Does anyone have an idea of the overall diameter of the stock throttle body? What kind of result would we get if we swapped it for a larger one? Correct me if I am wrong, but Mazda decided to use a single throttle body, because a progressive-style one because the RENESIS does not work well under low-speeds; the engine has to do a lot of work to get the car moving. Also, what would the effect of swapping throttle bodies have on the electronics running the system?

 

Unless the stock throttle body is a choke point for intake flow (at WOT, since its whole purpose at lower settings is to be a choke point to a varying extent), it's probably unlikely that you'd notice much difference, and that would only come (if ever) at throttle settings where the "open" area of the new TB exceeded the WOT area of the stock component, and even that's probably unlikely given the volumetric efficiency of the stock system according to Hymee's data.

Probably wouldn't have too much effect on the electronics, since from the sounds of things the fuel flow is determined by the ECU based on MAF readings, unless you can somehow get the MAF off the maps in the code (which would likely require FI if Mazda did their job right)

 

Thank you for the explanation brgreene . So, I suppose that the aftermarket companies that make throttle bodies are pretty much shooting too much BS?

 

If you use a larger one, you'll lose a little low end power. Throttle response may get a little snappy as well. You probably won't get a benefit from one since the maf and the airbox are far larger restrictions. The throttlebody is drive by wire anyways so you'd have to retrofit the electric motor to it.

The reason the Renesis uses a single throttle plate is because of an advance in technology over the older rotaries. The older rotaries used 3 plate throttlebodies. The primary plate only fed the primary ports. The other two throttle plates fed the two outer ports. The primary plate was also set up so that it could open up almost 20% before the other plates began to open. The logic is that at low throttle/speed all of the engines air is going to flow through the primary ports only. This increases air intake velocity and makes for more power off idle. At anywhere more than 20% throttle, all of the plates are open. While this may sound like a good idea it was very flawed. If you were at low rpm's and floored it, you may have too much port area since all of the ports get air and the car actually makes less power than if it only had two open ports. The other issue is that the secondary ports collect with each other after the throttlebody (exclude the '89-'91 nonturbo RX-7). Even though these ports don't have any intake air flowing through them at part throttle, they still do have air pulses going back and forth from rotor to rotor.

The Renesis has a single throttle plate. There are actuators that close off the different intake runners based on rpm, not throttle position. At low rpm's the primary ports are the only one's to get air. The secondary ports are closed off. The good thing about the way this is now done is that this valve closes off the path for air to bounce back and forth between rotors. This also applies to the auxillary ports. This is only possible with electronic throttle. Since the total intake runner area of only the primary ports is relatively small, it would be very easy to get full flow to them through a large throttlebody. After about 1/3 throttle or so, the car may as well be floored. The electronic throttle monitors the needs of the engine with the pedal position and then opens the plate only as far as it need go for that scenario. All of this keeps taking place as rpms rise. The easiest way to prove this happens is to go search the thread about the Greddy e-manage. The printout pictures on the forum show the throttle modulated a little.

 

The benefit of replacing the throttle body would vary with each engine, and each throttle.

I haven't seen any aftermarket TB's for the Renesis, and I wouldn't imagine that there's much to gain from using one with this engine. Possibly there could be some room for improvement in the valve actuation speed, but maybe not even that (I haven't seen any tech data on that, or anything to comare it to if I had).

I have seen aftermarket throttles for older carburated engines (trucks/muscle cars mainly). Some of those older engines, there might be some utility to it, since you've aso got a wide selection of aftermarket carbs, FI systems, heads, valves, cams, rebore kits, etc.

If one were to take a 350 cu in engine, and rebore to a greater displacement and add a bigger carb, the original TB is possibly going to become a choke point on volumetric flow even at WOT, and then there'd be big gains to be had in uprgading.

 

Perhaps the rotary engine's displacement is too small to make any significant gains with a larger throttle body?