Plenum
04-05-2019, 07:52 PM
#16
Very good questions !
I have been looking into that and then, finally (about 2 years ago) decided for IPD, ..that came with a large intake air (rubber) tube (marked IPD) .
But, for sure, this also mean that you have to change the TB (move up to match ipd, i.e.: 74mm)
Note that at this point, the IPD distribute air into two tubes going to left and right in the air box.
These two distribution tubes are each close to the arrival diameter (74mm), ..or, it looks to me that the "weakest point” in the arrival of the airflow, is the long intake tube, the throttle box and the "plenum" ! (as after that, the flow is on two tubes, then airbox ..and then into 6 to each intake in the head.
If you calculate the difference in surface (Pi * r Square), from 68 to 74, ..you got a 18% increase over the OEM intake surface ..at the “weakest point”.
But, for sure, by adding intake surfaces, ..we reduce the intake pressure, so the volume of air in the intake is for sure not 18% higher !
I think one of the good work to do, is to have a pair of head that would be ported by a good professional (there are a lot of people having this knowledge from all the racing experience out there !)
By the way, (before head porting) my next thinking about the engine flow was about the header exhaust tubes, as the OEM design is absolutely awful.
I tried my own design, and frankly, I think I was lucky on my first try, as I’m pretty happy of the results.
But, I’m a strange guy, so my goals are most probably NOT like the major part of the customers for that (exhaust lines) :
I do not like the noise, I do not like to attire attention, and I love to be in Laguna Seca, where most of the time, the noise is limited to 90dB !
Or, what I have built is not a noise making machine, but having a goal for the best possible airflow, that would be as silent as possible !
Oups, ..sorry, ..this last part is out of topic !
I have been looking into that and then, finally (about 2 years ago) decided for IPD, ..that came with a large intake air (rubber) tube (marked IPD) .
But, for sure, this also mean that you have to change the TB (move up to match ipd, i.e.: 74mm)
Note that at this point, the IPD distribute air into two tubes going to left and right in the air box.
These two distribution tubes are each close to the arrival diameter (74mm), ..or, it looks to me that the "weakest point” in the arrival of the airflow, is the long intake tube, the throttle box and the "plenum" ! (as after that, the flow is on two tubes, then airbox ..and then into 6 to each intake in the head.
If you calculate the difference in surface (Pi * r Square), from 68 to 74, ..you got a 18% increase over the OEM intake surface ..at the “weakest point”.
But, for sure, by adding intake surfaces, ..we reduce the intake pressure, so the volume of air in the intake is for sure not 18% higher !
I think one of the good work to do, is to have a pair of head that would be ported by a good professional (there are a lot of people having this knowledge from all the racing experience out there !)
By the way, (before head porting) my next thinking about the engine flow was about the header exhaust tubes, as the OEM design is absolutely awful.
I tried my own design, and frankly, I think I was lucky on my first try, as I’m pretty happy of the results.
But, I’m a strange guy, so my goals are most probably NOT like the major part of the customers for that (exhaust lines) :
I do not like the noise, I do not like to attire attention, and I love to be in Laguna Seca, where most of the time, the noise is limited to 90dB !
Or, what I have built is not a noise making machine, but having a goal for the best possible airflow, that would be as silent as possible !
Oups, ..sorry, ..this last part is out of topic !
Last edited by GVA-SFO; 04-07-2019 at 12:41 PM.
04-11-2019, 08:26 PM
#19
My feeling is “touching” the plenum only is not going to “change the World”.
Air filter, intake tube, plenum, exhaust headers, are all acting like kind of links in a chain.
Frankly, I do not know if the plenum ..is the weakest link.
And I do not know if “math” do exist to point the weakest one ?
In my side, I really felt good, ..after changing them all, which I did one after each other, starting in the air flow order !
Now, if you want my gut feeling, I would say that the Boxster M96 exhaust headers are pretty horrible !
..my “2 cents” !
It is also true, that I did that on a 3.2 (2001 S), and having on mind a very clear point : do not make more noise !
Air filter, intake tube, plenum, exhaust headers, are all acting like kind of links in a chain.
Frankly, I do not know if the plenum ..is the weakest link.
And I do not know if “math” do exist to point the weakest one ?
In my side, I really felt good, ..after changing them all, which I did one after each other, starting in the air flow order !
Now, if you want my gut feeling, I would say that the Boxster M96 exhaust headers are pretty horrible !
..my “2 cents” !
It is also true, that I did that on a 3.2 (2001 S), and having on mind a very clear point : do not make more noise !
Last edited by GVA-SFO; 04-13-2019 at 01:23 AM.