You re totally changing the engine, it's fuel and ignition maps will need to be changed too.

Buy a custom chip, it will get the car started, then run it it on a dyno to get a fuel/air ratio curve, send that back and you get a chip tailored to the car as it sits. Some guys have had to repeat to get perfection.

Or go the Motec route, where all the tweeking is done on the dyno and then finalized by driving.

 

Have Steve Wong do a custom chip for you. You can be with him while the car is on the Dyno.

 

The problem with Motec is knock sensing. They have a knock sensor box available but programming it is a bit of a nightmare.

My reasoning is that Porsche built the early X51 engines with RS cams + 3.8 liters and used the stock DME. My engine is not that much different than that. Schrick cams just have a touch more lift and modest changes in duration (mostly later exhaust valve closure) on a 114 deg. lobe center.

 

But with the extra compression you have from the new P&C's timing will be critical.

There are other options other than Motec. I have a ViPec in my car with full knock control without any add-on system. Works perfectly.

 

The problem is without an engine dyno and cylinder pressure monitoring you can't come up with a map plotting load (throttle angle), RPM and advance to get a complex set of curves like the one below. A chassis dyno won't cut it except maybe for mixture trim.



This is what an old time mechanical advance curve looked like, the best one could hope for without cylinder pressure monitoring

 

Most of the guys that do any custom tuning are using the base map as the starting point, so the map will look something like you Motronic curve.

As for load, Throttle in our cars is used for WOT timing changes as well as idle speed control. The majority of the load figures comes from the MAF.

While the best way to tune any engine is on an engine dyno with cylinder pressure, exhaust temperature and in our case head temperature. It is possible to get a very good tune from a chassis dyno. My car was tuned on a chassis dyno and fine tuned on the road, i am using MAP and Throtttle position instead of MAF and TP. My car idles perfectly and dead steady, is supper smooth throughout the rev range, has no tip-in lag. Overall I would say it drives much better than stock. (Well before the engine rebuild )

 

i'm having dinner this evening w/ a friend that did sort of what you are doing, stock 993 '95 3.6 bottom end, Steve Weiner did the heads w/ RS valves & RS cams.

Steve Wong chip, I think that he is on the 3rd one, but am not sure could still be the second. I'll see if he cares to comment.

I know that I'm very pleased w/ both of mine, I bought the custom chip for the 3.8RS vram but Steve had it nailed right out of the box so I never had it redone.


I also have an older version w/ a much higher rev limit, it also runs like stink but I never felt comfortable about engine life expectancy at raised rev limits w/o a completely beefed up bottom end, I just replaced the stock rod bolts w/ Arp.

 

Trophy: Interesting on the throttle position in relation to MAF for load values. I can't change as much as you can in Canada.

Bill: Liquor your friend up until he cares to comment.