peejay

I have a dual DCOE manifold for a 4 port 13B. It looks really sweet. I wanted to do twin DCOE type throttle bodies on my bridge port but ran out of motivation when the Holley manifold setup works so well.

BLUE TII

iTrader: (9)

^^
my favorite intake manifold look for the 13B is the "wrap around" Star Mazda maifold with the DCOE throttle bodies.

Peejay, dual DCOE = 4 throttle plates? I hadnt seen that 13B manifold.

j_tso

iTrader: (2)

It was made by TWM and up until a few years ago Pierce Manifolds listed it with kit.
I'm also going to use one on my next engine, would love to do EFI but I already have the carbs.

tramsey

Glad to see this thread is still getting some input. Someone tell me, the consensus seems to be that 4 port > 6 port. But some other threads I've read say that both builds, when streetported, yield similar hp results and that it's only once you go bridge port or p port that the 4 port shows dominance. How true is this?

Some other modifications I plan on doing that I failed to mention is that I will combine this engine build with an RX-8 6 speed transmission and a 4.8 ring and pinion, so I'm really trying to focus on getting that top end power; again, around 8.5k peak.

I guess considering these goals, what do you agree with or would do differently?

tramsey

Lovely looking engine bay btw, Holdfast. I like that air box

j9fd3s

iTrader: (3)

i don't have much to add, but i have tried a lake cities style intake, and it works great. i thought it would be all top end, but it just worked everywhere. possible that getting rid of the bends helps a lot

second you might consider an Rx8 motor, it makes 230hp stock, its 60 more than an FC NA engine, and only 35hp short of a 12A P port.

j_tso

iTrader: (2)

Doesn't the Renesis need that fancy staged intake manifold with ECU to make 230hp?
I've seen adapters to attach a Holley style manifold but have not seen power figures from EFI/carbs.

j9fd3s

iTrader: (3)

yeah, but you could just put a completely stock setup in the car and be done with it...

this one is a 4 port with a holley and its making 175 at the wheels, which is not bad! https://www.rx7club.com/1st-gen-gene.../#post12465083

the 13B-MSP is easy to overlook, but it is an option. i could replace my 12A PP, with one and have the same power, potentially smog legal too. it does loose all of the drama and excitement though... probably most of the throttle response, and its ugly

BLUE TII

iTrader: (9)

Lets not forget to say in this thread that the 13B-MSP Renesis 230hp is 180rwhp.

To put it in the perspective of this thread.
_______________

Another issue to re-focus our perspective on-

My view is 90% of 13B Naturally Aspirated builds through the years have been 6 port because those are the cars/engines that came naturally aspirated here.
Of those builds there have been a handful through the years that have made over 200rwhp and those were below 220rwhp.

The much smaller number of 4 port 13B Naturally Aspirated builds being done through the years have returned more 200rwhp plus results and some of those have been over 220rwhp with much less cost/work (stock intake manifolds).

Then, if you want to progress to a bridge port and a solid 250rwhp you want 4 port again.

The highest hp 6 port based engines had their port runners ported to 4 port.

I feel the little round 6 port 2ndary and aux port runners just hit peak velocity and drop flow too early to consistently make over 200rwhp despite their superior port timing.

peejay

Street port T2 is way better than a 6 port of any port. And I have tried all iterations of 6 port except for full bridge or aux port only (have never had working aux port sleeves): stock ports, mild street port, extreme early opening street port, secondary ports opened up to one big giant port, bridge ported lower secondaries only, full half bridge...

Bear in mind too that Mazda probably sold more 13Bs between 1974 and 1978 than they sold non turbo FCs, so it isn't fair to say that the majority have been 6 port, more like the majority that still existed in recent memory were 6 port.

j9fd3s

iTrader: (3)

i'm not sure what goes on in there, but i agree there is some mis-match between the port area, port timing, flow rate and velocity in the 6 port. on paper it should/could make more power than it does.
its like by the time the port timing works, there isn't enough flow or something like that.

j9fd3s

iTrader: (3)

it also seems to be that to make big power, there is a process. usually one needs to try different exhausts, and intakes and just see what the engine likes

https://www.rx7club.com/naturally-as...-while-801325/

https://www.rx7club.com/naturally-as...3bre-n-818133/

6italia0

with similar porting and setup the 4 port will always outperform a 6 port. It is only in stock form that a 6 port shows greater results vs a 4 port. With porting not only is power both better and more linear, but the torque output is much better on the low end and midrange and higher at a given rpm with a lower peak torque. This also plays a role in fuel efficiency as well. Higher torque at a lower rpm means the engine isn’t working as hard to move the car which results in greater fuel economy. People have been beating a dead horse with 6 ports for decades trying to improve it, but they always fall short compared to 6 ports and many deny this fact simply because they know nothing about the older 4 port 70s style motors.

The renesis engines are both very different, but also fall into the same trends as the older engines. The 6 port renesis we all know makes much more power than the 4 port and slightly less torque, but very few have really dabbled with modifying the 4 port and for some reason keep beating a dead horse trying to modify the 6 port which just results in laughably minuscule top end gain at the expense of a severely degraded powerband and a raised peak torque meaning at a given rpm it’s making less torque and therefore working harder to move the car resulting in decreased fuel efficiency. The 6 port renesis is already a maxed out motor limited by its stock ecu. The same stock motor in the star/formula Mazda cars makes between 250-260whp as it’s a fully dialed in unrestricted engine with a transaxle bolted to it (this means very little drivetrain loss). Now take a 4 port renesis and open up the exhaust ports to at least standard 6 port size and port the secondaries using a streetport template meant for and older 4 port and the results seen in a friend’s otherwise stock 4 port car with a manual 5 speed swap were 212WHP and 169WTQ. The power his engine made is certainly doable with a 6 port, but the torque output is well outside of the 6 port realm without boost. Its for this reason that I’m going to build a similar engine for my SA and tune it with a standalone to control the stock renesis intake system to either meet or exceed those results and the motor it will replace is my 76-78 RX-5 based large streetport (intake and exhaust) 13B using series 5 NA rotors making 172whp and 138wtq using a 465cfm racing beat holley and full racing beat streetport exhaust (this setup also gets me about 17-19mpg city and 20-24mpg highway). Apparently none of this is supposed to be doable, but here I am doing it and any one of you can do it too (unless it’s with a 6 port, then I’m sorry for your loss).


How my SA is currently setup (total shitbox, but it works)

Current porting in my RX-5 13B now

Porting that will be used in the 4 port renesis I’m building