Smoother Vtec Transition

[fixy]

Hello. I have a comfused situation. I made a few modifications on my 2002vfr, to gain more power and smoother vtec transition. What is the power gain I don't know, I did't yet go to dyno center. But the vtec transition isn't smoother. it is much harder then before. how could i fix this problem.

my modifications:

- leovince slipons

- removed CAT and O2 sensor(installed 330ohm resistors)

- K&N air filter

- removed snorkl, larger intake hole on the airbox

- power commander 3 usb with this map(http://www.vfrdiscussion.com/forum/index.php/topic/31520-04-vfr-dynotuned-results-1093hp-592tq/)

Thanks for the answers

[CandyRedRC46]

i would just try a few more 2002-2005 maps. none of them will be perfect until you get your own made. just try them all until you find one that is a little better. but really you need to make your own if you want it to be perfect.

[VFRBert]

Synchronize the starter valves.

Instead of synchronizing the carbs on early models, you have to synchronize the startervalves.

http://www.vfrdiscussion.com/forum/index.php/topic/33-starter-valve-syncronization-vtec/

[Cogswell]

From your post it's not entirely clear if you're referring to low(er) RPM stumbling / surging which is quite common, or the transition to 4 valves / cylinder operation (VTEC transition) that occurs at 6,800 RPM on your 2002. If it's the surging issue, you have done the right things and as suggested, just need to experiment with the fuel maps in your Power Commander to get it where you want. If you are referring to VTEC when it engages at 6,800 rpm, I don't believe there is any way to change that. As far as power gains go, save your dyno money. Power gains will be negligible, if any.

[fixy]

The problem is the transition on 6800rpm, when it goes to 4 valve. The thing is that when this transition starts, the feeling is like in a certain moment (1/1000 of a second) the power drops from 100% to 50%, in the next moment the power is 200%. It is quite annoying, cause no matter what the throttle position it does that, and it is hard to drive, cause when accelerating from the corners, when I'm still leaned down when I', opening the throttle I must watch that I'm not in the vtec transition zone, below 5000rpm, or above 7500rpm.

I know that is the power gain in a moment, but when I drove my friends vfr his power gain is much smoother, but my friends bike has 25000km drives, my bike has 60.000km in its back.

It the procedure (http://www.vfrdiscus...onization-vtec/) the solution for my problem, or do I have to play with the maps. I'm asking, cause in the near future(few months) I will go to our tuning center with dyno run, and they will make my own costum map for PC3 and I want to fix the vtec transition, or I wont to know if I can do it when they will make my costum map.

Thank you for the answers.

Mitja

Slovenija

[VFRBert]

Synchronising the startervalves makes the transition much smoother, do this or have it done before the mapping of the pc3

[triharder]

I agree it doesn't make any sense but the starter valve sync smoothed mine out on a "07".

Its worth trying to see if it helps.

[CandyRedRC46]

A starter valve sync will only effect idle and very small throttle openings. If you understand what the starter valves do you will understand that they will not make a difference in say 25% or greater throttle openings. The starter valves sync should improve off idle throttle response though. If you find a competent dyno shop and they are familiar with vtec and how it operates, they will be able to fix your rough vtec transition.

[VFRBert]

On technical day's of the Dutch VFR forum, every time, 1 or more vtecs are synchronized, and the comment of the owner is always the same: The vtec transition is much smoother.

The synchronisation affects a much wider range of the trottle opening, than most people think. For a long time, Honda stated, that startervalve synchronisation was not nesecessary, they even didn't do that properly in the factory, but they were wrong. Some technicians of the Dutch forum, made a manual, wich was downloaded even by dealers, who couldn't get the info from Honda. Buy a Carbtune and do it yourself. Cheaper than spending a lot of money at a workshop. And when you follow the step by step manual, not difficult to do.

[Baileyrock]

I would venture to say it's a fueling issue at transition!

Mapping can/will make a Huge difference on how smooth or ruff the Vtec transition feels.

W/O dyno tuning using A/F ratio's your only choice is to just try as many maps as needed to find the one that best improves your transition.

There's many Great maps here in our download section, but you might need Euro maps instead of the one's we use here.

Good Luck!

BR

[CandyRedRC46]

^^^^^^this

End thread

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[fixy]

I will download a few maps, and try them and I will see.

[cookaboorra]

It's ok for me. Thank you so much for the intelligent, useful piece of advices.
One thing: ( and, if you agree, please consider me sligtly dumb... ) : owning a 2002 vtec.....a final word could be spent about the benefits of installing a 98 header, wether not a full 98 exhaust ? Please, inform me.....

