neoboi

I was just wondering does the 12A have a 4-port or a 6-port induction system and also does the 13B has one either and can yall explain what an induction system do?

Thanks,
NEWBIE~~~>Brian

hornbm

as far as I am aware, there was never a 6 port 12a.

speckamp

There was never an american sold 6-port 12A. I believe there may have been one in Japan/Australia.

All the normally aspirated 13B's in the US ever put in an RX-7 were 6-port. All that means is there are two extra intake ports above the regular ones in the end plates that are opened by exhaust backpressure via a rotating sleeve valve. These extend the "port open" time and allow more air to flow for better top-end power. This is more or less like VTEC/VVT as the duration the port is open and the amout of volume it can flow (in boingers that's usually called "lift") is altered by the 5th and 6th ports opening.

This probably sounds like a lot, but you can do a quick google search (or search the forum here) for pictures of how it all works.

An induction system by the way is simply big words for "how the air gets into the motor." It's the opposite of an exhaust system, which is big words for "how the air gets out of the motor."

YMMV, Hope I helped,
matt

neoboi

Thanks, I get what yall mean now but does the 12A have an induction system?

-Brian

rotarygod

iTrader: (1)

I love speckamp's way of saying this. An "induction system" is just simply a way of saying intake system, or intake manifold, or intake ports, etc. So yes the 12A and every other engine for that matter has one.

The 12A 6-ports were only sold in Japan (as far as I know) in 1981-'82.

Duration on a piston engine isn't called "lift" it's called "duration". Lift is the height to which the valve opens to. Duration is the length of time it is open for. The camshaft controls both of these but it is possible to have a low lift, long duration cam timing or a short duration high lift engine as well as any other combo you can imagine. On a rotary the size of the port determines duration based on where the opening and closing sides of the port are located. The larger the port, the greater the timing and hence more duration. This also has the same effect as more lift on a piston engine. Greater lift has greater flow potential. So does a larger port although the rotary doesn't truly have any "lift". V-tec works by increasing the timing or duration of the engine. (Variable Timing Electronically Controlled). Some of the more advanced setups also control lift. The 6-port system is in essence the first vtec type of system but was done over 20 years ago.

hornbm

wow! I never knew there was a 6 port 12a.

How well did it perform?

Spac

Appallingly. They were SO de-tuned is was embarrasssing. Mazda tried to make it as "piston like" as they could - lots of torque etc. It didn't work: The old 10A was faster.

Australia never got them either. There are a fair few here, having arrived as second hand motors.

And for the train-spotters... there's some doubt regarding the exact production years etc - there are a cuple of Series 1 (steel bumper) RX-7s that have been privately imported that appear to have factory fitted 12A 6-ports.

Rota_Motor

about the 6 port 12As I dont think they were in the series 1s, as I have a japspec S1 and it has a 4 port, I am pretty sure 6 port 12A's werent introduced until maybe 81/82 or so, around the same time japan got the 12AT. I am pretty sure every japanese RX-7 after the iontroduction of them got either a 6 port 12A or turbo 12A, much the same as the FC got six port or turbo 13B.

djmickyg

the 6 port was never down here in astralia either, (as far as i know) it was used in the cosmo in japa, just like the 12at.
it was ment to have improved low down torque.
a guy i talk to down here has one in his S1 and says he can get wheel spin from 2700rpm.

djmickyg

i got the jspec 2 and they did get a 4 port and the smallest ported carbby too

speckamp

Just to be clear, since I think maybe the thread starter may be asking something different and we're just not getting it.

Facts:

All engines are big air pumps.
There are systems to bring air into, fuel into, and the burnt gasses out of the engine.
Burning of the fuel is controlled (In a gasoline engine) by an ignition system.

Normal Aspiration means that the reciprocating assembly of the engine draws the air into the chambers by itself. This is the most common "induction system" on a production engine.

Forced Induction is the process of FORCING (heh, good name, eh?) air into the chambers. This comes in 2 forms. Belt driven pumps are called Superchargers, exhaust gas driven pumps are called turbochargers. Each has their advantages and drawbacks that I won't get into here.

Okay, now that that's done, to re-iterate, ALL US Sold STOCK 1st Generation RX-7's came with either a type-12A or type-13B rotary engine.

The former is a 1.1(or 1.2 depending on how you round)litre, normally aspirated, carburated, 4 port, twin rotor engine.

The latter is a 1.3litre normally aspirated, fuel injected 6 port twin rotor.

NO first generation RX-7 in the US came equipped with forced induction from the factory.

For a further explanation of how the 6 port system works, click www.ub3rgeek.net/~mernisse/RX-7/6PI.jpg That link and take a look.

#5 is the actuator that opens the aux (5th and 6th) ports.

#7 is the rotary sleeve valve that actually opens the ports.

You can see the 6 ports in the block (two in the center plate and 4 in the end plates (2 front 2 rear))

Hope I helped.
matt

neoboi

Thanks yall, yall helped me a lot, the picture was great, it helped me understand it much better.

-Brian

Spac

Rota, I know what you're saying, and I don't have any hard evidence against this - BUT I have seen two (and heard of another couple) of S1s with 12A 6-ports. Apparently factory fitted. All cars have been of the same (low) spec, too.

I'm not trying to re-write histroy here, but I am suspecting that the current version is not 100% right.

rotarygod

iTrader: (1)

I always thought that the 12A 6-port motors came in a different car in Japan not in the RX-7?

Spac

Yeah, they were in the HB Cosmos (we got them here with MA or FE piston motors and called them 929s).

I haven't seen anything official either way regarding 12A 6-port RX-7s.

Rotor13B

Someone awhile back had one in his 7. Can't remember who it was though.