After abit of knowledge really.......

What are the benefits of having the Vtec point lowered in an FI applications?

Better flow? More HP?, More driverable? Easier to drive?

What is the new optium point for Vtec to engage? Is there a general rule that at a given PSI the point should be lowered?

All information welcome!

 

I feel the principle is fairly similar whether NA or FI... lowering the VTEC point creates a more linear power curve with a much more usable mid-range. Look at the typical baseline dyno graph with stock VTEC engagement. There is a noticeable spike in power when VTEC engages (you feel it while driving too). Instead of having that spike of power, you can lower the VTEC point down and create a more gradual sloping power curve.

This is a graph from my S back when it was NA.



The pink line is a bone-stock baseline pull. Note the spike in the power and torque curves starting right around 6,250 RPM. This is the stock VTEC engagement point. The blue line is an un-tuned pull with STR bolt-ons (I/H/E). Note that the jump in the power and torque curve is far more pronounced at this point. It feels like a kick in the pants on the street (relative, nothing compared to building boost /> ), noticeable difference in power when VTEC activates.

Now the red line is a "tuned" pull with the same STR mods. The VTEC engagement point was lowered to 5,000 RPM (still higher than most people run). See how the power curve is far more linear in the mid-range, eliminating that jump from before. All that area between the blue and red lines from 5,500 to 6,750 RPM is usable power gained. Its a solid 17 HP in places just from lowering VTEC.

On top of the power gain, the car feels linear and predictable... when autocrossing that power jump from entering an un-tuned VTEC could really screw you up if it occurred while the car was in an upset condition. With a predictable and linear power curve it makes the car easier to handle and prevents you from having to correct from a sudden surge of power.

This may all be information you already knew. I don't know that there is a given magic number for VTEC engagement. I have seen people going as low as the 3,000's. I kept it at 5,000 when I was in STR trim because my tuning options were limited. If I had AEM or Hondata capability, I would probably go somewhere between 4,000-4,500. But all these changes should be made while on a dyno followed by a test pull, then tuning corrections, then a final pull to verify that your A/F curve is safe and the car is putting out power like it should.

Also remember where your car idles at highway speeds. If your VTEC is set low, and your throttle position limit is set low, you may be in VTEC on the highway!!! I had a few issues with my throttle position limit being set too low and the car trying to flip into VTEC when I didn't want it to. Its as easy as raising the limit up a few percent, but just something to watch out for.

As for other people's experience on VTEC engagement point when running an FI setup, I am all ears. Some good info can come from this thread!

 

wait until Vtec hit in the corner and your are running at 6200 and think you can give a little more gas and surprise Vtec clicks at 6500.
I've lowered it to 5000 much more predictable.

 

Giles, a well well known tuner who spends countless hours on each s2000 here in New England seems to set it at 4000rpm and told me after countless hours/days/years it has proven to give you a much better mid-range. I still hear the switch over and feel better driving it like that. I really wouldn't want that VTEC kick at 6200rpm with boost. Not sure how much id like that lol.

 

Tubular manifolds like vtec set around 4k and log manifolds like vtec between 5-7k.

 

THIS


there is no "sweet spot"


Your tuner will set this based on real world data, and how your car/setup reacts to changes.

The setup will dictate where this needs to be. Not this thread.

 

Each engine is unique and requires the tuner to determine the sweet spot.

 

and CT/VT/KW/SOT SC likes 4kish. these are all just starting points. dyno tune will dictate best spot.

 

Thanks for all the information so far.

I'm currently running a Comptech SC Aftercooled @14psi, AEM ecu, ID1000 etc... my tuner has set the Vtec at around 5-5.5k and I wanted to obtain as much information so I can understand why it's been set at this value.

I've read as others have mentioned that they can be set as low as 3K when supercharged, so I want to have the best possible understanding before I question it, so I don't look like a dumb ass

 

I want to say mines set between 5-6k also. Running a Comptech SC at 15psi. I just let Jeff Evans do his thing.