i want to rebuild my engine and do a nice port job (not myself) with a dellorto. so im thinking a 4 port. maybe a 4 port 13b, or cosmo.....




also, anyone know a good source with write ups on each port job, pro's and cons?

 

look for tall ports

 

rotorhousings: 74-75 have biggest exhaust ports.

plates: 74-75 have tallest ports but they are not gas nitrided so they don't last as long. 79+ plates are better because they are gas nitrided.

You can have the older plates nitrided, but it's not worth the effort and expense since 79+ are a better deal.

 

i'm assuming that you're doing the '87 motor you have listed in your signature. just get some T2 primary and secondary housings. i'm sure they'll give you more than you NEED for the street after porting - and more than likely they'll be more affordable than trying to get an RE or REW motor.

 

WRONG! Rotor housings from '74-'75 have the smallest exhaust ports ever manufactured on a 13B (or atleast on the outside). I've also compared the port size and shape on the chrome side to a set of R5 housings and they looked almost identical. It was easier to port the R5 exhaust ports.

As for the side plates, the '74-'75 may have largish ports on the inside, but the intermediate has short ports on the outside. I'd rather do an R5 or Y intermediate because they have tall ports on the outside, and can be streetported larger than stock '74-'75 ports on the inside. Nitrided too.

The limiting factor in porting your plates is the casting itself (waterjacket). I don't know which plates allow the largest ports, but I've gone pretty big with a set of R5s so far.

 

Must have been 74-75 12a rotor housings Jeff. I've read in the Mazda Comp catalog they are the ones to have with Rx2/Rx3.

I stand corrected on the b rotorhousings.

 

It probably was. '74-'75 12A rotors are also the only ones with symetrical compression uh bathtubs. All others, newer and older, were asymetrical.

Check this out. It's got Y side plates and '74-'75 13B rotor housings. Copy and paste the URL or use the drag and drop method. http://www.geocities.com/cd23c01/black01.jpg