My hope is that this thread might continue to promote a dialogue to help explain the i-Vtec technology. Again, this is a whole new thing for me. I've just come off 5 years of coming to understand the Cadillac 5L North Star engine in a 96 Sedan Deville w/ 285HP and can see 27MPG at highway cruising speeds. Quite phenomenal in my book.

Now I own a new "state of the art" 2010 Honda FIT. My desire is to get to know how and why it does what it does - not too interested in bells and whistles.

I think the thread is aptly named. Final drive ratio economy/power is directly related to the engine it connected to. This i=Vtec is one smart engine stock. I'm seeing guys playing with all sorts of engine mods bvut not seeing a real understanding of what's going on.

The L15 is a 16 valve 4 cylinder engine. The two intake valves operate as a pair on a pair of low profile cams. At a certain point those cams get locked to a single high profile cam. Essentially oil pressure activates the locking pin to allow that to happen. This changes the intake characteristics to be more efficient at high RPM.

Daemione, I believe you're suggesting a 3-stage operation. 1st stage single intake valve - 2nd stage both intake valves - 3rd stage both intake vales high cam lobe. I don't believe the L15 behaves that way. You might be thinking of the D15B, D15B 1.5l SOHC VTEC

You are correct in that with the L15 the intake cam is capable of advancing between 25 and 50 degrees (depending upon engine configuration) during operation. Phase changes are implemented by a computer controlled, oil driven adjustable cam gear. Phasing is determined by a combination of engine load and rpm, ranging from fully retarded at idle to somewhat advanced at full throttle and low rpm.

I do agree that crossover is the wrong term - it does engage the high profile cam at a certain point, however. Question is at what point. RPM, oil pressure, ECU are all involved.

I'm really not convinced a sixth gear a solution, to be honest I'm loving the engine/gear box as it is. I can drop out of 5th at any speed I choose and know the engine is going to give me its best.

As far as the lower gears I'm discovering I simply need to be a bit more patient when shifting, that's all. I am positive that this is a characteristic if the DBW - drive by wire accelerator. Takes a feather weight foot and NOT slamming it to the floor. No Detroit here my man.

Hoping others chime in as well. Need some collective knowledge/love here.
K_C_

 

Interesting read:https://www.fitfreak.net/forums/fit-...tio-gears.html

 

Not what I said at all . . .

There's no high profile cam, valve lift & duration are both unchanged. The only change is both intake valves operating vs. just the one.

Here's an article to check out if you're interested in all the gritty details . . .

 

Hey thanks Daemione - it's the gritty details I'm looking for.

Very interesting article. With all the variants of the Vtec [it has had a long history] it's good to have a better understanding of what's up under the hood. The power curve shown says it all and supports what I've been feeling in the drive when hitting down to 4th at cruising speed - little FIT has balls - now I have a better idea as to why.

The motor-cross guys already know this, and I'm just beginning to discover that group.

+ to you -- now what about that 6th gear over-drive???????????
K_C_

 

I was sent an inquiry from Honda shortly after purchasing my Fit in 2006 that wanted suggestions as to what improvements would I like to see implemented on future models and one of my answers was closer gear ratio spacing on 3rd through 5th gears and over driven 5th..... I had received similar correspondence from BMW after purchasing a new to the market R1100GS motorcycle in 1994 and all of the changes that I listed as suggested changes for improvement were made on the next version of the bike..... Since Honda has done little else but styling improvements and increasing the size of the recent model that doesn't lend itself to after market improvements I have chosen to just continue driving what I have with what I have done to it and maybe one of these days get another BMW motorcycle.

 

That article describes the GD's L15A motor and not the L15A used in the GE. The VTEC used in the newer iteration of L15 is more like the VTEC first released by Honda. The GD variant is an economy type of VTEC. If you don't believe there is a crossover of low to high cam, then why does VTEC activate only above 5400 on the GE? The GE L15A also is using all 16 valves all the time, unlike the GD where it uses either 12 or 16. Look at the date of that article, it is written in March 2005.

 

I am pretty sure the VTEC transition occurs at under 4K RPM on the GD models but is felt at higher revs when accelerating due to the length of the intake runners..... The Hondata ECU reflash changes the RPM of VTEC actuation on the KWSC high boost kit but I don't know at what RPM it occurs.

 

You are right TC, completely different system to the GE's setup. It's as was described, it is activating the 2nd intake valve, unlike the GE where it is activating a high lobe on the cam at 5400rpms.

 

People, i believe you should be reading this

Honda L-Series SOHC i-VTEC Engines for the new GD Honda Fit/Jazz

with regards to i-vtec switchover on the new (GE) L15 and not

The Truly Amazing Honda Fit/Jazz

which is based on the old L15 (GD).

EDIT: The top link says "new GD Honda Fit/Jazz", they made a mistake. Its for the GE engine.

 

Ah, I hadn't realized the 12v/16v implementation had changed that much in GD vs. GE - thanks for the correction. I'm not sure it was every really specified in this thread which engine was under discussion, my guess is we've all been talking about whichever we happen to own . . .

Makes me really wonder how much of a pain in the rectum a head swap would be. Parts list: Cylinder head, ECU, MAF sensor, exhaust outlet . . . modified wiring harness?

