Hondata Flashpro and vtec-E on the GD3
 

I own a 07 Honda Fit Sport M/T and I don't know if any of you is bothered by this but I hate that vtec changeover comes around 2800-3500 RPM, depending on how you're pushing the gas pedal (Except on 5th gear, which is on after 2800rpm regardless).

Where I live, most highways are 65mph speed limit, and at 65mph I'm usually around 3200rpms with vtec on. I get SHITTY, I mean REAL SHITTY mpg when I'm driving on those high speed highways because of vtec. I can get from point A to point B through the main and longer road, with stop lights and all that, with about a quarter gas tank. Now, when I take the highway, which is shorter and overall a better and "straighter" road, I use about half a tank of gas.

Now, the question is, Can I safely increase the vtec changeover to around 3500-4000rpm using Hondata Flashpro? I'm asking since vtec-e is a system that I'm not very knowledgeable on, and I'm not aware if there are any major differences from i-vtec or the classic vtec. I don't want to increase the changeover so much that I will mess up my engine.

Thanks in advance,

~KiRa

changing it wont help you. There is something else that is going on if you are getting better city MPG than highway. I could cruise at 70-75mph all day and still pull close to 40 mpg on the highway.

I agree with Chris! The GD Fit's vtec system is a 12/16 valve system like the older D16. When we played with the engagement point on my car, it did some terrible things to the torque curve and subsequently MPG and such. IF the FlashPro will even work on your ECU (is your car the same as a USDM market Fit?) it may be worth the $$$ just to data log what your car is currently doing!

Without significant VE mods, there is no advantage to moving the cam switchover

^ Take DSM's words as gospel on such subjects!

Is yours A/T or M/T, GE or GD? I understand A/T gets better highway mpg than M/T. If I cruise at 55mph highway I get about 35mpg, it only happens when I go further on to 60-65mph (vtec on).

I'm only running W-R manifold, sri, full 2-1/4" exhaust.

I just want to know if increasing the changeover by 500-1000rpm will not damage my valvetrain/pistons, since on dohc engines, if you increase the changeover too much it does indeed damage valvetrain; especially on cams with very little duration.

Not sure where you got the idea that damage will be incurred if you change the cam-lobe switch point, because that's not true.. you are just ruining your airflow. Let alone short duration increasingly the likelihood of this.

Changing the lift phasing angle too much on either end, like opening too early/closing too late on the exhaust stroke, could cause contact, but that is a separate discussion.

Which brings me back to what was explained earlier, there is no advantage in changing your VTEC settings if you don't have significant VE mods.

VTEC isn't just a switch either, it is load dependent and is not necessarily on during cruise at 65. There is a logic programmed into VTEC operation.

So again, no.. there is no advantage to what you are proposing.

There are other ways to tweak fuel economy in your tune, but based on the mods youve shared with us.. VTEC alteration is not one of them.

A "driver mod" may be in order as no one else is having fuel economy issues due to "VTEC"

MT GD. Guarantee that the mileage issue isn't related to the gearing. Could be plugs, O2 sensor, cat, many other "emissions" equipment that is not working to its full potential causing the ECU to compensate and using more fuel.

I would murder for this... (Not really) I need to do some digging and see what's up on my fit... Last tank I got 24mpg with mixed driving.

The valvetrain/engine damage is not something I can vouch for personally. It was something I was reading in honda-tech forums a while ago. I can't remember clearly, but it had to do something about if changeover was increased too much, and if the duration of the lobe is low, then when the changeover occurred it cause valve/piston contact. But like I said, it's not something I'm personally experienced with.

Hey, come on, I'm no engineer, but I know the basic logic in the vtec system. It works with hydraulic pressure, and in roller rocker arms there is a small pin that gets pushed in, forcing the higher profile lobe to be in action for both intake valves.

