Brideport Powerhouse?
03-28-05, 12:52 PM
#26
Now remember everyone, just because you got partial throttle on your 4bbl and gas is only flowing thru the non-bridged primary street ports, doesn't mean that exhaust is not moving up via the pocket in the rotor and thru the bridged secondaries and diluting the intake charge. Because that is what is happening. Idle is still lumpy and MPG decreases. I talked to a very good rotary engine builder who put a 13b half bridge in his 2nd gen and could not stand the 45 minute commute to work every day. He took it out and sold it.
Have you considered a short bridge port? Just cut bridge ports into the upper half of the port. This way less intake/exhaust overlap and exhaust > gas dilution.
Here is someone who did it:
https://www.rx7club.com/showthread.p...t=short+bridge
And a reply to some of my questions:
The idle was lumpy and it would sit there and rock back and forth about 1200 rpm. When in gear it would run smooth as long as there is light load on it, lets say gradually accelerating or in fifth gear maintaining 65 mph. it would run smooth. But nuetral throttle or initial off throttle it would bark just like a 2 stroke dirt bike. The bridge port was only about 1 1/4 inch long but it was extended into the water O ring groove so it is like a cam with a lot of lift but relatively short duration. The power peaked at 9,300 and torque was around 6,700, it went to 11,200 rpm on that dyno run so at 9,300 that is all it had. How often it went over 8.500rpm? very often is the only way i can answer you, I usually shift at 9,500 when I am on it. The only problem I had was after about 2 years of street driving the silicone to seal the housing where the water O ring was cut started to leak. It will not over heat and may be loose a cup of water every week but it was wetting the plugs when you let the motor sit over night and making it difficult to start cold. 22 mpg was with a 85 GSL-SE 5speed with 0.711 fifth gear. With the heavier early rotors you will see signs of over reving but with 89 and up rotors if you stay low 9k rpm range it will be ok.
Have you considered a short bridge port? Just cut bridge ports into the upper half of the port. This way less intake/exhaust overlap and exhaust > gas dilution.
Here is someone who did it:
https://www.rx7club.com/showthread.p...t=short+bridge
And a reply to some of my questions:
The idle was lumpy and it would sit there and rock back and forth about 1200 rpm. When in gear it would run smooth as long as there is light load on it, lets say gradually accelerating or in fifth gear maintaining 65 mph. it would run smooth. But nuetral throttle or initial off throttle it would bark just like a 2 stroke dirt bike. The bridge port was only about 1 1/4 inch long but it was extended into the water O ring groove so it is like a cam with a lot of lift but relatively short duration. The power peaked at 9,300 and torque was around 6,700, it went to 11,200 rpm on that dyno run so at 9,300 that is all it had. How often it went over 8.500rpm? very often is the only way i can answer you, I usually shift at 9,500 when I am on it. The only problem I had was after about 2 years of street driving the silicone to seal the housing where the water O ring was cut started to leak. It will not over heat and may be loose a cup of water every week but it was wetting the plugs when you let the motor sit over night and making it difficult to start cold. 22 mpg was with a 85 GSL-SE 5speed with 0.711 fifth gear. With the heavier early rotors you will see signs of over reving but with 89 and up rotors if you stay low 9k rpm range it will be ok.
03-29-05, 06:47 AM
#27
Australian Idle
Join Date: Jan 2002
Location: Canberra, Australia
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fitzwarryne - fuel consumption wasn't a great issue as it was not a daily driver. It is a car for having fun in, and some forms of fun involve driving very quickly. Driveability was ride quality was a consideration though (and "value") hence why the porting is relatively conservative. The fact that I will drive it for an hour and a half to get to the race track weighed in the builders mind. If it were unregistered and a trailer queen then a full j-port would be the ticket.
As it is, there are so many other components in the driveline that need considering that outright power almost becomes secondary. For a car running timed laps or road stages the best bang for buck is still tyres... but that is for another thread
.
Drivefast7 - thanks, that was the point I was trying to make.
As it is, there are so many other components in the driveline that need considering that outright power almost becomes secondary. For a car running timed laps or road stages the best bang for buck is still tyres... but that is for another thread
. Drivefast7 - thanks, that was the point I was trying to make.
