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Old 04-15-2013, 08:57 AM   #1
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New Project - Tuning my 3.4L for POWER

i have goodies coming this week.

the problem
i am getting pulled by cayman S's on the back straight at road atlanta. i am lighter, ergo i am down on power!

the hypothesis
all my mods (3.4L swap, custom intake, cat bypass, headers, race exhaust, pulleys, AC delete, etc) are too much for the stock 996 ECU tune. AF ratios likely incorrect.

the solution
generate current fuel & spark maps
set car up to dyno itself
use AFC to modify AF ratio
determine how fuel is affecting spark
calculate ideal AF map
dial it in


this will be fun! i have an Innovate LC1 wideband O2 sensor & controller. it will hook up to an Innovate OT-2. basically, the wideband sensor AND my OBD II data will be integrated & wirelessly logged to my iPad. the software will take inputs for weight, wheel diameter, frontal area, Cd & gear ratio. i will be able to log spark, AF ratio, RPM, TPS, MAP, calculated load, OPEN/CLOSED MAF state, etc. the log files can be emailed from my iPad to my PC for detailed analysis.

the logs will actually calculate HP & torque. accurate or not, it should at least be precise since it is using the mechanical relationship between RPM & vehicle speed to determine velocity. should be great for analyzing whether a particular change is helping or hurting.

i will have my current spark & AF maps w/ initial dyno in a week or so. after that, the games will commence.

questions / comments in the meantime are appreciated; i know some you have done this before (JAAY!). cheers.
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Old 04-15-2013, 09:33 AM   #2
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Subscribed. There's valuable information in this to be had. Wish you luck.
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Old 04-15-2013, 09:47 AM   #3
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Guessing: Injectors &/or fuel pump not putting out like they should. Air induction mods are allowing too much extra heat into engine &/or engine compartment.
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Old 04-15-2013, 09:59 AM   #4
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Guessing: Injectors &/or fuel pump not putting out like they should. Air induction mods are allowing too much extra heat into engine &/or engine compartment.
good guesses; we'll see. my first thought was similar: inadequate fuel. JAAY's experience, and those of others who have done this swap, is an extreme rich condition (he was 10 to 1!!). in my case, i do see a lot of soot across the back of my bumper that gathers over time.

i wonder if the flow charicteristics of the 996 air box don't translate well to a straight-through MAF housing. on the 996, the MAF is VERY close to the airbox inlet & not entirely round.
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Old 04-15-2013, 09:59 AM   #5
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variocam+ would account for some of the hp on the table vs the cayman.

but if we are not comparing to caymans but rather looking at 10:1 afrs using stock tune, then why? if the maf was consistently over-metering the air (resulting in more fuel than required) then the o2 sensors would pick up on it and adjust the fuel trims. similarily if you had leaky injectors or an over-performing fuel pump producing more fuel than expected then the 02 sensors would notice and adjust trims.

so, perhaps new o2 sensors? a quick trip to auto atlanta shows that the 986 02 sensor has a different part number that the 996; most likely due to lead length, but perhaps they are different beasts in other ways?

otherwise, the ecu will add more fuel to keep the heads cool if it is nervous about something - timing, octane, etc. - what gas are you running and is it a row or na 996 tune?

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Old 04-15-2013, 10:00 AM   #6
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variocam+?
nope; i have a 3.4L from a '99. i have varioRAM (which is hooked up & functional), but only standard varioCAM.
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Old 04-15-2013, 10:19 AM   #7
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good guesses; we'll see. my first thought was similar: inadequate fuel. JAAY's experience, and those of others who have done this swap, is an extreme rich condition (he was 10 to 1!!). in my case, i do see a lot of soot across the back of my bumper that gathers over time.

i wonder if the flow charicteristics of the 996 air box don't translate well to a straight-through MAF housing. on the 996, the MAF is VERY close to the airbox inlet & not entirely round.
I recently installed 987 airbox & MAF tube with 997 plenum "T" & T/B, then reflashed with '00 LEV 996 map for my 3.6 boxster engine & it seems to work very well. Pulls to 7400 very smoothly.
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Old 04-15-2013, 10:25 AM   #8
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A good project to investigate and a common problem on 996/Boxster conversions.

Some observations while running regularly with 3.4L Boxster conversions and 987 Cay S 3.4L:

The 987 has a nice wide, fat torque curve which allows them to put down power early on corner exit. A 996 3.4L tends to have a more narrow torque curve requiring more shifting to stay in the sweet spot. I suspect a well tuned and displacement-matched intake and exhaust along with software remapping will fatten up the torque curve and make the most out of a 996 3.4L in the Boxster.

One problem that has been reported is sonic pulses from the valve train traveling back up the intake and actually fouling the MAF sensor readings. Does the intake require a helmholtz chamber to neutralize these pulses?
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Old 04-15-2013, 10:27 AM   #9
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i was reading over some chatter about a similar issue on another forum. one guy said his AF issue was solved by raising his fuel rail. he was using the boxster fuel rails w/ the 996 injectors. when he raised the rails to the right height, his AF problem went away.

this doesn't make sense to me. anyone see what i'm missing?