My CEL light has never gone on and I get extremely good mpg as long as vtec is not on. Once the changeover occurs, my mpg drops around 3fold. Which makes sense since a higher profile lobe is in action and the valves are opening more plus there are two intake valves in action instead of one. I understand increasing might kill my mid torque/hp by a little, but this issue is killing me since I have to drive every weekend to campus from medical residency.

Now, if my o2 sensor or any other electronic parts were not working properly, I would also get shitty mpg while cruising with vtec off. But like I said, it happens on highways as soon as I get past 60mph when vtec goes on. If I cruise at 55mph with vtec off I get 30 something mpg. It's kinda shitty that the gd's vtec cangeover is so slow. I miss when my s2k was streetable... I could be driving at 80mph on 6th gear without vtec on.

Has it ever occurred to you that you have no idea what you are talking about?

The "logic" I was referring to is the list of parameters the ECU accounts for when activating the solenoid that lets pressure in/out for the cam switch. Not the logic behind why Honda uses VTEC or how it works :rotfl:

Second, what does "my mpg drops around 3fold" even mean? Your mileage is cut down to a 1/3 of what it would be out of VTEC? I'm not even sure I want an answer to that.

Your available torque at cruise is what helps or hurts your fuel economy. You want more torque where you are cruising.. high VE at low RPM/TPS means the engine has to do less work to maintain speed. That means less fuel is required in case I have to spell it out.

There are several tables that determine whether or not VTEC is to be activated, and there is a window for switchover.

You can do 70mph and not have VTEC activate by default. It is not directly RPM based.

But what do I know, I only tune these things. :rolleyes:

I do motor builds, I don't "program". And that's why I'm here, to learn something I don't know. No need to be a douchebag about it. If your hobby is going into other people's threads on online forums, and act like a highschool teenager, I'm going to kindly ask you to just leave my topic, as I want to know the answer to the original question which is on the first post of the topic.

If when you said "logic" about vtec you were referring to the ECU programming dedicated to the vtec function, then you could had specified it. I cannot read minds, less through a forum. Both are "logical" statements; one is mechanical and the other is digital/electric. (By the way, some ECU's like AEM V2 standalone don't use the vtec solenoid).

Since you don't know a simple math expression, let me explain it to you elementary style. Suppose you have a 12 inch piece of thread. You're going to fold that thread in three equal sizes. How long is your thread now? The answer is 4". So, if I was getting 30 mpg, "3fold" would be 10mpg.

On the Honda Fit, the vtec-E is not like regular vtec on dohc engines or regular vtec on the sohc D series engine, which activates at the same programmed rpm regardless of the throttle position. It's programmed to react to how you push the gas pedal, but of course within a certain range of 2800-3500rpm. Now, I have tested this myself with a "vtec light" on the Fit; on 5th gear, my gd3 vtec is always on after 2800rpm regardless of throttle position (Don't know if this is supposed to be like this, or there is something wrong with my ecu).

I know that the amount of torque (and horsepower) produced by X amount of fuel is what determines your mpg mostly (that and other factors like gear ratio and weight, etc.), but when vtec is on, the engine will want more fuel so the oem ecu programming says: "Hey, fuel injectors, you need to send in more fuel because an extra intake valve is opening per cylinder plus they are opening further in and that opening now last longer (lift/duration)", and that's whats killing my mpg after 55mph.

Last but not least, this will be the end of the vtec side stuff bs this has turned into. I'm pretty sure you want to quote me again and discuss your vast vtec and tunning knowledge, but I'm not interested in going at it anymore.

The question still remains: Can I increase the vtec-e changeover safely to the 3500-4000rpm range safely on my L15a with Hondata Flashpro?

I checked almost everything, so the last thing I did was put on a "vtec light", and, indeed, vtec is coming on at 2800rpms on 5th gear every time for some reason regardless of throttle position. :-\

Food for thought:
Attachment 21504

These are some of the metrics the ECU uses to activate VTEC.. you'll notice it is partly load dependent, as evidenced by the table I have up in this cal from a client of mine.

