What would be the difference between the 84mm, 82mm, and the 75mm plenum and throttle body, any recommendations for a stock 997.1 TT ?

 

I would first spend the money on things like exhaust, tune, maybe VTG upgrades and some ICs... you will not see the DIFFERENCE your looking for on a stock 997tt.
all those mm figures are measured ID and OD.. and in many cases the 82mm is really the 75 mm just measured inside...
markski

 

I recently installed an 82mm ipd plenum and gt3 tb. It was by no means quantum leap in performance but there was a subtle increase in acceleration. Marksi is right if you want a big increase in power start with what he recommended. There was a thread on here where ipd put a plenum on longboarder's car and dynoed before and after and he gained over 25 hp on a stock car. I think its worth the cost but it won't transform your driving experience, just gives a subtle improvement

 

what about highly modified cars? Cars with above 800whp?

 

Well the logical thing I guess would be you need to increase all the air paths as you would be running bigger turbos which in turn need more air in and force more air out so have a bigger inlet plenum and TB you would assume would help but I'm sure to do it properly you would have to do calculations which I do not understand and most tuners do not from what I see.

So we usually just assume and bolt parts on and hope for the best

 

Not sure about the ECU's on the 997.1's but on the 997.2's, modifications will not add any HP/TQ about a certain RPM (~ 5,000) because the ECU has sophisticated logic checks that will reduce boost/timing to bring torque figures within factory specs.


So when I did the IPD plenum on my otherwise stock Turbo S, it gained +30/35 AWHP/TQ in the mid range but by 5,000 RPM, the gains were zero as the ECU compensated for the additional airflow. Now with the GIAC tune, I'm able to take advantage of the better flow from the plenum at all points in the RPM range.


So bottom line if you are going to do any upgrades, a tune is the first thing to do.

 

Thank you all for the advise.

 

Stock TB and plenum is fine till 650whp in my opinion.