I-VTEC > VVTLI > VTEC

toyota made vvtli to be better than vtec, so honda answered back with ivtec.

vtec always kicks in at a specific rpm, so does vvtli, but they do some shit with automatically adjusting timing, not cams, sometin else i forgot. where i-vtec will engage at different points, depending on when it thinks u need it, I THINK. someone correct me if i'm wrong

 

[QUOTE]Originally posted by Ludatic
[B]I-VTEC > VVTLI > VTEC

where i-vtec will engage at different points, depending on when it thinks u need it, I THINK.

 

1. Camless operating systems - Currently there are none used in production cars, nor are any being used in any major form of motorsports (at least not on gasoline engines - more in a second). All current F1 engines utilize camshafts operating valves. However, instead of valve springs, pneumatics are used to close the valves. Springs can still operate quite effectively up to 16k-17k rpm, but pneumatics are more reliable and don't wear out as quickly as valve springs - especially with the rather large valve sizes utilized in F1 engines (note that Yamaha's R6 engine uses valve springs on a production engine at reaches 16k rpm).

At present, several solutions have been tried with respect to infinitely variable valve events. BMW, on the new 745i and the Euro market 318, uses a system which allows the cam lift to vary almost infinitely within a fixed range by varying the pivot point of the cam follower (using another cam in fact). The system has not yet been utilized to produce a truly power focused engine, but it does allow nice gains in torque, fuel economy and breadth of power band.

The future solutions discussed, including electrically operated solenoids are still in development. The electrically operated system looks to be less attractive than other options. As mentioned, a higher voltage electrical system is the first necessity. Once this is in place, then you've got to worry about durability, cycle time and overall control. Its the second of these three things that is an issue right now. Currently, the limitation on cycle times for available solenoid technology (that fits within space and power requirements) limits maximum rpm capability to about 4000-5000 rpm. Electrical solenoids also don't like heat - which they create plenty of, and which they are subjected to. A more reasonable solution that could be implemented more quickly appears to be a pneumatically controlled valve. The system essentially uses solenoids to control air pressure. A spring is retained and in the off position the valve is left in the middle of its travel range. When air pressure is applied properly, it will either open or close. Apparently, this system is easier to control and the solenoid technology for the air switch is simpler and faster. Perhaps the best testament to its functionality is that a diesel engine semi truck equipped with this technology competed in the Pikes Peak Hill Climb and finished the race (might have even won its class, but I don't remember). The developer claims that they have run gasoline engines up to much higher rpms as well.

Which of these solutions (or perhaps a previously unrevealed method) is eventually used is an unknown. However, I can tell you that the biggest gains will not come in peak power (at least for engines like an F20C), but rather in fuel economy, emisssions, and low end power. And for extremely high specific output engines, the gains in low end, economy, etc. will not be that large due to other constraints in engine design - in particular cylinder head design, which is not yet, unfortunately, variable - thus, the head required to flow enough air for 120hp/liter will have some limitations at lower rpms in terms of port velocity.

2. Ferrari cam systems - interestingly, Ferrari has been experimenting with something called ballistic valvetrain technology. Essentially, it creates a controlled form of valve float. Normally you don't want the valve tip to leave the cam. However, Ferrari is trying to take advantage of this. At higher rpm, as forces from cam to valve increase, the valve essentially goes ballistic, increasing lift and duration at high rpm when you need it most. Quite interesting. Elegant in conception, although production execution may be difficult.

3. i-VTEC is quite tunable. I've been providing dyno time to Hondata, who alters Honda ECU's. When accessing the ECU, you can alter the advance curve of the intake cam on the RSX-S engine. Obviously its one more variable to tune, which adds complexity, but a knowledgeable tuner will be able to optimize it for whatever purpose he/she chooses.

4. 3-lobes. The reason for separate low rpm lobes on traditional DOHC VTEC engines is to improve mixture motion (usually swirl) by staggering the opening/closing, lift and duration. At high rpm the relative benefit of such variability is outweighed by the need for monster lift and duration in this particular sort of application.

UL

p.s. - that link on the Celica and VVTLi is quite biased, and frankly, wrong in several respects.

 

Preach on brother Lurker... Thanks for all the great info, I should have checked up on the electric valve system in race cars before I posted, but the lazy days of summer got to me. So does this mean I am going to have to trade my '02 in for an '03 with i-VTEC?

 

To supliment my S (not ideal transport for me, wife, 2 kids ) I have a Honda Stream 2.0SE Sport i-VTEC. The engine is a delight to drive - the power delivery is effortless - very linear and smooth.