One of the things that had us concerned was that the RS pan has a vent hole in it that seems to be allowing airflow to the lightly finned dry sump oil pan of the engine. 

We were going to cut a matching hole for the dry sump pan in the 911R diffuser which would have messed up its effectiveness. However, the engine has a pretty effective water to oil cooler, and it's a dry sump so not much oil is in there anyway. 


Here is a closer look at the dry dump pan vent hole in the stock GT3 pan.

One of our friends that has a 991.1 GT3 has added the 911R rear diffuser 18 months ago and has done numerous track days with no heating issues.  Also, when we looked at a brand new 991.2 GT3s, we noticed that it did not have a hole either in its pan, so we decided to install the 911R diffuser as is with no hole. 


Here is the stock RS pan on the right compared to the 911R diffuser on the left.

As you can see the 911R diffuser is much bigger and covers more of the car's bottom. The outer strakes cant outward to improve the diffusion ratio, making it more effective.


The 911R diffuser bolted right in using the same allen bolts as stock. It was super easy to get it back into place. 

After starting the bolts by hand, we simply tightened them with an allen wrench, and we were done!

Finally, we wiped the 911R diffuser down. It was covered with an oily residue and dust from the factory. We think it might have been rubber lubricant from the grommets. 


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Thursday, February 15, 2018 3:13 PM
What possible reason could Porsche have for not making that a stock part on the RS? I mean, I understand the base model Carrera.
Mike Kojima
Mike Kojimalink
Thursday, February 15, 2018 3:21 PM
Maybe because the 911R was developed after the RS? The 991.2 GT3 has a rear diffuser, possibly this same part.
Thursday, February 15, 2018 9:08 PM
Great oem mod.
Would be cool extend the vortex generators out on the muffler and past it in stainless and weld it on. Make it look like oem as well.
Thursday, February 15, 2018 9:29 PM
This article is a great illustration as to why Porsche went with a mid-engine layout for their newest 911 racing machines. The rear diffuser you installed is a lovely part, but it is so dinky in its proportions. The angled portion is not very tall or deep and just looks anemic compared to functional after-market diffusers I have seen on other front-engine and mid-engine cars. That rear-engine layout just doesn't leave much room for a big, bad diffuser.
Mike Kojima
Mike Kojimalink
Thursday, February 15, 2018 11:32 PM
KKOG, what a great idea!
Mike Kojima
Mike Kojimalink
Thursday, February 15, 2018 11:33 PM
StrangeLiform, you are 100% correct.
Saturday, February 17, 2018 4:01 AM
The hole in the plate is not for the PDK, the PDK is in front of the engine!
Mike Kojima
Mike Kojimalink
Saturday, February 17, 2018 6:16 PM
you are right, I don't know what I was thinking! I was staring right at it too. A Porsche "expert" told me it was the pan for the PDK and I turned off my brain I guess.
Tuesday, February 20, 2018 10:34 AM

The 2018 GT3 comes with a proper diffuser now!

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