sa22c_Drifter

Ok, I got a guy who really wants a 1st gen. He just recently bought a '90 13b carburated FC3S and he wants to trade for my '84 12a street ported FB. Now, I commented this to my friend and he said quote-on-quote "NO!, 6 port 13b's were a piece of ****, don't trade your 12a those 6 port engines sucked ***".

Is this true, are 4 ports better than 6 ports, is that a good trade....the guy still has to go see my car to see if he likes it so the deal isn't closed yet. But let's say he wants to go through with it, should I trade??

LongDuck

There's a reason why Mazda went with '6'-port 13b's in everything after 1986 - it's because outside of turbocharging, the '6'-port engines develop more horsepower and greater low-end torque than a 4-port motor.

The major difference between 4- and 6- port motors is that the extra 2 ports in a '6'-port are opened only when they're needed (via exhaust backpressure 84/85 SE's or airpump valving on 2nd Gen cars). This ability to only modify the intake air velocity in the plenum is what broadens the torque band of a '6'-port engine. With 4 ports, you only get one flow rate, regardless of engine rpm or fuel flow - that means that to get more power, you have to flow more air, and you'll eventually be topped out. With '6'-port designs, once the 4 standard ports are topped out, you can open up the remaining 2 ports to get more airflow out of it, increasing power.

The turbo engines didn't use '6'-port engines, because they have augmented airflow due to overpressure, i.e., the additional 2 ports aren't needed.

sa22c_Drifter

ooohh but are they reliable???

RacerX7fb

My first GSL-SE when I purchased it had 116,000 miles on it back when I purchased it in 1992.. I drove that car daily, autocrossed and drag raced it on weekends... only main modification was an RB header system. 10 years later and with over 282,000 miles on the odometer that engine was replaced with a 'fresher' used engine.. but it was STILL running, just not as strongly as it did ten years prior when I first got the car... it never gave me any problems.
So your question to how reliable a 6 port engine is over a 4 port one is relative, and comes down to how well the car is taken care of... one not being better than the other.
12A's are more prone to have the dowel pin oil leak whereas 6-port 13Bs do not.
FC electrical issues are a different story but not engine related.

hornbm

FYI for the rx8 mazda uses a 4 port 13b for the automatic, rated at 200 HP, and a 6 port for the manual rated at 238 HP. Yes in a N/A form, 6 ports are better than four.

The only disadvantage 6 ports have over 4 ports, is 6 port motors cant be ported very much, where as 4 port motors can.

rotarygod

iTrader: (1)

They can't be ported much because with their already long timing they essentially are ported compared to the 4 port engines. You can only go so far.

LongDuck

Also, the 84/85 SE 13b's were some of the strongest built, since Mazda chose to use 3mm apex seals instead of 2mm seals in earlier engines. These are cast-iron and provide good sealing with minimal wear, with only a slight increase in moving internal friction. Also the heavier weight of the rotors accounted for part of the torque increase in the lower part of the powerband, and the oil system was beefed up with 17.5mm oil pump rotors, instead of 12.5mm rotors in the 12a cars. All of these features helped to increase reliability of the SE's over the earlier 12a cars, and I would also argue over the later 86+ 2nd Gen cars.

After 1st Gen cars, the 13b motors all got EFI, with 4 fuel injectors to better 'stage' flow, back to 2mm apex seals to decrease internal friction (and free up some extra horsepower), and bump it up to 145 horses in the low- to mid- range cars. Turbo cars had lightened rotors with lower compression rates to decrease chances for detonation, and also only came with 4-port intake - again because the air is forced in, rather than drawn in. HTH, good discussion,

cosmicbang

There is more to the story. Mazda had to work with the government emissions and fuel economy regulations. The 6-port engine was the best solution and superior under those conditions.

Building an engine not subject to any restrictions, a 4-port will have more power than a 6-port, and comparable torque, other things equal. One large port is better than two smaller ones.

In your case there are far more factors involved than simply the number of ports.

Wankelguy

I think you hit the nail on the head with that post.

Another downfall of the 6-port motors is the sleeves themselves, which have a nasty propensity for sticking.
Just another thing to go wrong in my opinion.

Junia

Take the 6 port. You can still port them if you want but thats up to you. I have a friend that has a 6 port 13b bridged with nitrous that runs NICE . The car is badass but its not a mazda. He has the motor in a old Datsun 1200.