maf and throttle body diameter

[jaykay]

I am still considering it (Cayman diverter tee) because a factory designed flow geometry/route would be in place and there would be no fiddle with the intake tube; the geometry would be known. I also noted the hard turn after the throttle body...perhaps this works well with partial throttle postions..maybe not. The 997 looks (my car is wapped up in storeage so I can't do or see anything right now) like it points away from the left side so one has to put in a nice big radius there to get the flow path oriented the right way..smoothly

I am glad you are happy with the 997 diveter tee; sound like it is the one from your description! I have not bought it yet as I cant get to my engine for a while anyway. Your set up sounds good too. I was thinking Cayman box or Sparkers set up....I think Techart uses a bmc can.

Difficult to say exactly but I would think acoutic pluses would interact with the incoming charge as well as the left and right plenum walls; my horse sense tells me that a GT3 TB on 3.2L might give you a high range power band that would be hard to drive on the street. I think the intake velocity might drop off too much at lower rpm.

I have a feeling that the DME will adapt to a slightly larger MAF housing as BR indicated. It is not what you would expect but that is the indication I got from a tuner....

Originally Posted by The Radium King

i'm pretty sure it's vacuum driven same as on the resonance tube, so i would guess a tee would work. the presence of the flap drives the cost cost of that plenum up over $200 new (vs $48 from suncoast for the 997 unit) but there should be lots of take-offs available used from cayman guys moving to the ipd product. note also that it has two aos connections, so you'll have to plug one or buy a cayman aos line as well. another observation is the hard left turn the air has to make once past the throttle body, vs on a plenum that is more square to the intake.

the 997 plenum is BIG and has very smooth radii. it comes out straight instead of angling off like the original so the old intake pipe can't be reused. note that you have to install it upside down to put the aos connection on the proper side.

i've got a bmc direct air injection (dia) intake that i'm going to use for an airbox, as well as a bmw maf housing coming that i am told is the appropriate size (part # 0280217502 for those interested, but i can't confirm until i have it in my hands) and have found a source for flexible, silicone, 3" ducting to connect the throttle body to the maf housing. it should look very professional when done, regardless of what airbox used (oem or aftermarket). note that the bmc universal airboxes come in two sizes - 70 mm and 85 mm; you want the 85 mm otherwise you are introducing a restriction upstream of your 76 mm maf housing.

one thing interesting to note that the plenum/intake runner connections are 3.5" in diameter on each side, so the air expands once it passes through the smaller throttle body. that leads me to believe two things: any intake pulse tuning must happen in the runners themselves and the plenum is just a ready source of air (ie, making it bigger won't reduce low-end power) and anything i can do to get the air to the plenum as efficiently as possible will be of benefit (bigger throttle body, bigger ducting, etc., to the limit set by the maf housing at 3"). this begs dialogue on the next step of intake mods - a larger maf housing. the 3.4 996 engines use a larger maf housing that you could use in conjuntion with the gt3 throttle body, etc., but modifications of the ecu would be required to recalibrate maf readings.

[The Radium King]

you're right; with a plenum that exits straight out from the intake i'll have to put in a larger radius curve further upstream as the intake runners themselves are canted to the left a bit. i'm just thinking that the further i put that from the 90 degree bend that happens at the actual plenum the better. the thought of the cayman plenum is attractive, however, as the resonsnace flap used on that plenum is now used on the dfi 911's also, so it must work (i think it is a low end/top end compromise, l however). further, as you note, it should be plug and play with a 987 airbox (which is a way better unit that the 986). i have a line on a cayman plenum if you are interested; pm me for details.

regarding the dme adapting to the larger maf housing i agree, BR has gobs more experence than most of the rest of us combined and says it works. he said in a different thread that he's going to try it on one of his cars and see if the air/fuel ratios adapt. i know i have read of people doing 3.4 swaps and not having the maf appropriate to their dme and having problems, so definitive results would be nice. it may be an issue of cumulative change, also; the dme can adapt to the maf change, and the dme can adapt to a higher flow intake, but both a higher flow intake (and exhaust, etc.) combined with the maf change change may exceed the learning capacity of the dme.

i'll tell you what: you do the cayman change, i'll do the 997 change, and we'll meet in the middle and compare (manitoba - geographic centre of canada - gimli motorsports park)!

[jaykay]

Alright a high noon drag race duel at Gimli! With any luck we won't get disturbed by any dead stick 767s

I was actually driving through Radium down into Nelson BC just a while ago...phew what drive still did get me primed enough for the out right speed of track driving the following week

Originally Posted by The Radium King

you're right; with a plenum that exits straight out from the intake i'll have to put in a larger radius curve further upstream as the intake runners themselves are canted to the left a bit. i'm just thinking that the further i put that from the 90 degree bend that happens at the actual plenum the better. the thought of the cayman plenum is attractive, however, as the resonsnace flap used on that plenum is now used on the dfi 911's also, so it must work (i think it is a low end/top end compromise, l however). further, as you note, it should be plug and play with a 987 airbox (which is a way better unit that the 986). i have a line on a cayman plenum if you are interested; pm me for details.

regarding the dme adapting to the larger maf housing i agree, BR has gobs more experence than most of the rest of us combined and says it works. he said in a different thread that he's going to try it on one of his cars and see if the air/fuel ratios adapt. i know i have read of people doing 3.4 swaps and not having the maf appropriate to their dme and having problems, so definitive results would be nice. it may be an issue of cumulative change, also; the dme can adapt to the maf change, and the dme can adapt to a higher flow intake, but both a higher flow intake (and exhaust, etc.) combined with the maf change change may exceed the learning capacity of the dme.

i'll tell you what: you do the cayman change, i'll do the 997 change, and we'll meet in the middle and compare (manitoba - geographic centre of canada - gimli motorsports park)!

[Johnny Danger]

So what's the final verdict ? Is it the cayman or 997 plenum that should be mated to the 76mm throttle body ?

[jaykay]

Mr. Danger

The face off has not gone down yet! We would need an air lift and snow ploughs!

Hmmm delving into this a bit. It seems the "tune" can be upset with addition/deletion of a distributor flap. The resonance flap us tuned to work with or without. I believe I would need a Caymanesque tune to make use of the sophisticated intake system.
I am not sure about the worth of this and can't do this myself. I think the distributor flap would certainly mitigate any low end losses associated with the larger TB.....just a guess. The engine experts might better answer this

It may be just spy vs spy at Gimli...as I will be likely running a big 3.8 diverter tee.
Shhhh don't tell Trk