(FWIW, i know that the 986 & 996 injectors are identical. my personal solution was to modify the 996 rails to work on the 986, so this issue is not a concern to me).
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Old 04-15-2013, 11:17 AM   #10
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One problem that has been reported is sonic pulses from the valve train traveling back up the intake and actually fouling the MAF sensor readings. Does the intake require a helmholtz chamber to neutralize these pulses?
interesting observation; i wonder if that is why there was a resonator on the original intake? anyway, i should be able to log MAF voltage vs. RPM at WOT. if there are any anomalies, i can probably program them out.
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Old 04-15-2013, 12:58 PM   #11
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Quote:
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i was reading over some chatter about a similar issue on another forum. one guy said his AF issue was solved by raising his fuel rail. he was using the boxster fuel rails w/ the 996 injectors. when he raised the rails to the right height, his AF problem went away.

this doesn't make sense to me. anyone see what i'm missing?

(FWIW, i know that the 986 & 996 injectors are identical. my personal solution was to modify the 996 rails to work on the 986, so this issue is not a concern to me).
Fuel pressure and injector setting differences in conjunction with intake airflow differences....just a thought
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Old 04-15-2013, 01:33 PM   #12
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ltft should adapt to all that fuel stuff unless it is out of adaptable range, at which point it should chuck a code. freaky maf readings due to turbulence or pressure beat waves should also trigger a code. i think either the 02 sensors are off or the computer wants it to be at 10:1 if it is running that way without codes.
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Old 04-15-2013, 03:18 PM   #13
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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.
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Old 04-15-2013, 03:53 PM   #14
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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.
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Old 04-15-2013, 05:55 PM   #15
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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
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Old 04-16-2013, 07:57 AM   #16
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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 doesnít 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 doesnít 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 isnít 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 youíll find that porsche wants a 10:1 at wot to deal with vagaries in fuel octane, etc. itís all really moot because, regardless of the cause of bad afrs, if you can improve them Ö

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!
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Old 04-16-2013, 08:40 AM   #17
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nope; i have a 3.4L from a '99. i have varioRAM (which is hooked up & functional), but only standard varioCAM.
Insite is your MAF housing tube I.D. 3.5" ?
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Old 04-16-2013, 08:43 AM   #18
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certainly there are lots of different variables. one thing is for certain: the stock ECU map for a 996 contains no fuel ratios near 10:1. it's a losing proposition: less power, more emissions, worse mileage. the only cars that need to run in the 10's are augmented (turbo, supercharger). the extra intake heat & cylinder pressures raise the probability of knock. the extra fuel is used to cool the charge (latent heat required to vaporize fuel is around 300kJ/kg) & stabilize the flame front.

the accuracy of MAF readings in a given system is largely irrelevant so long as it is PRECISE. the ECU is tuned to the specifics of that vehicle. if the MAF reads 20% low compared to reality because of flow idiosyncrosies, it doesn't matter, because they program the ECU with maps that take that into account. that means that with a completely different intake, the stock 996 maps on my car may be irrelevant even though the engine is from a 996.

most NA cars will make good power between 12.3 and 13.5 AFR. i will be generating maps at WOT that model lambda from around .83 to .92 in 1% increments across the RPM band. i will plot HP vs. RPM vs. AFR, chosing the power path & programming the computer accordingly. i will also monitor knock to make sure things are safe. one thing i need to learn more about is ethanol in fuel. does RON+MON/2 account for the anti-knock properties of ethanol? i.e. does ethylated 93 octane fuel have a higher EFFECTIVE octane rating?

i digress. at any rate, as i do all of this, i will have many pretty charts, graphs and tables to spell it all out. it will be cool. my guess: 50HP (crank). quote me on that.
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Old 04-16-2013, 08:52 AM   #19
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Insite is your MAF housing tube I.D. 3.5" ?
yup. i use a BMC airbox w/ silicone plumbing to a 3.5" MAF housing.
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Old 04-16-2013, 09:14 AM   #20
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most NA cars will make good power between 12.3 and 13.5 AFR. i will be generating maps at WOT that model lambda from around .83 to .92 in 1% increments across the RPM band. i will plot HP vs. RPM vs. AFR, chosing the power path & programming the computer accordingly. i will also monitor knock to make sure things are safe. one thing i need to learn more about is ethanol in fuel. does RON+MON/2 account for the anti-knock properties of ethanol? i.e. does ethylated 93 octane fuel have a higher EFFECTIVE octane rating?

I have wondered this too. I'm guessing that it is unregulated other than to insure it has the posted octane as a minimum. Consumer reports a 15% reduction in MPG when using "Gasohol"
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