jun11

First, I'd like to say that I'm happy with my tune and this question is for informational purposes only. I'm tuning my car for track use on my own with rented dyno time so I can learn.

My understanding (and the way I've tuned) is to find the cross point between torque curves on the low/high cams. That puts my car right at 5900. I found it interesting that the Spoon ECU actually uses the same engagement point.

Here is my question:
How are people tuning the AP1 for lower VTEC engagement? Every attempt at timing/fuel brings my torque curve intersection to 5800-5900. However, I've seen people claim to have a 4000-4500 engagement point in the AP1.

Current setup:
Stock intake with Mugen filter
Spoon TB
Fujitsubo header
Gernby Exhaust

flanders

With those mods you will probably gain 20-30hp with a VTEC at around 4000rpm instead of the stock engagement point.
Do you have an aftermarket ecu or what are you using to tune?

jun11

I'm using KPro4...

I'll admit that I tried to lower it to 4100 for a few runs, but it was either too rich or too lean no matter what I did. I was going to try to pull timing on the high cam, but I ended up leaving it. That's what sparked the question. I wasn't sure what kind of timing should be used for the transition. The timing was jumping from about 27° on the low cam to 30° on the high cam and it would just fall on it's face until about 6k. AFR was between 12 and 12.5. I tried richen it up to 11.5, but that didn't help much.
Some more info... I'm at 5280ft. so I had to scale my load tables down since my MAP never goes above 80 kpa.

zeroptzero

almost all cars with lowered vtec points that low had a test pipe, that was the one mod that allowed the change to work properly.

jun11

The Gernby exhaust is the design Urge uses for their exhaust... Test pipe isn't needed.

flanders

12.5 AFR is good, don't go lower than that, wouldn't mess to much with the timing unless on a dyno.
Are you sure you are loosing power when you lower the VTEC, have you tried using virtual dyno to compare your logs?

jun11

I've been renting dyno time while I learn all of this. What I was trying to figure out is the relation of ignition timing on the low cam vs the high cam during transition.

Logs, and even watching the speedometer, show the flatlining. I'm not new to tuning but I am new to tuning VTEC. I understand that more timing earlier will produce more power on the high cam, but I'm wondering about the step from the low cam. I'll build two new timing tables with advance rising earlier.

flanders

The Hondata included tune for the 06+ model has VTEC at 3900rpm, I would use that as a base and then try to smooth out the fuel tables.

jun11

Last night, after my last post, I decided create a timing map based on a 4300 engagement point. I used my knowledge of ignition tuning and tried not to let the high cam get in the way of my thought process (my brain gets hung up on the crossover)...
Anyway, I put it side by side with the tune you mentioned and I found some very interesting similarities/differences....

Here are the low speed graphs starting with mine. I based my table off of a theoretical 4300 engagement point whereas the Hondata tune used a 3900 as you mentioned. We are both engaging at about 27° advance.

AP1 w/ 4300 engagement low speed

AP2 w/ 3900 engagement low speed

Now the highspeed... The AP2 tune jumps up almost 7° of advance whereas mine only increased by 0.5°.


AP1 w/ 4300 engagement high speed

AP2 w/ 3900 engagement high speed

Also interesting... My tune climbs in advance after the change and the AP2 tune starts dropping almost immediately. I'm going to log both, but I'm going to hypothesize that the AP2 can handle the 7° jump because of the volumetric difference.