maf and throttle body diameter

[blue2000s]

I'm using Fluent in these simulations.

A Y will be more efficient than a T for airflow in a steady state, that's correct.

Keep in mind that with three cylinders to a plenum, there is a pretty much constant flow of air into the plenum when the engine is kept at a constant speed. There is always a cylinder pulling air. The pulses that influence secondary pressure waves are important, but they are secondary in nature so the influence on flow is on a much lower order than the primary vacuum pulled by the cylinders themselves.

Here are three more simulations varying on the one I posted earlier. The first one just adds a sloped wedge to the original T. The second adds a large radius to the T junction and the last one combines the radius with the wedge.





The volume flow rate results show that the T and T with wedge have almost identical flow rates. The radius-ed T with and without the wedge are both almost the same flow rates but are about 30% greater than the standard T.

[jaykay]

Originally Posted by blue2000s

I'm using Fluent in these simulations.

A Y will be more efficient than a T for airflow in a steady state, that's correct.

Keep in mind that with three cylinders to a plenum, there is a pretty much constant flow of air into the plenum when the engine is kept at a constant speed. There is always a cylinder pulling air. The pulses that influence secondary pressure waves are important, but they are secondary in nature so the influence on flow is on a much lower order than the primary vacuum pulled by the cylinders themselves.

Here are three more simulations varying on the one I posted earlier. The first one just adds a sloped wedge to the original T. The second adds a large radius to the T junction and the last one combines the radius with the wedge.





The volume flow rate results show that the T and T with wedge have almost identical flow rates. The radius-ed T with and without the wedge are both almost the same flow rates but are about 30% greater than the standard T.

Well done; well put. I was just considering any tendency to pull from bank to bank when the firing order is such that there is a strong intake pull from one side versus the other.

Looks like in theory the 'y' has some definite benefits...now comes the hard part part of testing varying shapes and geometries.

[Johnny Danger]

Am I correct in saying, rather than spending a $1000 + on the IPD set-up, it sounds like using a 74mm 996 throttle body, along with a 996 "T" that has been modified by Pedro, is the best and most cost effective way to improve the oem design ?

[AndyA6]

Originally Posted by Johnny Danger

Am I correct in saying, rather than spending a $1000 + on the IPD set-up, it sounds like using a 74mm 996 throttle body, along with a 996 "T" that has been modified by Pedro, is the best and most cost effective way to improve the oem design ?

Seems right to me!

[blue2000s]

Originally Posted by Johnny Danger

Am I correct in saying, rather than spending a $1000 + on the IPD set-up, it sounds like using a 74mm 996 throttle body, along with a 996 "T" that has been modified by Pedro, is the best and most cost effective way to improve the oem design ?

The IPD plenum rounds the inside corner of the T slightly so it's a little closer to the Y. Significantly more than the stock and 996 T. That's the important improvement, not the splitter.

That's what I'm showing. The rounded T flows significantly better than the standard T. The splitter doesn't do anything to the flow of either of them.

[The Radium King]

ok, update.

caveat - analysis officially works only for 3.2 S, but only because i don’t know anything about 2.5/2.7/2.9 intake systems.

whereby, airflow is limited by the smallest constriction in the system,

whereby, the only diameter that is inviolate is the maf housing which is fixed at 3” (to make it bigger would confuse the computer).

whereby, the throttle body is sized at 2.67”, introducing an unnecessary constriction in the system.

let it be stated that a 3” throttle body would increase intake efficiency.

now, the cayman, 996 and 997 all have 3” throttle bodies and share the same Porsche part number, so are interchangeable.

997 throttle bodies are hard to find, but there are lots of 996 units around (one currently on ebay for $100) and lots of cayman units around as folks take them off to install the ipd product (i just found one for $100 over at planet 9).

now then, with a larger throttle body we need a larger intake plenum. given that the throttle bodies are interchangeable so should the plenums. therefore we have 5 choices:

cayman ($300) - this dog doesn’t hunt. it has that funky resonance flapper, which results in a different aos arrangement and throttle body positioned further upstream.

996 ($60) - this would work, but the 997 piece is better.

997 ($60) - this is the guy you want. similar to the 986 but improved - larger diameter, matching aos connection, comes straight out instead of at an angle, improved flow characteristics. improved flow characteristics? as per earlier in this thread, it was shown that you want the inside radii as the air turns the corner into the intake runners to be as rounded as possible. examining images of the 997 plenum on pedros site (here: TechnoPower2 Kit ) it is evident that the 997 plenum has as much radius as possible given space constraints. in fact, the radius is better than that of the ipd product (images and dyno here: 986 Boxster / S | IPD Plenums ).

technotorque 3 ($300) - this is just a modified 997 plenum, with the addition of a splitter. as shown in this thread, the splitter does not contribute to airflow efficiency. this is further evinced by a guy on planet 9 who put a larger throttle body on his car and got a dyno; gains were equivalent to ipd but without the splitter or the cost (here: 75mm TB and Cayman Plenum upgrade for 987 - Articles ).

ipd ($850) - as above, i can see no benefit to paying $850 when i can get equal or more gain from a $60 part.

so, $100 Cayman/996/997 throttle body, $60 997 plenum, a 3” duct to the maf housing, a pair of silicone adaptors to mate to the intake runners, and some hardware (the larger throttle bodies are actually thinner and require shorter bolts). in for under $200 and a 10 hp gain (if you believe the above dyno).

[jaykay]

RK you are really chasing this down. I had though the 997 "plenum" had much longer stem section that would move the throttle body further down towards the oil cooler....had assumed that there would likely be little room for it. What would be the effect of moving the throttle body further upstream?

You now need to make up a special short silicon pipe that goes from throttle body to MAF

....or maybe I have got it wrong

Okay looks like I am confused as to what the 997 piece looks like

[The Radium King]

it's the 987/cayman that has the long-neck plenum. the 997 is shown in the link to pedro's site below and is quite stubby. i think the 987/cayman have the long neck to distance the throttle body from the resonance flapper on the plenum, there to add more low rpm torque similar to the resonance tube on our cars. the problem with this is that that flapper is an obstacle to airflow at high rpm/airflow situations. it also must mess with the vacuum available, as the 987/cayman aos has two connections at the plenum.