I've read some speculation about Mazda increasing the size of the rotors in the Renesis engine as a way to increase the power. Is there any way to estimate what the Renesis engine power output would be if the engine increased to, say, 1.5 Liters? I'm sure plenty of assumptions would be needed, but it would be interesting to estimate......

 

With the same power and volumetric efficiency a good estimate would be 238 hp X (1.5/1.3)=274 hp. However, most people have said the new engine would have 90 mm wide rotors versus the current 80 mm. This works out to 267 hp.

 

I have wondered that myself, that people quote a 1.5-1.6L size and then say the car will have 300 or so hp (maybe according to the Mazda method of calc hp ) and was wondering if as size increases so does the volumetric effiency, or whether they could include a retune of the engine to make it produce more hp.

 

what??

no the vE would probably go down, 'cuase of the side port to volume ratio. at any given rpm, the air charge would need to move at a higher velocity to fill at the same rate, at higher rpms reducing efficiency... this along with maximum piston speed is what lead to the lower redline for the F22C (a stroked F20C, the old S2000 engine).

at lower engine speeds, though, supposing the same port sizes, you'd have much better horsepower because of that larger displacement, and quite possibly more horsepower overall, but it'd be tough to hit the same rpm (the e-shaft too is getting longer by 2 cm at least, and in the heavier eccentric spots), and extremely tough to hit the same level of vE at the higher rpms.

the exhaust gas temp problems will still exist, and i'm praying Mazda will get **** right for the 2006 model (where hopefully they'll change some things, like the catalyst's proximity to the engine or something) and we'll get the whole shabang from the factory.

 

Wakeech, I was hoping to get a response from you. Could you take any guesses?

 

Until wakeech answers I can name a few things. They could increase the ports and retune the ECU, because supposedly the 1.3 can put out 280hp.

 

i dont know, but id love to see a 20b renisis!!! it would prbably be rated at 350hp, but then down rated to 238, and most ppl probably will get about 270rwhp...hahaha

 

well, actually, the ports are already on the verge of "as big as they get" in 6 port mode (much larger than the Series 5 motor, and all iterations of the 4 port 13BREW from the factory, due to the smaller beam height of the apex seals, allowing the ports to extend outward toward the perhiphery of the side housing... this also means that there is a whole lot less room to cut a bridge port, it may well be even impossible). for a high tuned turbo motor, a 4 port version would improve flow over the current 6 port design, but again there's that comprimise between low and high rpm horsepower.

if they were to go out another 1cm on the width of the rotors... oh, i dunno... say the redline comes down 1000rpm, and the horsepower goes up to... a rated 275-290hp (depending on lots of things that i could only postulate on...which is one of the only things i'm actually good at) at the flywheel to make it competitive with all other Japanese cars at this price level.

one thing that was talked about a long time ago which (surprisingly enough) hasn't come up again (and again, and again) is the idea of having a relocated tertiary, or even further a new quarternary port on the perhiphery of the rotor housing, now that the exhaust ports are on the side housings (thus resulting in an acceptable, even beneficial amount of overlap during high rpm operation). the only issue here would be how to valve this port effectively, as it could potentially hurt efficiency significantly when closed, and would seldom be utilized.

:D *feels so smart*

 

IF they do get a 1.5L out no one will buy it .. why? cause the gas milage would be like BS!

 

not necessarily.

the 13BMSP is actually suppost to be a good 22-24mpg combined at the correct level of tune... but at those A/F ratios the engine fries catalysts too fast (they must survive for 10 years to comply with new emissions regulations). so that's why the power is down, fuel economy is sucking, and all this stuff... just wait for them to get it all fixed up, and it shouldn't be nearly as bad as all this.

 

Wakeech, can you give me a quick rundown on all the engine designations please.

 

Also with a bigger torquier engine the final drive ratio could be a lot less steep...maybe 4.10 or even 3.909....should help with fuel economy.

 

ummm... ok. i'll skip the turbos.

the 13B is the longest running engine size for the Mazda rotary (and in my opinion, the second most awesome behind the 4 rotor). they were first seen in the RX-3's of yore(1978 was their last year), and were at first 4 port all-motor engines.

then in '85 you've got your Series 4 13B, first seen in the last year of the SA/FB (Japan and North America chassis designation for First Gen RX-7), making 135hp on a 9.4:1 compression ratio at 6000 rpm. i don't know the redline, but i'm guessing 7500rpm.

for the '86 Second Gen RX-7, it debuted with an extremely similar iteration of the 13B, making a mildly higher 146hp.

in '89 the facelifted Second Gen RX-7 was sporting the new Series 5 13B, making a higher 160hp at 7000rpm, with compression ratios now up to 9.7:1 and a redline at 8000rpm. the last model year of this RX-7 (and the grand GTUs) was 1991.

now in '04, we have the Series 8 (?) 13B-MSP, for Mulit-Side Port. with a 10:1 compression ratio, S-DIAS system (lightyears ahead of the old DEI system), far lighter rotors, and 9000rpm redline, it was originally tuned for 247hp at the flywheel. due to the emissions regulations, as everyone now knows, the horsepower is rated a very optimistic 238hp.

 

Cool....good info wakeech...redline on the 1st 6 port 13B in the FB, was 7000RPM....also 7000RPM for the early (86-88) FC 13B 6-port.

 

ah yeah!! i forgot to mention: all 13B non-turbo engines from the Series 4 onward have been 6 port motors.

 

except for the automatic RX8 which is 4 port

 

I remember someone posting about suggesting a relocated tertiary port/fourth power port (did I post that?). Instead of increasing displacement, why not settle for gasoline direct injection? Unfortunately, the United States' fuel grades are pretty cruddy, so I guess that is out of the question. But, someday...Some European cars use GDI (I hear their fuel grades are much higher than ours), which allows for ultra-lean combustion, more power, and better fuel economy. I remember when Mazda designed a stratified charge rotary engine years ago. The results were pretty close to what the production RENESIS is doing now, about 220 hp, all while utilizing a smaller displacement.

 

well, my first concern would be injector placement, where location on the exterior would pose a problem (it'd be awful tight up above the trailing plug). and after that, i'd wonder about how many injectors would be needed, and whether a good location for the injectors could be found that wouldn't interfere with all the other things arleady happening on that side of the engine (which kinda gos back to my first concern). then thirdly, with a lean burn system (which the 13BMSP is already suppost to incorperate, but we all know the ending of that story... supposedly it was tested at running around 21:1 at idle... yeah, i know, wow) with the power on, the already high EGTs will be higher, eh?? and that's already a problem as it is, sooo... displacement is good, DI or not.