Semi-PP thought/question

[My5ABaby]

Would it be feasible or possible to create a semi-pp engine where the peripheral ports opened and closed similar to the stock 5/6th ports on S4/S5 N/As? Basically the car would still have decent street drivability with the top end advantages of a semi-pp.

[N.RotaryTech]

I think it could be done.
Some type of setup with ITB, individual runners, etc.

[PercentSevenC]

It's been discussed a lot, but I don't know of anyone who's actually done it that way. I'm not sure how well it would even work. I spent a considerable amount of time trying to come up with a practical way to do it, but eventually decided I could achieve my streetability goals with a standard peripheral port, so the idea was scrapped.

[vex]

Would it be feasible or possible to create a semi-pp engine where the peripheral ports opened and closed similar to the stock 5/6th ports on S4/S5 N/As? Basically the car would still have decent street drivability with the top end advantages of a semi-pp.

Yes. It can be done. The port however wouldn't be that advantageous because it would only be as big as the 6PI sleeve itself. Any bigger and you don't have control of the port like you want, any smaller and you're not getting the benefit of the port.

If however you kept the bridge port and extended it down on the iron to the lower portion of the secondary port you can feasibly increase the single port size based on RPM and the 6PI system. The benefit of that? Hard to say. I'd be concerned about intake velocity, unknown reliability issues (water jacket leakage, etc).

To have a specific bridgeport open or close based on RPM value, that would take some engineering and some ingenious development of technology. I would think a simple flapper door attached to a solenoid or linear actuator would work well. Perhaps even a plumber would be better used. The benefits however would be far less for the gains they merit.

[NoDOHC]

When I considered this, the biggest issue was how to close the primary ports when not in use. Because the primary ports close well after the compression stroke has started, they will destroy most of the benefit of the peri-port. I have considered devconing all the ports shut except for the secondaries (5th and 6th port only) and using them for idle and the peri-ports above 4,000 rpm or so.

I have no doubt that this can be done, I just haven't found a good way to make it work well.

[diabolical1]

as with everything in life, money is the key. so whether you pay for R&D or you pay someone to do R&D, that's what it comes down to. my opinion: if your goal is the street (for anything other than a weekend ride) you'll probably end up a tad disappointed with the results.

when my semi-peripheral is completed, i do plan to do some street tuning just to see how feasible it is, but my goal is really for it to be run at the track, so if i fail on the street it's no big deal.

[diabolical1]

i just thought about something that i anticipate learning with my project. if you do choose to undertake this project, make sure to do your homework on exhaust porting. i think getting it right will be paramount to your success.

also, just an idea that i kicked around when i thought about semi-pp's and the street: maybe go with an oval-shaped intake port. the key will be controlling overlap. it may be ugly, but it can keep intake manifold design relatively simple.

[RotaryProphet]

Unless you can somehow close the p-port right -at- the housing, it's still going to allow intake air to flow around the apex seal and into the exhaust; you're really not going to get good driveability, even with the p-port closed.

If you move the port down low enough to prevent intake air from flowing around when the compression stroke starts, then you'll have exhaust flowing into the intake the other way... so either way you go, you still won't have the street manners of a non-p-port engine.