cook11

I am really new to the rotary world and I am wondering if you can run a semi peripheral port on a N/A carb 13B motor in conjunction with the stock inlet ports? Would this be a viable option instead of doing a full blown peripheral port? Thanks for any information I receive in advance!

j9fd3s

iTrader: (3)

yes, but for what goal?

cook11

No real goal in mind. More for curiosity sakes. So if I may ask, what are the benefits and drawbacks of this setup? Again I am completely unfamiliar with it and just thought maybe it offers something that all different ports out there cannot. Perhaps it offers PP power up in the higher rpm range while maintaining some useable power and torque in the lower RPM range? Kind of best of both worlds? Thanks!

BLUE TII

iTrader: (9)

Well, you have overlapping benefits that don't necessarily jive together.

Mazda added the 6 port induction to do just what you say you want to, extend the power band into the high rpm without impacting the low end rpm (6 ports close at low rpm).

RX-8 showed 6 port induction can make power to 9,000rpm with the right intake layout/tuning.

Semi- Peripheral port adds the possibility of the same late intake closing as 6 port induction- no gain there except that the more direct shot into the motor means more velocity/better chamber filling.
However, semi-p-port velocity/chamber filling will be negated by the higher side port volume therefore lower intake velocity while the 6 ports are open.

The second benefit of Semi-Peripheral port is the added overlap through earlier intake opening. This affects the powerband positively from idle to redline under full throttle as long as you have low restriction intake/exhaust.

One possible scenario for this 8 port semi-p-port layout might be-

an early closing semi-p-port (same as primary&secondary ports). This way you would use the semi-p-port as your primary port for best low end power and then bring in your primary and then secondary ports as more flow potential is needed with raising rpms and then finally bring in your late closing 6 ports to extend the breathing for the high rpms without impacting low end power.

Probably not what you had in mind!

If you operate the 6 port motor as normal with "normal" late closing additional semi-p-ports I don't see any advantage over a 4 port motor with semi-p-ports.

The smaller 6 port runners add additional intake resistance/lower flow potential over a 4 port motor as we have seen time and again a fully modded 4 port NA makes more power than a fully modded 6 port NA motor.

In addition, the 4 port motor with later than side port closing semi-p-port will get its late timing induction "squirt" once the side ports are closed. This allows higher intake velocity through reduction of port volume, less resistance (straight shot in) and the entire momentum of the 2ndary runner intake charge behind it (if semi-p-port shares 2ndary port intake runner as usual).

But hey, we don't really know till we try it.

cook11

So really after reading this....and from my interpretation there really isn't any valid proof that its a better option than going to a full peripheral port? Would a semi PP be easier on the apex seals than say a BP or full PP? Sorry I am trying to wrap my head around rotary terminology and theory right now....I need to erase my old piston engine knowledge....Is there a Holley or Weber carb manifold available on the market for a 13B semi PP? If so do they have some sort of secondary butterflies that open up at a certain RPM for the semi PP portion? I hope what I am asking makes some sense....

BLUE TII

iTrader: (9)

cook11 So really after reading this....and from my interpretation there really isn't any valid proof that its a better option than going to a full peripheral port?

Full peripheral port is the best for performance.

If you do a combo port (side and peripheral ports together) it is possible to achieve better drive-ability over a full much larger race sized peripheral port (at some cost to power).
But, not the way you are thinking by "closing off" the semi p-port (they are never closed).
You do it by making a smaller more drive-able peripheral port as your main port compared to the larger less drive-able race peripheral port.

Also, in a turbo application it is better to do a bridge or semi p-port (also called combo port) as the rotor partially physically blocks intake flow at some point causing a strong intake reversion pulse which limits how much boost goes out the exhaust during overlap.
A full peripheral intake port turbo motor does not have the intake port effectively blocked at any point, it either flows into the intake stroke, the exhaust stroke or both. You can build it and make great power, but the impact of throttle on power output is hard to judge.

You cannot fully close or block a peripheral port.

A small peripheral port is only partially blocked by the face of the rotor between the apex seal and the combustion tub. A large peripheral port is never effectively blocked as when the apex seal is at the top of the port the bottom is exposed to the rotor combustion tub leading to the exhaust.

People (including Mazda) have tried to stage semi-p-ports for drive-ability by closing off the smaller peripheral ports and it almost kinda sorta works, but not really.

In fact, it is better to always use the semi-p-port for best drive-ability and close off the side ports because there is an actual sealing grid of the side seals & oil seals that provide a total gas seal to close the side ports off to exhaust reversion into the intake stroke during overlap.

You may have to play with engine parts to see this.

The apex seal is a single horizontal line, so it can never fully close off a peripheral port with a gas seal unless the port is a smaller width than the contact surface of the apex seal (such as the trailing spark plug hole).
A peripheral port flows to one side of the apex seal or the other or both always. The small semi-p-port is partially blocked by the rotor face- not a complete gas seal.

It is the same with a bridge port. Bridge port is outside the rotor side seal & oil seal grid and does not receive a complete gas seal.

Because there is no complete gas seal with a peripheral port or bridge port-

when the throttle plate is closed off limiting intake flow, exhaust will be pulled through any small gaps into the expanding intake stroke instead of (the limited flow) intake going in there.

The exhaust reversion causes drive-ability issues because it dilutes the intake charge so it cannot support combustion.

The only way to stop this exhaust reversion into the intake stroke is to open the throttle so intake air goes into the intake stroke instead of exhaust or create a gas sealing grid to keep exhaust out of the intake stroke.

Sorry for the long rambling post...

j9fd3s

iTrader: (3)

i ask because after doing a couple of full P ports, there isn't much point in keeping the side ports. even a full sized P port can be fairly tame, they do perform worse than side ports at low throttle openings, but anything over 40% throttle the PP stomps all over the side port.

a smaller P port, in conjunction with side ports works well, basically you are adding port area, with a moderate port timing change. for a turbo car this is better than a full P port. the old scoot FD did 710ps@21psi with a port setup like this, its on you tube.

cook11

So if you were to run the stock unported factory side port and a semi PP on a non turbo application it would provide some performance gains without really effecting driveability and apex seal life? I have since seen a couple of videos of semi PP's and they seem to idle much smoother than a full PP motor.

j9fd3s

iTrader: (3)

i can get my PP to idle like a stock engine, although the brap brap idle is half the reason i did the PP!