GT3 82.5mm Throttle Body!

[Yellow986S]

Originally Posted by The Radium King

still going ...

if you want to go the ipd/gt3 route and increase your maf housing diameter, the cayman/987 is a match. further, the cayman/987 airbox is a HUGE improvement over the one that came with your 986. so, put in a 987 airbox and maf housing (the 986 and cayman/987 use the same maf) and you are now 83mm throughout. as already posted, this will f-up your cars tune, as the ecu uses the area of the maf housing to calculate airflow. this means:

1) hope the computer can adapt (if you search on this forum there is at least one person who has done such on track cars and had no issues);
2) expensive custom tune (Pedro is probably your best and least expensive option here); or
3) try to use an ecu map for a 996 3.4 e-throttle pre-variocam+. this map is designed for the larger maf housing diameter and *should* work on your car. cost would be the amount of time it takes your mechanic to push it with a piwis or pst2 (3 minutes). I eventually want to test this out but would love someone else to prove the concept ...

Is the 987 airbox a direct bolt on that I can swap? if not what needs to be done to make it work.

I understand now that the GT3 TB is too large and will do more harm than good unless I change the MAF, which I don't plan to do.

Can I use the 76mm 997 TB, 987 airbox, and Techno Torque plenum?

Will this affect the MAF and will I see any performance gains with this setup?
Thanks

[Shehadehd]

Originally Posted by Yellow986S

Is the 987 airbox a direct bolt on that I can swap? if not what needs to be done to make it work.



I understand now that the GT3 TB is too large and will do more harm than good unless I change the MAF, which I don't plan to do.



Can I use the 76mm 997 TB, 987 airbox, and Techno Torque plenum?



Will this affect the MAF and will I see any performance gains with this setup?

Thanks

I think TheRadiumKing has a long thread the answers just about any question you might have on the issue.

I'm not sure about the 987 airbox but there's a thread on it called 987 vs 986 airbox or something like that. It looks like a tad more than a bolt on

[onaFLYer]

Originally Posted by Shehadehd

I think TheRadiumKing has a long thread the answers just about any question you might have on the issue.

I'm not sure about the 987 airbox but there's a thread on it called 987 vs 986 airbox or something like that. It looks like a tad more than a bolt on

I actually started that thread sooo long ago, two years maybe, and my car still has minor issues with the maf and low speed drivability. Make sure you really want to take time to sort things out before making changes like this.

[The Radium King]

that's what I have - 987 airbox, maf housing from my 986 airbox, cayman tb (same as 996 or 997) and 997 plenum (I didn't see the need to pay the extra $ for the pedro unit). I am very happy with the result.

there is a thread here on how to modify the airbox to work - there is a 'muffler' on the outlet that needs to be dremmeled off, and an opening (where the outlet pipe opened into the muffler) that needs to be plugged - I used a waste piece of the muffler plastic and a $20 plastic welding kit off ebay to get it done.

to use the 986 maf housing, just saw it off your old airbox (smooth the edge) and fasten it to the 987 airbox.

you'll need a variety of silicone elbows and reducers, etc. for example, the 997 tb, while 3" (76mm) on the inside, is 3.25" (83mm) on the outside (thick metal lip). the maf housing, however, is approximately 3" ID and OD (thin plastic). so, you'll need to reduce to mate the two.

further, you'll have to make a hard 90 degree turn coming off the tb, as the 997 plenum (or pedro unit, as he just modifies a 997 plenum) doesn't angle like your oem plenum. i accomplished both by using a silicone 90 degree reducing elbow that goes from 3" to 3.25".

to attach the maf housing to the airbox you have a number of options. the airbox outlet has a flange on the end - you can saw this off and use a 3.25" to 3" silicone straight reducer to join the two (pls confirm the 3.25" dimension, as I didn't do it this way). or, I found that the 3.25" end of the reducer will press fit inside the flange, which is what I did (I inserted a 3.25" ring sawn off an old aluminum coupler inside the reducer to keep it from collapsing).

to join the whole assembly together I used a piece of the original ducting; inserted in the elbow at the tb end, and connected to the maf housing with a 3" silicone coupler at the other end. wrap in metal foil tape and done.

notes:

- airbox install is a ********************; I had to remove driver side intake manifold and bend up engine cover mounting tab to get it in.
- mounting points are the same for both airboxes, however, one point is a bolt on the 986 and a stud on the 987; I sawed the head of the 986 bolt, slotted it and made a stud out of it.
- you might have to jimmy your fuel tank vent line a bit.
- you can make fitting the elbow off the tb a little easier by sawing off the little flange on the engine compartment.
- may wish to incorporate an 'airflow smoother' to keep the maf readings stable - this is a honeycomb or mesh that sits in the airflow upstream of the maf. I got one off an old bmw maf pipe and fastened it to the end of the maf housing I had fabricated. does it do any good? no idea.