I think the VVA system referred to above deserves its own thread, so I'll try to keep to the original topic. It's an interesting idea, and I'd love to see what some of the tech guys around here think of it. Anyway, back to VTEC:
The advantages are obvious. I don't think we really need to try to list them because Honda and every "specific output freak" in the world has already written a dissertation on it. And yes, any presumed slight against turbocharging (unfair comparisons apply) is going to get my immediate attention. So here I go.
It's been said several times in this thread that speed is all we care about. Mileage and driveability mean nothing. Well, I'm continuing down that path. Disadvantages of VTEC for maximum performance:
- Extra valvetrain mass (weight)
This is pretty self-explanatory. Lightening the valvetrain generally makes it last longer, frees up power, heightens the redline, and extends the power curve (allowing you to shift later and stay in the fattest part of the power band).
- Added complexity and opportunities for breakdown
Why do many people abhor the FD3S RX-7? Over-complexity and poor reliability kill an otherwise excellent automobile. In racing, stuff breaks all the time. In short, nobody wants another expensive part that is more likely to break than one of those skinny Honda con rods. This added complexity alss makes the engines more expensive to produce. And though VTEC has been used mainly on four-cylinders, Honda will have to branch out if this technology is actually supposed to replace turbocharging. The NSX, for example, uses a V6. That means double the VTEC components. Since the search for ultimare power almost always leads to bigger engines, the first two VTEC disadvantages are going to get twice as big as larger engines use it in place of turbocharging.
- The absolutely useless low RPM profile
Lert's face it: if you're drag racing, a low-RPM cam profile is pointless. Yes, you can drive it to the track. Yes, it will idle smoothly. But, after that, all you have is a normal drag car with a typical lumpy cam profile, plus the two disadvantages listed above. And so VTEC is much more at home on a daily driver than a high performance machine.
- The difficulty of finding aftermarket cams
This used to be a much bigger deal than it is now, but it still factors in. Initially, aftermarket VTEC cams that worked were impossible to find. Thanks to precision CNC-machining, that has changed. Quality manufacturers can and do make good VTEC cams now, but the selection is still much thinner than for other engines.
That's just off the top of my head. In my opinion, VTEC is not for high-performance automobiles. The same applies to MIVEC, VVL, VVT-i, and any other approximations. And in any realm, it seems to me that there are some easy alternatives. Variable length intake runners and variable backpressure exahust are good examples. Harmonic optimization can give a lot of the same benefits as optimized cam timing. Variable intake manifolds seem to have been thrown to the side, but I still like them. And as far as exhaust, Nissan seems to be ditching variable capacity mufflers; they weren't that impressive anyway. Suzuki has exployed a simple system comprised of a computer-controlled butterfly valve in the exhaust stream to change the effective diameter of the pipe. I have long wanted to see this on a larger engine. My point is, I think there are several viable alternatives to VTEC that do not share in all of its disadvantages and also prove that it is
not the greatest thing ever invented.
And the brief on turbochargers: modern ball-bearing turbos coupled with electronic boost control can offer much more flexibility than in the past. But this is not even important if we're still talking maximum performance. At the drag strip, you can simply have a radical cam and a huge turbo, and hiding behind a VTEC sticker will not save anyone.
As usual, I apologize for being long-winded. The good news is: you'll get over it.
