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JCD
04-20-2008, 07:03 PM
I think I just herd an ad for a Chevrolet with variable valve timing.
They stole my idea, but it's my fault as I haven't done anything thing with it r 45 years.
Dose anyone Know anything about it?
Is the cam drive an electric servo? Are the valves solenoid operated? Is the drive train mechanical?
Which model is it in?
What is the millage?
What is the displacement?
What is the horsepower?

JCD

Dawai
04-20-2008, 07:10 PM
Rhoads has been doing that will Lifters since the 70s.. they leak down at slow speeds allowing a much radical cam to idle smoothly and pull better, but come back at top end.

DICKEYBIRD
04-20-2008, 07:25 PM
V.V.T. is usually actuated by solenoid controlled (engine oil pressure) hydraulics. The solenoid(s) is(are) actuated by the engine E.C.M (Electronic Control Module) and the particular RPM it advances or retards the cam(s) is controlled by software maps written by the programmers. It's been in use for a long time by many manufacturers. The manufacturer I'm familiar with (Jaguar) used it (in the states) in the 1997 XK8. It's been on every Jaguar V-8 since then and V-6 since 2000. I think it was used by other manufacturers much earlier and didn't necessarily use electronics for the control.

That's my story and I'm stickin' to it.:)

timcasbolt
04-20-2008, 07:27 PM
There is a wealth of information available on google and howstuffworks about this topic. It has advanced light years since the days of Rhoads lifters.

torker
04-20-2008, 08:11 PM
Interesting subject! Now.. does anyone know how the valves work in Formula One engines? Those things amaze me. 16,000 RPM!!!!!! Incredible!
I heard a brief blurb about them a couple years ago but not enough to understand how they work.
Russ

DICKEYBIRD
04-20-2008, 08:27 PM
Interesting subject! Now.. does anyone know how the valves work in Formula One engines? Those things amaze me. 16,000 RPM!!!!!! RussThey work mostly by the injection of vast amounts of CUBIC DOLLARS. "Speed costs money....just how fast can you afford to go?"

Back to more serious things, I think F1 engines use valve "springs" made from nitrogen charged bellows with a reservoir of high pressure nitrogen.

torker
04-20-2008, 09:10 PM
I was just sorta wondering if the Chev valves were a "trickle down" of F1 technology.

Mark Hockett
04-20-2008, 09:23 PM
Russ,
The F1 engines use electric solenoids and the nitrogen springs DICKEYBIRD mentioned. F1 is way beyond Chevy's variable cam timing. Many import cars have had variable cam timing for years so Chevy is even way behind in passenger car technology.

JCD
04-20-2008, 10:51 PM
16K seems fast for poppet valves.
Is anyone using rotary or other valve types in a 4 cycle engine?

Rookie machinist
04-21-2008, 12:14 AM
Varible vale timing is old news toyota/lexus has been using it for years. They use oil pressure to advance or retard the cam sprocket. I was going to post the tech data but I can't get the pic to transfer. I'll try again tomarrow.

Bguns
04-21-2008, 12:27 AM
Since early 80's or so ... MVT was air actuated....

Peter S
04-21-2008, 12:55 AM
Does anyone else remember the after market cam sprocket with variable timing that used to be offered for small block Chevs (1970's?). The sprocket (from memory) worked something like the advance/retard in the distributor, so the cam shaft could automatically advance in relation to the sprocket as the revs increased. I don't think it was ever more than a gimmick.

The Alfa Romeo engines from the 1980's? had a simple (I think vacuum controlled) advance unit on the end of one of their two cams. Now I guess most engine builders use them along with variable lift and a few other things. Some very clever bits of engineering - unlike the old Chev idea that appeared in Rodding magazines many years ago.
I have found this website good for this sort of thing:

http://www.autozine.org/

Oldbrock
04-21-2008, 01:05 AM
anybody know anything about desmadromic (spelling) cams that pull the valve shut as well as opening it. I think the Italians used it many years ago. Peter

robert
04-21-2008, 01:24 AM
anybody know anything about desmadromic (spelling) cams that pull the valve shut as well as opening it. I think the Italians used it many years ago. Peter

Ducati still does.---RG

bob ward
04-21-2008, 01:48 AM
Lance Reventlow spent vast sums of money late 50s early 60s trying to make desmo valves work in his indy cars and also I think in his Formula 1 cars.

Alguy
04-21-2008, 04:48 AM
A few years ago before i retired i was present when the engine group made presentation about an engine they were working on. It had no camshaft, push rods or rocker arms . the valves were moved by solenoids controled by a computer . I figure someday it will happen someone will do it. That will free up alot HP being consumed by the valve train.

fasto
04-21-2008, 09:15 AM
A few years ago before i retired i was present when the engine group made presentation about an engine they were working on. It had no camshaft, push rods or rocker arms . the valves were moved by solenoids controled by a computer . I figure someday it will happen someone will do it. That will free up alot HP being consumed by the valve train.

This is already reality on some BIG marine diesels, like 100,000 HP @ 70 RPM.

It makes reversing easier, too, as most BIG diesels like this just run backwards for reverse. Before, the camshafts were shifted under hydraulics to get a different set of lobes. Now, the CPU just loads a different valve & injection program.

Dawai
04-21-2008, 09:24 AM
That cam timing shift was called V-tec in the Honda. I have two here.

Shifting the timing angle of the camshaft changes the rpm range the engine produces in. degree Keyways in timing sprockets have done it for years. Problems with street engines is wear. If someone comes up with a auto-shift compensator for engines to time with the ecu they will be miles ahead.. right now they depend on replacement of "wore out" vehicles for timing solutions. Throw away.

When you go to the major parts suppliers for consumers, you only see mexicans here.. WHITE PEOPLE DO NOT GET THEIR HANDS DIRTY anymore. Lazy rascals have too much money.

PackardV8
04-21-2008, 11:22 AM
You gotta get out more, JCD. ;) Variable valve timing has been in OEM use for many years now. BMW has the most advanced setup just now. They vary both timing of both intake and exhaust and valve lift.

thnx, jack vines