polobai

Hi team, since I purchased my GT4 in February of this year, I have read up on the "big three" performance mods: Headers (race or street), a Tune (Cobb) and the IPD Plenum/GT3 throttle body/air filters combo. I was convinced on them all but have always had my doubts about the IPD plenum...always asking myself if it was worth it for the extra 1k or so for the performance benefit. For my particular setup, I am running the Cargraphic race headers with PSE, the Cobb accessport (currently on stage 2 OTS) and K&N filters (they were already in the car when I got it-didn't make sense to switch to the others in my case). At stage one with just stock headers and the filters, the car put down 348whp on a dynojet (about 403 hp to the crank with ~13.5 drivetrain loss). With the addition of the headers, I anticipate the car is making another 15-20 whp (around 420hp to the crank) although I have not re-dyno'ed to confirm). The next step is the IPD Plenum/GT3 throttle body to get to the magical 430 crank hp mark-but I am not convinced on the IPD Plenum (will explain more in a bit as to my reasoning). I had a hand in designing my short runner intake manifold for my previous Toyota Supra, so I had a bit of experience on the pro's and cons-one thing I knew for sure was that the throttle body had to be upgraded to the GT3's 82mm as thats where most of the power gains would be-just wished it would bolt onto the stock plenum. Here is my reasoning as to why upgrading to the IPD plenum is not worth the extra money in my case.

• IPD is Aluminum and transfers heat 10x more than plastic (though it does cool off faster than plastic)
• IPD has a "diverter" that aids with pushing air into the runners but it reduces the diameter of the primary pathways compared to stock (IPD does have a slightly larger secondary pathway)
• IPD is $1000 vs Stock
• IPD weighs about 4 lbs more than stock (not a huge deal but still)

If i could mate the GT3 throttlebody to the stock plenum and insulate the bottom side of the stock plenum-I think it will make similar gains...so the hunt was on for a stock plenum to work my magic . Here is a link showing some actual horsepower gains from insulating the bottom of the intake manifold on a Mustang- http://www.stangtv.com/project-cars/...ld-heatshield/

polobai

Notice the smaller primary (due to the diverter) but slightly larger secondary on the IPD
Here are some pics showing the difference in plenums taken from BBI's website:

polobai

Here you can see the diverter

polobai

polobai

m6 bolt and 17mm nut
The first order of business was to remove the factory "nutserts" from the stock plenum. To do this, you need a m6 bolt and a nut that is bigger than the nutsert-but smaller than the m6 bolt so it will pull the nutsert out as you tighten it. I found that an m6 bolt with a washer and a 17mm nut worked out well in my case.

polobai

Nutsert just smaller than the nut


Bolt with washer bigger than the nut

polobai

Here is how it goes together


Nutsert almost out


Here it is (I had already removed the others)

polobai

Now is where the fun starts. I had to widen the holes a bit on each corner. Then I purchased m6x50mm bolts and corresponding nuts to bolt the throttle body onto the plenum. If I had to do it again, I would get 55mm bolts as these were a bit short-but still workable.



The point of no return-I had to widen the holes a bit to make it fit-no big deal with a dremal.


using the stock gt3 gasket-it now fits


Here it is bolted up.

polobai

Bolted up with the throttle open, you can see that on the factory plenum, the ridge for the stock gasket is in the way.


Here you can see the gasket and ridge just to the inside


Pull off the stock gasket (but keep it)

jmartpr

I believe there's a GT3 TB spacer to mate it to the stock plenum....don't remember who the vender is but I'm sure it exist.

polobai

Ridge cut off using a dremal with a plastic cutting pad


Here it is smoothed out a bit.

polobai

There is...but its also $1000 from Agency Power i believe and does not solve for the problem with the stock gasket ridge above.

polobai

Now I could have stopped at the point where I smoothed off the ridge, however there will be an approximate 1.5 mm obstruction left just after the throttle body as the stock plenum is not 82mm wide, but closer to 76mm. This should not impact performance much if any-as this is happening after the air enters the throttle body (so after the throttle body)-the air will have to go somewhere once it enters the chamber. What it will impact slightly is the velocity the air can travel after the throttle body. What i decided to do to attempt to combat this was remove 3/16ths material from the flange and then smooth it out with silicone gasket maker so there is a more linear transition. If you attempt this yourself-be careful and dont remove too much material-otherwise it will go through the flange.


Additional 3/16ths material removed-yes, its ugly but I will smooth out


Smoothed casting ridges on interior of plenum

polobai

The silicone I used


Remember that OEM gasket I said to save? We will need that tab from it.


Cut the tab off using a blade

polobai

Silicone added and smoothed out using a putty knife-notice the tab added on the left and siliconed in place.


Shot with the throttle body back on. You will not need to use the OEM gasket, or the GT3 gasket-the silicone and nuts/bolts will secure the TB to the plenum.