im looking into getting a new exhaust, at least a header. i was looking around last night at racing beat and mazdatrix and i got confused. some came with actuators and o2 sensor, others did not. on an 84 13b, when (what rpm) and how do the last two ports open? does it have anything to do with the exhaust? so if i would get racing beats full dual exhaust with no o2 sensor would i be fine? what if i just got a header?

also, im looking into getting a holley or dellorto or some performance carb. if i were to replace just the upper intake manifold and leave the lower stock, would it affect the last two ports opening? or how about if i would replace both the upper AND lower manifold when i do actually get a carb, would this pose any problems?
basically, im just kinda confused as to how the whole 6 port thing works. am i worrying about nothing?

 

Where there is 2psi of exhaust backpressure, the ports open. (Roughly speaking... they don't pop right open but open gradually)

Lots of people just wire them open when they modify the exhaust, to ensure that they open fully. You do lose low-end torque that way, but so what.

 

Racing beat has a presilencer that contains the small exhaust output to open those ports (which are exhaust backpressure activated) for you.



You don't need the O2 sensor. Many people seem to run fine without it, even with the EFI.

No, it would work PERFECTLY, the way it should.


No, you would basically convert the engine into a "4" port (technically), make decent power, and have very little torque in the low end.

Yes. Get the headers with the RB pre-silencer, replace the Intake Filter with something that flows more, a'la Bonez or K&N. Then, if you want more power (and less reliability) go with the Dellorto or Weber sidedrafts.

 

but everything will work fine if i just get the header to begin with and get the presilencer later on?

 

Yep.

 

I just talked to Racing Beat yesterday and asked them if the Header for the GSL-SE came with an O2 sensor bung(sp?), and they said yes. So I am wondering if this was correct info from RB or if the person on the phone just didn't quite know and told me what i wanted to hear. I want a header with an O2 sensor bung(sp?) so i can hook up my air/fuel ratio meter.

 

I believe they do.

 

I know that Mazdatrix sells a RB with a bung, but do not know if RB actually makes it or Mazdatrix modifies it.

 

The best thing to do if you're going to go to a Dellorto or Weber on the stock lower intake is to remove ALL the 6 port hardware and cap off the 2 openings left on the manifold. The sleaves and internal actuator rods occupy an amazing amount of space in there and are a major restriction. True this will affect driveability in the low end, but cleaver jetting of the carb can make this situation tolerable.

If you take a look at the RB holley "six port" kits, you'll notice that the RB manifold has no six port function whatsoever...

Six port induction is a great thing for driveability and low end torque, but it really doesnt have a place in a high performance application. The power you lose in the low end will be gained in the upper ranges where it really matters .

 

well, this car will be used primarily for autox, some street use (for fun, not daily driver), and a few track events. does this affect your opinion on what to do as far as intake and the 6port is concerned? in autox, some low end torque would be greatly appreciated.

 

For autocross, the trick will be to stay in 1st instead of 2nd. You might have less low end torque, but power in the high end will be much more accessible, so this isnt really a problem. Of course, like I said before, I you want lots of low end torque or dont like reving so much for power, it's entirely possible to rejet your carb to be a low end torque monster.

The six port system is great, but it doesnt make a HUGE difference in low end power. Try proping the actuators so that the 5th and 6th ports are open at all times... you'll notice a difference, but it's not undriveable in any way.

 

I autocrossed with a stock 6 port but removed the actuators and installed a dellorto. The upper end increase was worth the sacrifice of the lower end power. I personally like the difference. I tend to race in the 7500rpm and up range, although I try not to shift so much. I will let it lug a little before shifting down a gear just to be smoother which creates quicker times.