DIY 987 Air Intake mod PART 3 !

[NewArt]

And so... does it run?
https://youtu.be/UTGbH-6Krvs

[The Radium King]

so, here's your math lesson.

area of the oem 3" maf holder = pi x radius squared = 7 sq in
area of the new 3.25" maf holder = 8.3 sq in
difference = 18.6% (and you can check my math; can't confirm i was sober when i did it)

what does this mean?

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.

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).

ok, so 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.

increase the diameter of the tube by 18.6% and you have 18.6% more air getting in than the ecu thinks there is. as a result it adds less fuel than needed, o2 sensors figure this out and ltfts are increased to add more fuel. so, you should be able to put your durametric on it and see a significant increase in your fra values (perhaps an 18.6% increase ?!?!?).

big deal, as long as you are within the .7 to 1.32 margin then you won't get a cel and life is good. except ... 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.

the problem? porsche was too cheap to use wide band o2 sensors in our cars (they do in the turbos, and the 987.2 cars; in their defense, this sytem 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). now then, take a 12.5:1 afr and increase the amount of air by 18.6% and what afr do you get - 14.8:1? pretty lean for a hard working engine. your fuel economy will be great, and your car will feel like it is on steriods (remember, 14.7:1 makes most power) but not so good for the engine.

my advice? get your tune asap, although i expect once your car balances our in 50 kms or so and your short term trims get moved into ltfts that you will get a cel for your idle rkats being screwed and perhaps transition to limp mode (where ecu meters air based on throttle position instead of maf reading).

or i could be wrong; you get what you pay for on the internet, hey.

[NewArt]

Great explanation Professor TRK!
So, do you think that the "Anniversary Edition" tuning would do the trick? That was my plan but I am open to suggestions!

[The Radium King]

yes it will.

[NewArt]

Just what I wanted to hear. Thanks!

[The Radium King]

my understanding is that the anniversary edition came w the larger maf holder so the ecu will be doing the proper math to calculate airflow. just don't go to the dyno and run at wot until you get the new flash.

this weekend i'll try to get a shot of my intake build for comparison.

[dlud]

Does anyone know the ID of the 2000 996 maf holder? I assume that it is the same as the 987 (?). And did the 2000 996 use the 74mm TB?

[NewArt]

Originally Posted by dlud

Does anyone know the ID of the 2000 996 maf holder? I assume that it is the same as the 987 (?). And did the 2000 996 use the 74mm TB?

MAF tube is 2.9” (74mm) ID on the 986 airbox. TB is 68mm IIRC

[dlud]

Thanks but I was wondering not about the 986, rather the 996 (2000). The reason I ask is that I know some have used the 996 tune for the 986 airbox/74mm TB upgrade. Trying to figure out the logic behind using the 996 tune. I have a 2000 S so I am unable to use the 2004 tune from the special edition.

[NewArt]

Thought that I might run this by you. I took the car out for a spin yesterday. It ran like crap for the first 10 minutes but then everything smoothed out. I guess that the DME was adapting during my drive. I didn't push the car at all, hardly getting above 4000 RPM. When I got back home I left the car idling and hooked up the Durametric to see what the fuel trims looked like. The results are a bit wonky but I haven't got my Anniversary Edition tune yet. In light of my recent air intake intervention, do you think that these results are to be expected or should I be looking for a leak?
FRA 1: 1.28
RKAT 1: 2.53
FRA 2: 1.29
RKAT 2: 2.67
MAF: 1.18V
9 kg/h
Let me know what you think.

[NewArt]

From TRK:
"they look pretty much as you should expect pre-tune. your rkats are idle trims and in %; around 2.5% each side which is high as expected but within the 4% spec. they are positive which means the ecu is adding fuel as expected.

your fra values are around 1.3; more than the 1.2 that i’d predicted but close enough for the cocktail napkin math that i’d done. again, they are positive which means adding fuel as expected and, very close to the 1.32 spec which triggers a cel.

so, i think you are good; science wins another one."

Thanks to The Radium King!

[NewArt]

Originally Posted by dlud

Thanks but I was wondering not about the 986, rather the 996 (2000). The reason I ask is that I know some have used the 996 tune for the 986 airbox/74mm TB upgrade. Trying to figure out the logic behind using the 996 tune. I have a 2000 S so I am unable to use the 2004 tune from the special edition.

Sorry, misread your question. Maybe the Radium King can answer this.

[Smallblock454]

Hello NewArt,

have a question. Your'e located in Canada, right? Does your car have 2 catalytic converters like the ROW cars, or does it have 4 catalytic converters, like the US cars?

EU 986 cars (228 HP, 260 HP, 266 HP) with ME 7.8 and 2 cats do have broadband o2 sensors.

Regards

[NewArt]

Originally Posted by Smallblock454

Hello NewArt,

have a question. Your'e located in Canada, right? Does your car have 2 catalytic converters like the ROW cars, or does it have 4 catalytic converters, like the US cars?

EU 986 cars (228 HP, 260 HP, 266 HP) with ME 7.8 and 2 cats do have broadband o2 sensors.

Regards

Mine is a North American spec so it had 4 cats. I have deleted the secondary cats. I was not aware that European cars had broadband O2 sensors. I got a cel yesterday when my FRA maxed out at 1.32. I have an appointment next week to get the Anniversary Edition tune. I thought that I might take the ROW version.

[Smallblock454]

Originally Posted by NewArt

Mine is a North American spec so it had 4 cats. I have deleted the secondary cats. I was not aware that European cars had broadband O2 sensors. I got a cel yesterday when my FRA maxed out at 1.32. I have an appointment next week to get the Anniversary Edition tune. I thought that I might take the ROW version.

Hello NewArt,

OK, thanks for the info.

Concerning the EU / ROW cars:

The EU / ROW 986 SE cars (266 HP) and also the base (228 HP) and S (260 HP) don't have the 2 front catalytic converters at the manifold like the US cars. They only have 2 "back" catalytic converters.

The broadband o2 sensors of the EU cars sit before and after the "back" cats. So there are 4 in sum. The OEM EU catalysators have 400 cells.

I'm not shure if the mapping needs to be different if you have front catalytic converters instead of back catalytic converters and non broadband 02 sensors instead of broadband o2 sensors, but i think it would make sense.

Regards