Carpokes Porsche Forum

Hey Everyone! I thought it would be interesting to have a dedicated thread on the debated topic of swapping an S2 intake manifold onto an S. There are threads on other forums, FB, etc of people that have successfully completed this swap, but unfortunately, there are no hard numbers to support any HP gains.

I had gone through the process of collecting all parts and installing then on my 1987 944 S. Unfortunately, I couldn't get the car to run right, which I believe to be the result of an aftermarket TPS and ICV. Had I used Bosch parts, I'm confident the swap would have been successful. I ended up going back to the factory S intake manifold. Nevertheless, I'll share the information here for those that want to explore this option.

Pros:
1) Improved throttle response
2) Easier access for maintenance (throttle body, TPS, ICV, etc.)
3) "Butt dyno" reports of more power - no actual dyno comparison (that I know of)
4) Aluminum IM (S2) vs. Magnesium (S) - better for paint or powdercoat if you want to pretty it up

Cons:
1) Cost and time to source all parts - figure $500 to $1,000 between used and new parts
2) Header panel removal to change air filter

Here is what you need:
-S2 intake manifold with throttle cable linkage
**VERY IMPORTANT - make sure all brackets on the IM are included (throttle cable support, Fuel Damper support). If you are missing those, it's VERY difficult to find those parts as most are with another intake manifold and won't be sold separately - they are also NLA from Porsche -S2 Throttle body
-S2 Throttle body to AFM boot
-S2 fuel rail
**you can use your "S" fuel rail but the top support bolt will not line up with the hole on the S2 intake
-S2 FPR (screw on fitting vs barb fitting on the S)
-S2 Fuel supply/return lines to Fuel Rail
-S2 Fuel supply/return lines from fuel rail to fuel damper
-S2 Throttle cable
-S2 AOS (especially if your S is an 87 model year)
-S2 Vacuum lines
-Vacuum restrictor valve (goes on vacuum hose from AOS to TB)
-S2 ICV hoses
-S2 dipstick and tube
-S2 AFM "Snorkel" and gasket (Connects AFM to airbox under header panel)
-S2 air box and filter
**Some just use a cone filter under the header panel instead of the factory airbox
-TPS wiring harness extension (I made this custom with Bosch style connectors)
-ICV wiring harness extension (you can try to stretch it but I wouldn't advise it)

Note 1: The S2 throttle body has coolant ports on the top - these can be capped off and aren't necessary. Note 2: Vacuum line routing is similar, albeit different to the S. It's not hard to figure out but wanted to call this out.
Note 3: No need for an S2 DME
Note 4: Take note if your S2 intake manifold is from an 89, or 90/91. The throttle cable linkage was updated (I forget which year) The old version of the linkage is NLA, so you will need to purchase the new style (available online) if you buy a new throttle cable. This is not necessary if you buy the IM and throttle cable from the same car What you can use from your S:
-Fuel Damper
-Fuel injectors
-TPS
-ICV
-AFM (you just turn it upside down)
-Plastic fuel rail cover

Recommended but not entirely necessary:
-S2 drivers side motor support arm - the S2 intake manifold is supported on the drivers side of the car by bolting to the arm. You could try to fab a bracket and drill/tap into your factory S arm if you are so inclined. Otherwise, it would only be supported by the allen bolts that mount to the head.
-S2 support bracket for the AFM "snorkel?" that keeps it from hitting the Headlight lifting bar.
Before
After

Thanks for this comprehensive write up.
Does the S2 airbox really fit below the NA/S header panel?

Thom wrote: Mon Feb 26, 2024 1:22 pm Thanks for this comprehensive write up.
Does the S2 airbox really fit below the NA/S header panel?

Sure does! It’s about the same size as the intercooler on a 951.

Interesting, thanks.
Because the header panel is smaller on the NA/S I was never sure if either the 951 intercooler or S2 airbox would fit in there.

Thom wrote: Tue Feb 27, 2024 6:30 am Interesting, thanks.
Because the header panel is smaller on the NA/S I was never sure if either the 951 intercooler or S2 airbox would fit in there.

