50mm S38 Throttle body Installation to S14 BMW M3
The reason I went to 50mm intake is that I wanted to try to make an adjustable intake system. The problem with 50mm runners is that the torque at low RPM will suffer. But since I’m planning to build adjustable length runners, I should be able to tune the length of it. According to my calculations I should be able to take advantage of the 2nd and 4th pulse.
What you need is 50mm throttle bodies from M5/M6 S38 engine.
Head needs to be modified to have the bigger studs and dowels. Also, make sure your intake ports are modified to support bigger intake.
In S38, Air from ICV enters the throttle bodies from below, not from the middle like in S14. Since the throttle bodies didn't come with this channel, I had to modify the throttle bodies so that I can use the same setup as in S14. What you need to do is as follows:
- Plug the holes at the bottom where S38 vacuum channel is connected. I used screws and epoxy to seal it. See picture 1
- Hole needs to be drilled between the ports. You need a long, 6mm drill to do it. The Hole needs to be drilled here as shown in the picture 2.
- 14mm holes are needed to be drilled so that you can use the idle adjustment assembly.
- Also the return hose from the idle adjustment piece has to be plugged. Otherwise the air returns back to the airbox.
Also following modifications are needed:
- Throttle linkage bar is too long, so it has to be cut
- Injector ramp mounting flange has to be moved. I cut the old one out and it was welded to a new location.
If you are planning to use the original airbox, it needs extensive modifications (Mine is for sale now if you are interested):
- Old intake horns won’t work and a new method had to be invented.
- Airbox support is too short, so I had to be extended.
- Airbox will hit the brake booster and has to be modified. I also moved the air inlet to the front.
Next step is to make adjustable length runners, but that’s another story. This was the reason to 9000rpm limit. Another interesting test would be to try out different firing orders as Renault F1 team tried out. See more details here: Renault firing order.