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Old 02-08-2018, 08:26 AM   #1
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987 Airbox and 74mm TB: MAF and tune issue

I have a 2000 S (3.2) and am in the process of putting in a 987 airbox and a 74mm throttle body. I've read much here and at other sites about this process and remain bewildered as to the best solution for the MAF and whether a tune or new ECU map will be required. So....

1. Is the best solution to use the 987 MAF tube/holder? (or alternatively hack the old 986 MAF tube onto the 987 airbox?).

2. Use the 986S MAF or the 987?

3. Use the stock 986S tune, another Porsche tune or custom?

I see a lot of back and forth in the forums on these issues but don't see that there was a final "best practice."

What combination has worked for a 3.2?

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Old 02-08-2018, 09:05 AM   #2
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i have a 2000S with 987 airbox, 997 plenum, and 74 mm throttle body.

originally i ran with the stock tune. i sawed the maf holder off the original airbox and mated it to the new airbox. i used the orginal maf. it worked well.

then, i installed the 987 maf holder. note that in your case the 986 and 987 maf are the same (different part # because the 987 unit comes with the holder and the 986 unit does not; avoid earlier 986 mafs, or 987.2 mafs). the 987 maf holder is a larger diameter and requires an updated tune to work properly. i am using a tune for a 996. this works well - i monitor fuel trims and all is well within spec. it is difficult to get a 996 tune on your car; you require the dme programming code from a dealer (hard to get) as well as a piwis/pst2 diagnostic tool (or a mechanic with one) and the knowhow to use it. you have these pieces and it is a 5 minute job.
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Old 02-08-2018, 09:34 AM   #3
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Thanks! Was there an advantage to using the 987 MAF holder vs the 986 MAF holder? I assume you made the change due to the smaller diameter of the 986 holder. I've wondered if the diameter difference is really significant overall to justify getting a new tune.

How did you mate the 986 MAF holder to the 987 airbox?
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Old 02-08-2018, 10:02 AM   #4
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yeah, i changed for two reasons:

- the 987 holder is larger, so you avoid the bottleneck. with the 986 holder the diameter decreases as it passes though the holder, then increases again, so you are doing work (compressing/accelerating air) for no reason.

- i wanted to see how the 996 tune worked on my car. i am of the opinion that porsche depowered the 986 engines so as to not compete too aggressively with the 996. a quick ratio analysis shows that the 986 3.2 makes less hp/litre than the 996 3.4. given that the two engines have the same bottom end, heads, etc., the only place porsche could throttle-down the 3.2 was exhaust, intake, and tune (fuel, timing). i made it my mission to transfer as many oem 996 parts onto my 3.2 as possible to try and gain some of that hp back. for exhaust i used the chinese stuff (fabspeed clone) and intake is discussed in this thread. 996 tune was the last piece of the puzzle.

regarding adapting the 986 holder to the 987 airbox, the best work i've seen was done by kram on this forum, who has posted images of his work. me, i sawed it off, pulled the airflow straightener off a similarly sized bmw maf holder and glued it in, and used a silicone reducing coupler to join it to the airbox (from siliconeintakes.com, but available on ebay i'm sure). with the coupler, the small end was sized to fit over the maf older, while the large end was sized to sleeve inside the flange on the airbox (i wanted to leave the flange on the airbox so that i could use a 987 holder in the future). i can send a pic, as i have the old tube just laying around at this point. note also that BMW makes a maf holder that is about the same diameter as the oem holder, takes the oem maf, and *i think* mates to the 987 airbox (can't recall, but can check when i get home if you like) - i didn't use it as the ID was not a 100% match to the original but is most likely close enough.

Last edited by The Radium King; 02-08-2018 at 10:16 AM. Reason: speling
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Old 02-08-2018, 11:50 AM   #5
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Thanks. I'll do a search for Kram's posts. If you could send a photo of the old tube (and anything else related to this) that would be much appreciated.

What was your final conclusion as to the value of using the 987 maf holder and the 996 tune vs the 986 maf holder and original tune?
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Old 02-08-2018, 12:15 PM   #6
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well. i live in the frozen north, so summers are spent driving (and keeping the car in brakes and tires) and winters are for futzing around. given that, my car usually gets on the road in the spring with a number of mods, and any increase in performance is hard to attribute. further, without dyno evidence, all comparisons are to my hazy memories of how the car performed from the fall previous.

having said that, i feel there is an improvement running the 996 tune. a totally subjective, seat of the pants (literally) statement. i have nothing quantifiable other than improved lap times which could easily be due to better driving or better tires. i assume the improvement is not so much in fueling as 14:1 is 14:1 in closed loop and i don't think they run the 996 leaner than the 986 at wot, but with the timing. i could possibly log the timing advance with my pst2 (not even sure if it can measure it) but have not bothered; i am happy with the changes i've made.
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Old 02-08-2018, 12:19 PM   #7
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here's my intake. note the coupler that inserts into the 987 airbox flange - i've put a reinforcing ring inside it to keep it from collapsing.

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Old 02-13-2018, 04:43 PM   #8
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Thanks! That's a short 90 at the TB. I assume you reduced the size of a more normal sized 90 by cutting each end back. Is the 90 a 3.25 OD? How is the airbox coupler held in?

I recognize that I'm really late to the game on the whole 987 airbox issue (recently acquired a 2000 S) but I wonder why folks haven't used the oem 986 maf, the 987 maf holder and just inserted a 3.25 OD/3.0 ID sleeve into the 987 maf, cutting a hole in the sleeve for the 986 maf (thereby avoiding the issues of a new tune and the marrying of the 986 and 987 maf holders). I thought I saw a mention in a thread somewhere of that possibility but haven't seen any further indications that anyone has pursued it. I haven't pulled out my 986 airbox yet to measure the internal dimensions of the maf holder. Perhaps it's not a consistent 3.0 ID (?).
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Old 02-13-2018, 06:05 PM   #9
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MAF tube is 2.9” (74mm) ID on the 986 airbox.
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Old 02-13-2018, 07:56 PM   #10
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Oh. Well, that makes more sense then.
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Old 02-17-2018, 04:03 PM   #11
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Guys get a wide band gauge in the car if you want to make these mods. I did these mods a long time ago. Dyno'd, wide band etc. Turns out the intake mods really messed things up. I was able to get the car dialed back to a good ratio and all was better.
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Old 02-17-2018, 06:30 PM   #12
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Interesting. What results did you see that you didn't like? How did you get things straightened out?
Thanks!

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