Forum » Practical Dyno Tuning » Variable Timing Cam Tuning

Variable Timing Cam Tuning

Practical Dyno Tuning

Discussion and questions related to the course Practical Dyno Tuning


Page 1
Author
994 Views

It has been a great learning experience for me since I've registered as a member. I'm interested to know what would be your choice or way of tuning the Variable Timing Cam for a K20A engine. I'm using Hondata Flashpro and am wondering how should I apply what I've learned here to tune the cam angle tables. As a thought process, this is what I came up with:

VTEC point set to 7k rpm, all dyno runs up till 6k rpm.

1. Steady state tuning for the low cam fuel and ignition tables (0, 15, 30, 40, 50 deg tabs).

2. Perform full power tune for the 0, 15, 30, 40, 50 deg tabs.

3. Fill in low cam table based on the results of the full power runs of the 5 low cam fuel and ignition tables.

4. Perform full power tune for all 5 tables with the newly input low cam values.

At this point, I have no idea how to tune the high cam maps. VTEC point set to 3k rpm and all dyno runs up till redline 8.6k rpm

1. Steady state tuning for high cam fuel and ignition tables (the rows under 4500, 5000, 5500 rpm). My target VTEC point is 5000-5100rpm.

2. Perform full power tune for the 0, 15, 30, 40, 50 deg tabs.

3. Fill in highcam table based on the results of the full power runs of the 5 low cam fuel and ignition tables.

4. Perform full power tune for all 5 tables with the newly input highcam values.

Find the crossing point of the best low and high cam torque curves (with all the cam angles dialed in). The point would be set for the VTEC to be activated.

I would like to hear your opinion(s) on this one.

Thank you all.

The WOT tuning of the Honda iVTEC system is actually quite simple. The way I approach the tuning is to start by getting the vtec changeover approximately correct by doing a run with the vtec changeover set to 3000 and a second run with it set to 7000. Set the vtec point where the two dyno runs intersect - Don't worry for now because you can revisit this later.

Now set all your cam maps to 0, 10, 20, 30, 40 and 50 deg and perform runs on the dyno. This will require you to spend some time in each cam map getting the fuel and ignition optimised too. Once you have 6 optimised runs on the dyno you can choose the best cam angle at each rpm point to build up a composite cam timing map - Basically choose the cam angle at each point in the rpm range that resulted in peak power/torque. It's likely that you'll see a trend where for example the engine never wants the cam timing to be 50 degrees in which case you can ignore that angle.

Once you have a composite map complete you can do a full run and ensure it does in fact give you maximum power. Often I tend to smooth the cam target values a little from the theoretical best values so that the cam control has a smooth target to track that it can actually achieve. If you try jumping 20-30 degrees in 500 rpm then the cam may not be able to keep up.

With this complete I now optimise the vtec point. Try moving it up and down in 200-500 rpm increments. You'll normally find that your initial point is going to be very close. WOT job done, but unfortunately the part throttle is a little harder to optimise. Simply copying the WOT cam angle all the way down the load axis of the map isn't going to be ideal as you generally find the engine will want less advance at cruise and 3000 rpm than it does at WOT at the same rpm.

You have two options here - You can spend the next week on the dyno optimising the cam control target at every zone in the table (close to impossible) or you can retain the part throttle cam timing map from a base file and modify it in the areas you're actually going to use the engine. What I tend to do is start with one of the base cam timing maps, perform the WOT tuning I've just described, and then smooth the cam targets from what I found was perfect at WOT down into the lower load areas of the map. This is to ensure I don't have any erratic cam timing targets and the cam target map is smooth and sensible. From there I'll spend some time in the areas the engine cruises at and find the optimal cam timing in these areas. This gives you a 95% result and the other areas of the cam timing map are generally just transitioned through and hence are less critical on engine operation.

Hi Andre, thank you for sharing your thoughts on this. Yes, I think the WOT runs will be pretty straight forward. The tricky part is the cam angle target maps in the load areas lesser than WOT. I'm going to try optimizing the individual fuel & ignition maps for each angle first and then work on the low and cruise areas of the cam angle target map by using the steady state tuning techniques. By holding the engine in a certain cell of interest, I shall change the angle and see how it affects the torque reading on the dyno. Of course, while doing this, the engine will be switching between the already optimized fuel & ignition maps for each angle. Will see how this goes.

Thanks a bunch Andre!