For variable chip timing, what's best boost or temp sensing?

[BJM]

Jay Carter has a variable timing chip using a boost harness. If you run a translator, you can now mount the ATS in the up pipe.

If you pull timing as boost rises you can raise timing in the main timing table. The instant boost rises, the ECM will pull timing.

If you use the ATS there is a delay before the temperature rises while the IC initially soaks up heat. By pulling timing with temperature, the higher timing would stay in longer by pulling timing only in response to turbo inefficiency, not just boost.

Has anyone compared the 2 methods? I was planning on moving the ATS but if one way was obviously better than the other I would do what works best.

 

[BoostKillsStres]

IMHO you need to pull timing in relation to boost as you only have so much octane to support a certain boost level. By the time the temp rises enough to warrant pulling timing your going to be needing headgaskets if you've been at full timing up to that point.

Just as an example with a stock IC in some testing data I've seen, it takes about 14 sec at WOT for the plenum temp to rise 30 degrees. And there was no temp rise in the first 8 seconds, so it all happened in the lat 6 seconds. There's no way you can run the car at full timing for 8 sec at full boost.
HTH

 

[BJM]

What you are saying then is the sensitivity to boost is much greater than to intake temps.

Taking bruce's advice I downloaded SAE paper 960497 and in summary they relate effects to how much octane number (ON)needs to change versus various parameters.

For intake temperature it varies by 1 ON / 7 deg C

For intake pressure it varies by 3-4 ON / 1.5 psi.

This seems to support the need to pull timing with boost.

For those guys who like higher compression engines the figure is 5 ON / CR

An interesting one for me is the relationship to exhaust back pressure of about 1 ON / 4.5 psi.

Has anyone ever measured the pressure across a catalytic converter?

 

[BoostKillsStres]

Yepper...I'd certainly pull timing with boost. People that have run the vari timing chip have seemed to like it. Pressure across the cat what cat

I just wish the stock ecm/sensors had another sensor we could steal/convert so I could run a variable timing setup and still be able to log my wideband o2 into DS which I'm currently doing with the boost sensing harness into the mat/ats line.. then I could really have some chip tuning fun....

 

[jastrckl]

talk to bob bailey about adding an A/D channel to the ecm. a little spendy but it's what lets ME-R guys run the map into the ECM. you could probably use it to log your wb instead.