Automotive Forums .com - the leading automotive community online! Automotive Forums .com - the leading automotive community online!
Automotive Forums .com - the leading automotive community online! 
-
Latest | 0 Rplys
Go Back   Automotive Forums .com Car Chat > Engineering/Technical
Engineering/Technical Ask technical questions about cars. Do you know how a car engine works?
Reply Show Printable Version Show Printable Version | Email this Page Email this Page | Subscription Subscribe to this Thread
 
Thread Tools Search this Thread
Old 01-02-2002, 03:06 AM   #1
tenzoracerevovii
AF Enthusiast
 
Join Date: Dec 2001
Posts: 659
Thanks: 0
Thanked 0 Times in 0 Posts
Vtec

ok.....i know this question might seem stupid to some of you........but i don't give a shit.......i want to know how vtec works.......i know that the cams have 3 lobes or whatever.....primary, secondary, and vtec.......and there is a vtec solenoid.......when you hit a certain rpm.....the cpu sends a signal and a "pin" slides through the lobes and connects them all..........the vtec lobe is bigger than the other lobes......now........since vtec is dohc.....does that mean one cam for intake and one cam for exhaust?......when vtec is not engaged, then the valves open up one at a time. so when vtec kicks in, it opens up both valves at the same time?......so more air in and air comes out faster........so does that "extra air flow" make the "boost" in power?.......am i correct........if not......please correct me.....thanks
__________________
i have type-r stickers on my bike, will it go faster?
-me


Don't you know, it's 10 hp for every sticker, 50 hp extra for every additional inch of rear spoiler behond stock height.
-obiewancoyote
tenzoracerevovii is offline   Reply With Quote
Old 01-02-2002, 12:48 PM   #2
CornerCarver
AF Newbie
 
CornerCarver's Avatar
 
Join Date: Jan 2002
Posts: 32
Thanks: 0
Thanked 0 Times in 0 Posts
Send a message via ICQ to CornerCarver
VTEC can be SOHC or DOHC. I think all of the SOHC VTEC motors have been intake only, while with the DOHC motors some have been intake only and some are both intake and exhaust.

Some versions of VTEC change cam lift and duration with the third lobe, some shut down the use of one valve during low rpm operation (as seen in the fuel efficiency and motorcycle versions).

The performance car versions of VTEC use a mild cam profile for lower rpm/cruising mode, for best fuel efficiency and emissions, and a hotter cam profile for high rpm/WOT situations, which allows for maximum flow at high rpm.

Basically any motor which uses conventional cams is a compromise. The best cam profile for low end/low rpm performance is very different from the best cam profile for high end/high rpm performance. High rpm calls for long duration and high lift to cram as much charge as possible into the combustion chamber. The problem is, at low rpm, optimal air velocity is lost with this long duration/high lift setup. Lower rpm requires the valves to be open less and for less time to keep the charge flowing optimally.

Consider sucking air through a straw. If you suck x amount of air through a small diameter straw, it will travel nice and fast. Suck the same amount of air through a big huge honking straw, and the same amount of air will travel slowly. Engines need the air to travel fast for the mixture to swirl around and pack into the combustion chamber for best results. The problem is, the small straw will only suck so much air. You need a small straw to suck small amounts of air (low rpm), and a big straw to suck large amounts of air (high rpm). Small straw - mild cam profile. Big straw - hot cam profile. Non-VTEC motors choose a in-between straw size that suits both as best a possible, but will never suit either one optimally.

VTEC is basically two sizes of straw for one engine... That said, any manufacturers variable valve timing and lift system is basically the same principal. Variable cam timing, that is another story...

Last edited by CornerCarver; 01-02-2002 at 02:20 PM.
CornerCarver is offline   Reply With Quote
Old 01-02-2002, 01:08 PM   #3
drift
AF Fanatic
 
drift's Avatar
 
Join Date: Dec 2001
Location: Newcastle, Washington
Posts: 13,231
Thanks: 0
Thanked 0 Times in 0 Posts
Send a message via AIM to drift
http://www.leecao.com/honda/index.html

everything you need to know about all VTEC forms, with pictures to help figure it out
drift is offline   Reply With Quote
Old 01-02-2002, 05:18 PM   #4
praxis
AF Enthusiast
 
Join Date: Dec 2001
Posts: 353
Thanks: 0
Thanked 0 Times in 0 Posts
cornercarver....I like the straw anology.
__________________

PraxisPerformanceAutoworks LLC High performance autoparts & accessories.
________________________
sales and specials...Konig wheels, Accmat carpets, Thermal exhaust, DragunFire mufflers
_____________________________
PraxisForums...informative information
____________________________
PraxisRacing is sponsoring. click for more info.
_____________________________
see PureHonda in its original colors-->
praxis is offline   Reply With Quote
Old 01-02-2002, 05:31 PM   #5
praxis
AF Enthusiast
 
Join Date: Dec 2001
Posts: 353
Thanks: 0
Thanked 0 Times in 0 Posts
Check out the post by VTEC-boi in this section (technical) entitled 'tech heads-check my work'...he has an article on his website (linked from the thread) that has a basic desription of how vtec works.
Attached Images
File Type: jpg tripod logo dot com.jpg (4.0 KB, 25 views)
__________________

PraxisPerformanceAutoworks LLC High performance autoparts & accessories.
________________________
sales and specials...Konig wheels, Accmat carpets, Thermal exhaust, DragunFire mufflers
_____________________________
PraxisForums...informative information
____________________________
PraxisRacing is sponsoring. click for more info.
_____________________________
see PureHonda in its original colors-->
praxis is offline   Reply With Quote
 
Similar Threads
Thread Thread Starter Forum Replies Last Post
vtec or not vtec gwako Engineering/Technical 20 05-05-2003 11:22 AM
whats the difference in the 4th gen si vtec and the vtec Got Boost? Prelude 10 08-31-2002 04:31 PM
Vtec Head on Non-Vtec? H22-Civic Si '92-'95 Civic | EL | Civic Hybrid | Civic GX NGV 0 05-19-2002 07:59 PM
Difference in VTec between Si and Vtec models? 69GPrix '92-'95 Civic | EL | Civic Hybrid | Civic GX NGV 5 05-11-2002 11:07 PM
ls/vtec how about a f22/vtec crazy_ss Engineering/Technical 9 01-19-2002 11:32 PM

Reply

POST REPLY TO THIS THREAD


Bookmarks
Go Back   Automotive Forums .com Car Chat > Engineering/Technical

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 12:14 AM.

Community Participation Guidelines | How to use your User Control Panel

Powered by: vBulletin | Copyright Jelsoft Enterprises Ltd.
 
 
no new posts