Vtec modifications?

Does anyone know if it is possible to lower the point at which the vtec kicks in. I have a 2003 VFR am looking in to power commanders and other power boosters, but if it was possible to make the vtec start up at around 3,000 rpm that would be the answer for me.

 

There are a few threads on here about how to switch it on all of the time. A few have experimented with it. There is also an aftermarket product from the UK that will slet you electronically do this as well. I don't remember if it is an ECU or just an in-line box like the PC is nor do I remember the name of it. I know that it wasn't cheap though, thats for certain.

Perhaps maybe just doing the usual airbox mods and a proper tuning on the dyno might take care of what you are wanting. The purpose of VTEC is to keep the velocity of the air coming in at a higher rate and theoretically giving you better power and torque on the low end. With proper dyno tuning, most report that the feel of the VTEC transition is eliminated and the dyno sheets show improved HP and torque curves.

Add in an aftermarket exhaust and headers without a catalytic converter (98-99 headers, dekelvic, or motad) and you start getting some gains that are noticible, especially on the low end. There are a lot of people between here and VFRD that have done just about everything to the VFR. Without getting inside the motor, there simply isn't much that you can do to get more power out of it. Adding 10HP is doable but if you are wanting 15HP or more it is fairly safe to say that you are being overly optimistic.

From the way you ask your question, it would seem as if you are seeking more in the low end, especially for a bit more torque and to get rid of some of the flat spots that are there before VTEC kicks in. De-pairing de-flappering, and de-snorkeling should help a little bit and the PC with a tune should take care of the flat spots and give it a few more ponies. The headers and cans will take care of the rest.

 

I would personally recommend doing the PCV and a dyno with exhaust and gearing. However, if everything about the VTEC is alright and you're simply looking to get it to engage earlier, you can sort of do that without getting too complex or expensive. If you just do the gearing it will basically trick the VTEC by getting the RPM's spun up faster. It will still read the same on the tach but at that point the tach, for all intents and purposes, will no longer be an accurate indicator. I would start with doing a -1 front sprocket ( about $20 ) and if that isn't enough than add two teeth to the rear sprocket as well ( $50-$100 ). If you do both the -1 and +2, you may or may not need a new chain. This will get you the low end you desire but will cost you some top-speed and tach range. Above and beyond earlier VTEC engagement, it will also move torque down low, adding more acceleration low, even when VTEC is not operating. Which in turn smooths out the VTEC transition. You'll never get it to hit as low as 3000 RPM but depending on how much you gear down, you could essentially get it to hit at what would have been around 4800 RPM give or take.

That's a little less technical than what the procedure actually accomplishes, but you get the idea.

 

Find some slipons you like the sound of, add 300 ohm resisters as O2 eliminators, Get a PC3 or PC5 with a custom tune and call it a day powerwise. The extra few HP you can get out of this motor over that will cost you big bucks. Better to spend the money in the suspension on this bike to make it faster.

 

If you want the vtech kick in at 3000 RPM............You will not able to ride on high way or long distance. You will kill the motor If it for track day...........carry on

 

Start by just doing everything one gear lower than you do now.

 

Bob has got a good point. While I wouldn't run around at high RPM in first gear, as long as you're not at perminant redline, you can certainly hold higher RPM ( above VTEC ) in mid-gears without hurting the bike at all. I know it may sound abusive but when you think about it, running at 7200 on a 11,700 redline is like running at 3000 with a 5500 redline. While canyoning, I rarely let the bike drop below VTEC and I've got 14,000 miles in two years, without a single mechanical problem.

 

they only cut the vtech out at low rpms to save fuel and provide better response at the bottom end. There is no reason to not keep it at 7k save for the amount of fuel you use.
How agressive do you need to be? trying to use your vfr to match/out match bussa's is pointless, but if your tracking it then you can use a resistor network on the tach line to give the vtech plunger the power to go into vtech mode, it only needs 7v.(i tested on mine as i want to make it come in around 7500rpm instead of 6800.

 

If you look at the stock dyno runs for both a pre V-tec and a V-tec engine you will see a gain in torque in lower RPM's.
In time you will adjust your riding style to fit the engines power delivery.
The only company I know of that sell a product that will change the V-tec is posted below, but your not gonna get 3,000 RPM's

RTD Ltd - Products - EMX-01