S4/S5 questions
 

I know this question has probably been asked a million times, but I am going to ask it for the 1,000,001st time. What is the difference in the engines for the 86-88 engines and the 89-92 engines? My 90 n/a is about to blow up ((I have water on my spark plugs, and it won't half start, and when it does I get a big puff of white smoke and it quickly runs the water out and begins to overheat...also, it is not leaking the water out externally, so I think it's just burning it off internally)) so I parked it for the time being, but I have two 86-88 engines on stand-by. I have heard something about the rotors being lighter in the latter years or something, but I don't know. In any case, I think my internals are still good, but I might have cracked the housing. I really just need to know if I can use an older housing on my newer engine if this is the case. Somebody please help as I want to get my baby back on the road asap!!

lets see if i searched I would find out that the s4 has a different MOP, rotors, intermediate housing, flywheel, front counter weight, intake are different. Please do some searching your questions have been answered a bunch o times

Hey man i feel u i got a 89 gtu and iam waiting to put a 90 ported motor in my baby so if u got two series 4 engines sell them and get a ported s5 or even stock motor and stick to a s5 motor cause u gotta do a few minor mods to put a s4 motor in and your car will be slower since its only 146 hp where as the s5 n/a is 160 hp so in my opinion sell the two s4,s and get another s5 or get a rebuild kit and learn to street port your s5.

ok so you have to do a few mods to get an s4 into an s5 but are there less/more/no mods of putting an s5 into an s4?

Putting an S5 engine in an S4 cannot be done without some modification.

I wasn't asking about using the entire S4 engine in my car, just maybe one rotor housing. I know that there are vast differences in the S4 and S5's themselves, but I was just wondering, since the engines are still fundamentally the same, if maybe the housings were interchangeable to any extent. If they are not then do any of you guys want to buy two S4 engines? One of them runs so I hear............. I just picked them up to tinker on a bit maybe, but since I don't really seem to be able to use them any way, and the engine in my car already is better, then I guess I don't really need them any more.

And thank you very much for the smug remarks mr. gadget, you were quite helpful in solving my problem. Oh, and try to work on the grammar a bit there buddy.

I put a S4 engine in my S5 car. It works really well too. I used the S5 wiring, sensors, intake system and emissions. It's pretty straight forward. I changed the S4 front cover to use the S5 MOP. I blocked off the EGR valve opening, with a plate from Racing beat. I had to grind off a little metal on the rear iron, so that the VDI would fit. That area is right next to the inspection cover on the rear iron. I used JB weld to block off the split air ports on the LIM. They are right under the primary intake ports. I changed the connecter for the temp gauge on the wiring harness. I passed emissions very well after I replaced the pre-cat and the main cat with a bolt on unit made by Catco. One problem, I think it's related to the swap, is that the idle has a very occasional MISS. It rarely does it though. It was sort of frustrating, because I didn't get a whole lot of help, and the fact that this was my first rotary project. Hell, If you live by me I can show you the car. Unless you really know what you are looking at, you can't tell that it's a S4 block. My car seems to have plenty of power too, for an N/A anyways. I did this swap because I had bought a low milage S4 parts car. If you are broke, then go for it. I doubt you'd notice any power diffrence.