Larry

I've felt it's boost in my car and I see the letters but I don't know what it is or how it works.

VTEC. hmmmmm

Anyone care to elucidate?

Thanks.

juniorbean

iTrader: (5)

I'm not sure you'll find a more detailed explination then this!!
http://asia.vtec.net/spfeature/vtecimpl/vtec1.html



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1998 Acura CL 3.0 (Iced Blue) ** Some mods, but who cares,
I want a Type-S... (CL or TL)!!

Moderator - 1st Gen Forum @ www.acura-cl.com

RAdams

Variable Valve Timing and Lift Electronic Control. (Yeah they chose what letters to use, but VVTLEC just doesn't sound cool).

I'll try to be thorough in explaining it so I'm not going to guarantee it'll be short:

Camshafts dictate valve events. Lift (how far the valve opens) & duration (how long the valve stays open) are controlled by the lobes on the camshaft. The lobes press on the rocker arms which, in turn, open the valves. On a "normal" OHC head, there is one cam lobe (and associated rocker) per valve. Honda's VTEC system employs an additional cam lobe and rocker arm for each pair of valves (in SOHC VTEC applications, such as the TL, VTEC operates only on the intake valves while the exhaust valves behave "normally". With DOHC VTEC applications VTEC operates on both the intake and exhaust valves). This additional rocker arm is placed in between the two conventional rocker arms. Before VTEC engages, the valves follow the "normal" cam profile -- the center rocker is not locked with the outer ones and therefore does not act upon the valves -- the outer "normal" rockers act directly upon the valves. The center rocker still follows the VTEC cam profile using a lost-motion assembly which is basically a small spring-loaded device that keeps the rocker following the VTEC lobe... it takes the place of a valve spring in this regard. However, since the rockers are still functioning independently, the center VTEC rocker is NOT affecting valve events and is effectively "freewheeling".

At a certain RPM, which varies by application, VTEC activates and the VTEC solenoid which applies oil pressure to lock the 3 rocker arms together via a small piston in the rockers. Now that they're locked together, the center rocker no longer "freewheels" and dictates the valve events according to the higher lift, longer duration profile of the VTEC lobe. Both valves now open further.. and stay open longer.

(The reason VTEC does not operate both intake and exhaust vales on SOHC applications is simply due to space constraints. There's not enough room on the cam to add 3 additional VTEC lobes for the exhaust valves... and it would make the rocker arrangement that much more complicated.)

While it's pretty remarkable by itself, Honda took it one step further with the low-RPM cam lobes [read: the "non-VTEC" ones]. The two lobes aren't the same height, and therefore do not create the same lift. This creates a "swirl" effect to the incoming air in the cylinder which promotes more efficient combustion and results in greater economy.

Here are two pictures that help illustrate the concepts above. They're from my Integra GS-R (which is DOHC VTEC) but the execution is very similar. First, the head:


You'll note there are 3 rockers for each pair of valves. The center (larger) rocker is the VTEC rocker.

Now the camshaft...

The outer lobes are the "conventional" ones. Note the difference in their heights... that's what creates the swirl effect I mentioned. The center (tallest) lobe is the VTEC lobe. It's taller (and wider at the "tip") therefore creating higher lift and longer duration.

I really hope that helped.

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2000 WDP 3.2TL non-NAV
AEM CAI w/bypass, Comptech header

<FONT COLOR="#800080" SIZE="1" FACE="Verdana, Arial">[This message has been edited by RAdams on May 11, 2001 @ ]</font>

TL-SorMaxima

Damn! Now THAT'S an explanation!

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2002 TL Type S
Nighthawk Black Pearl
Black interior

Larry

Geesh, now I'm really confused...

Which VTEC does the TL S have in it?
The DOHC, SOHC or Stage 3?

RAdams

Both the TL and TL-S are SOHC, so they're SOHC VTEC. VTEC operates only on the intake valves in this configuration.

Sorry I confused you.

Larry

Thanks RA and Juniorbean. I think I understand now.

It appears that the most performance comes from DOHC.

Guest

Now explain the 60 degree angle of the engine and how that helps improve HP.

oblio98

WOW! Mr Adams, that was a hell of a good explanation!

I always wondered just what the heck that was!

:-jon

hunter001

The 60 degree angle is a near-ideal angle for the "V" of a V6 engine. It is a very smooth performer. Some companies (including Honda in their 3.5V6 in the RL), employ a 90 degree V6, which is considered ideal in a V8 but not in a V6. There is a slight imbalance in the 90 degree configuration, which is cured by using additional balancing mechanisms.

But if the company manufactures both V6 and V8 engines, a 90 degree V6 can be manufactured on the same assembly line as a V8, which helps from a cost perspective.



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2000 Naples Gold 3.2TL/Navi - Factory Stock but with up-graded tires