VIDEO: Dry but fascinating explanation of variable valve timing
Honda K20Z3 featuring i-VTEC - click above image to watch the video
The powers that be are pleased you enjoyed the differential video so much. So much so that here's another. Dilemma: you want oodles of torque at low speeds because you must overcome one of Newton's pesky laws about bodies at rest tending to stay at rest. However, once you're at speed you'd like to substitute torque for power. Back in the old days, there wasn't a good solution. In fact, the best you could do was take the big block approach and provide more torque and horserpower than a car's suspension, brakes and driver could handle. There was also the European solution: diesels for torque, fancy-pants DOHC gas engines for power. Or the Japanese method: neither. But what if you wanted both?
Enter variable valve timing. Simply put, without variable valve timing, the valves open and close in a fixed pattern and there's no way to increase or decrease the amount of valve overlap (the percentage of time both intake and exhaust valves are open at once). Depending on the lumpiness of the cam, some engines are good for low-speed torque, some for high-rpm power (and/or valve float). With variable valve timing, the rate and duration of the camshaft striking the rocker arms can be altered, varying the valve overlap and resulting in both better low range torque and better high rpm power. Plus, you get the advantage of increased mileage throughout the power band (if you like). Nifty -- but how's it work? If you'd like to know, make the jump and watch the video.
Get a WordPress.com Blog
Reader Comments (Page 1 of 2)
the4thheat 6:36PM (8/09/2009)
VTEC uses the cam change variety while most other VVT systems use the cam phasing kind.
BTW how is Japan neither when Honda popularized the use of variable valve timing in commercial use (i.e. affordable vehicles people actually buy and not high end sports or race cars)? Between Honda and Toyota I would say there's a much higher proportion of cars on Japanese roads with variable valve timing than in Europe or the US.
Reply
xtasi 6:41PM (8/09/2009)
I think he is referring back to the 70's and 80's.
why not the LS2LS7? 7:11PM (8/09/2009)
He meant Japanese cars had no torque or HP. And he's right. They had very little torque and with the voluntary 280PS limit, the didn't have much power either.
I wouldn't say cam phasing is more popular than cam shift. It's more complex and expensive and can't vary open duration or amount, which are pretty important for getting the most output (after overlap).
Jonny Lieberman 7:14PM (8/09/2009)
I am referring to back in the 60s and 70s and a little bit of the 80s.
For instance, I spent nearly every day in high school in a 1968 Toyota Corona. i.e. neither.
naggs 6:27AM (8/10/2009)
ferrari uses a totally different system
hydraulic pressure slides the cam along its axis and there are acutally 3D cam profiles to alter lift and duration
MachinaDC5 1:17PM (8/10/2009)
I took it to mean what why not the LS2LS7? said.
Yaroukh 6:53PM (8/09/2009)
How about a new series on AB? "How stuff wors"?
Reply
Cameron 7:13PM (8/09/2009)
Along those same lines, what happened to the AB features about actual wrench-turning on "project" vehicles?
Brian 12:17AM (8/10/2009)
Cameron, a lot of those blog posts were made by Eric Bryant and he doesn't appear to be around anymore. His posts were generally very good but I think he made the mistake of reading the comments.
bmwMontreal 2:53PM (8/10/2009)
Second, more how stuff works.
paul 7:09PM (8/09/2009)
is it me or does the guy sound like an older richard hammond?
Reply
BigTeebo 7:26PM (8/09/2009)
He sounds just like the announcer from the BBC comedy series "Look around you".
kz1000ps 7:58PM (8/09/2009)
+1 for both Paul and BigTeebo!
Ben 7:17PM (8/09/2009)
Welcome to 1988, seriously VTEC was available on the CRX that year in Japan. But even if you mean variable lift/duaration AND variable timing. That was standard on some Hondas in 2000. Cool explanation but a little dated.
Reply
z-man 7:25PM (8/09/2009)
Though just as informative, I found this video to be more boring then the classic 40's Chevy vid explaining the differential.
Reply
Jonny Lieberman 7:28PM (8/09/2009)
Right! Which is why it got titled, "Dry but fascinating."
nrb 11:32AM (8/10/2009)
I wouldn't say it's as informative. The explanation of how a differential works was extremely well done. This one was OK and I'm glad ABG posted it, but the differential one was in another league.
JeremiahBWhite 8:21PM (8/09/2009)
Looks good. Maybe we are taking a step back nowadays?
Reply
Haub 8:26PM (8/09/2009)
Ah CDX. The auto tech school I go to uses this for extracurricular work.
Reply
Assass1n 10:11PM (8/09/2009)
That explains how they do VVT on DOHC engines. How does GM do it with their single cam SB engines?
Reply