j9fd3s

so ive been looking at a bunch of different engines and theres something i dont get.



the 4 port renisis engine (we changed one, leaked coolant between the irons), has small very round port runners 40mm?, but the actual port opening is HUGE (big big street port) engine makes 200ish hp, 06 is up to 212.



the cosmo 13b had GIANT port runners, and big secondary ports, but the primary ports are small. it is designed to haul around with an autmatic, in a big car.



the fd has smaller secondary ports, smallers runners, bit the primary ports are larger than the cosmo.



and then the fc motors seem to have medium sized ports and runners.



so it seems like mazda has been playing with port size/vs runner size, but its not clear why? why does the cosmo have such big runners (larger than the t2's), but smaller primary ports? i see where they want more midrange, but then why doesnt the fd share the large port runners?

fc3sboy1

toqure curve,,,,,,,,,,,,,,,,,,,,,, but not only did they change the intake ports they also played with the exhaust ports as well. i was told it was for toqure curve and the technolagy over the years have changed there design. also emissions was mentioned in that convo with ken from mazda japan.

RONIN FC

The huge port in the renesis is all about timing and charge velocity. A concept i think people are missing when they port their engines.

heretic

The only reasoning I could ever see for the luxury car engine (Cosmo) having huge port runners, is that there were some crackheads working at Mazda at the time.



The engines were intended to be dead and buried by 6500 and use a pair of small sequential turbos for smooth turbine-like low and midrange grunt. And then they make the port runners ENORMOUS.



Crackheads. That, or they were designing by committee and nobody agreed with each other.



Did the engine have to be homologated for any home market racing series?

rotarygod

The 06 auto is no longer a 4 port. It's the same 6 port as the manual with a lower redline.

j9fd3s

ah, we just got the 06's in a couple weeks ago, all sticks

j9fd3s

yeah if you look at the exhaust sleeves and the turbos, the sleeves actually direct exhaust gas AWAY from the turbos. its a wierd setup. maybe crackheads is right.

RONIN FC

My guess is there trying to induce a swirling effect. Just something else that could increase torque and midrange.



But were just speculating while the crackhead engineers did the research.

guitarjunkie28

big runner + small port = velocity

ColinRX7

Exactly..



Apply the same principle to a peripheral port. Would you have a huge port in the housing and tiny runners? Or tiny port timing in the rotor and gigantic runners? What would each do to velocity?



Some people don't realize what they are doing with their irons when they're porting. Everything needs to be taken into consideration. Port, bowl, runner diameter, runner length, runner bends, dynamic chamber (if applicable), throttle size, etc. It's all a work of art the pulse makes from the port to the atmosphere.