mellow65

iTrader: (2)

i have been doing tons and tons of reading about engines on here, and being new to RX-7s it's the main difference between them and most every other car out there. i am still working to grasp things about these engines and the best way to find out is to ask somewhat thought out questions.

what i have is a 82 rally car with a street ported 12a. it's a great engine and i can't see anything major happening to it anytime soon to it but as the engine is the only thing i don't have a spare for i am thinking i would like to build one for the fateful day if the 12a ever takes a dump.

with all my reading i find the 13b mostly came in a 6 port set up. and from what i understand the extra 2 ports didn't really come into play until the upper rpm. And i then assume that they were probably computer controlled. so if you are removing all the computer equipment can those extra ports work like they are supposed to?

one of my many thoughts was to basically copy something along the lines of mazdatrix 4 port 13b. utilizing the 12a side housings, 84-85 GSLSE 13B rotor housings (so you don't have the little "wing" things in the exhaust), and 89-92 Non-turbo rotors and street port the whole thing. but not have the $6000 price tag.

i'm just wondering truly if it's worth the 6 ports or not? I have heard some bad things about pins coming out and flying around in the combustion chamber. or of people just zip tying their extra ports open and not having much drive ability until the upper RPMs.

also if i was planning on using the lighter 89+ NA rotors would it be worth just finding a engine from those years to make sure i had all the proper weights and eccentric shafts for the build?

i know i'm still light years away from turning my first wrench on an engine but i'm just trying to get my ducks in a row before i even buy my first part.

thanks

Starfox07

S3 and S4 13b's auxiliary ports are controlled via exhaust gasses and are in no way related to ECU functionality. S5's were electric but I am not entirely familiar with how they work other than that.

My S3 has no 6 port function (they're always open) and honestly I cannot tell the difference on the low end whatsoever.

If you wish to build a 4 port 13b, you should probably start with an 86-88 13b turbo block, as it is a 4 port. RX8 internals are, at the moment, the cheapest parts new (this is true guys isn't it?) and with their light weight and high compression, are very good for N/A engines.

If you are building a street port, the differences between a 4 port and 6 port are slim. The more extreme the porting, the more in favor (from what I have seen) of 4 ports it becomes.

If you look around there is a 191whp very lightly streetported 13b (1st gen GSL-SE) owned by a member on here. It is a 6 port with no auxiliary port functionality.

mellow65

iTrader: (2)

so maybe to think of the KISS (keep it simple stupid) i should kind of keep my train of thought towards the 4 port idea. especially like you are saying there isn't going to be much difference between the 2 if porting is going to be involved.

so when you are saying that i should start with a 86-88 turbo motor, is there any other reason to do that other then the fact that its a 4 port?

i was thinking something along the line of this clicky.

that utilizes some 12a parts and then uses the 13b housings. which as housings go the GSL-SEs are the cheapest 13b housings that i found. over $100 cheaper then any other.

but with the RX-8 rotors, i thought i read something that mazda moved some side seals or something. would they still work or would something need to be modified?

also when balancing a engine what do you need to keep the same? would you need to keep the flywheel/counterweight and rotors from all the same engine? like to use RX-8 stuff i would need to find RX-8 counterweight and flywheel?

or if i'm just using the 89+ NA rotors i would need to use the 89+ NA counterweight/flywheel?

Starfox07

I haven't built any engines so I don't know the specifics. RX8 rotors will work in any 13b, but I'm not sure what needs to be done.

Street ported 4 ports and 6 ports are roughly equal, but you don't want to port a 6 port further than that.