New Project - Tuning my 3.4L for POWER

[insite]

long term fuel trims don't really do much except use the 02 sensors to set the AFR to 14.7 near idle. at higher load & RPMs, the (narrow band) O2 sensors can't really tell what the AFR is. the ECU uses the MAF to calculate, using a table, how much fuel to send based on a trimmed out 14.7 idle AFR + some offset values.

once you are over about 3k RPM and 30% throttle, the fuel amount is basically an educated guess based on MAF readings and offset tables.

since my engine will perform so much differently at wide open throttle (WOT), there is a good chance that the ECU tables won't get me to the right AFR's. there really is no way to know without measurement.

on another note, my logger came today. pretty slick piece of equipment! i fired it up to look at my fuel trims and MAF readings. fuel trims are small (<3%). one interesting note: the MAF at idle should be around 15 kg/hr. mine is over 20! so, at least at idle, i am flowing a LOT more air than stock. my guess is that flow advantage decays as RPM's go up, so i am likely getting way too much fuel at high RPM/Load values.

i will get the wideband hooked up & start logging later in the week.

[JAAY]

How many of you actually know your afrs???? I'd love to see a stock curve. I'd bet there all rich as hell on Boxsters. - detuned to preserve the carrera.

[Topless]

Here is one guys 3.4L tuning solution that was featured in Excellence magazine. He is a regular street driver and not a shop owner or track rat.

986 Boxster story

There used to be tons of Dyno data for 2.5 Spec Boxsters regarding different exhausts, underdrive pulleys, intakes etc. but all of it was lost when Brad's site went down. As I recall there was concern for the cars running too lean with straight pipes and actually ran better with a muffler of some type. Too bad it's gone.

These cars are all running lean with a stock 2.5 showing the best tune and a steady AFR.
http://boxcar-racing.com/forum/index.php?topic=688.0

[The Radium King]

I LOVE this.

from what i understand there are three base maps - timing, idle, and fueling.

the fueling map is three dimensional and uses rpm and airflow to determine how much fuel to deliver.

typically, the lower-rpm end of the map delivers a stoichiometric air fuel ratio (14.7:1) which gets richer (more gas) as rpms increase (to cool engine, avoid knock, etc.).

the o2 sensors are the only true indicator of afr that the computer gets, but the narrow band o2 sensors are only really creating long term fuel trims for the low-rpm area of the map as they do not work outside of a small range centred around 14.7:1.

at low rpm the stock porsche engine is designed to have a pulse-tuned intake and backpressure from the exhaust to improve cylinder scavenging and fill. on an engine with intake and exhaust modified to increase airflow at high rpm, some of these low rpm benefits will be reduced. this is why most folks see a reduction in low to mid-rpm torque but with an overall increase in power in the upper rpm ranges. to the computer this means the engine is drawing less air at low rpm. the o2 sensors should detect this and reduce fuel as a response. when the rpms increase and the engine is breathing more freely the computer doesn’t know it and you should actually go into a lean condition. the leaner condition at wot is supported by the comments from topless.

another possibility is that the 02 sensors are no longer working properly. in this scenario the computer doesn’t detect the reduced airflow at lower rpm and continues to fuel as planned, resulting in a rich condition. this should transition to a less rich condition as rpms increase.

oddly, you are getting more airflow than expected, but that is at idle which is a different map.

otherwise, the computer is looking at throttle position as well as maf output, so one presumes that any wild fluctuations in maf output would get detected and ignored. a maf that is consistently reading off due to steady-state turbulence might be a culprit. my understanding is that there is also a maf calibration map, so any consistent maf inaccuracies should be addressed by the computer as determined by low-rpm o2 sensor feedback.

if the maf is metering more air than is actually flowing (ie, located in a high pressure area of the intake such as the outside of a bend) and, as rpms increase, the inaccuracies of the maf readings increase in a greater than linear manner such that more air is metered than is actually flowing beyond what has been accounted for in the maf calibration map, the mixture will get rich and the computer would not know it. in this case the best solution would be to simulate the 996 intake geometry and locate the maf as close as possible to the air box.

regardless, we are talking a 996 engine with 996 tune. presumably Porsche isn’t leaving any power on the table with this combo. i find it hard to believe that intake and exhaust modifications can have such a drastic effect on afr. i think the real test would be to compare your wideband o2 results to a stock 996, or even get your hands on the base map for a 996 to see what the afrs are supposed to be from Porsche. my thinking is that you’ll find that porsche wants a 10:1 at wot to deal with vagaries in fuel octane, etc. it’s all really moot because, regardless of the cause of bad afrs, if you can improve them …

insite, I am watching this and will be next in line; you have proven results from jaay and the guy topless posted about, and now, hopefully you!