Variable Valve timing

[OVERSTEER]

I know variable valve timing was first used in a production car in 1991 with the Honda NSX, but when was it first used in a car, ever? I need that info for an assignment i'm doing at college, and any help on that question would be appreciated.

[Jukebox]

It's a method that advances camshaft timing to improve engine performance. A hydraulic mechanism on the cam drive uses oil pressure to rotate the cam's position slightly as engine speed changes. This increases valve duration to produce more horsepower at higher rpms. Variable valve timing is also known as the VTEC and used by most of Honda cars nowadays. Other carmakers followed suit, such as BMW & Toyota.

When i'm not so sure, maybe you could visit the Honda site and search.

[enzo]

Doubt it was the first time it was done, but we had a small block Chevy in a drag car that we could change the cam timing while on the track back in '69. Mechanism was nothing more than an extra link in the timing chain, and a set of idler gears on a slider mechanism controlled from the cockpit. Worked great.

[OVERSTEER]

I know what Variable valve timing is used for, it's when was it first used in a car ever that i'm looking for, I need it for the part in my introduction that has the history of this Technology.
Any links that anyone knows about will be very much appreciated.

[roscoe]

I'm not sure when it was first used in prototype form but Alfa Romeo had it on production cars around 1981, long before the likes of Honda etc. It was used either on a Guiletta or an Alfetta, I think it also had a turbo. Like a lot of things I think you will find it was first used in motorsport.

[Arneal]

VVT and VTEC are not the same thing. Jukebox describes VVT. VTEC uses multiple camlobes. The low speed lobes have relatively mild lift and duration, the highspeed lobes are much more aggressive. The change over point is typically around 5000rpm.

Hondas i-VTEC engines combine VVT and VTEC.

I've looked all around the web for info on the first use of VVT, but can't find anything. Good luck OVERSTEER.

[Jukebox]

VTEC stands for a combination of Variable Valve Timing and Lift Electronic Control to be precise. Car manufacturers came up with different names but it's all the same which will only be felt on higher revs (variable rpms to different carmakers), Toyota calls it VVT, BMW calls it double VANOS and Porsche calls it VarioCam.

i-VTEC is a combination of VTEC and Variable Timing Control.

[con-rod]

Just to mention Ferrari have there own system (not sure which cars though) and Jag too.

[Arneal]

Lets define what we are talking about.

Cam Phasing VVT - varies the valve timing by shifting the phase angle of the camshafts. The camshaft is rotated depending on RPM and sometimes other factors. It can be done either in a continuous fashion or in discrete steps. This is by far the commonest system and the least effective. Note that it does not vary the lift or the duration.

This system is called Double VANOS by BMW, VarioCam by Porsche and VVT-i by Toyota. It is also used by Ferrari, Ford, Jaguar, Audi, Volkswagon, Subaru, Renault and others.


Cam Changing VVT - varies the valve lift and duration in discrete steps by using multiple lobes to drive the valves. Low speed lobes are tuned for torque and high speed lobes have greater lift and duration for race car like horsepower. Note the timing can not be changed continuosly as in the other system.

This system is called VTEC by Honda.


Cam Phasing and Cam Changing VVT - Combines the two systems.

Honda calls it i-VTEC, Porsche VarioCam PLUS, Toyota VVTL-i.

This is a very good link:
http://autozine.kyul.net/technical_s...gine/vvt_2.htm

[calais]

Originally posted by roscoe
I'm not sure when it was first used in prototype form but Alfa Romeo had it on production cars around 1981, long before the likes of Honda etc. It was used either on a Guiletta or an Alfetta, I think it also had a turbo. Like a lot of things I think you will find it was first used in motorsport.

variable cam timing on an alfa?????
what, when the timing belt became loose??

[alfasud]

Originally posted by calais


variable cam timing on an alfa?????
what, when the timing belt became loose??

I think you will find that the 1980's Giulietta (note spelling) and Alfetta had chain driven overhead cams.... otherwise it would have been quite funny.

I'm told the main benefits were 1) marketing and 2) allows good overlap for top end and not only better drivability at lower revs but most importantly passes emissions tests, which is difficult with lots of overlap.

Don't think the VVT was ever combined with a Turbo on the factory cars (Alfa 75 Turbo didn't have VVT), but they did combine with twin spark head in the Alfa 75 Twinspark, giving 148bhp from 1962cc, which wasn't bad for mid 80's saloon with 2 valves per cylinder.

[alfasud]

Did a bit of research and it seems that Alfa Romeo first used VVT (Cam Phasing type) in the Bosch Fuel Injected Spider and Alfetta models sold in the U.S.A. I've found a couple of references to these with 1980 being the first year:

http://www.google.com/search?q=alfa+...ve+timing+1980

And before someone tells me the carsfromitaly.com links don't work:
http://www.carsfromitaly.com/alfaromeo/index.html

You need to then select "Models", then select "Spider" to take you to the correct page.

I'm not sure if the advantage is so great in racing, as you change gears to keep in a reasonably narrow rev range. I know every little bit helps, and I'm sure it's at least been tried in F1, but maybe not before 1980.