What makes the S5 n/a more powerful than the S4?
 

I did a search for this but couldn't find an answer. Is it merely the different intake that produced this 14hp gain? If not, what else contributes to the gain? thanks.

upped compression (9.4 to 9.7)
VDI intake system.
different intake manifold design
8000rpm redline (lighter rotors)

how was the compression upped? strictly by rotor design or somethign with the housings?

if so, would this mean you can swap s4 n/a rotors for s5 n/a rotors and achieve a higher redline and a bit more power?

The dish shaped indentations on the rotor faces were smaller. I am 99% sure that you can swap them and raise the redline.

the S5 rotors were machines a little cleaner. to put S5 rotors in an S4 motor, the front counterweight and flywheel need to be changed or an imbalance will make hte engine vibrate

hmmm......interesting

Not without also replacing the flywheel. The S4 flywheel is heavier than the S5 and really can't go much past 8500 before it becomes a time bomb.


as far as what changed in the engines:

The engines themselves used new lighter, higher compression rotors. The combustion recesses on the rotors were fully machined and chromed for heat control. With the machining, the compression ratios of each of the rotor's combustion chambers as well as rotor weight, could be more closely matched. The side seal thickness was reduced from 1.0 mm to 0.7 mm. The compression ratio for the normally aspirated models jumped to 9.7 and 9.0 for the turbo respectively (up from the 9.4 and 8.5). For both increased emission restrictions and better engine management the engine computer was speed was doubled.

On the normally aspirated (NA) engines the changes allowed the redline to be increased to 8000 RPM. A rotary valve was added between the intake tracks which started opening at 4500 RPM. This variable dynamic intake (VDI) valve enhanced the DEI (Dynamic Effect Intake) by altering the length of the fuel/air mixture path based on engine speed and load. The airflow meter was also changed from the flapper type to a linear type for reduced cost, air resistance and more precise measurement. The oil metering pump was changed from a mechanical pump to an electronic model for more effective lubrication and reduced oil consumption. These engine modifications raised the output of the NA 13B to 160 HP @ 7000 RPM and 140 lbft of torque @ 4000 RPM. The power band was effectively widened, giving more usable power at lower RPMs.

The Turbo II received a new turbocharger. Mazda called it the "Completely Independent Twin Scroll". The impeller was fed directly at the exhaust port. The Mazda press release in 1989 said: “This permits the powerful exhaust pulse generated by the opening of the exhaust port to directly hit the turbine blades without interference from the exhaust from the other rotor." This newer design resulted in reduced turbo lag and increased torque. The new electronically controlled wastegate allowed higher boost pressures and quicker response. The modifications resulted in the peak torque smoothed through the 2000 to 5000 RPM band. The horsepower also climbed another 18 ponies to give the revised Turbo II a Mazda claimed total of 200 horse power @ 6500 RPM and 196 lb-ft of torque at 3500 RPM.

Nuff said Icemark.:D

great info. gotta love diehard rotorheads

Of course icemark completely covers the subject making us all have wasted posts. :), this man (Icemark) is a genius you'll learn that soon after he answers all of your questions.

Icemark is definatly a man to ask questions to.. he know's it all

BOW to icemark! He OWNES ALL

-Markus

*bowing down* I thank thee o' great Icemark for enlightening thy newbie! *gets up off ground*

eh hem

Don't S4's have VDI also? Or do you mean they changed it? VDI has to do with the aux ports opening correct? when do they open on S4's?

No, S4s only have 5th/6th ports. The VDI came only on the 89-91 N/A 13B.

See on the stock 13B it runs out of breathing room around 6000-6500 RPM and there are no HP gains after that. What the VDI does is changes the length of the intake runners and dynamic effect at around 5500 RPM giving the extra breathing up to around 7200 RPM (after that again HP starts dropping off). For those Honda guys, its operation is simular to that of a Vtec engine (but of course years before Honda ever did it).

But the 5th/6th ports are simply ports that open around 3800 (the same spot the 2ndary injectors light up) so that there is now additional fuel and air being forced into the engine to keep up with the demand at higher RPM. In a twin cam piston engine this is compairable/simular to the 2ndarys coming on line at higher RPM.

Ice, the VDI system is effectively variable length intake runners, so it's not at all comparable to V-TEC. Some V-TEC engines have variable length intake manifolds as well.

However the 6-port induction system is the rotary's direct equivalent to V-TEC, because it alters port timing and duration the same way V-TEC alter camshaft timing, duration and lift.

But Mazda still came up with it well before Honda. ;)

Thanks for the correction

variable intake lengths go back to the early 80s with toyotas iirc. would the VDI not working make the upper revs feel flat on a stock engine?

Yes it would.