Is there a way to tell a S4 NA engine from a S5 engine just by looking in the engine bay. The engine in my 91 is not original and I'd like to make sure I'm dealing with the later engine before I start to modify.

TODD

 

On the older series the workds: "13B injection" are below the service on top of the engine, and stand out on the 91 series

 

EGR?? S4 had one, S5 didn't?

 

um...
basically the intake manifold look different
on the N/A at least
well if Tii with stock intercooler ...

 

the s4 and s5 look alot different.

At least between my two rx7s', they do.

One sure fire way to tell the difference between the 91 s5 N/A engine block (that I just replaced with an s4 87 N/A) is to look at the actuators that hook up to the lower intake manidold.

The 87 N/A's have these piddly two actuators.

The 91 N/A's have big beefy hulk actuators.

Hulk smash!

That's one way, eh?

Oh and btw, DC350.... Its good to see that you haven't killed yourself with some stupid motorcycle.

 

Pretty ahrd to reference aginst if you havenm't seen both, though.

This is an easy one: The water outlet neck on the engine is aluminum with a rad cap on it on S4's, and black plastic on S5's with no rad cap. Although it is possible to put on the S4 pump assembly on the s5 engine, and vice-versa, it is unlikely.

The S4 UIM says 13B injection in black painted letters on the top.

There is a pair of holes above the top (trailing) spark plugs on the S5 engines. (In turbo models, this is where the knock sensor was moved to). If the block is smooth, it has S4 rotor housings.

Those are the easiest ones to spot... I can go on if needed.

 

easy to tell, one looks like a 4 legged octopus, the other looks like a lego block

 

The forum is sooo much better now, but the damn search function is still wacky...but heres a pic of my old s4 n/a engine, if it doesnt look like that, its an s5.

 

This is an s5 intake manifold



That is pretty much the easiest way to tell the engines apart.

 

Thanks for the info guys. I bought my 91 NA as an everyday/work car. My weekend toy is a Porsche 911SC. I told myself I would not modify the RX-7 -- just use it for work and errands. As you probably guessed, that idea lasted about a week. Now I have two toys to tinker with in my spare time. Oh, by the way, I do have the later S5 engine. It just doesn't seem to run as strong as I expected. I'm ripping the cats off this weekend. Hopefully, I'll get a difference -- at least at the topend, where it doesn't pull well.

TODD

 

intake manifold. (everyone seems to have said that already)