Those 4 piston brakes possibly saved my life last sunday! I hit a deer on the interstate but if it weren't for those brakes i would have hit it A LOT faster.

Just to follow up, my 4 lug rear calipers worked with the 5 lug solid rotors, no issues.

Also went ahead and replaced both tie rods, ball joints and got Corksport SS brake lines.
Went with advance auto rotors and Hawk HPS pads.
Getting tires and alignment this week and I'll hopefully be ok for a while.
New struts/springs are next on the list. Followed by poly bushings.

I have an s4 4-lug base model. Single Piston caliper fronts, non-vented rears. I'd like to get 4-piston front calipers and vented rear discs but I don't intend to do a 5-lug swap since I like my rims.

Will the 4-piston calipers bolt on to my spindle? Are the rear calipers for the vented rotors different in any way other than the wider bracket and will they bolt? And do I need to change my master cylinder as well?

I looked in the forums and this thread is the best for this topic I think.

All the base models for S4s and S5s had single piston calipers but one is 4 lug and one is 5 lug, so the knuckles should be the same right? Whether 5 lug or 4 lug.

See Aaron's how to: http://www.aaroncake.net/RX-7/4lug4potbrakes.htm

I'm also looking to do this next... But only in the front. Is there even a 4 piston rear caliper option? I thought all the rear calipers were the same.

Also would anyone have feedback or comments on pedal height after conversion? And would a new master cylinder ever be needed?

I was wondering this and checked Mazdtrix. They differentiate between ABS/non ABS and AAS/non AAS, but not between 4 and single piston front calipers. I think that it's simply the fixed calipers have pistons 1/4 the area of the floating units, or the pistons are slightly larger and the reduced flex compensates for the increased pedal travel?

The idea with 4-pots, aside from the cred and sex appeal, is that there is more mass to draw heat away from the rotors and pads. And to prolong the boiling of the brake fluid. A DD won't need them. Even an autocross car probably won't need them. But Ryouske Takahashi and someone who tracks the car would need them. But...since when is Rx7 ownership about need? :)

Oh, the rear calipers are different, but identical aside from width. The vented rotors are thicker and the caliper integrates the parking brake, so they need slightly deeper calipers for the vented rotors.

Sorry, Glory, but I disagree with most of this.

The FC's "soft pedal" is the result of design specs and tester preference, not caliper flex. Even FC's originally equipped with the 4-piston calipers exhibit what many (myself included) consider a "spongy" pedal...brakes work fine, they just don't "feel" like it.
A bigger booster/MC combo can fix this.

The "idea" with 4-pot calipers is greater and more even clamping power on the pads, not heat dissipation. The larger and more enclosed caliper body is actually worse than the single piston slider caliper in heat retention (but you are correct that this is all moot in a street car).

I am having a heck of a time finding the right rotors for mine for some reason. I picked up these duralast PN: 3194 and the flathead holes are not lining up with what I have. The ones they are sending me are 1 3/8 from outside of each hole (Flathead edge to lug throughhole outside edge) and the ones that I need have 1 5/8 space between them. I know they introduced abs in 87 or 88, My 86 GXL does not have abs, but has the AAS and 4 piston calipers. My car sits on jackstands until I can figure this out. The hubs seem to be shiny, like alluminum- could they be aftermarket and thats why these parts arent fitting?

Mine didn't match up either. I just went with it. I don't think the screws are that important.