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Colorado Rotary Engine shop, Rotary Engine REbuild

6 Min Read

Rotary engine porting | Bigger does not = better - Why it matters

Rotary Engine Shop ColoradoThe rotary engine has changed the porting over the years, improving performance and reducing emissions. 

Intake porting: This is where a lot of gains can be made, on the other side, also a lot of trouble can be created.
Before every build, I want to be sure what the realistic expectations are. How do you plan on driving your car, are you going to the track and/or the mountains. Bigger isn't always better.

From the 4 port NA / turbo housings to the 6 ports (GSL-SE, S4, S5 to the Renesis), every one of these has potential unique to themselves. 
With our altitude, every modification must be understood and compliment the engine as a whole. 

From fuel / air going in to exhaust pulses at the tailpipe, the rotary engine wants to breathe
How do we like to port engines for performance here in Colorado?

Street Porting Rotary EngineBecause the rotor spins at ⅓ the speed of the eccentric shaft, this slow speed means that the intake charge capacity comes from airflow as well as volume.

  • Just making the ports larger might work well at high RPM, but will certainly suffer at low / mid range RPM's. 

If you have a performance street car, improving porting must be focused on the mid-range as most driving will be within this range.

I'd much rather have the punch from 4-6000 rpm than just at the high end. Understand on where you plan on running the motor and build from there. Sure, the motor will pull past 8500, how well it pulls up to that will be more important for actual street driving. The other benefit is that when you do rev it high, the next shift will put the rpm right in the sweet spot where it pulls the most.

Compare that to the motor that will primarily see track time (like at High Plains or Pueblo Motorsports Park). At these tracks, anything less than 3500 rpm will only be when driving around the paddock. 

Next, we take a deeper look at the exhaust. What goes in must go out. The rate of velocity / volume is the other area where gains can be made, especially with normally aspirated engines. 

Rotary Engine REbuilds | lets get startedIf you have a restrictive exhaust, no matter how good the intake system is, performance will suffer, unless you have the Renesis motor. Everything changed when these motors went to the side port exhaust. 

Port matching and overlap timing is critical on these motors. Build the motor for what you intend to use it for. How the ports are shaped, when they open and close will all contribute to overall performance. A good engine builder will discuss this in detail with physical evidence of past builds.

Next we will talk about tuning, albeit carburator or fuel injection.


Topics:   Colorado Rotary Engine shop, Rotary Engine REbuild

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