Greetings from Mont Blanc

[CandyRedRC46]

Honestly I bought my bike stock. I put on a motad header and two brothers slip on,BMC filter, deflap'd and desnorkeked and had a custom pc3 dyno tune made. I didn't notice any real power gain. But it did drop a considerable amount of weight. Recently I found a two brothers full exhaust, port matched my throttle bodies to larger velocity stacks and traded my pc3 for a rapid bike 2 with ignition advance. Here I noticed a very big power gain and my trap speed has increased about 10 mph in the 1/4 mile.

[HondaVFR800]

At idle, the starter valves provide 100% of the air required by the motor to run. As soon as you open the throttle, the 4 throttle body plates begin to open, providing additional air, together with the starter valves. There is now overlap of the 2 air sources to the point where a fully opens throttle provides 99% (my guess to explain the point) and the starter valves provide the remainder. It may be a linear transition or it may be exponential (most likely) from one air provider to the other (anyone know for sure?) but the influence of the starter valves would diminish very quickly. I sort of recall some saying that from 4% throttle the starter valves have no bearing on running performance.

With the vtec transition occurring at 6800rpm (and most likely large throttle openings), i can not see the setting of the starter valves having any noticeable effect.

If you are messing :smile2: with the fuel delivery with a power commander and you are getting issues at vtec initiation, then you have got the fueling wrong at this point. I have a Dobeck TFI fitted to my 2011 vfr and the recommended Dobeck settings practically leaves the increase in fuel by the TFI at 6800rpm as negligible, not far off the stock Honda mapping. Maybe put the pc settings near stock above 5000rpm and see what it's like.

VFR's simply need their fueling sorted out from closed throttle to about 5000rpm. Beyond that, stock fueling is OK.

FYI, other than the Dobeck TFI (which is brilliantly simple and can be adjusted by seat of the pants trial on a ride), i have the PAIR valve lines blocked off where the pipes connect to the f&r reed valves (blocking only at the PAIR valve itself caused issues for my bike),the O2 sensors eliminated (as required by the TFI) and a Staintune slip-on exhausts. By my observations, the PAIR system actually dumps air back into the cylinders via the reed valves, leaning out the mixture. Block the PAIR valves and I had to increase the idle speed via the idle speed screw and adjust the fast idle wax valve to let more air in via the starter valves on cold start. The engine needed more air. Snorkel and flapper valve mods for me did nothing other than make more noise. If the air box is truly tuned, modding it for street use especially is likely to be detrimental as you loose the ram air effect at lower throttle openings. Only one cylinder at a time needs air from the air box and the snorkel cross-section adequately suffices, especially at low speeds.

My bike hauls ass from 3000rpm and has no flat spots anywhere within the rev range. Going through 6800rpm brings about a change in engine/exhaust note as the vtec kicks in but does not unsettle the bike in any way. The power is so good below vtec point that the power transition is linear.

With the TFI, on level ground i can ride at 60km/h @ 3000rpm with no drive-line snatch. Roundabouts are now not intimidating. The transition from closed to open throttle is now 95% perfect, as good as it's going to get with fuel injection.

The vtec is probably the thing i like least about the VFR. The aural pleasure below vtec is destroyed when the vtec kicks in and the racket starts. Fortunately, with the strong bottom end performance my engine has, unless i am really going for it, vtec rarely intervenes and spoils the fun. Short shift and let the torque do the work.

[cookaboorra]

Honestly I bought my bike stock. I put on a motad header and two brothers slip on,BMC filter, deflap'd and desnorkeked and had a custom pc3 dyno tune made. I didn't notice any real power gain. But it did drop a considerable amount of weight. Recently I found a two brothers full exhaust, port matched my throttle bodies to larger velocity stacks and traded my pc3 for a rapid bike 2 with ignition advance. Here I noticed a very big power gain and my trap speed has increased about 10 mph in the 1/4 mile.

rapid bike 2 with ignition advance... GOLD FOR ME !!! ( I also have a Daytona t595 and there is a freeware able to adjust the timing advance table... UNBELIEVABLE. IT PULLS LIKE A TRAIN.)

I have found that without the 02 sensors and without the PC3 the bike runs very well !!! I think it has sorta "no emission map" engaged with 02's turned off, because it behaves smoothly even with catless '98 bigger headers and leovinces..... and mileage has softened a lot.....