Jump to content

NA VCT timing -tuning suggestions please

Recommended Posts

Hi Everyone,

I've been mucking around with pcmtec for a little while now and I've been really pleased with the results.

I started by getting injectors right (turns out that aftermarket ones aren't actually the same as stock ones) by changing the injector slopes to match actual. 

Then new extractors and the associated changing of the AUF0061 values using LTFT data logging. Somewhere around the middle of this process the intake manifold gasket failed without me noticing - fixed that - LTFT stays within 2% between petrol fills. Very happy.

Love driving this car.


Now to the question....

Lately I was watching a Haltec video about tuning the VCT in a Nissan "something or another" in which they have a two stage Cam solinoid and they showed how to get the most out of that situation (trigger it after 5000rpm) and get more area under the torque curve. At the end of the video they suggested that there was even more to be gained from VCT in our Barras. Ok great, how do we do that!?

I've had a look for any info on the forums and I haven't  found much on the topic. Someone suggested there was possible power from a few degrees change -which way? The only thing that I have found is a note that Roland made in 2021 to someone who had done a barra swap into their land cruiser who was saying that torque was low - Roland suggested adjusting 

 "the VCT intake timing and set it up as per the full throttle timing at part throttle, this will remove the pseudo EGR (exhaust gas re circulation) that Ford use to dilute the intake charge. You'll make sightly more torque but you'll find that it definitely uses more fuel at cruise."

So now looking at this table has only left me with more questions. Is the highest load scale really the best timing for the cam? Or has ford limited the power output to save the engine? Can I just leave the settings below the first 3 rows and copy the top down over what is left? How can I test the outcome I only have the roadDYNO. I'm very interested in your ideas.

Link to comment
Share on other sites

Changing it at low load is a waste of fuel imo. You want your car to use frig all fuel when tootling around but when you floor it you don't care. FYI you'll use about 20% more fuel for no gain if you change it in the low load areas.

When you log it, you can see what load numbers it uses through the rpm range and at various throttle positions. It'll be along the 0.9 and 1.0 lines mostly at WOT. While you're logging, see what it is at 100kph cruise. It'll be around 0.4 load mostly. Even 50% tps will have around 0.8 load.

Have a look at the most aggressive part of the WOT cam timing. It's easy to spot cos instead of positive numbers, it'll have negative numbers up to about 3000rpm or whatever. Copy this entire row and paste it to 0.8 load, up to the highest load point. Using this very simple method you'll have the extra acceleration that advancing the cam timing provides, while still keeping stock fuel economy at cruise. As far as testing the outcome you either put it on a real dyno or use virtual dyno. You'll feel it anyway, it makes quite a considerable difference to how the car drives.

Something to keep in mind is this raises cylinder pressure at lower rpm so will tolerate less ign timing, but this isn't an issue when the knock sensors are switched on. Needless to say you have to run your car on 98 to realize power gains, anything less will have the knock sensors pulling timing non stop.

  • Like 3
Link to comment
Share on other sites

What Puff said. In an NA you'll be able to safely do draggy pulls in 2nd gear to test the power difference as well, just need to find somewhere safe and flat. On a turbo car even in stock turbo form you quickly need a dyno to do this safely and repeatably.

  • Like 1
Link to comment
Share on other sites

So I had a look at one of my latest data logs


and here is my intake VCT table


So it seems like load when I'm normally driving doesn't get above 0.6. Above that clearly I can paste the 0.9 row. Or perhaps just adjust the 0.7 row by splitting the difference between the 0.6 and 0.9 rows. It's interesting that they didn't bother with a 0.8 row. There is quite a ramp up between the 0.7 and 0.9 rows. I will try this one out today and report back soon. 


Cheers for the help Roland and Puffwagon.

  • Like 1
Link to comment
Share on other sites

Are you logging the correct load? Those units looks incorrect. Can you see if there is another load parameter you can log? 

What edition of the software (pro?) and which osid are you using? I will get it checked to see if there is an error on our end, the units should show 0-1.0 not 1,000.

Link to comment
Share on other sites

5 hours ago, adhdesigns said:

It's interesting that they didn't bother with a 0.8 row.

Yeah I was thinking about a different table axis when I said that. Either do what you've done or copy the 0.9 row to the 0.7 row.

Link to comment
Share on other sites

Like Puffwagon said I was logging rpm against throttle position. The throttle position axis for some strange reason labeled itself "Load". Anyway it let me see where and how often I see the high loads and hopefully I don't throw away my fuel economy. We will see. I took it for a run today. No complaints and I'm pleased with what I noticed.

Need to drive it some more.

Cheers folks

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Unfortunately, your content contains terms that we do not allow. Please edit your content to remove the highlighted words below.
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...