Each car flows differently so its impossible to have a single tune that always results in the same AFR.
If you need 103's on a 3.4 setup to kill knock you're doing it wrong.
Each car flows differently so its impossible to have a single tune that always results in the same AFR.
If you need 103's on a 3.4 setup to kill knock you're doing it wrong.
It IS possible to lock in WOT AFR. The O.E. does this for each car they build. Also note that I said on average for the DHP PCM. Certainly as in your statement each car WOULD flow differently if a customer used a different cold air kit from the "Thrasher" and similar setups that DHP calibrated with back in the day. If a calibration is done properly, i.e. 1) Injector flow data properly established and the correct injector slope entered into the calibration and 2) The MAF table's transfer function corrected for any changes sensor selection, placement or air box design, etc. Then whatever is commanded for P.E. enrichment in the PCM should be constant. Normally .1 to .2 A/F ratio variance should be expected at wot on a factory setup from car to car. During part throttle conditions we need to correct to stoichiometry., (14.64 on gasoline approximately 14.17 is on E10), to provide the catalyst with the proper feed gases to ensure reduction of NOx and oxidize CO and HC. This bandwidth is very narrow meaning we cannot run 15.2:1 and expect a reduction in NOx nor can we assume that at 14.2:1 on non ethanol gasoline can we expect to oxidize all excess HC that is leaving the combustion chamber.
If you are doing your own tuning you need ensure you have entered the correct injector slope in the IFR table and then to force the PCM to run open loop at a fixed target A/F ratio and correct the MAF transfer function to a quality lab grade A/F sensor like a Horiba or a Lambda Pro., and then airflow changes in the engine will be correctly fueled unless you run out of MAF resolution.
I helped Greg Banish of Calibrated Success produce a GM calibration video on just this subject and he has kindly included some very valuable injector flow data for common injectors used in performance applications.
As far as the KR and Plug heat range issue is concerned I don't think on an non Intercooled 3800 that you can remove ENOUGH heat from the combustion chamber at WOT! The delta T, (blower outlet temp vs inlet temp) from the M90 is pretty extreme even at factory blower RPM's and air density and temps just get worse as we overspeed the blowers. On blown cars I like to run as cold of a plug as I can get away with that doesn't misfire during cold and idle conditions. Keep in mind that for a plug to properly remove heat from a combustion chamber it must also be tight! Loose plugs are dangerous! So you are not doing anything wrong trying to do all you can to remove excess heat from the combustion chamber because you have induced so much from the air inlet temp in the first place! However changes in plug heat range only affect a minute part of the process and are really only effective IMO to keep the plug itself from inducing preignition from creating electrode hotspots.
In tuning to be so far to the left of the "spark hook" with retarded timing is only throwing away horsepower and at some point can cause a rise in EGT with a negative effect there as well. The question remains do you really need 103's on a lightly modded 3800? The community has always said no, you are doing something wrong or something is wrong with your setup if you have that issue. I'm merely suggesting that this particular application is troublesome because it lacks an intercooler so removing excess heat from the plug tip will not hurt unless it causes misfire or incomplete combustion. It basically helps to remove a variable in the KR factor. Throw an efficient intercooler, a good cam and headers that scavenge real well and the plugs could now be too cold and misfire! The classic thinking on most 3800 forums is that you have "arrived" and now you NEED 103's because you can now run a 2.8" pulley cause you tossed all the heat back in with the pulley! So does the combustion chamber know that you have serious mods on top of it? Nope it pretty much sees that all that heat and prays for some induced EGR via camshaft overlap to help cool the combustion chamber! Does anyone ever dare to run a 3.4" pulley with serious mods? Nope, we all want 15 psi of boost no matter how crappy the air density is!
To get back on track for our person who asked the questions is by all means be sure to get some sort of a scan tool in place to see if you are getting KR under any conditions. If so after ensuring adequate octane, fuel pressure, and no exhaust restrictions and a healthy engine that's not huffing 50 octane oil into the combustion chamber, see if that KR is gone or reduced during cooler ambient temps and work towards reducing blower outlet temps however you can. If you can get 15 degrees of timing at WOT with no KR you are doing OK in my opinion! But if you have to throw any more fuel to the engine than 11.3:1 on an accurate wideband I feel you'll need to look at some other issues. 104's should be perfect and if you used 103's as insurance so that the plugs wouldn't induce PI that's ok.
