Putting an S52 manifold back on an OBD1 S50 manifold-swapped S52

[PL8Racing]

We picked up a 1995 e36 M3 with an S52 OBD1 swap including the S50 intake manifold. We're actually looking to put the S52 manifold back on the car to try to improve the low-end torque. We're high-end horsepower limited in our NASA ST-5 race class and currently having to run a restrictor plate to get to the desired weight-to-horsepower ratio anyway, so thinking maybe putting the S52 manifold back on might knock down that high end HP a bit and give us a boost in the low-end torque, which is better for acceleration.

We still have most of the original S52 intake and throttle body parts. I think we want to keep it OBD 1 so we don't have to put a bunch of stuff back on the car, and ideally would like to be able to swap back without a ton of effort. Does anyone know what's involved here?

[blckstrm]

It's a lot of re-routing vacuum hoses. It took me hours to do the swap - it wasn't fast by any means.

I've had this same discussion with a friend - I don't think you're crazy. This is a good way to get more low-end when you already have too much high end.

But I also don't know why you think you'll need to switch back.

[zackinf]

Something to take note of:

OBD1 and OBD2 intake air temp sensors are not compatible with each other.

OBD1 intake air temp sensor is threaded, while OBD2 has a clip design of some sort iirc.

You'll need to find a way to block off the IAT hole on the OBD2 manifold, and perhaps tap a location to screw in the OBD1 intake air temp sensor. They are scaled differently and you can't just plug in the OBD2 IAT to your harness, if you're running on OBD1 already

[zackinf]

Maybe you could refer to the instructions of a M50 manifold conversion kit, like here: https://www.turnermotorsport.com/p-3...52s52/?pdk=AAE

And reverse engineer your way to install the S52 manifold.

All the best

[PL8Racing]

It's a lot of re-routing vacuum hoses. It took me hours to do the swap - it wasn't fast by any means.

I've had this same discussion with a friend - I don't think you're crazy. This is a good way to get more low-end when you already have too much high end.

But I also don't know why you think you'll need to switch back.

Will do some dyno runs and see how it behaves. We have a chip tune for optimized for S52 w/S50 manifold, so not sure what we'll gain or lose where. Worse case, if the torque/power curves don't prove to be advantageous, we'll swap back. There could also be tracks like COTA where we need to run w/more high end HP vs. more low-end torque. It really depends on what the dyno shows us. We also may end up swapping our ECU for a more tunable option, and we may be able to have more flexibility with the S50 manifold. Hard to know without putting it on a dyno and seeing what we see.

[PL8Racing]

Something to take note of:

OBD1 and OBD2 intake air temp sensors are not compatible with each other.

OBD1 intake air temp sensor is threaded, while OBD2 has a clip design of some sort iirc.

You'll need to find a way to block off the IAT hole on the OBD2 manifold, and perhaps tap a location to screw in the OBD1 intake air temp sensor. They are scaled differently and you can't just plug in the OBD2 IAT to your harness, if you're running on OBD1 already

Thanks. This is the type of info I was interested in. I'll take a look to see what I can figure out.