Port styles and differences
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From: Bellingham WA
Port styles and differences
So im totally new to rotarys and ive been seeing all this talk of "street port" "bridge port" "p-port" ect. what are these and what are the differences? My guess is a porting of the intake ports for better flow?
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From: https://www2.mazda.com/en/100th/
Mazda has had many different porting configurations over the years, depending on the year, market, or racing class, if it is a race engine. using the factory porting styles as a start the aftermarket builders have come up with a few as well.
generally both the intake and exhaust ports are changed, but how much depends on which engine you're starting with, and what kind of port style you are doing.
"street port" this is the mildest of the ports, and as the name implies works well on the street. in 1974 Mazda introduced a revised set of engines with larger ports than the previous engines, then in 1976, due to the fuel crisis, took them away. so the smallest street port, is just to open your 76-85 engine up to the 74 spec. the aftermarket templates are all a little bigger than this. since this port is basically a port that was offered from the factory you get a small gain, but also you keep your gas mileage, and it idles like stock, etc. it also works with the stock intake.
in 1986 Mazda introduced an again revised engine, and the non turbo variant had two ports added that open with high rpm and load, this gives most of the power of the street port, but the rest of the time its more optimal for low rpm, low speed running. different port template.
"bridge port" this is the next biggest port. due to the way the rotary is built the limit to opening up the intake port is that the corner seal needs to be supported. so what is done is add a second port, creating a bridge between them. there are all kinds of variations on the bridge port, but because of the location, it ends up giving fairly radical port timing. this gives it the characteristic brap brap idle. power usually jumps a lot, but idle is bad, no chance of it passing a smog test. the traditional setup was originally for racing, and it tends to be thirsty and loud, but it doesn't need to be.
"peripheral port" this one is very simple, it moves the intake ports from the side housings, to the periphery of the rotor housing. used in most of the race cars from 1977 on, in IMSA, le mans, etc. its very efficient, so power increase is large, yet the port timing can be less radical than the bridge port, so it also can be more tame. Mazda claimed 690hp from the 4 rotor, and if you divide by 2, that is 345hp. idle is like a bridge, emissions are impossible, it doesn't like part throttle, but race cars are ok with that. per hp, fuel consumption is lower too.
generally both the intake and exhaust ports are changed, but how much depends on which engine you're starting with, and what kind of port style you are doing.
"street port" this is the mildest of the ports, and as the name implies works well on the street. in 1974 Mazda introduced a revised set of engines with larger ports than the previous engines, then in 1976, due to the fuel crisis, took them away. so the smallest street port, is just to open your 76-85 engine up to the 74 spec. the aftermarket templates are all a little bigger than this. since this port is basically a port that was offered from the factory you get a small gain, but also you keep your gas mileage, and it idles like stock, etc. it also works with the stock intake.
in 1986 Mazda introduced an again revised engine, and the non turbo variant had two ports added that open with high rpm and load, this gives most of the power of the street port, but the rest of the time its more optimal for low rpm, low speed running. different port template.
"bridge port" this is the next biggest port. due to the way the rotary is built the limit to opening up the intake port is that the corner seal needs to be supported. so what is done is add a second port, creating a bridge between them. there are all kinds of variations on the bridge port, but because of the location, it ends up giving fairly radical port timing. this gives it the characteristic brap brap idle. power usually jumps a lot, but idle is bad, no chance of it passing a smog test. the traditional setup was originally for racing, and it tends to be thirsty and loud, but it doesn't need to be.
"peripheral port" this one is very simple, it moves the intake ports from the side housings, to the periphery of the rotor housing. used in most of the race cars from 1977 on, in IMSA, le mans, etc. its very efficient, so power increase is large, yet the port timing can be less radical than the bridge port, so it also can be more tame. Mazda claimed 690hp from the 4 rotor, and if you divide by 2, that is 345hp. idle is like a bridge, emissions are impossible, it doesn't like part throttle, but race cars are ok with that. per hp, fuel consumption is lower too.
another thread: https://www.rx7club.com/new-member-r...rimer-1039179/
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