blackedoutFC3S

iTrader: (7)

Alright guys so I'm having a lot of trouble finding an S5 Turbo motor for my 89 GXL to rebuild and swap in. I've had a WTB: thread in both the Midwest and 2nd Gen Parts section but have not gotten any feedback on them of any for sale. But, there seem to be plenty of S4 Turbo II engines in the area for cheap. So, I was thinking about buying an S4 Turbo engine rebuilding it with a large street port, running the engine with a full S5 intake manifold as well as throttle body, S5 turbo throttle cable, and all emissions removed with block of plates. I'll also be using the stock N/A wiring harness and modify it to connect to the knock sensor, with an S5 turbo ecu. For now I'll probably stick with the stock N/A rearend with a Mazdatrix driveshaft. I also plan on using the S5 MAF, and pressure sensor. Basically I'm gonna try and get an S4 TII shortblock and build it up piece by piece.

First off, I was curious if this sounds like a good start to a build. I know people have used the S4 block with S5 manifolds, I just didn't know what all would be required to use these together, or as long as you have all S5 with an S4 block things will be fine. Also, I've I know the S4 Turbo has a twin scroll system where as the S5 does not, so I believe with everything S5 on an S4 block I would have to run the S5 turbo because of the twin scroll system. Also, I was curious weather it would be better to use the S4 or S5 tranmission with the system.

If there's anything else I was missing, please let me know. Basically the main point is running an S4 Turbo II block with everything else on the engine S5. I know it's a lot but thanks for the help to whoever reads through this and helps out, it'll help alot. If i missed anything and this is confusing my bad. Thanks fellas.

RotaryRocket88

iTrader: (7)

Swap on a S5 TII front cover (or premix) & use whatever transmission you can get. S4 & S5 TII transmissions are almost identical except for 5th gear ratios. All J-specs are .806:1 & US-specs are either .711:1 or .762:1.

blackedoutFC3S

iTrader: (7)

Alright so with the S5 cover on I should be good to go with the S4 block?

RotaryRocket88

iTrader: (7)

Yep. Usually it's the other way around (S5 block w/ S4 components), but you'll find a ton of threads on this. Rotary resurrection has a small writeup on the S4 -> S5 swap too.

blackedoutFC3S

iTrader: (7)

Haha ya I'm still hoping to find a complete S5 turbo motor but I guess I'll deal with what I have ha.

And thanks a lot for the help man!

KhanArtisT

iTrader: (2)

You can use the S4 turbo as long as you remove the twin scroll, which is easy and recommended unless you need boost as early as possible. But if you don't have one laying around I recommend that you buy an S5 for the larger turbine housing, divided manifold and bigger wastegate.

blackedoutFC3S

iTrader: (7)

If I build the engine from scrap, I'll go with S5, which either way I would prefer but If I have to get an S4 TII longblock then I'll probably remove the scroll which I've read about people doing.

RotaryRocket88

iTrader: (7)

Whichever turbo you use, port the wastegate first. This is much easier on a S5 turbo, since the S4 will need a larger flap welded in. The S5 wastegate can easily be expanded to have the area of a 35mm single or more, while the S4 is limited to ~23mm (w/out welding).

KhanArtisT

iTrader: (2)

Yeah porting the WG is good, it would be a bitch to have to remove the turbo again if you get boost creep. All you need is a washer tack welded on the flapper if you want to port the S4 to 32mm+, be sure to grind away some material from the plate that bolts on the housing to allow more travel too.

g14novak

iTrader: (1)

I'd personally go for the S4 over the S5 motor, but definately get a S5 turbo. From my understanding, the S4's actually have lower compression, making them better for boost. Sounds to me like you pretty much have it all mapped out though. But if your going to be going into large porting, I'd recommend going to a stand-alone if you can afford it. If not, at least swap out the harness and don't use the N/A one. Just personal preference since I'm having trouble with my harness right now.

blackedoutFC3S

iTrader: (7)

So reading from https://www.rx7club.com/2nd-generation-specific-1986-1992-17/my-s4-na-s4-5-turbo-build-thread-pics-774510/ it looks like I can change out the front cover, omp, S5 harness, ECU and the opposite injectors I should be good?

87 t-66

iTrader: (133)

i would also use the s4 t2 waterpump and housing because of the metal thermostat neck...and i would use the s5 alt because of the higher amperage. other than that it looks like you are on the right track

blackedoutFC3S

iTrader: (7)

Ya I'm thinking about maybe getting an FD alt for the build but I'll just see. Hopefully I can find an S5 engine here soon but If not I guess I'll keep an eye out for a good price on an S4 as well.

blackedoutFC3S

iTrader: (7)

So, I have a buddy doing a rebuild on the REW, he's wanting to switch rotors for my S4 TII rotors. If I go the leightweight flywheel route, in order for it to be correctly balanced do I need to get the REW flywheel and counterweight? I searched but couldn't find exactly what I was looking for. Thanks fellas.

blackedoutFC3S

iTrader: (7)

Bump for some help, still can't find what im looking for

RotaryRocket88

iTrader: (7)

Counterweights must match the rotors. But since both S5 TII and REW rotors are 9:1, I believe you could just use a lightweight flywheel and counterweight designed for an S5 TII. Someone correct me if I'm wrong, but the rotors should be identical in weight.

blackedoutFC3S

iTrader: (7)

Thats what I was wondering, mazdatrix has the flywheel it says for 7s from 89-95, so that must be what I'm looking at getting. Thanks alot for the help again man.