maf and throttle body diameter

[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.