well my 87 na is over the 150k mark and is running fantastic but i am just trying to think ahead as i need and use my car everyday. About a week ago i picked up a non running 86 base for 300 bucks and am thinking of rebuilding the motor in it as a backup for when mine inevidably melts ha ha. Since ther is not a rush on the rebuild i was wondering how i should go about it and what kinds of parts i should use and what i should do while the motor is apart. My biggest question is if s5 rotors would fit and work without a fuss and what kinds of gains i'd get with the higher compression and lighter wieght. (of course power and response i'm not that dull, i'm lookin for numbers ha ha) Im going for an upgrade in proformance but this is my first rotary and i've only been working on it for ten months, so i want to keep it on the milder side of the spectrum. I am open to any and all suggestions, thanks!

 

s5 rotors will work just fine in an s4 engine as long as you swap in the counterweights to go with them. I think thats all there is to it but I'll wait for someone else to back me up on it too. Make sure you go with a series 5 rear auto counterweight on an aftermarket flywheel or just swap your stock s4 n/a flywheel for a stock s5 n/a flywheel if you change the rotating assembly.

As far as gains go, you will see a small gain. Whats the difference between s5 NA and s4 NA horsepower wise, like 13hp at the flywheel? I've read that most of that gain is from the s5's variable dynamic intake, although I'm sure a little comes from the rotors as well.

 

its not that hard just swap the front counterweight and use stock s5 flywheel like what absence says.

also as far as i know theyre just higher compression with minimal gain on the stock na block.

 

would it be better just to rebuild it with the s4 rotors to avoid the hassle of swapping the flywheels and counterwights? and how much am i looking to be spending on a rebiuld? best place to get apex seals and gasket kit?

 

The s5 intake manifolds provide a bigger benefit than the s5 rotors.

 

will these bolt to the s4 block? will it affect aux ports?

 

yes, no

 

sweet! getting alot of good info guys thanks! Any other suggestions? any power adders i could add that'll improve my gas usage or at least keep me over 22mpg (my best now is 26) on normal driving? Best places for apex seals and gaskets and approximation on how much it is gonna cost?

 

yea s4 n/a rotors higher compression than s5 and the intake mani is better

 

i thought s5 had higher compression?

is ther anything i can do to get higher compression or greater displacement form s4 rotors? just an idea i was contimplating haha

 

S5 are 9.7:1 and S4 is 9.4:1.

You can add material to the dish of the s4 rotors but its not worth it. Just get S5 rotors and be done.

 

would it be worth the money to get s5 rotors if i am already swapping to s5 mannifolds? any prices fo a rebuild? places for parts??

 

The s5 N/A manifolds are not a 1 hour swap so be warned. Read the archive for a DIY how-to.

 

This is the first thread i saw talking about differences between S4 and S5 engines, but since i'm picking up an S4 engine on Sunday... and I have a 1990 Convertible (S5), will I have any issues. Sorry to Thread jack, the S5 engine is in bad need of a rebuild and probably has rotor/housing issues, so the replacement bottom end of an S4 is the route I decided to go... before I realized there were slight differences.

If I just took the short block (rotating assembly) from the S4 and mated it to everything in my S5 (accessories, manifolds, etc...) will i have any issues? Wanting to know if i should cancel on getting the S4 block and going with an S5 instead. I'm only out a $50 deposit if i cancel.

Thanks in advance.

Brian
http://2010.ChevyNovaLN.com/rx7/

 

Complete s4 internals in an s5 block will work just fine, just be sure to either get a stock s4 flywheel or if you have an aftermarket flywheel, get a s4 auto counterweight.

 

well, I wouldn't be transplanting the internals to the S5 block. I just want to take the potentially good S4 rotating assembly and bolt it to all the accessories, transmission, etc.. that i already have and be on my way.

So, the S4 housing(s) wouldn't be pulled apart, just mated to the stuff I have. is that a problem? no issues with intake, motor mounts, etc...

Sounds like I'd probably want to swap the flywheel from my S5 engine onto the S4, unless thats not cool?

Brian

 

Oh you mean the entire short block, not the rotating assembly? The rotating assembly is literally just that - everything inside the engine that rotates. The e shaft, bearings, rotors, counterweights, etc.

Yes the s5 manifolds will bolt right up to the s4 short block but the wiring harness may have to be modified to fit the s5 block (I'll need someone else to give you an answer on this). You may need to swap the front cover, but again, I'll need someone else to give you an answer on this.

 

sorry about that, I started wondering if I should've have just said the entire shortblock but i kept saying rotating assembly, even when i was talking to my coworkers. had a term stuck in my head.

so yeah, i'm wondering if i shouldn't just cancel getting that S4 shortblock and take the $50 hit. I really dont want to have a non-standard setup, i just want to drive it lol, not troubleshoot it.

Brian

 

if you have to wonder, then the s4 na and the s5 na engines are almost the same. on the s5 engine, what makes the power is primarily the intake manifold.