Wow this is a nice thread. The plenum does more then one job.
1) place to mount the tb
2) connect the two intake halves

Now here is what I have learned. The tb needs to flow into the plenum not just be a tee connection (stock form) there needs to be a nice radius to help direct air flow not just drive it into the back of the plenum then spill over it to the halves. The next part is the two intake halves re verb between each other. This maybe more important the the size of the tb. I know if John is going to do some testing we will know a little more. A little quick math and 860 rwhp is about 1500 cfm. So I would say the stock black intake halves are good for 750cfm each so unless the stock tb and plenum can flow that it would be the weak link there based on what I have seen with my motor.

 

Here's a picture of the new (GT2 I think) inlet manifolds
Does anybody know their flow rates - as this is what the rest of the system should be matched to




AND - If you haven't seen the video, have a look at this link to the Porsche website
Just click the play button in the video window

http://www.porsche.com/microsite/tec...lectedVariant=

 

Yeh nobody changes intakes or even talks about them. In American hop up communites it's one of the first and easiest things to do. Its unfortunate that the first thing air hits after entering the TB is the back wall of the T plenium! Im sure the IPD one does a good job smoothing things out. But who knows what the intake runners can or do flow!? They may be the limit and may need attention. The same for the heads! Building the ideal motor I would certainly port my heads, particularly with larger displacement. Lets assume you can get the air to them head flow is ultra important and i cant believe people arent doing it while the engines are apart. If you think the vendors are porting your heads ur wrong! They are sending them out. Its a closely guarded art and anyone known for porting can port these heads too and give you flow bench numbers. I would also do a custom intake with larger runners that I'm sure any fab shop could make. I would run the shortest pre turbo intake system with the gentlest curves and most uniform diameter possible. The most
Important factor for volume of flow is tube diameter but tube length is important too. Ohm's law for all u science guys. A long length system like we see from the factory is an issue! From air intake to TB is quite a tortuous and convoluted journey. Air encounters drag along the entire surface of the tube and slows and disrupts air flow. Also the twist, kimks, turns, and upsize/down size it encounters really produces turbulent non laminar flow. But this is all perfect world stuff so if money is no object its something to think about. If money is an issue its just something to talk about! I expect this is one reason all the fender intake guys immediately notice much quicker throttle response and spool. There are a lot of factors.

 

Yeh the injector port is integrated with this where on the 996 the intake is connected to the heads with that silly rubber piece via manifold injection port. So it's intake to rubber pieces to injector port housing which finally itself bolts to the actual head. I wonder if this piece would fit if we got rid of 996 set up. Would be nice. I would do custom intake that runs front to back and runners emerge from a central air chamber. **** on the T plenum!! It's a bad design!!

 

NG with 996 heads and cams.. I use the 997.1 and made about 60 more rwhp over the 996tt ones. I am going to try a new setup when the motor is ready to go back in.

 

The oil cooler is in the way somewhat. but the 997.1tt intakes are so much better and work with the 996 ports. they are made of plastic so no heat soak and also have the injector bosses on them, they bolt right on down to the heads with O-rings. The plenum is a larger ID too. The 997 GT-2 runs big boost stock. The stock 996 intake halves have a lower port that on the 993tt is connected, just throwing that out there

 

Nice to know!! No reason for custom intake then. Porsche knew the T plenum sucks . Glad they fixed it.

 

I am using an IPD plenum with the 997 75mm TB with my billet Alpha3076 setup. To be honest I do not know if there were any gains from it since it went on same time as the Alpha kit. Some older dynos had dips in them at the end, I do not see that in mine. When I was getting it some told me not to bother - but they were on closeout at one of the vendors at price I couldnt say no to.

https://www.6speedonline.com/forums/...num-996tt.html

that thread made them seem legit - but i realize anything could be manipulated. i hope you do some independent back to back dynos of the plenum...

 

I am going this winter for 3076s and full supporting mods but TB&Plenum and also headers, going to use stock TB and ported headers.

My setup will be like : 3076, 4.5 IC, 2nd fuel pump & injectors, Y pipe, EBC, aso.

I will use the money saved on those for upgraded axles, hope I am right on my option.

 

Here are some pics of a intake I used

 

Wow ...Pretty trick...You must know what you are doing...

 

The only thing I know I am doing is spending lot of money on a 9 year old car! Guess you picked up something in those pic's

 

HI,I was at one of my head porters,Harley stuff, the other day to get something flowed and he enlightened me on this....Even though are stock TBs are 68mm,they have a throttle shaft and plate which causes turbulance and some restriction in the bore...So,he said that TB will flow less then a 68 mm straight pipe,Y-pipe mouth in our case....He thinks on the size of a 64mm straight thru pipe if he had to take a guess....Thats why I use and make more power with smaller flatslide carbs over butterfly style carbs with bigger bores..
So,maybe a 74 mm TB might help with a stock Y-pipe after all??...Turbo Mike told me also that the stock Y-pipe is fine and I would be wasting my money,,,atleast at my level??...Just some more thoughts here to confuse us.....lol...

 

Good info John!

I'm currently looking into the relationship between the y-pipes and the 'chambers' in the inlet manifold

 

I like the box that says ***