Turbo on RX-8

[Chibana]

While I can agree that compared to older rotary powered vehicles the RX-8 is heavy, this isn't a fair comparison. All modern cars are heavy. Compared to almost any other car you could compare it too, the RX-8 is lighter, sometimes by several hundred pounds. I think Mazda did a good job in keeping it's weight under control when so many other performance cars and supposed sports cars are pushing 3500 or more pounds. Hell, the new Camaro is what, 3900 lbs. with the V8? Even with the V6 it's still over 3800 lbs., I think. I'm all for a smaller, lighter 16x powered car for the next generation, but then again, I may not fit in such a car (the MX-5 was out for me for just that reason).

Having said that, I'm curious as to why the RENESIS is not as good at producing higher power numbers as older Wankels. As far as I can tell, it's the side exhaust port configuration, resulting in that 90 degree bend in the exhaust path. Are there other issues?

[Nutsid]

Originally Posted by Chibana

While I can agree that compared to older rotary powered vehicles the RX-8 is heavy, this isn't a fair comparison. All modern cars are heavy. Compared to almost any other car you could compare it too, the RX-8 is lighter, sometimes by several hundred pounds. I think Mazda did a good job in keeping it's weight under control when so many other performance cars and supposed sports cars are pushing 3500 or more pounds. Hell, the new Camaro is what, 3900 lbs. with the V8? Even with the V6 it's still over 3800 lbs., I think. I'm all for a smaller, lighter 16x powered car for the next generation, but then again, I may not fit in such a car (the MX-5 was out for me for just that reason).

Having said that, I'm curious as to why the RENESIS is not as good at producing higher power numbers as older Wankels. As far as I can tell, it's the side exhaust port configuration, resulting in that 90 degree bend in the exhaust path. Are there other issues?

Oh, I agree with the weight by today's standards entirely. I actually think that a base model is really light all things considered. I'm simply stating my personal preference. I could do without my electric seat, my sunroof, my heated seats. The R3 package, for example, sounds perfect to me. Well, at least as close to perfect as you can get in a modern day car. I'm sure I'd still be longing for more weight loss, but I can understand entirely that modern day regulations prohibit the days of the FB.

And the reasoning the Renesis can't make the power older rotaries can is because of the ports. Older rotaries (ie - 13B-RE and 13B-REW) utilized large intake ports. The Renesis, albeit large, is also sacrificing port size due to its six port design (at least in the manual version), and therefore you can't have the ports as large. If you made a solid opening for the intake ports in a Renesis, however, you'd sacrifice your low end torque, and let's face it, it isn't a grand amount down there.

The six port design for a rotary only works excellent as a means to stay naturally aspirated. Four ports are what you want for a turbo application. Having said that, I am really curious as to what would happen if you ported a four port to have the same closing timing as a six port, and turbocharged it using lower compression rotors. If I had way too much money I'd test that out. If you'd notice, though, all the turbocharged rotaries that Mazda has ever produced have been four ports. Good reason for that.

[reddozen]

Originally Posted by Nutsid

Oh, I agree with the weight by today's standards entirely. I actually think that a base model is really light all things considered. I'm simply stating my personal preference. I could do without my electric seat, my sunroof, my heated seats. The R3 package, for example, sounds perfect to me. Well, at least as close to perfect as you can get in a modern day car. I'm sure I'd still be longing for more weight loss, but I can understand entirely that modern day regulations prohibit the days of the FB.

And the reasoning the Renesis can't make the power older rotaries can is because of the ports. Older rotaries (ie - 13B-RE and 13B-REW) utilized large intake ports. The Renesis, albeit large, is also sacrificing port size due to its six port design (at least in the manual version), and therefore you can't have the ports as large. If you made a solid opening for the intake ports in a Renesis, however, you'd sacrifice your low end torque, and let's face it, it isn't a grand amount down there.

The six port design for a rotary only works excellent as a means to stay naturally aspirated. Four ports are what you want for a turbo application. Having said that, I am really curious as to what would happen if you ported a four port to have the same closing timing as a six port, and turbocharged it using lower compression rotors. If I had way too much money I'd test that out. If you'd notice, though, all the turbocharged rotaries that Mazda has ever produced have been four ports. Good reason for that.

I'm actually having mine bridge ported currently. While I can agree with some of your statements, I think a lot of people are underestimating the Renesis. Chris is getting 500HP with his setup, yes, but he's not currently using the 5th or 6th ports, and he's only boosting to 15~16lbs of boost. Once he's popping the aux ports and running a higher boost, there's no telling just what kind of power he'll be putting down. He wants to run 19~20lbs.

They'll trying porting a 4 port eventually, but I don't think the ports are all that bigger than the ones in the 6 port in regards to the Renesis. Regardless, it'll be hard to tell which is better till more people are playing with them.

I was going to do an engine swap in the 8 till I got to talking to Brian Cain about it, and we both kind of agree that there's a lot of untapped potential in the Renesis block. Even with a bridge port, I'll have a lot less overlap than a stock 13b. Bigger port and more well behaved motor. Just my thoughts really, but we'll see once everything's in and running.

Chibana,
The exhaust port isn't the weak link. It's the upper intake manifold. This starts to get choked for air between 450~500 HP.