maf and throttle body diameter

[AndyA6]

Bump for the latest update?

[The Radium King]

all the parts in except for one. it looks like it will go together easy. finally understand why porsche uses a tb smaller than the maf housing; the maf is a thin-walled plastic and the inside diameter (3") is about the same as the outside diameter (3"). the throttle body, however, is cast; the inside diameter is 2.67" while the outside is 3". that way you can use a 3" pipe to join maf and tb but have a smaller tb as a result.

so, by going to a 3" tb to match the 3" maf, the throttle body has a 3.25" outside diameter. i've got a 90 degree reducing elbow (3.25" to 3") on order to join the two; once it arrives i'll assemble.

[Johnny Danger]

Go TRK go !

[AndyA6]

Thanks! Would you post a few pics once done?

[jaykay]

Blast he is ahead of me! Just have the throttle body in today! It's very shinny. 997 Diverter tee and hardware awaiting shipping. I can report that the Cayman piping is easier in that it will have only one reduction from the MAF as far as I can see. Have to pick up (if it is good) the Cayman airbox on the weekend.

....Trk thanks for the leads got an expensive tb out them

May do another version with the stock airbox

[jacabean]

does anyone have a parts list for this mod. ? i would really like to give this a go .

[jaykay]

Some eye candy:






The 3.8 diverter tee is big! This the 74.5mm TB on it.

[jaykay]

and one more:

[Stiletto Pat]

Bump to see if there are any new developments!!

[shalco]

Hi, I came across this thread this morning while looking for a solution to my own induction problems.

A solution being put here is to use the 997 plenum. Now this does not curve unlike cayman/boxster plenums.

I currently use the engine & induction setup from a late 3.6 996. Now the plenum angle is similar to that of the 997. The issue it gives is that to connect the TB to the airbox you have to immediately use a v sharp immediate 90 degree bend in order to clear the bulkhead to the rear of the luggage compartment.

My feeling is that any gains from this plenum will be negated by this v tight 90degree turn into the TB. I can provide pics if that helps.

Any thoughts??

[The Radium King]

sure. with your setup (or a 997) you need the immediate 90 off the throttle body, but benefit from an equal 90 turn into each intake manifold. with the oem setup you get a shallower approach to the throttle body, but a resultant 135 degree bend to one of the intake manifolds - more opporutnity for delamination, turbulent flow on the inside of the curve and reduced airflow.

[jaykay]

I see a lot of engine conversion intake plumbing with sharp 90s into the throttle body. I personally will try to avoid this with the largest radius 90 out the throttle body I can find and then a 30 deg to correct for the angle away from the intake side.....currently I am eye balling it and have not measured the engine intake diverter tee angle.

Interestly I have noted pitting on the inside of my low time cayman tb, coincident with the outside radius bend of the cayman diverter tee and intake path. This gives me the feeling that presenting the air flow straight through the tb may have some value; less turbulence

[shalco]

Thanks for that, I hadn't considered the problem of the tighter inside radius on the curved plenum.

My car is an older 2.5 so was a cable throttle. I can confirm upgrading to a cable 996 3.4 TB is a big increase in power. I think this starts at 76mm & tapers down to maybe 74mm-ish at the butterfly.

I do have a previously fitted cable 80mm TB. This was an aftermarket ebay Nissan GTR TB. Its a good fit just needed oversized mounting holes, & an adapted bmw iacv plumbed in to the aos take off. It did from memory lack some torque below 4000 rpm compared to the 3.4 TB.

I think I may revisit this set up as I think its a shorter length compared to the 3.4 which means a less angled pipe could be connected.

[Stiletto Pat]

Gotta Bump this up - looking for the latest from you intake enthusiasts!

[berty987]

The cayman uses the same 74mm TB as the 3.6 996 and early 997 3.6/3.8. The gen 2 DFI 3.8 L engined 997 uses the larger 82mm TB. Regarding the mounting tees for the 74mm TB the cayman 987 and the 996 / 997 both use a larger diameter bore on the cross section that links the two halves of the intake manifold. Whichever you fit , you need to install a silicone reducer to get it to connect to the existing 986 / 987 intake manifolds. The 2006 and later boxster/ cayman use the 74mm TB and revised intake manifolds as standard in both 2.7 and 3.4 engines. I did a little write up on the 74mm TB fitted to an early 987 3.2S here :

75mm TB and Cayman Plenum upgrade for 987 - Articles

Note : If you fit a 987 airbox and MAF to a 986 (as was standard in the 550 anniversary) the install applies though the second diverter after the throttle body would not be connected or operational on a 986. The intake manifolds of the 986 were carried over to the early 987 models up to 2006 when the M97 engine was introduced.

For you guys with 986's I guess you have the option to break out the inner wall that divides the air paths post TB and remove the diverter flap as well. The cayman diverter flap looks wrong to me , its across the airstream creating a baffle whereas the earlier 987 boxster unit had the diverter parallel to the air stream , so created no restriction when open.

[Johnny Danger]

So, for the mechanically impaired, where are we at now in terms of the parts and equipment necessary to complete this modification ? What are the actual specs regarding choice of TB and plenum ?

[berty987]

For an E gas 986 (ie electronic rather than cable operated throttle body) you need a 74 mm Tb from a 3.6 Cayenne / 3.4 cayman or boxster or late model 2.7 cayman/boxster 996 605 115 01 / 997 605 115 00 and either the 996 tee 996 110 116 01 or the cayman tee 987 110 116 01 plus shorter screws 900 385 025 04 (4 off) , and larger clamps 90-110mm 999 512 539 01. You then need to buy two silicone reducers 102mm to 89mm (ideally 99 to 89 but they don't exist) plus some fabric tape (to pack out the slack on the intake tee under the silicone hose) and lengths of silicone tube to connect the air box / maf to the throttle body intake. If you use the 987 cayman inlet it may be possible to simply use the accordian tube from the 997 or cayman 987 to join the throttle body to the airbox/ maf 987 110 222 00 or 996 part 997 110 223 00.

You can identify the parts/ options using the online parts catalogue here :

http://www.porsche.com/all/media/pdf/originalparts/en/E_987_KATALOG.pdf

Just use the M97.20/21/22 option under the 987 model or the m96.05 under the 996 for 74mm TB parts.

Though i've not tried it , the 944 airbox tube looks like it may also be worth a look as a connector between the Throttle body and airbox housing if using the 996 tee, it already has a nice radiused curve.

[Johnny Danger]

So, has the 76mm TB been ruled out ?

[The Radium King]

the 74 mm, 75 mm and 76 mm is just different people measuring the same thing. call it 3" and be done. similarily, for reducers use 3.75" to 3.5" that are readily available.

[Stiletto Pat]

Bump for any new developments....