O I am looking into porting one of my extra engines. What is everyone's thoughts on the type of porting they would do and why. I prefer to do a bit of street racing but I want that edge to kill these mustangs. Thanks for the help.

 

What porting?
74 spec

Why?
Because it's the best choice for the street.

 

Intake and exhaust. Street port, bridge port. I will not go Peripheral port though that's too much. I was looking at the templates the RB has and thought it might be a nice investment for one of my rebuilds.

 

I have seen you say this in many threads. What exactly is the spec in relation to 85 12a?

 

I was a bit confused at it also. I don't know what spec because this isn't getting run in a SCCA or any other sanctioned race it's street racing and that's it.

 

I was looking at racing beats templates. If there is a better place to get plates I am all ears.

 

for 74 Mazda basically street ported the engines, and then in 76 they had to unstreet port the engines, to try and get better mileage.

so compared to a 76-85 12A the 74-75 engines have ports that close 10 degrees later, and the so does the exhaust (i think).

like Jeff says, its prefect for a street car, as that's what its for.

 

How can the 74 irons be identified?

 

74 irons have 3B in raised letters and they are not nitrided. If you can find one, make a paper template.

74 spec ports close at 50 degrees. To compare with 76-85, those close at 40 degrees.

Where do RB streetports close at you ask? At 60 degrees. RB also opens earlier too, but you need a big intake manifold, big carb and a big exhaust which all cost money to properly do an RB streetport. Otherwise it ends up slower on the street than a stockport. You lose low end, especially with a 12A.

 

I am porting and polishing my one of my intakes now. And the carb is getting stripped and ported and jetted. Exhaust is already upgraded. Ignition is direct fire so I would hope this might be enough. Or do you disagree that that's enough for the RB street port?

 

Not to be abrupt but he has already answered that question:

" but you need a big intake manifold, big carb"

I say take his advice and go with the 74 spec, a 12 A with no low end power is not fun to drive.

 

The nikki works well on the aforementioned '74 intake port, so I wouldnt waste my time on the RB template... Id try to source a '74 template from one of the many old men on the site who have them...

 

Ok so does anyone know these older people that may have a 74 template. I will start searching now for one.

 

http://www.mazdatrix.com/toolport.htm

Ok so this link says they have steer porting for 74-78. Is that what I am looking for?

 

Nope. That's a streetporting template.

Here is a way to get 74 spec templates from a newer engine. Look for any stock ported T2 or FD end iron. Don't do an intermediate plate because the primaries on those were small for the injectors. Get one of the end plates. They open and close right at 74 spec. You can make a paper template from one of those. Only catch here is the very bottom of the port is a little lower and different than any 85 and older. You can ignore this area.

Put out a wtb for a dead T2 or FD end plate. Make sure it hasn't ever been ported. Probably best to avoid a cracked one as the dowel pin may be a little off. But a water damaged one could work.

 

I just happen to have a TII iron and did just that:



Obviously the closing time is delayed, but is the opening supposed to be the same as the 12A's ?


TII exhaust port is also right about same size as Racing Beat's streetable exhaust port template.

 

You want to make another paper copy of that and mail it to me?

 

Yes, the opening timing is the same as the 12A.

You'll notice the T2 exhaust opens at the same time as a stock US-spec 12A. The closing edge is where they differ. When I port up, I like to leave an anti-reversion lip. Some people just port out until they hit the sleeve but that removes the lip. The anti-reversion lip helps drive a turbo more efficiently. j9fd3s knows more about this.

 

the FC exhaust port and manifold is designed to have an anti reversion and silencing quality. with the anti reversion thing, there are a series of steps, the exhaust can flow out more easily than it can go in.

the manifold acts as a resonance chamber, which decouples the exhaust behind it from any tuning, and also helps dampen the pulses, which are where the noise comes from.

the net/net is that the engine with these things is more tolerant of exhaust back pressure

 

I'll save you the wait, here are PDFs of the templates for intake and exhaust.

Intake port with TII closing - ignore the blotch in the corner. There's an outline for one dowel pin so when you can use that and then align it with the port opening and oil seal line since they're the same as 12A. Like Jeff20B said, ignore the part that extends further down the stock 12A port.

Here's the 12A exhaust lengthened to TII closing time.

Of course remember to print 1:1 scale.

To further illustrate what Jeff20B said about the exhaust ports, here's a 12A right beside a TII housing. The glare lining up the bottom was complete luck.

 

Thank you so much. You just saved me a drive of about 4 hours. I will print them today.

 

Bridge port. It's the only way to fly. It's like a street port but with mid range and low end power too. You lose a lot of drivability but on the other hand it also doesn't idle like crap like a stock or street port. (Like crap = smooth like a Camry)

 

lmao! i got my P port to idle smooth, and immediately switched it back to the brapping. i didn't go P port for it to be boring!

 

I have 3 12a's so I figure by the time I am done I will have various stages of porting once I get one to do just what I want it to I will get a 2nd gen and start modding that one. My hole is to own each gen of the RX7 but I want each of them built by me and just the way I want them.

 

Has anyone used the aluminum epoxy stuff they sell at racingbeat.com. I am curious to know if it would work for my first botched up intake port job...