pk13

hey, after getting interested into rotaries roughly a month ago, i finally decided to buy one later this year lol . As i live in Australia, theres certain rules that apply for beginner drivers so turbos and superchargers are out of the picture . So i looked up porting for the n/a's.



Now, my question is wouldn't a small bridgeport [the port is not enlarged but rather just the addition of the "eyebrow"] also known as a "baby bridgeport" be less loud in regards to a normal bridgeport [port is mildly enlarged with the addition of the "eyebrow"]. Also in comparison i would like to know how an extended port [roughly double the size of a stock port] would compare to the previous mentioned ports noise and performance wise.



The reason for this comparision is because theres a legal noise level here at around 90db, but i dont mind going a lil over . I'm pretty sure people would mention "it depends on the exhausts" but after some reserch i have gathered the basic idea from peoples opinions that "trying to make a bridgeport reach the legal noise requirements, a properly tuned extended port would make equal or perhaps even more power and still be closer to legal noise level then the bridge" but here's where i want to compare the "baby bridgeport" to the extended port noise and power wise instead of the popular normal bridgeport.



Also, im looking at the series 4 and 5 fc's but due to those engines having 6 ports, i wanted to know more info on how i could change the end plates back to 4, this would make porting easier. i heard bout using the endplates from the 12a engine for this process but im not too sure. Info on the subject would be helpful.



Thanks for the help in advance don't flame me if i got any info wrong, i only know about rotaries for a month

Kim

Welcome to this part of the internet

You really should join up on the Australian Rotary forum.

http://ausrotary.dntinternet.com/forums/index.php



Going for a "Baby" bridge, never heard that one before but it sounds cute, could mean alot of things, like:

Half Bridge, where you only bridge the 5/6th ports

Small Bridge, where you don't cut into the rotorhousings to make room for larger port



Regardless it will be louder than the stock ports due to more overlap between the intake and exhaust-cycle.

You might as well streetport(extend port) the primary and secondary's too while it's allready apart. With N/A power you will regret not doing it once You get used to whatever the powerlevel the babybridge might make.(We allways want more)



If You want to go 4port, get the TurboII end-irons, hell, maybe even the center-iron as some people say they have a better port configuration, personally I don't know, never seen a TII iron. S4 or S5 rotors, dont use TII as the obviously have lower C/R.

Rx-8 rotors might be an option too, they have 10:1 C/R which is the highest possible, S5 are 9.7:1 so if you have those, dont spend the money on Rx-8 ones.



-Kim

pk13

thanks for the reply kim, when i get my car the first thing im gonna do is get an engine rebuild as usually these cars have round 100,000+km on them already, so when they open it up might as well change the end plates to a 4port and get it ported.



I can relate to you about always searching for more power , and nothing is worse then spending a substantial amount of money only to be unhappy with what you get . So thats why im deciding between a small bridge port or a large extended port. I've looked into the half bridge but its not really something im interested in and the full bridge is just a headache to pass noise pollution levels, no emission limits here in Australia .



As you mentioned small bridge, can u explain how that compares to a large extend port performance and noise wise?



This would be great help.

Kim

Small 4-port bridge will not make as much low end power as an extend port.

For some people anything is streetable as long as it runs, others, myself included, wants streetability without all the sideeffects.

You can have good power and a quiet exhaust at the same time, but i'm not the right guy to ask about exhaust tuning.



My old FC was extend ported, manifold matched a.s.o. with a true dual exhaust system exiting through the stock mufflers. It was nice and not too loud during city traffic, but would still roar like a beast at WOT.

pk13

Thanks for the info, it cleared alot of things up, course im going to consult my mechanic bout the subject but i would like to know what path im taking my car . I'm sort of a perfectionist haha



p.s. just noticed your signiture thingy, hiliarious!! coz its soo true!!!

j9fd3s

this question is a big grey area, i'm not sure i'm not talking out my *** too.



Fact: you can have a nice full bradge and make it quiet too, ive driven one, well its not quiet, but it would have passed a noise test.



NOT FACT: our thinking is that to see the gains from a bridgeport, you need to have pretty big ones, the downsides appear right away (rough idle, poor cruise). so the thinking is that a good street port will equal the power of a small bridge and have a better all around perfomance (idle, cruise, noise)



The Future: it is possible with lots of good mufflers, to make a bridge quiet, also with efi instead of a carb, drivability should improve too. if you put the right combo together your small bridge could prolly work better than the street port. exhaust is key, intake is key.

pk13

Just decided to go with the extend port route as it seems to be easier to comply with the law.



thanks for the help guys

j200pruf

In Aus, the IPRA race cars are getting close to 300hp off what is a fairly small bridge port, granted they are spinning up near 12k.

heretic

A rack of straight through mufflers will do the trick for the noise. Physical size is key. Bullet mufflers are about the same as pipes as far as muffling goes. The more volume in the mufflers, the less volume at the tailpipe.



The only technology is in getting the muffler array to fit under the car. There is at least one remarkably fast RX-7 with a giant muffler mounted sideways under the rear bumper in addition to the usual muffling devices under the floor.



Additional hint: Bends are mufflers too. Guys with single exhaust FCs should give thought to running the exhaust down the right side, just for the convenient bend in the middle of the system. Two smaller diameter muffler systems would work much better than a single exhaust, though.





All of that said, a non bridged port will be much more pleasant to drive at 5-10% output, where most driving is done. The bridge port will make much more low end torque, but you can't not use it.