Over the past year and a half I've been restoring my GSL-SE. New paint, a new S5 NA engine assembled, and the FC subframe swap is done. Well, the subframe itself is installed at least.

Subframe swap questions:

• Can you use the GSL-SE power steering pump on an S5 engine to power a 2-port FC rack?
• Can you use GSL-SE front calipers with 4-lug FC rotors or do I need FC calipers?

Engine questions:

• Any issues running my GSL-SE parts (intake, injectors, ECM, etc) on the S5 keg during break-in? I know the spark plug holes are further apart so I am worried about timing. Eventually I'll swap to the S5 intake and ECM for more power

 

the GSL-SE intake/ecu stuff is all plug and play on the S5 engine, which is nice. everything will work, even the emissions. i would use at least the FC exhaust manifold though, its better.

 

S4 base model (4 lug) front calipers are the same as the GSL-SE I believe, but the bracket is different, so you would need, at minimum, the S4 brake caliper bracket. The S4 base model brakes are usually very cheap since most people don't want them. It's what I run on my FC subframe swapped FB's and they work very well.

I run manual steering, so I can't say for certain if your SE PS pump will work with the FC rack, but I can't imagine why it wouldn't. I doubt Mazda changed much about them over the years.

 

The only reason I want to use the GSL-SE calipers is because I have 4-pot calipers here ready to install but they wont fit under my original wheels with the proper 4-pot rotors. I don't feel like buying wheels yet, so I just want whatever brakes will work the cheapest. The rotors will already be $40 more or less wasted

 

S4 base model calipers are almost the same as 12A. The 12A caliper bolts up to the FC hanger (and, presumably, vice-versa) if you use the appropriate slide pin.

I say "almost" because I have one 12A caliper and one FC caliper on my car, which has a full FC suspension swap. I bought new pads, because the OEM brake pads that now have close to 240k on them are now worn out. This is when I learned that 12A calipers are sliiightly shallower than FC calipers. 12A caliper plus new FC pads equals no fit.