Im in the middle of an engine swap of a S5 GTU-s engine into my 87 RX.
Im wondering if I can just use the S5 manifolds instead of the S4, for that extra 15 HP or however it is now.
I can see theres alot of differences in the vacuum line diagrams I've been able to find, but im just lost as to what I need to keep to pass emissions an all that fun stuff. Oh yea i swapped the front cover off the old S4 engine onto the S5.
Thanx to anybody who helps

 

IIRC i think the S5 engine had a hire compression ratio compared to the S4 engine, thus more Hp. I would not think changing the S4 for the S5 would make power at all. Maybe throttle responce..

 

9.7 comparedd to 9.4, but the s5 manifold also has the vdi-variable dynamic intake. which helps the power curve. i think there was a mismatch with maybe s4 top and s5 lower that made a really nice power curve not sure exactly how it went. Are you going to be using the s5 harness?

 

[QUOTE=Phantomkid; Are you going to be using the s5 harness?[/QUOTE]

No, I left all the electrical from the stock S4 in the engine bay.
My main problem right now is trying to figure out what vacuum and electrical to keep S5 or things that need to be S4, also I need to keep as much emissions components so I can register this car and drive legally, to break in the new engine an such.

I wonder if I need to have the 6port sleeves on the RPM switch to be activated? I think I read that S4 sleeves are activated via backpressure from the cat but S5 sleeves are turned electronically.
Well I've been having fun at least through this -what I thought would be a 3 day engine swap Turned into now going on a month+ project.
I have searched on the S5 engine swap into a S4 chassis, but I cant seem to find it anymore, so I'm just asking for some rotary guru's that could maybe chime in with some tips of what I need to do so I may be able to enjoy my Seven on the road! A month of not driving my RX has been harsh.
oh well at least I've gained a buttload of knowledge

 

S5 ports and the VDI are operated by the air pump. Not by electronics.

 

The S4 intake is known as the "Competition Intake" from Mazda.

 

Ok so how about those solenoid deals on the driverside of the engine? Are those S5 specific? i know they are not in the same order as the S4, plus I think theres an extra plug. Isnt one of these plugins for the EGR of the S4? Thus I dont need one of them becuz the S5 does not have the EGR. i know that much..

Now if i just wanted to for some reason, run the S4 manifolds, upper and lower on the S5 block, what would I do with that VDI hole beneathe the center intakes? JB weld it closed? Or should I just figure out what I need to do to make S5 mani's work???
im gettin so confused with these vacuum an electrical differences.

 

The VDI and AUX are opeated by the air pump but are activated electronically by the ECU using the solenoids.

The HP you get really depends on the compression as well. I put a set of S5 manifolds on my old S4 engine, it had 85psi on all faces. Made decent power I though after the swap. The engine poped later on and I swapped in S4 block with S5 rotors and put the S5 manifold on as well. I have 115psi on all faces. The engine was rebuilt before I put it in. Makes a lot more power then my other s4 block made.

you can see here how I used the solenoids, stock wiring, rpms switches and the air pump to operate the VDI and AUX.

 

Oh thankyou so much rotaMan99! Once i get off work im so gonna read all this an order all the parts problly so I can have ma FC running again you rock man!!

 

I should probubly note that I used the Fuel Pressure Regualtor Solenoid and The EGR solenoid on the setup I did in that thread.

Just don't forget anything like I did. Makes for a very aggravating job.

 

Don't do this. It serves no purpose and will defeat the purpose of having the VDI manifold. Not to mention that the S4 DC and S5 UIM wont even match up at ALL.

If you want to keep emmisions, you need to run the S4 LIM on the S4 block. But if you don't want emmisions, use the S5 LIM for a MUCH easier installation.

 

you're trying to pass emissions too? this is going to be a mess

 

There should be no problem passing emmisions with everything working correctly.

He would be able to have better access to the air pumps pressure if he used the S5 ACV.

 

Thanks for the input guy's. Now its my weekend finally! Hopefully i have all the parts I need to get this beast running at least b4 it snows again. it just rained for a day straight an now all the snows melted around here, I so want my fc driveable b4 it snows again...problly tonight oh well I'll see what I can get done

 

You have to use the S5 lower at least or you wont pass emissions,