Tuning VVT -- Establishing a baseline

[Bruce Nunnally]

Tuning VVT — Establishing a Baseline

Posted on June 22, 2013by bwnunnally

Variable valve timing allows tuning of the camshaft timing across the RPM range. In my 2008 Cadillac STS-V, the DOHC engine allows individual tuning for exhaust and intake cams.

This graph shows today’s run delivered torque and calc hp vs supercharger boost and supercharger inlet vacuum in psi. It is provided as a baseline comparison for how the engine performed today.

Read More: http://caddyinfo.com/wordpress/tuning-vvt/

Finally, this graphic shows the VVT operation — the gold line is the intake cam position, and the green line is the exhaust cam position. Basically, in the pressure range the V is running, the intake cam is commanded to 20 degrees, while the exhaust cam goes from 5 degrees at low RPM to 2 degrees midrange to 4 degrees at high RPM.

In our previous experiment, I changed the exhaust cam to show a more expected pattern similar to lower pressure settings by adding 1 degree at 4800 and 2 degrees of cam position from 5200 on. We did not see a improvement or degradation, so it was reset it to OEM for this run.

It surprises me that the VVT cam position has so much waver to it. I am not sure if this is an effect of the variance in the boost, or if this is a cause of the variance in the boost.

[Cadillac Jim]

I think that we are seeing jitter in the control function that is below the level which would measurably affect performance.

[Bruce Nunnally]

As I was looking at my tuning posts from the STS-V and discussions I wondered why I had stopped testing & posting. I see that the Duke arrived in June 13 and so my car hobby time got diverted.

Hopefully now I can continue testing & mods of the STS-V and the XLR. Today I got a new laptop battery for my win98 laptop that I use only for hptuners/ car stuff, which should make it easier for test setup.

[Bruce Nunnally]

Update: http://caddyinfo.com/wordpress/quick-sts-v-tune-check-in/

[Bruce Nunnally]

http://caddyinfo.com/wordpress/hptuners-delivered-torque-virtual-dyno-sc-losses/

I have been quoting delivered HP values in recent articles, and these are quick and easy to ref. This is a PCM calculated value that converts air flow to torque using air/fuel ratio and spark advance.

In an article here http://caddyinfo.com/wordpress/wheel-hp-calcualted-hp-and-you/ I showed a comparison of calculated hp for my STS-V vs Virtual Dyno results.

In that analysis I found there were 26% losses from calc hp to virtual dyno. My current theory is that delivered hp does not account for supercharger losses, or the hp to turn the supercharger. Further, With est transmission losses at 20%, that analysis shows supercharger turning loss to be ~6%, or as accurately can be modelled as 40 hp.