While grinding away at a port opening to follow the pattern of a porting template is pretty easy to do, these templates are 2-dimensional and only define the port opening shape/timing/rate at which the ports open and close. They do not define the arguably more important 3-dimensional shape of the port duct in the iron which greatly affects velocity and air flow (CFM) into the combustion chamber, which are what determines the power potential and character of the engine.
Because of this, two engines using the same template can have drastically varying results in terms of power, response, and drivability and the end result will come down to the experience and knowledge of the person doing the porting of the duct.
When it comes to Bridgeports, most templates offered online are very similar to each other in shape, timing, and overlap and not many offer a small “Turbo-Bridge” / “Tick-Tack” Port. For Semi Peripheral Ports, there really aren’t templates of any sort. Changing the size and location of the Bridgeport and the size and angle of the Semi-PP will affect the amount of overlap of the intake and exhaust.
It is very rare to find the results of methodical testing like those done by Sidney Critic on the 13B rotary engine. These graphs show how minor changes to the radius of the port duct and bridge port opening has a big impact on the Cubic Feet per Minute (CFM) airflow. His YouTube channel has a lot of great information and data on the rotary engine.
Due to the many variables in port shape/timing and the port duct shape, it is difficult to generalize the characteristics of a given port job and is the reason why there are opposing opinions and disagreements on the drivability, characteristics, and performance of a given port job. People tend to assume that their performance results are the ONLY characteristics achieved by that porting type.
It takes methodical trial and error of different shapes, curves, and dimensions of the port duct, and experimenting with different port timing and overlap combinations to really improve the performance of the engine without significant compromises. It is possible for a more aggressive port job from one engine builder to have better driving, idle characteristics, and make more power than a poorly done “Mild” Street Port by another engine builder. Choosing a credible and experienced engine builder who understands your goals and objectives will give you a better driving car and a more enjoyable result.
Our engine builder Abel Ibarra has tested countless combinations over the years of different port shape, timing and the shape of the port ducting to end up with his final port design that he keeps close to him. This is very similar to the ‘secret sauce’ of camshaft design on piston engines, which are often closely-guarded secrets by camshaft designers who are not willing to give away their knowledge for free.
OUR BUILD PLAN
For our engine build, the goal is to have a wide, flat torque curve and make power at high RPM power without sacrificing low RPM performance and idle quality. We are going to accomplish this by minimizing the increase in overlap with the size and location of the smaller “Turbo-Bridge” / “Tick-Tack” Port, maintaining a smaller primary port size and not opening it up to the size of the secondary port, and utilizing a Semi Peripheral Port for the improved airflow and power potential at high RPM. This should still give us a nice, flat torque curve well above 8,000rpm without affecting drivability.
In the previous article discussing the lightening of the rotors, we mentioned our engine builder Abel Ibarra’s history and background as one of the fastest rotary guys in the ¼ mile in the world. This experience has led him to some processes that I will go over, but not all of the secrecy of his ports, which from what has been said thus far, you can kind of get an idea of the direction of the port design.
19 comments
Great article and build. As a non-rotary guy, I haven’t seen any extreme power builds that are quiet. I would love to see a 4 rotor/3 rotor big build or even a 250hp NA build but actually be OEM quiet. Is it possible??
Thank you. We are shooting for over 600whp with this build while being as quiet and streetable as possible. We are going to use the largest mufflers currently on the market so stay tuned to see how quiet the setup will be.
Part of why a rotary is so loud is that there is no poppet valve to should the port so there is a lot stronger exhaust pulse coming out of the port.
ahhh that makes a lot of sense. cant wait for the rest of the build, especially the quiet part
The exhaust port also opens much quicker than a cam controlled exhaust port.
Fantastic article. I think I finally (sort of) understand all the different rotary porting types that I have read about for decades now. This engine is going to be killer!
In my opinion one of the best rotary tech references out there period.
Why wouldn’t you radius the edges of the port to enhance flow? Seems like a no-brainer to me.
Probably to avoid snagging a seal
I the young age of 14 in 1974 when USAC was using Ported Rotory engines for Competition use in their Sprint Cars .
As far as I know , I was one of VERY FEW duing this .
They were DEVASTATINGLY FAST & HAD A WORKING POWERBAND OF 7000-12000+ R.P.M.s .
The n they Outlawed them like they did with the 426 “HEMI”s
Some body talk!!! In PR we use that in the 80 and 90! En Puerto Rico nosotros usamos eso desde Los anos 1980, cuando Los motors con mas caballaje empezaron a romper Los housing en El area del pase del aceite Denison a la torcion del motor y tambien dependia de donde estaba agarrado El motor, Esto es para Los que trabajar I motors desde Los anos 1980! Pero tambien Les haciamos Algo a Los rotors que yo nunca e visto a nadie comentar!!! Que Tenga buen dia!
Translation:
“In Puerto Rico we used that since the 1980s, when the engines with more horsepower began to break the housing in the area of the Denison oil pass to the engine torque and also depended on where the engine was caught, this is for those who work I motors since the 1980s! But we also did Something to The Rotors that I’ve never seen anyone comment on!!! Have a good day!”
What did you do in the 80s and 90s? Porting?
What did you do to the rotors that you have not seen
Yes, the rear iron can crack resulting in a disastrous oil pressure loss and oil spraying all over the engine bay. There are some tricks to prevent this issue.
What did you do to the rotors that no one has commented on?
Thanks for the comment.
I had many talks involving regard’s too what port I wanted to use. No one explained it as well as this article. Half Bridge it is, I didn’t want to compromise on the lower RPM range whist still having a Brap
I’m glad to hear the article helped your understanding of different bridge ports. Just keep in mind the major takeaway of porting can vary greatly depending on who is doing the work. You can have an aggressive street port with worse low rpm performance than a mild, full bridge port. A half bridge probably be a good idea for your goals and would safeguard a little against a bad port job, but it’s worth it to have an experienced person do the porting.
The rotary engine is a breakthrough in engineering which was destroyed by pollution devices mandated by politicians normally aspirated engines are light and powerful and will last much longer then most high performance piston engines I still daily drive my 1988 RX7 which I streetported myself and enjoy the smooth idle and tork throughout the power band. This engine got a bad deal. And yes I get great mileag.
The Rotary Engine is a very unique engine
Seems like if you had some way to independently throttle an added peripheral port, you could get the best of both port styles. Has this been attempted?
Really excited to see this build evolve & article series, you’ve got a great team behind this build,
I was wondering if you considered other modern alternative to filling block water jacket for Periph. Port, people have had issues with epoxies, but is this due to incorrect choice of epoxy, prep., execution, etc.?
Here’s some info on alternatives
https://m.youtube.com/watch?v=Z9FBcSZruP8
https://m.youtube.com/watch?v=pnSdMd4XXzQ
https://m.youtube.com/watch?v=lRjCuvLCEbo
https://m.youtube.com/watch?v=SkTHNRqZDKc
https://m.youtube.com/watch?v=egU7I3V_Gv4
This is a awesome! Thanks for your guys for posting this. When I do my build I will fallow this one. I did work with CTP and WPC with the info from you guys on another project.