S4 vs S5 13BT
 

I've got a 1988 10AE, and since I've had it it's had an S5 13B-T in it with all s4 parts on it. lately I've gotten a PILE of s5 parts, and now an s4 13B-T has landed in my lap.

my last setup was s5 block with s4 manifolds, and my new setup is going to be s4 block with s5 manifolds. How much of a power/driving difference is there going to be? 7000RPM is the absolute max that I should rev a stock s4 motor to, right (especially in the upper gears?)

Are they pretty similar?

Short answer - they are basically the same.

Long answer - the compression ratio difference is going to make the Kouki motor a little peppier at low RPM's.

You're using the same turbo on both engines, right?


-Ted

Aren't the endplates different?

I heard the sparkplugs are located in different spots and S5's make more power per psi. (Given the same compression ratio. Is this true?)

Rear iron is stronger at the oil filter pedestal, but this has nothing to do with more power. :)

Yes, the Kouki rotor housing spark plug positions are lower - thus, more ignition timing advance.

I doubt you'll feel the difference.



-Ted

Ignition timing is a reference to the eccentric shaft in degrees. Moving the spark plug lower does not advance the ignition timing, the rotor is still in the same position when the sprak plug fires, ignition is unchanged. The rotor is still in the same position when it starts being puched forward, but the rate at which it is being pushed forward is changed.
Timing is a reference to engine position, not to spark plug location.
Moving the spark plug position changes where the flame front propogates. Some areas are more efficient.

The rotor position might be identical, but having the spark plugs fire "more forward" does have some effect on ignition timing.
Are you implying it isn't?


-Ted

are the intake and exhaust port locations identical?
Plus that may affect timing, but so what? if they are lower they fire later by default, right?

How can it? Ignition timing is a position-based reference to the rotor/eccentric shaft position, not spark plug location.
Mazda didn't change the timing between the S4 and S5 models despite the change in spark plug position.

The intake port runners on the Series 5 engine are taller than the Series 4. There's more potential power to be had with them.

B

Brian, any comment on spark plug position affecting timing?

When it comes down to it, it's the ignition and combustion upon the "leverage" of the rotor (in this case).
Firing at the rotor with advanced ignition timing with higher spark plug positions is *almost* the same as firing at the rotor at less ignition timing with lower spark plug positions.

Think about it in terms of a piston engine...
The reference of the spark plug firing versus the position of the piston position...
You can argue that repositioning of the spark plug in a rotary engine would be equal to repositioning of the spark plug in a piston motor by moving it around in the head.
Now, it's right and it's wrong.
In one sense, it's true.
But, for a piston motor the "position" of the combustion chamber is static - it doesn't move.
In a rotary engine, the "position" of the combustion chamber is dynamic - it's constantly moving.
In that sense, it's false.

BTW, the Kouki turbo primary intake ports open 10-degrees later than the Zenki turbo primary ports - this is all found in the FSM in the specs section at the back.


-Ted

And how does longer runners tranlate into "more power"?


-Ted

It's kind of funny, because it's frankenstien now, just in a completely different way that it was before.

BEFORE:
S5 block. S4 Manifolds, turbo, TB, etc, etc, etc
NOW:
S4 Block. S5 Manifolds, S5 Turbo, S4 TB (I think I have to use an S4 TB, but if not then I'll use the S5 - it looks a little bigger), s4 other stuff.

Other mods (stays the same) - top mount with spayer, 3" exhaust, ghetto intake with cold air box.

I've got an s5 turbo available so I figured that I may as well use it, better wastegate design/etc.

Which block is better when they are both built up?

When pinned, ported, and both with S5 manifolds, do they make the same power/reliability? (assuming equal compression)

the S5 motor is dead now due to boost creep. Both were stock, I'm assuming.
I haven't checked the compression on the s4 block, but it seems to be a good strong motor, I pulled it out of a car with 80,000 miles.

Why would Mazda change a very expensive casting when they could simply have adjusted the timing maps in the ECU if it only affected timing?

ANYWAYS, back on topic here, how much of a power difference am I going to see? any other differences?

The 7000RPM redline kinda sucks.. I used to wind the car out to 7500, but oh well.

Zenki - stronger rotors, but less compression - 8.5:1

Kouki - lighters rotors, more compression - 9.0:1 ; reinforced oil filter pedestal, hardened stationary gears


At ultimate block strength, the Kouki engine is stronger.
At insane boost levels, the Zenki rotors are desirable due to them being more "dent resistant" from detonation.