Engine differences? Please help. (pics inside)
 

Ok, I have an 89 RX-7 convertible, and when I got it, it had one rotor not sealing. So, after a year or two I found an 87 coupe with a remanufactured engine, papers say it was bought and installed in 2001. The coupe has a cracked frame, the rear suspension has separated from the frame, and the car has severe body damage. I picked it up for 900, and I figured I'll get my money back by parting it out easily.

Well, I got around to finally pulling the engines, and I got the newer reman. engine in the Convertible's engine bay. However, I have noticed that there are differences between the two engines. The fuel rail has different connectors on the coupe's engine. The intake manifold is also different.

I pulled the ECU out of the coupe, and it is N326. I haven't pulled the ECU out of the convertible yet, because the interior is so nice I didn't want to disassemble it just yet.

Here are some pictures of the two. I'm unsure if I will need to swap ECUs and wire harnasses between the two cars. I did some searching around here last night and found that (maybe) the ecu is different for the convertible.


Can someone tell me what will need to be done to get the new engine running in the convertible? Would it be as simple as just swapping the intake manifolds?

First - new engine from the coupe
http://mywebpages.comcast.net/evans.k/PICT0202.JPG

Second - bad engine from the conv.
http://mywebpages.comcast.net/evans.k/PICT0197.JPG

Pretty much - that's it.
There may be some port matching to be done between the S4 block & the S5 LIM.

Do you need emissions stuff in MI?

Well, both of these cars had EGR blocked up when I got them. There is no emissions testing in Michigan. I don't plan on attempting to fix this either :P

Am I to assume the engine from the coupe is S4? I really know nothing about these cars.

Yes, the coupe engine is S4.
You just want the bare block, with the EGR blocked off.

You will want everything else (including the MOP) from the vert, so it's ECU will be happy.

See this thread:
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/s4-s5-engine-swap-327921/

then read this page:
http://homepage.mac.com/carldavis/intake.html

Most people like to put the S5 engine into the S4 car because of some improvements...your going backwards.

If you want to use the block from the 87, you'll remove everything from the 87 engine block down to the bare core. Then you'll remove the front cover off the engine and replace it from the cover from the 89. Then transfer over the vacuum spider and all of the intake pieces from the 89 engine onto the 87 block, except the Lower Intake Manifold... You'll need to use the 87 LIM if you want the ACV to work.

After that, you'll be fine. Just remember that the redline of the S4 engine is 7000 RPM and the 89 engine is 8000 RPM. Let me know if you have any specific questions.

To use the 89 OMP, you will need to swap the front cover off the 89 engine.

Do not switch the flywheels. The flywheel must stay on the engine it came with for balancing.

Hmm.. well I wish I had come here before starting this.

While I thought I was nearly done, I see now that there are quite a few more things to do, and it might even be more worth my time to simply rebuild the S5 (currently sitting on the ground in the garage, looks to be a pretty straightforward rebuild process) and reinstall that, then just sell off the S4.

Sell the S4 engine, that should give you enough to rebuild the S5 engine your self, maybe even enough to send it to somehwere like Rotary Ressurection.

I'd recommend it! Disassemble the S5 engine and see what's bad inside. There are many ways to attack this rebuild...

You could use the parts from the S4 engine and the S5 engine, then have one strong motor, or only replace the bad parts on the S5 engine and have 2 good motors, or you could just install the S4 engine block in the car.

Before you start anything though, you should get your hands on the rotary bebuild video to give you an idea how hard it is. Good Luck!

Actually, I've got the rotary rebuild video. I've had it for a few years anticipating the purchase of an RX7. I've wanted one forever.

I think I'll sell this S4 on ebay, it's remanufactured, and it has only about 30k on it and the rebuilt transmission with a fairly new clutch (I inspected the clutch myself).

I figure I'll make what I paid for the entire car out of just this engine, then I can still part the car out. I'm pretty sure the apex seals on the back rotor are bad, because I get no compression on that rotor. When it was running (on just the one rotor) it was spitting gas. Actually, it spit so much gas that it filled the muffler up, and backfired, blowing the muffler wide open in an explosion that was so loud I was deaf in my left ear for about half a week.

I'm sure the apex seals are bad though because on top of no compression, the car had sat for approx. 1 year without having been run to keep things in order.