wanted to come back and update this thread;

went to a full peripheral with a large turbo. About as extreme as it gets on porting and turbo, as I wanted to experience the absolute maximum of overlap and forced induction.

-the misfiring / spooling thing doesn't seem to have much affect. I don't notice the engine building boost from misfiring, with any sort of "run-away" boost building / powerband. It actually feel just like a normal rotary once you are over about 10-15% throttle.

-under the 10-15% throttle range, there is brap-brap-brap, which is occuring because of the vaccum/exchaust reversion. This can be felt lightly in the drivetrain, kind of like a chug-chug-chug down the road like you're riding on a train or something. But as soon as you open past 10%, and the manifold pressure changes closer to atmosphere, or you go into boost, everything feels smooth and normal

-when doing a large bridge/semi-pp or full, the key is to have a very large compressor. Yes of course you really need a large hotside/turbine, but usually the turbine/hotside is sized accordingly to drive the compressor. The reason you need a larger compressor, is because the engine has a greater theoretical VE in loaded ranges. So imagine your engine have an extra 20+% more displacement. Now the engine will ingest 20% more CFM in all the same high loaded areas as a sideport/typical port. Additionally, you'll want a turbocharger that is not only large enough to keep up with the CFM demand, but also will keep backpressure closer to 1:1 ratio. If you have the properly sized turbo for the VE of the engine, that matches the porting torque profile, then naturally you wont have much back-pressure.

^example. I assumed an s480 80mm would be enough. It wasn't because the engine wants to ingest over 180lb/min of air, at the pressure ratio that it uses, in boost at WOT. The compressor chart of an s480 is below 120lbs in this area. This lowers the efficiency of the compressor, as the shaft is overspinning, and now we end up maxing out the turbine flow and building backpressure consequentially. While this may be ok on a sideport, this will cause reversion under boost on bridge/semi-pport. So to the guys out there thinking one of these small EFR's or etc for "fast spool" under 2500rpm, while running an engine with porting that targets 9k+ powerband, its not going to work out to well. The backpressure will lower your power on the top end. Rule of thumb here, if you need to increase duty cycle to maintain your boost curve, the turbo isn't large enough for a high overlap engine

-aside from the fact that its a little rough under 10% throttle in 1st gear, it's definitely the most fun I've ever had. Still needs a little more testing out and needs to hit the track, small stupid unrelated issues keep plaguing the setup. But eventually with a will, there's a way

To anyone that see's this thread,

Get the big *** turbo,
Get the huge *** porting,
Smile

Life is short

 

As someone who is 36 years old and driven and built many stock port, large street port, half bridge and full
bridge motors, I completely disagree. . Your setup
is extreme and that was your intention. You mentally prepared yourself for the drive ability and annoyances that come with a monster port. The older I get, the more I enjoy the drive ability of a stock port or very small port setup with EFR or sequential twins.

For the the subject matter at hand, I’m yet to see proof bridge porting has ever increased down low response. Every setup
i see it moves the power band to the right. There is minimal data on semi-PP setups but they seem to be the route I would go personally if I was building a 600+ hp two rotor or all out 450hp road coarse setup for the overall power band and lowered boost pressures.

 

The insinuation that a large port car won't have better response down low is a misconception when really its gear dependent.. Sure....if you are cruising in 4th or 5th lugging it at 2500-3000 rpms and you got WOT with a big port big turbo car, nothing much is going to happen. Doing so though, and expecting a different result is a product of not understanding your car or not knowing how to drive it. I've found that my semi port has killer response down low in lower gears even with what most on here consider a large laggy turbo.


Case in point. This is a semi peripheral port with HUGE street port irons that only pulls about 7" of vacuum going from cruise at ~3000 rpms directly to WOT in 2nd gear, and 3rd doing the same in 3rd didn't net any big change from this.

I will say driveability does suffer some with a huge port car and it isn't something you'd ever want to DD, but I don't think FD RX7s are really considered by anyone to be daily drivers and those who get into it with that mentality more often than not either end up going v8 or getting rid of it. To me and I believe the majority of the FD community, they're weekend warrior cars. I don't mind a little extra brap in trade the performance benefits that it yields when its in hard throttle when I'm out rotoring about.

Skeese