So I am going to build a street ported motor with SE housings and 12a irons. Will be a carbed 48IDA. How much real horsepower will I get at the wheels using the higher compression S5 rotors compared to the SE rotors? I figure it will cost me at least another $1500 bucks to use used S5 rotors. Will I see dramatic gains and a significantly faster car for shelling out that kind of dough?

 

Sad to say, but no. I have done that S5 rotor swap and my "butt" dyno showed no significant increase when using S5 rotors; but thats not to say you won't achieve added performance that a computer aided dyno could read.

Your real gains; however, are going to be from switching to the 4-port 12A plates. That made a quite noticable increase in performance for me while still just keeping the stock rotors. Very much worth the cost of the upgrade and I would recommend it highly.

Also - who is raping you $1500 for S5 rotors? For that price, just but a JDM core S5 turbo motor and be done with it!

Good luck!

 

sorry for the newbie question... just curious but what advantages do the 4 port 12a plates have over the 13b 6 port plates? i have heard of this a few times but i never understood why everyone wants a 4 port. is it the port work that can be done to these irons that make them more desirable?

 

I was recently faced with the some question when my 13B 4 port ate an apex seal. It ruined the old school rotor and housing (NLA) so I had to buy two of everything.

I spoke with an engine guy @ Mazdatrix and he said the difference in power would be about 5%, but added that an additional advantage is that they are lighter. the reduction in the rotating assembly weight will result in a engine that will rev more quickly. IDK how much difference this will make, my parts are on the way so I will see soon.

 

I'd love to take the credit, but you just answered your own question. The 12A plates allow for a more aggressive street port to be performed....not to mention better selection of manifolds, etc.

 

thanks keith for clearing that up. this forum rocks! i currently have a 6 port with a street port. when this engine goes south, i would like to build an engine like the above. who knows how long that will be tho... this engine is relatively new. i wish i knew this when i was getting the engine rebuilt. lol thanks again.

 

Hoang - FYI - the 12A plates only work for pre 86 13b's due to the location of the water o-rings. Just so you know. I don't know what year 13b you have.......but assume its the GSL-SE motor........

 

Do the old 13b 4port plates offer the same advantages over 6 port plates as 12a's?

 

keith,

you are correct, my engine is from a GSL-SE. good info to know. wouldnt want waste my time and money buying the wrong parts. thanks

hoang

 

Yes. Most are not nitrided, but you can port them just as far or farther. Ask Jeff20B for details, as he's familiar with the casting variations.

 

$1500 is an estimate but probably realistic. Would need 2 used rotors (2-300), complete rebuild kit (1200), and the proper counter weights (200).

 

Ahhh, so thats the estimate for the full build. You made it sound like $1500 for just the used rotors alone. Don't forget to add the porting templates and tools. Might as well port it while its open! Always add in a extra hundred for fluids, oil, grease, hylomar, etc.

Keep us posted!

 

Ya, no thats not the estimate for the build. That is really what the S5 rotors would cost to install above and beyond the build because I wouldn't have any of the proper seals or counter weights to use from the original SE motor. Really not worth it if all you gain is 5-10 HP!!!

 

I rebuilt my REPU motor recently, switched from the heavy 11.5lb rotors to the S5 n/a rotors. The engine certainly does rev up faster. Noticed that from the second it fired up for the 1st time!!

They took 4 POUNDS off the rotating assembly. Plus the apex seals are narrower and won't wear the rotor housings as much. And lighter. Dual apex seal springs. Dual dowel pins holding the rotor gear in place. Higher compression ratio. Can increase redline by another 1000 rpms. It was a no brainer for me.

Get a Rx8 e-shaft too. They're cheap, .4lbs lighter, have chamfered oil ports and no wear = higher oil pressure and tighter tolerances compared to a used shaft. Rx8 stationary gears too. The slope is slippery!

 

lol, yes, but its still cheaper than a honda...

 

much better if you take the entire RX-8 internals, not just the e-shaft

 

1+ with wacky your just throwing the balance off using parts from different years and mods...

 

yes, but that's why we know glen, and tom

 

I thought to make the Rx8 rotors work in a non renesis block you have to run ceramic apex seals since the Rx8 apex seals were never designed to cross a peripheral exhaust port and will warp. Or machine the apex seal slot deeper to use a taller, stronger pre 2004 apex seal.

Has anyone proven that 8 rotors make more hp than S5 NA rotors?

FWIW I had my rotating assembly balanced. It's quite smooth.

 

I heard the same thing, but do not know how valid it is. Makes sence, but I can't prove it.

 

Mazda Competition had some ceramic apex seals made up just for this purpose.

 

its been done before...my buddies at Sidepex. using TII block with complete RX-8 internals/seals, front and rear counter weight and such.

 

but if you ask me for the benefit of S5 rotors? you may gain a little bit more HP than the heavier pre-86 rotors, but there are other factors involved such as weight of the car, porting, intake set-up and tuning to name a few. so, you cant really feel the difference just like using a 3.90 gears vs. 4.10.

For N/A, I prefer the 3mm seals since I have good result and still going and going

 

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/rx8-rotors-n-fc-update-334609/

 

true. i went from an s4 na shortblock in my gsl-se to a gsl-se shortblock with 9.7's. the gsl-se ports are smaller than the s4's so it was down on power up top, but it had more under 2500 with the 9.7's

my friend had a 13B Bp engine and going from 9.4 to 9.7 was something like a 30hp gain.

either way i think it makes the 74-85 rotors paper weights