I want a non turbo engine but cant decide to go with 4 port or 6 port. My questions is are 6 ports always going be better than 4 ports in non turbo applications because of its two stages of power band? (low rpm and high rpm). Is this why rx8 high output engines uses this auxliary port still on their manual trans? I plan only going with a street port with ITB's. Also are there any benefits of a 12a engine over the 13b besides better torque? It's going on an FB by they way. Thanks 4 the help.

 

i have a 6port 12a in my rx7. its a full cut monster bridgeport. i love it. ive had 4ports in factory and bridgeport form and now id never not use a 6port. even tho its full bridge its like a factory engine round town apart from its 2000rpm idle and its pluse. it pulls hard to about 10,000rpm . im pulling it aprt this week for freshn up as its running carbon apex etc if you want photos or more info email me on urquhart.glenn@yahoo.co.nz Also its running 4 flatslide carbs off a suzuki gsxr1000. with jet mods and few other wee changes

 

i didnt even know they had 12a 6 ports. Yes if dont mind i would like pictures of your set up.

 

12A has less torque and less power than a 13B, but it gets better gas mileage if you're into that sort of thing. 4-ports are better than 6 for peak power, but 6-ports will give you better low-end if you have fully functional aux. ports.

Don't waste your time with a 12A 6-port since they weren't available in the States anyway and you'll have a hard time finding a suitable intake manifold. If you want a 6-port motor just pick up an '84+ NA 13B.

 

6-ports suck! They have way too much timing, and a lot of port surface area which increases pumping losses.

You could open the ports up into one huge port, but then you've just killed airflow velocity.

4-ports allow you to get any port timing you want and efficient airflow.

I have never seen a 6-port dyno sheet that had good torque figures. It's always about 10-20ft-lb less than a four port. I'd been paying attention because I had to rebuild my engine with 6-port housings because I killed one of my TII housings. My engine made 145ft-lb at the wheels. 6-ports I've seen were all in the 110-120ft-lb range. Yuck!

 

First question is what you are planning to do with the FB since there is no chance of streeting it legally with ITB's. FE's and six ports all use the smallest ones to idle and feed emissions gear, so if you are dumping all that entails there is no reason not to go 4 port. ITB's and weber style carbs can support massive top end but are tough to pressurize effectively at modest revs and stumble. A 12A with close to stock ports and a four barrel carb can both get you into trouble and idle in traffic with the a/c on and return 20-25 MPG but porting/pulling the exhaust sleeve and cramming a
Holley on there will get you to 15-18 with a lumpy idle. A 13B, with either two or four injectors and the complicated intake may get slightly better mileage but no extra power and will be a lot tougher to troubleshoot through all the valves and sensors.

The beautiful thing about the early chassis are simplicity, the less complicated you can make it the more reliable it will be. Later cars are much too complicated and needy, though they make more power under ideal conditions out in the street little issues can quickly go out of spec and sink your ship.

 

s5 and MSP (Rx-8) system will give you the broadest streetable and useable torque band because of the variable length intake runners.

 

here is my new 12a 6p0rt out of a 1986 cosmo. these photos show start of cutting out new full bridgeport. this is my 2nd one of these ive ported. this one got less wear on plates so im useing these this time... running carbons etc etc. ill post finished porting work when done.

IM aware that is not tidy at moment. START OF THE PORT WORK. will post more on way through... along with finished with flatsilde carbs and a running video

i do not join the bridge or the ports as it makes it a *** to drive. i leave the sleeves out and back fill the under cut to help flow.. apart from it 2100rpm idle its like factory engine to drive and pulls hard to 10,000 ish rpm. last one dynod made 187hp with jetted nikki carb. this one is will be running the gsxr flatside carbs etc so im looking forward to seeing what it does on street and dyno... dyno means **** all is it yuck to drive on the road. last 6port bp made bit less power than other bp 4ports but faster than any ive raced on the street

 

I'm defenetly going for good MPG also I just forgot to mention it. 20-25 mpg sounds good if i go with the 12A but I want to have a little fun with it too. I guess 6 ports is out of the question, but which is the best 13b 4 port to use. Im thinking about the 13brew from an FD and using 89-91 FC N/A rotors, what you guys think about that... has it ever been used in this set up?

 

small up date on my 12a 6port full bridge.. getting closer to being ready. going monster bridgeport now

 

I could consistently get 27-30mpg with a 12A. 33 one time when everything was just right.

I could get 23mpg with my half bridge non turbo 13BT. I haven't driven my new 6-port street port 13B much but it was getting about 20mpg in the four or five days it existed between building it and blowing it up.

Long story short, I'm probably going to be doing a V6 this winter.

 

Cutting the housings wont effect anything? Are you running the 2 piece seals?

 

im running carbon apex seals... 1 peice. dont like steel seals as they hard on your housings... yes carbons dont last as long as steels but cheaper than housongs. im getting about 45,000km out of a set on the street before it gets hard to start

 

or just build one of these and be done with it.
just hard to find a car to fit it in.

 

Too bad that 6 rotor is a bit of a joke. Have Hurley posted up any videos of if running? I've never seen any. Did you noticed the intermediate plates are all short runner? When did they build this thing? Back before tall port Y plates were easy to get?

 

as far as im aware no one has ever had one running.. and i still think this one is as you see it.

 

Too bad Hurely never completely finished it. Heck I could stack six 13B rotor housings and five tall port Y intermdiates, thow in two eccentric shafts and a flywheel and pulley hub so it looks complete too. lol what ever.

Hey, any pictures of your completed ports? I too am doing a 6 port 12A. I considered bridging it, but need lots more information. I've got a Holley 390 that would be perfect for it.

 

any answers on 13brew with 89-91 fc rotors?

 

I'd go with a TII and S5 NA internals. If you're carbing it, find a Rotary Engineering dual Weber DCD setup for a 13B, have an adapter plate made for the intake. You can then bridge the secondaries, yet it will drive like a street port on the primaries. I have a 1/2-sp 1/2bp 12A in the widebody with the Weber DCDs. I get 24-26 mpg on the highway and hang onto my *** when the secondaries open up.

 

im nearly finished it. ill email you photos etc when done and a running video. wont a 390 holley be a bit small for a bridgeport? we dont use holleys here we use side drafts or ida or rejetted and mod nikki

 

I'll have to decide what I'll do. I look forward to seeing the photos.

 

whats wrong with 13b rew with s5 rotors NA. Im asking because i have a 13b rew already

 

nothing! it would be a good combo

 

! the P port idles at 900...

 

i can get mine to idle at 1000 but it dont pluse even. got a nice pluse at around 1600rpm idle but i wind idle up to 2000ish to give a nice crisp fast pluse.....
NOTE just a bit of **** factor the idle