Good point - I didn't think of that. It was definitely a tight squeeze. Given the location, I would think an aftermarket cone filter would give better airflow anyway. Add a vented header panel and it should breathe pretty easy - sort of like a "Ram Air" effect, if it wasn't for the restrictive AFM.

This is an interesting swap, and there's good information on what's needed to accomplish it. However, there appears to be no data on the practical value. Without proper before and after data, how can one consider the swap? Perhaps someone with access to a chassis dyno can show some real-world data on before and after results.

michaelmount123 wrote: Wed Feb 28, 2024 11:40 am This is an interesting swap, and there's good information on what's needed to accomplish it. However, there appears to be no data on the practical value. Without proper before and after data, how can one consider the swap? Perhaps someone with access to a chassis dyno can show some real-world data on before and after results.

I have been talking to a friend about doing this, and also putting a 968 intake manifold on my S2 for a comparison as well. All with stock engine management, stock air box, stock filters. Hoping to do it later this year...

I am of the opinion that an S2 manifold on an S1 is a downgrade. The S1 intake (if I am not mistaken from what I have read) is tuned, and the S2 is not, since it had the displacement bump.

michaelmount123 wrote: Wed Feb 28, 2024 11:40 am This is an interesting swap, and there's good information on what's needed to accomplish it. However, there appears to be no data on the practical value. Without proper before and after data, how can one consider the swap? Perhaps someone with access to a chassis dyno can show some real-world data on before and after results.

I can understand your point, but many get the "modification bug" and are looking to do something different to see if it works. From my research, the 968 has been reported to have the "best flow" of all the 16V IM's. However, it uses a different Throttle Body and TPS than the S and S2. I originally purchased a 968 IM to attempt the conversion but abandoned it once I went with the S2 swap instead. The only things that are CONFIRMED is improved throttle response and it is MUCH easier to access key items for maintenance and/or repair.

stitch2k1 wrote: Wed Feb 28, 2024 12:48 pm I am of the opinion that an S2 manifold on an S1 is a downgrade. The S1 intake (if I am not mistaken from what I have read) is tuned, and the S2 is not, since it had the displacement bump.

I don't have sufficient data to support any claims, but just looking at the setup of the 2 systems makes me believe the S2 is a more efficient setup. On the original S, air has to pass through the airbox (in the hot engine bay), travel through the AFM, through a long plastic tube, make a 180 degree turn, then through the throttle body and into the intake manifold. Not to mention the additional length of the throttle cable that requires a pulley to also make a 180 degree turn back to the throttle body.

The S2 has a much more direct flow setup (airbox or cone filter under the header panel - shielded from engine heat) and if the AFM could be taken out of the equation (like with a MAF) it would be as close to a ram air setup as could be on a 944.

stitch2k1 wrote: Wed Feb 28, 2024 12:48 pm I have been talking to a friend about doing this, and also putting a 968 intake manifold on my S2 for a comparison as well. All with stock engine management, stock air box, stock filters. Hoping to do it later this year...

If the S2 throttle body bolts up to the 968 manifold, this would be a great test - especially if a dyno is available to provide results. The 968 has a totally different throttle position sensor (and MUCH less expensive than a 944), so I don't think the S2 DME will get the proper readings unless it has an S1/S2 TPS.

NCGermerican wrote: Wed Feb 28, 2024 1:50 pm The S2 has a much more direct flow setup (airbox or cone filter under the header panel - shielded from engine heat) and if the AFM could be taken out of the equation (like with a MAF) it would be as close to a ram air setup as could be on a 944.

The S2 airbox will still get heat soak from proximity to the radiator. It's also a very inefficient airbox set up. Can't really describe it other than if you see one you would get it. No doubt in my mind that a good cone filter would do better, which I also intend to dyno test.

NCGermerican wrote: Wed Feb 28, 2024 1:50 pm If the S2 throttle body bolts up to the 968 manifold, this would be a great test - especially if a dyno is available to provide results. The 968 has a totally different throttle position sensor (and MUCH less expensive than a 944), so I don't think the S2 DME will get the proper readings unless it has an S1/S2 TPS.

Not sure about this. I'll figure something out.