I'm shortly going to be the proud owner of a '90 base model (I believe) RX-7 with a blown motor. I don't know what's wrong with the motor; I'm eventually planning on a V8 swap of some kind. I really wasn't thinking about even trying to get this thing running without an engine swap.
HOWEVER, I've found an '87 S4 automatic with a good motor and a blown trans for cheap. I'm thinking in the short run I could swap the good motor into the S5 and at least have some fun while I accumulate parts for the V8 swap. I don't know what trim level the S4 is (haven't looked at it yet).
I know there were differences between the S4 13b (146 hp) and the S5 (160 hp). Are they internal, external, or both?
Will the S4 motor bolt in and run with the S5 accessories?
Is the motor in the automatic cars any different than the manual one (a la early Miata)?
Any other weirdness or quirks to watch out for with the swap?
Is there a chance that the automatic car will have an LSD? I know it'll have 3.91 gears, which will be nice to have if I keep the stock rear end when I go V8 (or I can sell it to Miata guys).
S4 has lower compression rotors and a mechanical OMP if my brain is working today. I think you can just switch the anicillary stuff from the S5 and run it though.
If anything I'd run pre-mix oil anyway just to be safe.
There are differences both internal and external. If you don't live in an emmissions inspection required area, this will be alot easier.
I am in the process of putting an S5 motor in my S4 car.
Differences are:
S5's don't have EGR and S4's do (you will need a block off plate for the S4 EGR)
S5's have an electric OMP (oil metering pump) S4 is mechanical. You WILL have to swap over the front cover and OMP to get the computer to be happy. OR, you can run with the S4 front cover and OMP and keep the S5 OMP hooked-up but zip tied somewhere out of the way (not supplying oil anywhere, just electrically hooked up).
The intake manifolds are different. You SHOULD be able to use the entire S5 manifold on the S4 engine. There is one port that will not be on the S4 engine (small square port in the center of the engine). This port shouldn't effect anything. The intake manifolds are drastically different. The S5 has air-pump operated "6-ports". The S4 had exhaust back pressure to operate the ports. You can search this topic on RX7club and it will come up with a ton of info on what to do about the ports.
The S5 engines also have VDI. This is why you want to run the S5 intake.
S5 engines have a 1000 rpm higher redline. This is why they make more power. The rotors are lighter and have slightly higher compression also.
The water neck is different between S4 and S5. You shouldn't have to swap the necks over. This way, you will have 2 radiator caps. Not an issue. However, for future reference, you can't go the other way. The S4's only have a radiator cap on teh water neck of the engine. If you used an S5 water neck, it wouldn't have a place to put water into the system.
These are the differences that are relevant to your question. If you have any more questions, or specific questions, feel free to ask.
The flexplate will need to be removed and a similar series flywheel will need to be put on. YOU CAN NOT MIX AND MATCH S4 and S5 flywheels. The weights are different. You will need to find an S4 flywheel in order to do this. I "THINK" it needs to be from an NA, not a TII.
Hope this helps!
Rob R.
The automatic MAY have an LSD.
No emissions where I'm at, although they do a visual inspection that's supposed to include all emissions equipment being present including catalytic converter.
Appreciate the info. I'm going to have to do some thinking.
Hey Psteav - I may know where you can get 5 lug parts if you ever want to go that route. I have no info beyond that.
Screw OMP, go premix. Night and day difference on rotor housing wear after you disassemble it - much safer.
the 3.91s are all open diff.
there are mostly just intake side and electronic related differences which makes wiring a nightmare. however you can put all your S4 stuff on the S5 short block (be sure to still use the S5 flywheel because the rear counterweight is still in it) and everything will work fine. (as long as you premix)
singleslammer wrote:
Hey Psteav - I may know where you can get 5 lug parts if you ever want to go that route. I have no info beyond that.
Car's a '90, dude. It's already 5-lug. I think Starlet fumes have affected your brain.
fidelity101 wrote:
Screw OMP, go premix. Night and day difference on rotor housing wear after you disassemble it - much safer.
the 3.91s are all open diff.
there are mostly just intake side and electronic related differences which makes wiring a nightmare. however you can put all your S4 stuff on the S5 short block (be sure to still use the S5 flywheel because the rear counterweight is still in it) and everything will work fine. (as long as you premix)
Think you're thinking backwards, dude. S4 engine into S5 chassis, not the other way around. Or am I missing something?
In reply to psteav:
doesn't matter what short block you put in the chassis just make sure the flywheel matches the block and the intake manifold/electronics match the chassis.
fidelity101 wrote:
Screw OMP, go premix. Night and day difference on rotor housing wear after you disassemble it - much safer.
the 3.91s are all open diff.
there are mostly just intake side and electronic related differences which makes wiring a nightmare. however you can put all your S4 stuff on the S5 short block (be sure to still use the S5 flywheel because the rear counterweight is still in it) and everything will work fine. (as long as you premix)
2 things: If the OP uses the S5 electronics, the car will not operate properly (it will be in limp mode) if the S5 OMP is not hooked up to the computer.
Second, I am pretty sure that the automatic convertibles and the automatic SE sport cars had an LSD.
About the S5 OMP: 1) they are valuable if working. New ones are $1500 and up. 2) Even if working, if the PCM thinks it's not it can and will go into limp mode. It's aggravating as hell when it happens.
S4/S5 crank angle sensors are NOT wired the same. Ask me how I know. The VDC is run by the S5 PCM, it's possible to, if using the stock air injection pump, to 'tee' it into the pressure lines going to the 6 port actuators. That means it will do its thing at ~3500 RPM. IIRC the stock PCM activation is at ~5k.
Something else to note is that 86 and early 87 S4 RX-7 engines (up to serial number 550168) used low-impedance injectors, while mid 87-onwards used high impedance injectors. This thread has some useful info on how to determine which type you have.
http://www.rx7club.com/2nd-generation-specific-1986-1992-17/low-impedance-vs-high-impedance-injectors-866137/#post9532011
You will need to add resistors if you have low-impedance injectors.
All I have to add is that the 87 will have regular seatbelts. The 90 has those annoying death trap auto seatbelts. I hate them with such a burning passion...
clutchsmoke wrote:
All I have to add is that the 87 will have regular seatbelts. The 90 has those annoying death trap auto seatbelts. I hate them with such a burning passion...
^^ This.
If the interior colors are the same swap over the belts and interior panel bits to get rid of the stupid electric-motor belts.
Swap the S5 block into the S4 car. Change the front cover. Be sure to double check your end play again and make sure you don't mess up your thrust bearings.
http://www.mazdatrix.com/faq/pulley.htm
The warning about the flywheel is spot on. Find an S4 5 speed NA flywheel and put it in there, using the S5 flywheel you have isn't a good idea. The front counterweight shouldn't have to be changed.
If you swap belts, the carpet on the S5 is different from the S4 to accommodate the silly lap belt. If you swap in the S4 belts, you can hide it, it isn't very noticeable. OR, for true expert mode, get a carpet out of a Canadian s5 RX-7, they didn't use the mouse belts up there, so you can get s5 carpet colors without the missing piece. I suppose you could get a carpet from a 3rd party aftermarket company, too, if you specify it is for a Canadian 1990 RX-7.
Brett_Murphy wrote:
Swap the S5 block into the S4 car. Change the front cover. Be sure to double check your end play again and make sure you don't mess up your thrust bearings.
No. No title on the S4, and it's an automatic. Plus I think the S5 looks better, and I don't give a E36 M3 about automatic belts.
