Type 1: Phasing (either intake or exhaust). The theory here is not changing valve lift or duration, just changing the timing on the intake (and/or) exhaust cam on the fly to vary the valve overlap. This is lower cost to do, and usually requires some sort of hardware using solenoids or other mechanical controllers to adjust how much you phase and how complicated you phase them. For example, you might envision a simple, exhaust only phasor that is digital: One exhaust valve cam timing adjustment setting at a certain RPM and another that "switches" above a certain RPM. You could do this for the intake, then you could have discrete timing settings for each at different RPMs up to nearly infinite RPM/Engine torque related phasing for both intake and exhaust. The key here is no change in lift.

Type 2: Variable Cam Profiling. More expensive application, he working method here (example is the honda V.V.T. and most of the really complicated F1 type race engines) is a varied cam profile along the axis of the cam. Here you can change timing, lift and duration by blending the cam profiles from moderate to aggressive. The change in profile is achieved by moving the cams along their axis to get the desired timing changes. Again, you can do this digitally (two settings), multiple settings or nearly infinite with a very complicated and fine adjust controller, and do this on the intake and/or exhaust.

I'm sure some of this will get corrected by the more engine-savvy posters, but that's a bird's eye view of the technology.

There are other ways to do this as well, but most have very limited practical applications and are not really suitable for much outside a laboratory. A long while ago, while in engineering school, I knew a couple of guys from GM who built a "variable solenoid valve" 4 cyl 2.0 liter engine (I think in GM Research). Very neat, loud and clattery as hell, but it was amazing the amount of adjustment of power that was achieved on the dyno. I don't think it was ever in a car.
 

·
Registered
Joined
·
1,570 Posts
Thanks Solsticeman!

Useful info. It sounds like one system just changes the valve timing by moving the timing chain/belt back and forth and the other system changes the cam profile by pushing the camshaft in and out. I have to catch up with the times as most of the cars I have owned had push rods and some didn't even have overhead valves! Here's to the future!:cheers
 

·
Registered
Joined
·
275 Posts
Is really pretty easy with an overhead cam engine because the timing chain/belt is so long. The simplest form involves a horizontal bar about halfway between the crank and the cam(s) with an idler gear at each end that contacts the chain/belt. Offset to one side and you advance the cams, to the other and retard.

Does require a slack side tensioner with more authority than usual and the timing change available is limited. But the big advantage is that a lot less force is required than anything involving movement of the cam and no special lifters are required.

Now this only affects the valve timing and affects both cams equally but is relatively easy to retrofit to an existing engine.
 

·
Registered
Joined
·
2,153 Posts
Good read, mceb. Thanks for digging that up!

I own a 2003 Saturn VUE with the 2.2L ecotec, and I'm actually a member of that forum. Honestly, I haven't really begun doing much research on the ecotec, since I have no serious plans to mod my VUE. Since a version of the ecotec will be going in the Solstice, I guess I'll start paying more attention.

I can tell you that the 2.2L ecotec in my VUE is gutless below 4,000 RPM. Good to see that they're steering the VVT tuning toward the low end.

Interestingly, the ecotec used in the VUE application already has some of the features mentioned in that article, such as throttle-by-wire (hope they tweek that some for the Solstice), coil-on-plug ignition, a cast aluminum oil pan with webbing, and (I'm pretty sure) balance shafts. I think there were other features mentioned that are incorporated into my VUE, but I don't remember which ones. I know for sure I don't have the added displacement, or variable valve timing. Can't wait to drive a car with the revised 2.4L version. When is the cobalt expected to hit dealerships?
 

·
Premium Member
Joined
·
5,206 Posts
AeroDave said:
I am very curious about the mechanism of the computer controled variable valve timing. Exactly how does a computer adjust the valve lifter? Does anyone know?

Found this, you should find it interesting.

http://www.billzilla.org/vvtvtec.htm
 

·
Registered
Joined
·
275 Posts
From the Ecotec pictures I have seen it looks a lot like the early Toyota VVT with a bulge on the end of the intake cam which means advancing and retarding the intake only, no change in duration and exhaust is static.

Question is will it be a two position cam or multi position. First is relatively easy/cheap and suits the general's style.
 

·
Registered
Joined
·
172 Posts
I thought I read somewhere that the cam would phase thoughout the RPM range. I don't think it will be a simple two position setup. I think it will be setup like the 4.2 in the Trailblazer.
 

·
Registered
Joined
·
1,844 Posts
Hate to admit that I haven't read about what Honda has progressed to with their VTEC now, but you left out a important feature when they started in '92. Back then, with a single cam, at lower RPM's there's only one inlet and one outlet valve per cylinder. At 4500 RPM a solinoid opens to use engine oil to move the cam so extra lobes start to spin and open an additional inlet valve, changing from 2 valves per cylindar to 3. At the same time , those new lobes change the profile to the other 8 valves, giving higher lift and duration .
Torque curve is a two hump camel with peaks around 2800 and 5200. Numbers are approximate (service manual's buried in the trunk). Things were simpler back then and it hasn't given any problems over the years.
 

·
Registered
Joined
·
275 Posts
Well, several months before the cars are available, GM produces a "Preliminary Service Manual" so that techs can be familiar with the car when it arrives. There also may be a seperate training manual just on the engine and that might be available now.

That should describe exactly what the engine does.
 
1 - 12 of 12 Posts
Top