"I don't thnk there is as much difference in the attitude of people on this board as you think...when comparing the damaging effects of:
- too high compression with single plugs, and
- running chips with more aggressive timing and fuel delivery maps."
- Wil Ferch -
The opposite is really the case if you thoroughly read and understand the well
written posts on the above linked thread. Those posts indicate a very conservative
view when changing the compression ratio which is not the case for those
considering the use of a performance chip. The other thread on a CR change
raises concern about even a very minor CR change.
Just like the uncertainties with the use higher CRs, there're uncertainties
with performance chips, but these seem to get ignored because many promote
them or haven't noticed issues, e.g. sub-audible pinging. It's kinda like the blind
following the blind when it comes to performance chips.
Obviously there're many who have concern about the issues I raise or you
wouldn't see the slams/attacks & hostility toward my posts on performance
chips, with few or any intelligent comments/responses (yours). The usual
post you'll see is; "My engine hasn't blown-up." or "Where's the data to
indicate there's a perfromance chip problem?". You don't see this challenge
on the use of a higher CR, even though the issues are very similar.
Yes, as you say, some performance chips are less aggressive than others,
but they all take the ignition advance maps into a higher risk area as my data
(
www.systemsc.com/tests.htm ) indicate, to achieve a noticeable responsiveness.
There was a reason Porsche set the CRs and the timing maps to what
they determined to be the max in the '88 & '89 3.2. Additional performance
required Porsche to use twin plugs and a DSP knock sensing system (a special
microcontroller that operates in parallel to the fuel/ignition microcontroller)
in the 964 & 993 to allow higher ignition advance maps.
No chip supplier has the resources to properly test and evaluate a performance
chip supplied as Porsche can. The same applies to using higher CRs. Most/all chip
suppliers just test/program the chips by driving a test vehicle on the street.
In reading the CR thread, one should get an idea of the proper methodolgy for
proper testing and evaluation, whether it's a performance chip or a higher CR.
"The factory did the same thing in their various chip offering up to and including the "cup" chip."
- Wil Ferch -
Porsche did NOT change the timing maps in the Club Sport DME unit from the stock
'88/'89 DME, only the rev limit (>~300 RPM). So, here for racing Porsche could
have "pushed" the timing maps, but they didn't. Thus, one should consider all
performance chip timing maps as beyond what Porsche considered appropriate.
Noteable quotes from here:
http://forums.pelicanparts.com/showthread.php?threadid=260251
"The vast majority of chips that have triggered serious engine damage over the past 15 years seemed to have been sourced from folks who didn't understand & grasp that the West Coast has totally different gasolines from the East Coast and never tested their products with 91 and 92 octane fuels"
- Steve Weiner -
"Engine parameters also affect octane requirements. Excessive deck height promotes detonation as does incorrect spark plug heat range, aggressive ignition mapping, and lean fuel mixtures in these hemispherical, lazy (low swirl) combustion chambers. Everything must be right to PREVENT detonation from low RPM to redline and at all throttle positions.
Hopefully, the reason for Porsche's decision to incorporate active knock-sensing into the last generation of air-cooled engines is clearer,.....one cannot always control the above variables well enough to prevent serious internal engine damage. This is why one must be more conservative when building and operating a high-compression 911 motor without adaptive knock-sensing."
- Steve Weiner -
"Quite obviously, this is something that is very difficult to quantify so unless one performs annual borescope inspections, one cannot really know anything aside from load-type dyno testing and doing plug cuts. IMHO, this latter methodology is a "Kentucky Windage" approach and not recommended. Its unfortunate that the pre-3.6's do not have knock-sensors and thus the ability to "eavesdrop" and listen to knock-sensor activity like one can do with the 3.6's using various scan tools & Engine Management."
- Steve Weiner -