Here is a good one. At what RPM does the larger VTEC cam kick in on the L15? Does it effect both the intake and exhaust side? or just the intake?

 

This system is different than previous variations of vtec. One of the intake valves remains closed until a certain rpm/load is achieved....IIRC it happens about 3800rpms. A locking pin engages the other intake valve for the rest of the rev band. There is actually no "high lift" cam in this car.

 

OK, so at 3800rpm the second intake valve opens? so we have two for intake and two for exhaust? 16 vales in total. At idle how many are working?

 

12 valves at idle - 1 intake / 2 exhaust

 

You sure about that?

 

Check out this TOV article out for all the details of L series engine. Discussed is both the 1.5L LSeries VTECH (Canada and US) and the iDSI engine used elsewhere.

http://asia.vtec.net/Series/FitJazz/lseries/index.html

There is some really cool technology in this engine I didn't know about before I decided.
Molydebnum coated pisons,
Offset con rods,
Roller bearing on the valve rocker arms,
Timing chain instead of a belt,

More reasons I'm glad I'm buying a Fit.

 

wow very cool, very nice writeup

 

Per's wong's article:

"The VTEC mechanism on the L15A VTEC is that of a 1-valve/2-valve system for the intake side only. The exhaust side always functions as a 2-valve system. So the L15A VTEC is a 12valve/16valve system."

...yes I AM sure

 

The newest issue of Sport Compact Car describes how the L series' VTEC works

 

I gotta get that. I don't even know how VTEC currently works.

 

Is L15 VTEC something like VTEC-E used in D17A2 engine?

I think 7th gen Civic's engine works kinda like that as well...

VTEC used to maximumize fuel efficiency, not performance oriented.

 

It wouldnt make any sense at all for VTEC to be a technology to maximize fuel efficiency, if it was then it wouldnt engage so high in the RPM band. The Fit is a rare exception in that unlike the majority of VTEC powered Honda models, the VTEC engagement point is well under the usual 5-6K RPM range.

 

This quote is straight from VTEC-E description in wikipedia.

Or here's another good link to what VTEC-E is.
http://www.leecao.com/honda/vtec/sohcvtece.html

I think they are pretty similar.

 

huh? no, sorry. Most Honda VTECs engage well before that. Only a few engaged in the 5k+ range and those engines are long gone.

 

my s2000 switches over at 6k

 

the b16 in my old si engaged around 5400

 

VTEC
Part of the balance between efficiency and power is made possible by Honda's VTEC variable valve timing system. In the Fit's 16-valve SOHC engine, the VTEC system employs a two rocker arm design (per cylinder on the intake valves) with friction-reducing roller followers for each pair of intake valves, along with intake cam lobes configured to optimize both low- and high-speed operation. Depending on engine load and rpm, an electronic controller determines which cam profile will be used and exactly how the intake valves will operate (usually around 3,400 rpm).
At low revs, where low lift and shorter duration provide optimal operation, the timing of the two intake valves is staggered and the lift asymmetrically skewed in favor of the primary valve. This helps to create a swirl effect within the combustion chamber that increases the efficiency of the burn process. At higher rpm, a hydraulically actuated spool valve causes a locking pin to engage the secondary rocker arm with the primary one, transitioning the secondary valve into a long-duration mode that increases the volume of air/fuel mixture moving into the combustion chamber. The additional air/fuel mixture helps increase power at high rpms.

Hopefully TOV isn't pissed about me re posting their info. I guess the second intake valve does not stay completely closed. I don't believe that there is a full changeover for all valves from low lift to high lift like, for instance, the b18c/b16c/b16b motors.

 

That's not what the NA shop maunal says! I think other items on our car's are different here too...

Per Jeff at Temple of VTEC -
"At around 3400 rpms (depending upon conditions), the VTEC spool valve engages a locking pin, which couples the second intake rocker arm to the primary follower, bringing the secondary intake valve into action, which allows the combustion chamber to gulp more mixture."

 

For anyone that likes pictures instead of just words I think you'll like this:

What does the VTEC system in a Honda engine do?
http://auto.howstuffworks.com/question229.htm

And make sure which one you're talking about.


DOHC VTEC
http://www.leecao.com/honda/vtec/dohcvtec.html

SOHC VTEC
http://www.leecao.com/honda/vtec/sohcvtec.html

SOHC VTEC-E
http://www.leecao.com/honda/vtec/sohcvtece.html

3-Stage VTEC
http://www.leecao.com/honda/vtec/3stagevtec.html

Here is some light reading as well on VTEC Missconceptions.
http://www.leecao.com/honda/vtec/commonmiss.html

It is my understanding that on the U.S. FIT the other valves open between 3400 and 3800 rpms I suspect the difference in the ranges are transmission related. My M/T opens them at about 3500rpm's as I can both feel and hear the change. It's almost like it was kicked in the rear when accelerating to Hwy. speed.

That was when it was stock since I've changed the headers and installed a CAI the transition has not been as noticable, the acceleration seems to be more fluid now but it's still there.


I don't think this would be complete without the Pros and Cons of VTEC technology.
http://auto.howstuffworks.com/framed...tec/index.html

Found this info helpful when I first got my Fit and was comparing it to my Brothers Scion Xb over the phone which has the VVT-i = Variable Valve Timing with Intelligence engine.

The Honda VTEC compares more to the Toyota VVTL-i because they both can alter valve lift (and duration) as well as valve timing.
Toyota has now ceased production of its VVTL-i engines for most markets, because the engine does not meet Euro IV specifications for emissions.

VTEC (which stands for Variable Valve Timing and Lift Electronic Control)
VVT-i (which stands for Variable Valve Timing with intelligence)
VVTL-i (which stands for Variable Valve Timing and Lift with intelligence)

VTEC is an electronic and mechanical system in some Honda engines that allows the engine to effectively have multiple camshafts. As the engine moves into different rpm ranges, the engine's computer can activate alternate lobes on the camshaft and change the cam's timing.

VVTL-i uses an oil pressure switch which pushes a sliding pin under the slipper follower on each rocker arm. This in effect, switches to the high lobe causing high lift and longer duration.

For reference to this info, http://en.wikipedia.org/wiki/VVT-i

Think I went a stray on this but one thing led to another besides if you're going to fully understand it this gives you more points of view on how it can do what it does and why.

I want the 3-Stage VTEC. The D15B is a 1.5L engine that is capable of about 54mpg and is rated for about 128HP.

 

so if the the Fit operates at 12 valves at low rpm and 16 valves at high rpm with only two cam lobes on the intake, then the vtec is like the k20A3 engine except it doesn't have vtc (intelligent)??