Which has more power: SP 4 or 6 port 13b
 

I'm trying to plan out the future of my car here.

I'm looking for max power, so i'm thinking:

Rebuilt, 4 port street port 13b (changed from 6 port gsl-se engine)

and a nice carb, perhaps a mazdatrix or racing beat kit.

which would produce more power? 13b 6 port SP or that setup above?

peace

Geoff

(dont tell me to search cause i'm too lazy )

Also, would i be able to use 4 port side housings on my 6 port engine?

13b 4 ports will make more power. The advantage of the six port 13b is better drivability. If you are going to be running an aftermarket carb, a four port is probably more suitable.

Ryan

The advantage of a 4 port is the ability to do alot bigger porting work to it. If you are not porting then I would probably bet the 6-port will be able to make more power.

You can use the 4 port side plates as long as your 6 port engine is a 84 or 85 GSL-SE housings. Cus starting in 86 they moved the water O rings into the plates. where as 85 and earlier engines all have the O rings in the AL housings. So basically to build a good 4 port engine you need GSL-SE AL housings and a set of 4 port plates. The 4 port plates can come from any 12a or 13b that was manufactured that is non 2nd gen. Also i would much rather run a 4 port over a 6 any day as long as it has mods to it. If you were looking for just a stock engine the 6 ports have a little more tourque adn pwr in stock but are pretty limited for much more pwr. Where as with a big street port 4 port, header, and a good IDA carb youll make close to 180-200 at the wheels. So ya thats the story. I run a 4 port 13b in my repu and it runs good. I ported the secondarys some, but i still have the stock intake and exhaust on it, so its really limited. It runs good though. Also people will tell you that the 75 and 76 plates are the best since they have the largest ports, that true, but i dont think its as big of a deal as people think it is. The runners leading from outside the engine into the port are a little taller but as far as inside the port timing can be ported to match on any of the 4 port plates. you might just have to grind a little more on some than others. One more thing, i would totally recomend a weber 48 ida to unleash as much pwr as possible out of the engine.

CJG

Beauty. Yeah i have a 6 port 13b from an 85 GSL-SE (my car) that i'm going to be using for the housings.

Looks like 4 port for me!!

Awesome! thanks!!

Geoff

That is also what I plan to do in the future. I am just unsure on one thing though. I have heard that '89 and up rotors are lighter and the you can use them and the shaft with the GSL-SE housing and 4 port plates. But some people say they will have interferance, does anyone know if this is true?

if someone has both the '74-'85 and the '86-'96 style rotor housings and rotors, then it should be pretty simple to tell if there is an interference problem. just trace and compare them.

Well, its probably not a matter of just tracing. I think you need to get an engine appart and put a plate down and and a housing on top. then set a rotor down and use a feeler guage to check the rotor to housing clearence. that should be the only clearence you should have to worry about. the spec should be no closer than ten thousenths from the closest point of the rotor to the housing. If it is too close, then have the rotor faces ground which is like $50 a rotor and then balance the rotating essembly. that like $320. but then you will have a nice balanced, light engine assembly that will be vearing pleaseing in the smoothness.

CJG

Moremzada also mentioned to me that you can use the high compression rotors out of a later model second to bump the compression on the 13B -4 port.

I have been thinking of doing that myself.

well, i'd totally have to agree with you in that it wouldn't be just a matter of tracing, but that should be a pretty good start. i'm thinking if the difference is really in the peritrochoid shapes of the older vs. newer rotor housings, then it should be measurable if you have them side by side. likewise, the rotors would have be shaped differently as well. again, i agree that it would probably be fairly minute differences.

The difference in rotor/housing shapes between pre-86 and the later rotors is only a few thousandths of an inch. I have heard of some people using them with success and I have heard that you shouldn't interchange them at all. I have never tried personally so I can't say if I recommend it.

The 4 port motors flow more air due to less turbulence and less boundary interference from such small runners. They can be ported nice and large and make great power.

The 6 port motors despite their relatively poor flow characteristics are still capable of some really nice horsepower numbers and good drivability. The reason for this is velocity and port timing. The auxillary port is open up to 80 degrees atdc vs 65-70 degrees of a real big streetport 4 port. This added timing (6 port) is good for top end power but the port runner air flow is horrible due to the amount of area that the actuator rods take up and the shape of the sleeves. Pineapple sleeves surprisingly only add 1% airflow through the runner. The problem lies in the area that the rods take up. This turbulence and the small ports all contribute to the 6 ports lousy flow capabilities. Now for the reason why they still regardless make some good horsepower numbers. Since there are two port runners in the outside housings they are obviously smaller. Smaller ports have more velocity (duh). All of the air flowing through the lower runner when the aux. ports are closed contribute to good low end power. When the port opens there is good mid-high rpm power. The top end is strong due to the fact that as the rotor closes over the lower port ALL of the remaining air in the intake runner is forced by inertia throught the upper runner speeding it up and ramcharging itself into the engine. Velocity plays an important role in the low end and high end on the 6 port motors. This is why it is a bad idea to siamese the ports even though the runners are still seperate. It may work alright due to less turbulence but some velocity will be lost and therefore power in various spots in the usable rpm range.

I didn't really answer the question as to which can make more power since they both have some really good potential if done correctly. I would still have to say the 4 port would win. However I have seen 190 rwhp with the aux. ports still working so there is some power to be had there as well.

well, to be honest, i never really thought much about the 6-port's making THAT much power until i saw Directfreak say that his SE was making about 215 HP in another thread. that's only about 15 HP less than the most powerful streetported 4-port i've ever seen ... so, yes they obviously can be a force to be reckoned with.

however, rotarygod, i must say that that was the best explanation i've seen thus far. it was technical enough to explain it, but not so far as to go over the head's of the masses. good job! ;)

Yes, thank you very much!

This all sounds great for you guys, but my brakes still squeak!:(

Just put some 90w gear oil on your brake rotors. that will stop the squeeking and improve braking.jk

CJG