maf and throttle body diameter

[jacabean]

what kind of realistic gains can be made by this mod ? if it is just a few h.p. like 5 or less i do not think it is worth the cost. if you can get about 10 to 15 h.p. then i think it would a good value. does anyone have any solid numbers for gains on a 3.2 engine ?

[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.

[jaykay]

Yes you are right...I started to think out loud without checking first

This looks like a viable option to try!

[The Radium King]

it's kinda exciting; if we can get 10 hp for under $200 it becomes the best bank-for-buck mod currently available. twice as much hp as the under-drive pulley for the same price, almost as much hp as a $1000 tune or $2000 exhaust setup.

[Johnny Danger]

King,

Seriously, what is the likelihood that you will actually make one ? I'm on the fence about spending $1000 plus on the IPD set-up, and I would very much like to see if your design works. If, so, I'll be your first customer .

[jaykay]

I didn't know that there was a Carrera S throttle body at 76 mm and dedicated plenum. Thought there was just a 74mm and then the 82mm GT3 which would be too big I think.

Which one did the Planet 9 fellow use? 76 shouldn't hurt?? I think reducers are easy but a nice pipe from the tb to MAF may be trickier

It is very exciting!!! I was just going to put 996 stuff in there as a trial.

[The Radium King]

it's already been done by j.fro (see his posts earlier in the thread) i'm only fine-tuning his work by stating that the 997 plenum is a bit more advanced than the 996 (but interchangeable) and should produce better airflow, and that the pedro splitter is not required (hence lowering the price). and located some dynos to justify the work.

for me, the cayman throttle body is on it's way.

on my next parts order i'll get the 997 plenum (997 110 416 03; auto atlanta online parts diagrams are your friend when it comes to comparing parts and part numbers) and throttle body bolts. once they arrive i'll confirm diameters of the reducers and hose clamps required.

from what was posted by j.fro, and what is shown on the pedro board, the aos vent line appears to use different connectors so i'll have to confirm diameter and get some tubing for that.

i'll probably use some cheap 3" flexible duct to the maf housing until i get my new intake happening.

once everything is done i can post a list of parts required and my impressions of the end result (no dyno or anything). i'm slow, and shipping takes forever to my neck of the woods, so no results anytime soon ...

[jaykay]

Yes I am with you ....plus it's cold up here!

The driving season and mod season are co-incident

Yes I saw his post after mine. I had assumed that my 997 plenum suggestion wouldn't fit as he had gone 996

It looks like it has nice radii as you pointed out. Let us know about the diameters when you get the 997. The hardest part will getting the right silicon parts to fit nicely and look like factory quality

[Johnny Danger]

No worries King, the Dangermobile has been put away for the season as well. But, as Spring draws near, I'd love to be able to implement your design .

[AndyA6]

I love this forum!!! Can't wait to do this myself!

[The Radium King]

ok, here's the quote from suncoast:

997-110-416-03 DISTRIBUTOR T 1 42.43
900-385-025-04 HEXAGON-HEAD 4 0.27 1.08
997-110-319-00 RUBBER SEALIN 1 5.49 5.49
N-011-524-27 WASHER 4 0.15 0.60
999-512-539-01 HOSE CLAMP 2 3.05 6.10

thats for the new plenum, four shorter throttle body bolts and washers, a gasket for between the throttle body and plenum, and two larger hose clamps for the larger plenum outlets. total $55.70 + $100 throttle body = $155.70 so far. all i need now is ductwork to the throttle body ($20 spectre flex duct from ebay until i figure out the geometry of my pending cold air intake) plenum outlet reducers (i'll wait for the parts to come so that i can confirm required diameters) and some tubing for the aos (only if i can't reuse oem; if not, i think i'll go with transparent so that i can monitor just what the aos is venting into my intake).

i still think i'll get in for under $200.

[onaFLYer]

This is great stuff, I was this <> close to pulling the trigger on the IPD plenum. Now I have a whole new direction for a fraction of the price.

Thanks for sharing this guys.

[Johnny Danger]

TRK,

Build one - build one - build one !