 

Oh, and to veer slightly more on-topic - I still maintain that there's not much place for a 6th gear that's higher than our current over-drive gear (5th).

As I understand it, 6 speed transmissions fall into one of two categories. The first, on small displacement higher revving engines like ours, the 6th gear serves the role our current 5th does, and that gives more flexibility in tightening up gear ratios 2 through 5. So you've got more gear choices to make sure you can wring the maximum amount of power out of the engine, no matter what speed you're coming out of a corner.

And in the second scenario, a 6th gear can be added as a "super over-drive" to get better fuel efficiency at highway speeds. But this is only going to work on an engine with a mountain of low-end torque (e.g. LS1, etc.). When you start looking at engine speeds vs. mph on most GM 6 speed offerings, it becomes pretty obvious it would never work on an engine like ours. 80 mph @ 1500 rpms? Not gonna happen . . . the GD L15 struggles enough @ 2500 rpms.

And it's worth pointing out, rpms are not the fuel efficiency killer that people make them out to be. For example, at any constant cruising speed between 55 & 65mph, I get the same gas mileage in 4th gear as I do in 5th. Better, if there are hills. There just isn't enough oomph in 5th gear, and the engine has to work twice as hard.

 

The JDM mission could use a 6th cog. Our 5th ratio is a .854 compared to the NA market .727 (this is for the GE). For around town it works just fine, but I have noticed on the highway that the car could use a 6th gear...hello CR-Z mission...MAYBE?!?!

 

And is the final ratio the same on the jdm? I'd like to know in Europe too. And nobody talked about having a 6th gear doing 80 @ 1500rpm, but just a 6th gear (or a 5th with all the gears longer) similar to the 5th gear in the automatic model. People just have to think about downshifting a gear or two in a hill, at "low" speeds, when it's really windy/snowing. But being at nearly 4000rpm at 80mph is pointless on the fit. It's a v-tec, it's not a V6, but it's not a hayabusa either, or even a b16. This thing cut off at 7k rpm...

Also, for good fuel economy, how does the vtec in the fit 2008+ compared to the technology in the civic vx Vtec

 

Actually the JDM final is a 4.294 where as the NA model is a 4.62. It results in the JDM achieving 10mph less top speed (137 vs. 147), but it is has more speed in gears 1 - 3 and falls into VTEC from 3 to 4 to 5 whereas the NA model only falls into VTEC from 4 to 5. Also I don't know if the Fit would be able to achieve 147mph in stock form, maybe with a nice long downward slope. Although at redline on mine I can just about hit the speed limiter of 180km/h in 4th, just under it. Need a speed cut, something the J's reflash provides.

Gear ratios on the GE8 MT...

JDM: 3.461, 1.869, 1.303, 1.054, .853 and a final of 4.294
NA: 3.308, 1.87, 1.303, .949, .727 and a final of 4.62

 

180 in 4th gear doesn't seem to be any shorter than the usdm 4th gear...

And japanese make mostly city driving + they buy as many A/T cars than in the us, so I would not take them as a reference to make a well geared manual transmission (they make some good too) or able to handle the highway well.

 

I suppose. I guess it goes with my theory that they know Americans don't want to be bothered with the terrible inconvenience of downshifting while driving their stick shift cars...and I say, if that's the case, buy the stinking automatic.

Call me crazy, but I always have it in 5th gear at 35. It lopes around at that speed perfectly comfortably, and it returns outstanding mileage doing that. I almost can't imagine driving down a 35 mph street in town here staying in 3rd gear. It would drive me nuts. The car would feel twitchy and lurchy and noisy. I drove at 35 in 5th in my old Focus too, and in my '93 Escort. Am I nuts?

I have this same thing with my Fit. In warmer weather (i.e. not winter), I'll easily get upper 30s driving around town on my way to and from work. But a drive up north for a weekend doing 70 on the highway? Mileage drops a decent bit. People don't believe me when I say that.

 

I can't imagine how you can bear to have it in 5th gear at 35MPH....you have to be spinning like 1800RPM. There's just too little power below about 3000RPM.

 

If I am not in stop and go traffic or going up an incline I shift into 5Th and see RPMs drop just below idle speed before down shift to a lower gear..... Of course I don't try to accelerate or apply full throttle, but a very light touch on the accelerator to keep moving and the revs high enough for proper oil circulation and my shifter in hand for a down shift as needed.... With only 1/2 of the 8 intake vales opening at low revs and the ECU pulling back ignition timing you won't hurt anything unless you go slow enough to lose oil pressure.

 

I guess tastes vary. I usually shift at about 2500 RPM, and that oftentimes makes me accelerate quicker than much of the traffic around me. If I'm on relatively flat roads going 35 and have no reason to instantly "need" lots more power, why sit their droning the engine at 3000 RPM while throttling the heck out of it when it will purr along nicely at 1600 RPM in 5th? To keep the car going steadily down the road, it takes very little power. It has plenty of juice to keep it at that speed even on slight inclines with fairly minimal throttle application too.

 

Use a scangauge or a kiwi or something, I think you'll be surprised by the mileage you're NOT getting by making your engine run at that low a speed.