ViperDude152

Hey,

On the 2nd Gen rx7s they have the 5/6th ports and on the Series 5s they have the VDI port. Does the Rx8 have anything similar to these ports? Do they open up with an actuator?

Justin

rotarygod

The manual transmission RX-8s have the 6 port engine while the autos get the 4 port. The "6 ports" or auxillary ports are controlled a little differently this time. The sleeves are rotated from the outside so there is no airflow robbing rods in the way. The shape of the sleeves is also refined internally. Instead of only the VDI system, the Renesis uses a different setup. At low rpms only the intermediate housing ports are open for air to go into. At a higher rpm the lower outer ports open up and even higher still the auxillary ports open. Each port has it's own runner and this helps to keep power high throughout the rpm range. The RX-8 has a single blade drive by wire throttlebody. The RX-7s used a 3 plate cable throttlebody that only opened the primary blade for less than 20% throttle. If you stepped on the gas the rest of the plates would open leaving all of the runners to take in air. The aux ports on the 2nd gen kicked in at about 3800 rpm. The Renesis opens them at 6500. The VDI system is still used on the Renesis but only for the primary and secondary ports. The aux ports are not affected by it as their intake runners have been tuned around their benefit. The answer to your question in simple terms is yes the RX-8 still has the aux ports (standard transmission cars) and the VDI but adds so much more.

ViperDude152

Ya with the 3 port TB on the rx7 you loose so much low end power when they all open up at low rpms. I have been modifying the TB to try to make that better but not a big success.

So, on the rx7 there are 4 ports open pretty much all the time. 2 of those 4 get air when those secondary throttle plates in the TB open up which is basically all the time if you stop on it like you said. Then at 3800 rpm the Auxilary ports open up to let more air in. Then around 5000 rpm the VDI port opens up to use pressure waves to create more power blah blah blah. Which I understand.

Now The Rx8, Out of the 6 ports, only 2 are open at low rpms and then at the other 2 open up later on at around 3800? Then the other 2 ports open up at 6500 rpm?

Am I understanding this right? If so. That woud definatly solve the low throttle responce and the low power at low rpms.

Justin -

rotarygod

The primary ports only are open up to 3750 rpm. At 3750 the secondaries come in until 6250 rpm. At 6250 rpm the aux ports open. At 7250 rpm the VDI valve opens as well as a different intake pipe into the air filter housing.

ViperDude152

hmmm very interesting

"The primary ports only are open up to 3750 rpm. " you mean they are the only ports open untill 3750 and then they continue to be open and the next ports open up? I just like to clarify stuff

Justin

rotarygod

That's it.

ViperDude152

Thanks, hmmm. Awsome. but now i wonder why the rx8 doesnt reach over 220 hp. hm. People say that it runs rich at high rpms. I wonder what the air:fuel ratio is and if it could be saftly leaned out and possibly get more power.

Now I wunder if i can transfer that similar port timing to the rx7s. hmmm

rotarygod

The cars tuning is all messed up from the factory. Paul Yaw has a Renesis on his engine stand and he says that the engine in its stock form is capable of 250 hp.

I suspect that the port timing on the Renesis is very close to the streetport version of a modded 6 port 13B. You can only go so far over before the corner seal will fall in. Thats about all they did. The exhaust port timing you won't even get close on. The peripheral exhaust port of the 13B vs the side ports of the Renesis have drastically different timing. The Renesis also has much more port area so the exhaust can get out faster. This has always been what 13B porting has tried to do but the port timing increases alot as well when this is done. The exhaust ports on the older rotaries is already too long. By shortening their port duration and increasing the port area, Mazda has made an engine with exhaust timing that gives better performance. There is also no more port overlap so emissions are down. Gas mileage should increase but that is a tuning issue. If I were to take a guess, I would say that porting won't be terribly significant on the Renesis. It will be hard to make the intake ports any larger. The exhaust might be enlarged though. The important thing will be to smooth out the transition from port runner to port better to reduce turbulence. You need to use what you have to it's fullest before worrying about making it bigger.

ViperDude152

Ya. basically I was going to try to open the secondary ports on the rx7 with an electronic actuator and a RPM switch. The ports will open and close at the throttle body. I'll disconnect the throttle linkage between the primary and secondary plates and just only have the primary plates on the throttle cable and have the secondary plates on a RPM switch and Actuator.

Porting will come when im ready to rebuild my motor..

"The peripheral exhaust port of the 13B vs the side ports of the Renesis " - Posted Earlier.

Hmm I thought the side ports were worse then the Peripheral ports. Since not ALL if the exhaust flows out with a side port since you need room for the APEX seals to ride on. Right?

Hope you dont mind me picking your brain.

Justin