I very much doubt you are hitting VTEC and suddenly moving so much more air mass that your fuel consumption goes from 30mpg to 10 mpg, which is why I made it a point to highlight that phrasing.

VTEC is not the problem here. It is likely a combination of the environment/commute and the driver. Your mods have a part in this too.

There is likely nothing wrong mechanically or electronically.

You can argue that one till you are blue in the face for all I care however. Go get a scangauge if you aren't up to taking the plunge on FlashPro.. and frankly I think that is a good thing as Spunkster/Hondata and the other mods on their customer service forum probably wouldn't want to deal with a google university know-it-all, we don't really need you as an ambassador for our community there anyways.

There are only two threads in the Fit section from other users so you'll stand out for sure.

so would it be safe to say that 2 1/4" piping could be a culprit here? I mean he, from what I read, doesn't have any forced induction warranting the increase in diameter? aka, not enough back pressure?

Lowered exhaust velocity isn't helping him, certainly.

Combined with the W-R intake manifold a generic short ram, mediocre fuel, non flat terrain, or any number of external factors and you find your fuel economy taking a noticeable hit.

How many miles on the car, oil type, fuel grade, ethanol content, spark plug condition, valve lash, tire pressure, wheel bearing condition, alignment, transmission health, actual driver habits.. list goes on and on lol

Please stop reporting dms as abusive.although his delivery meyhod isn't always that of a prince, he has answered yoir question quite thoroughly.

Yes I can be a dick..
http://i.qkme.me/3qqn1s.jpg

But I won't lie to you and it's pretty much always a straight answer.

Isn't that what I've been saying? the MAP reading is changed as the TP changes, but this is only on the newer Hondas. Older hondas, like my 01 s2000, vtec always kicks in @6000rpm with oem ecu settings regardless of TP. You can change this to work like newer hondas by getting a 3-4 bar map sensor and programmable standalone (that's the ap1 case at least)

I did some logging today at a local dyno; apparently the previous owner of my gd3 had the lower boundary @ 2200 and the upper boundary @ 2800, but the fact that you're ignoring that I've been yelling "HEY MY VTEC IS KICKING IN @ 2800 RPM, I EVEN USED A VTEC LIGHT TO TEST IT" has been the biggest setback of this discussion. You're not here, so saying straight out "NO, YOUR VTEC DOESN'T COME ON @2800rpm. NO *PUT BLINDFOLD AND EARPLUGS ON* I CAN'T HEAR YOU NANANANANA. THIS HAS LOGICS!". I mean come on, that's just like when religious fanatics unite to discuss their beliefs.

Apparently I'm a "google university know-it-all"; funny, I am not the one on some guy's topic telling him what's wrong with his car (without even driving or testing the car). Right.

Now, that the argument is over... This issue had been going on before the mods, when everything was stock. I just decided to address this now since this is my residency year and I'm going to be traveling a lot.

As for the oil, I'm using full synthetic mobil 1, the car is on 70k miles, 93 octane fuel (Not sure about the ethanol content on gas in my country. I don't use ethanol additives regularly though), 2k miles iridium sparks, 31 psi tire pressure, valve clearance should be stock or close to stock (I bought this recently and I have never messed with the cylinder head), wheel bearings are perfect, car was aligned last month, transmission sounds and feels good (I did an oil change and put amsoil syncromesh on it two months ago), and my driving habits on this car are ok.

Again, I will repeat what happens: I cruise at 55mph @2600rpm, I get 30+ mpg; I cruise at 60mph @2800+ rpm (vtec kicks in; vtec light comes on and car gets louder), I get around 10mpg.
I have scheduled to fix this on Friday, now, I want to know if it's safe to increase the changeover to a lower boundary of 3200rpm and a higher of maybe 4000rpm without being in risk of valve/piston contact on changeover at the higher rpm range. I'm not asking if this is going to kill my air/fuel mix. the ecu will be tuned to get the best out of it while increasing the changeover.

I hope this last post can end the needless side discussions.

~KiRa