Semi-Peripheral Porting (“Semi-PP) are becoming increasingly popular, where a small peripheral port is added to the aluminum housings and the side ports in the engine irons are retained. This is extremely effective at improving air flow and power at high rpm, even more than Bridgeports. Increased overlap from Semi-PPs create the “brap, brap, brap” exhaust note and exhaust volume is also increased. There are companies who are offering intake manifolds with extra runners that feed these ports and bolt right up to the engine. Semi-PPs are rumored to have been around since the 70’s as a means of cheating the rulebook in road racing and sneaking more air into the engine through the intake manifold.
Semi-pp’s are cut through the water jacket and require epoxy like JB Weld to seal the water jacket and the port tube in place. Fortunately, this is on the cold side of the motor so the change in cooling should not impact the block that much. Due to the high rpm air flow of Semi-PP’s, this port is used a lot in boosted applications to flatten the torque curve well past 8-9,000rpm and are considered more effective than Bridgeports.
One major advantage of Peripheral Ports and Semi-PPs is that the center of the apex seals is exposed to cold air as it passes over the port opening. This briefly gives the seals a break from constantly touching the hot housing, which reduces the temperature and greatly improves the reliability of the apex seals. Some apex seals that have durability problems tend to thrive and surpass other apex seals in reliability and performance when used in Semi-PP applications that better cool the apex seal.
Many consider this an extreme port that is not good for street driving due to the belief that overlap is increased, having “zero” low rpm power and response, jerky part-throttle drivability, and a poor idle. However, not all Semi-PPs are made the same and the diameter of the port, and the location/angle of the port affects flow and timing of the additional port.
PORTING VARIABILITY
Rotary engine porting can be a controversial topic because there are no standards or numerical defining parameters for different port types, the difference between a “Mild” or “Aggressive” Street Port, a “N/A” vs “Turbo” port, and the difficulty of measuring changes to the port duct shape, which plays a crucial role in the performance of the engine. The three main port categories that we mentioned (Street, Bridge, Peripheral) are just fundamental outlines of how and where the housings are modified to improve airflow.
Generally speaking, things that are not well-understood, defined, or easily measured are often considered an “art” or “black-magic” and those with decades of experience testing different iterations tend to not freely share their hard-earned knowledge and secrets. Rotary engine porting, piston engine porting, and camshaft design are prime examples of this.
While it’s easy to measure fundamental aspects like the port shape/timing of a rotary (which are rarely discussed), or the camshaft lift and duration on a piston engine; it is the nuances in the design and execution that are not easily measured, often overlooked, and misunderstood which tend to play a far larger role in the peak power, powerband, character, durability, drivability, and idle quality of the engine. Because of this and the countless variables in how the port duct can be shaped; the end result of a port job can vary greatly from one engine builder to another.
When it comes to porting templates, one size does not fit all and bigger is not always better. Templates that are sold online are not always the best, most advanced, or ideal for various applications. A given intake porting template will not always be efficient or ideal for both a stock and modified exhaust port. The relationship between intake and exhaust port timing and overlap is crucial and it is imperative that they work together as a system. Very minor changes in not only overlap, but the shape of the port and the rate the port opens and closes also plays a major role in the overall character and performance of an engine.
Intake and exhaust templates should be sold together and matched for a specific application and goal, but the vast majority of companies who sell templates online do not do this, have vague descriptions of the port shape, do not list port timing numbers, and leave customers to their own devices without much direction.
20 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.
Hi Mike,
How much does the cryo treatment run for the rotating assembly and housings, if you don’t mind me asking? I’ve worked out a breakdown for WPC treatment costs, but didn’t consider the benefits of cryogenics.
Also, I know Turblown makes a great upper & lower intake manifold with semi P-ports for the REW, but one thing I always wondered was: what if the ports were staged, kind of what Mazda did with the Renesis 6-port? Primaries always open, secondaries opening at say 4500-ish rpm, semi p-port opening at 6000-ish rpm. Staging either with slide throttles or double roller barrel throttles ($$$ though). This would keep near stock low-rpm idle quality and drivability, while progressively extending the torque and power curves. What do you think, worth it or too complex for the gains?
I should probably ask Turblown about this, but if intake port staging is not worth it, would a tappered semi p-port runner help increase air velocity and fuel atomization at low rpm (without choking at high rpm)? And what if the primary fuel injectors were those in the semi p-ports, would that gain any type of stratified charge effect (which was experimented on in the early developpment days of the Wankel)?
Finally, I ate up the whole hour long video you did with Rob Dahm. Lots of useful information there.
There are so many ideas I would like to tinker around and test, but unfortunately I don’t have Rob’s budget haha!
Keep these articles coming!