987 air intake: latest developments

[dlud]

Originally Posted by The Radium King

ow; that's a lot of pesos. here's my intake ...



oem coupler at the maf holder introduces the bend early on so no contact with the transmission, and provides some isolation to keep engine vibration from affecting maf readings, then just a short coupler and a long-leg silcone elbow.

Did you cut down the 90 degree at the throttle body? When I try to use a 3.25" 90 at my throttle body I run out of space and it hits the rear firewall.

[The Radium King]

for sure you have to cut it back.

[jaykay]

Originally Posted by NewArt

I must say that although I am pleased with the outcome (yet to be confirmed), getting the tune from the Porsche dealer was executed at dealer rates. Since this is not a procedure that they often (ever) do, it took quite a bit of time for my tech to research the possibilities and get my okay and then push the tune. I spent 3 hours there but they only charged me for 2. And hey, I got free espresso and a complimentary car wash!

Which tunes are currently available and which one did you end up getting? What were the names given in the PWIS?

I believe the possible candidates for a 2000 to 2002 Boxster S 3.2 DME are: 1999 to 2002 996 3.4 and 996 3.4 ROW.

2003 to 2004 Boxster S 3.2 DME: 2003 to 2004 996 3.4 and 996 ROW; 550 Anniversary SE Spyder.

The separation at 2002 is due to the introduction of vario cam plus IIRC

[NewArt]

Yes, the Spyder tune that I got would only work with the 7.8 DME. The Radium King has a 996 tune on his earlier model and he can confirm that it was successful. I didn’t opt for the ROW Spyder tune although it was an option.

[NewArt]

Hooked up the Durametric to see the state of affairs:
MAF: 10-12 Kg/h
FRA1: 1.03
RKAT1: 2.72
FRA2: 1.03
RKAT2: 3.42
Guess I need to go leak hunting.

[NewArt]

So far, I haven’t found any leaks. I may have jumped the gun since the latest readings seem to indicate that the ecu is still adapting:
FRA 1: 1.03
RKAT1: 1.92
FRA2: 1.02
RKAT2: 2.30
Think I will wait for a few more drive cycles before I get too concerned!

[The Radium King]

your fras are rock solid and as good as factory - no problem there.

your rkats - idle trims - 1.9% and 2.3% - are higher but well within the 4% spec. idle is where a small vacuum leak will make itself most apparent but, as you say, they seem to be sorting themselves out. for comparison, my rkats were/are:

.32% and .28% with the larger throttle body but with stock maf holder and tune. this tells me idle is not thrown-off by the larger TB (which i had thought might happen given that idle is based mostly on throttle position and a larger TB will let more air through at any given position).

2.5% and 1.8% when i moved over to the 996 tune. rock solid at these numbers and within spec so no issue. due, i think, to the fact that the ecu is trying to tune for a 3.4 engine but only moving 3.2 litres (again, my understanding is that idle is mostly throttle position and not maf, so air not being metered). but then, trims would be negative in this case, so perhaps i have an air leak too?!?!?!?

[NewArt]

More snow forcasted for tomorrow. Have to wait and see if everything will adapt.

[Cunningr]

Originally Posted by The Radium King

DIY 987 Air Intake mod PART 3 !

I watched this the other day didnt catch the explaination of the numbers will watch again.

[Cunningr]

Originally Posted by The Radium King

DIY 987 Air Intake mod PART 3 !

Watched it again,i understand the install. What i dont understand are the numbers you keep saying look great. IE fra be interested in knower what you are evaluating and what they mean.

[NewArt]

FRA and RKAT are the short and long term fuel trim indicators. I will discuss this in my next video. If you would like to dive in to the in depth explanation, Schrodingers Box does a good job of explaining on YouTube.

[The Radium King]

fra and rkat are both long term fuel trim indicators. fra is for closed loop trim, rkat is for idle trim. there are no trims for open loop operation. these are not short-term fuel trims. i explain trims in the thread referenced. i've attached an edited version below:


your engine has three modes of operation - idle, closed loop, open loop.

idle long term fuel trim is the rkat value measured by your durametric and can vary by +/- 4%.

closed loop long term fuel trim is the fra value measured by your durametric. 1 is ideal, but you can swing between .7 and 1.32 before you get a cel. what is a ltft? closed loop, or low load as it is often called, is part throttle, medium rpm operation. the car isn't working too hard. you are cruising along. maf measures air, looks up the appropriate amount of fuel to add in a chart, o2 checks products of combustion in the exhaust to make sure everything is burning properly and, if not, either adds or takes away ('trims') fuel (these trims are initially short-term fuel trims - stft - which become ltfts if they stay consistent over a period of time). this check by the o2 sensor is what makes it a 'closed loop' operation.

in closed loop, the amount of fuel added is done to maintain an air fuel ratio (afr) of 14.7 parts air to 1 part fuel (14.7:1 - stoichiometric). according to 'science' this is the most efficient, powerful ratio that creates the best combustion. as a result, the narrow band o2 sensors in your exhaust are designed to operate just around 14.7:1 (as opposed to a wide band o2 sensor like the one your tuner uses which has a much broader operating range).

fyi, the ecu knows how much air is getting in because of the maf - the maf measures the volume of air hitting it. the ecu knows the size of the intake tube, so multiplies the amount of air hitting the maf by the area of the tube to calculate the total volume air being ingested.

now, open loop operation. this is also called high load, or wot (wide open throttle). this is when the engine is hot, under load, banging against the rev limiter. the ecu switches to open loop based on a number of considerations; rpm (high) temp (hot) throttle position (ie, throttle is wide open but rpms are down - you are lugging the engine or going up a hill or something and ecu will go to open loop).

what is open loop? this is when the ecu moves to an afr of 12 to 12.5:1. it adds more fuel. the idea is that the extra fuel helps keep things cool, and prevents a hot, hard working engine from detonating. note that porsche was too cheap to use wide band o2 sensors in our cars (they do in the 996 turbos and the 987 cars; in their defense, this system is designed to address aging components and not yahoos doing crazy things with their intakes) so there is no feedback on whether you are hitting the target afr or not - the ecu just calculates how much fuel to add based on maf reading (no trims). this lack of checks is what makes it 'open loop' operation.

[dlud]

So....in open loop does the ecu use the fra that was "learned" in closed loop to make the afr calculations?

[The Radium King]

Originally Posted by dlud

So....in open loop does the ecu use the fra that was "learned" in closed loop to make the afr calculations?

that's the best question i've heard yet. i had them same question and could not find the answer anywhere. nothing i could find in the bosch dme manuals i have. it would make sense that they would, however indications are that they do not. perhaps they think that they are throwing enough fuel at it that it shouldn't matter (remember, the system is designed to deal with aging components - small vacuum leaks that have more impact at idle than at wot, tired injectors, etc. - not major intake modifications). buy you a beer if you can find the definitive answer to that one.

[NewArt]

Thanks for that clarification TRK! I will reference you in my video and try not to lead my viewers astray! Bosch DME manuals eh? A little light reading for those long winter nights.

[Cunningr]

That was excellent reading I really learned a lot. I really appreciate you taking the time to type out that explanation. So this is basically the electronic injection version of setting jets correctly on an old carb.....

I should try to find some engine books to read, guess I am strange I enjoy reading tech manuals.