I think reading Felix's home page should be required reading before any one posts a new thread as it contains much practical wisdom.

Recently there was much discussion on the Forum regarding porting. A lot of the argument for example on bridgeporting as due to not stating what the port opening perimeters were. as Mike Angas says in his book you can build a bridgeport so small it has some semblance to streetability or a street port so large you lose almost all low-speed driveability. Thus, people giving the opening and closing degrees so
we know how big a port modification they are talking about.

However my main point is Felix quotes Racing Beat as saying
" we have had little successs in obtaining gains from either street-
porting or bridge-porting 6 port engines'

The advantages of the 6 port in stock form are well known. But does Racing Beat's experience mean that modifying a 6 port is not worthwhile. If this is correct much money has been wasted.

Does it mean much of the discussions on this Forum relating to the advantages of street porting only relate to 4 port engines?

Why did Mazda go back to 4 port when designing the 12at when the 6P had been the norm for jspec motors for 3 years?

There must be something in it otherwise why would Pinapple Racing develop a 6 port to 4 port conversion? Why are they discussions on modifying a 13b with 12a end housings?

Should people wanting to modify 13b engines go back to an older 4 port

Was the 12a 6P engine ever used outside Japan?

In conclusion, there must be opinion on the Forum as to whether Racing Beat is correct.

 

Do a search for "6 port bridge" I know Rice Racing and Crispeed both say that bridge port 6-port engines work rather well.

Probably the main problem with 6-port housings is that there's very little wall thickness so you can't open up the center ports, and the 5th and 6th ports are so high up that you can't really port them with a good blend from the port runner to the inside of the rotor housing, it can't ever be much more than a collection of 90 degree angles. The sleeve stuffers that Pineapple sells would help a lot, of course, but that's only one sharp angle that they fix, it does nothing for the other one... to fix that one would be a TON of work assuming there's even enough metal there to blend it.

 

Well I have ported a couple of the old 4 port 13b's and also a 12 a which is basicaly the same and a 6 port. I will say that I think you can actualy do more porting as far as your ability to change port openinga nd closing on the secondary's of the 4 port. With the 6 port your somewhat limited. Also as you all know quite a bit more work has to be done on the primary's of the 6 to get them even close to the size of the stock 4 ports. I have a question for ya. What do you guys do with the holes in the primary of the 6 ports. You know the ones that come down. Because when you start to port them those holes turn into nasty edges. JB weld? or what. When i did my friends motor i just did not go very big. Then on his secondarys i combined the the secondarys into on big port and basically made it a huge 4 port. I also took it up some too. Any ways I however personaly have a strong prefeerence towards the old 4 port engines.

CJG

 

can you give me a link to felixes page? I might have been there befor but i go to so many web pages i can't keep track. thanks.

CJG

 

http://mrmazda.members.atlantic.net/....html#APORTING

 

I have a street ported GSL-SE motor. Removed the sleeves also. It made a large difference in porting it.