1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

what would you choose? an engine enigma.

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Old Jul 26, 2008 | 04:03 AM
  #1  
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what would you choose? an engine enigma.

The subject 1981 with 12a blown rear rotor.

I have not driven the car for years and would like to resolve this.
I know of many different options. but would like opinions of the group.

It can be a 12a or 13b I already have the gsl-se front cover

Looking for 140-200 hp

must be civil, I really dont want a bridge or PP. As fun as it may be!

not looking to win races but for the entertainment value.

sub 8 sec 0-60

No Turbo

Would perfer FI. but a good steetable carb is a consideration.

I dont want to have to rev the **** out of it all the time, moderate low end grunt is sought after.

In FB fashion I have no budget for fancy pro rebuilds.

I am leaning toward : FC 13b 6PI retaining stock parts and using stock ECU w/ Racingbeat exhaust.

must work in all weather, Snow and Heat

Ill add more as I think of it
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Old Jul 26, 2008 | 07:06 AM
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I always thought the best combo for that would be a 13b streetport with appropriate weber carb.
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Old Jul 26, 2008 | 08:28 AM
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Originally Posted by bliffle
I always thought the best combo for that would be a 13b streetport with appropriate weber carb.
I had an 88 with the 13B - loved the torque/power of the engine and gas mileage was better than 12a, did not care for the car (or seats) or variable power steering. Cost and time are no issue? If they are, getting a 12a back in would be so much simpler I would think.
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Old Jul 26, 2008 | 11:57 AM
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-se rotating assy in -se housings and 4 port irons with big ports. This i assure you is a recipe for fun. I know there are other 4port 13b owners that can chime in to say the same.


isaac
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Old Jul 26, 2008 | 01:03 PM
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Here's your solution Richard. As a result of our MANY and LOOOONG conversations about what you want from your car, I woul sa you need the following......

6 port 13b with stock internals
Stock 12a transmission
Full racing beat street port exhaust (incl. the muffler)
2nd gen leading ignition
Stock trailing coil
Racing beat carb hat
GOOD nikki carb, possibly a sterling. (very dependable on both counts)
5 psi fuel pressure

This will put you in the 145-150 hp range. Very drivable, and still fun.
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Old Jul 26, 2008 | 01:17 PM
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Will a sterling carb be enough for a 6port? If so then you would have to have an adatpter plate made to mount it to the 13b intake manny whether stock or aftermarket.
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Old Jul 26, 2008 | 01:23 PM
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Originally Posted by flight_of_pain
-se rotating assy in -se housings and 4 port irons with big ports. This i assure you is a recipe for fun. I know there are other 4port 13b owners that can chime in to say the same.


isaac
Yes, and I am one of them. Before my current street ported 4-port setup, I had a street ported 6-port setup and I can assure you that the 4-port is far better.
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Old Jul 26, 2008 | 01:37 PM
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From: https://www2.mazda.com/en/100th/
well to break it down further.

12a and 13b cost within $50 to build, 13b will make more torque, so look for a 13b.

in the 13b world, a steet ported 4 port will touch 180-200hp, but so will an FC 6 port engine.

4 port or 6 port i guess depends on what you have available, and how you want the car to turn out.

4port with a carb, is old school.

id be doing a 6 port, s5 engine, because thats what ive got lying around
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Old Jul 26, 2008 | 05:39 PM
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I made the choice to do a ported S5 13b motor. makes the most power stock N/A of the 13b. 160bhp
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Old Jul 26, 2008 | 06:10 PM
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Well a budget certainly kills my N/A 20B idea. I'd say make yourself a 4 port 13B. Use your 12A irons, 13B housings from the SE as well as the eccentric shaft. From there you can use any 13B rotors you want(with the exception of the Renesis. You could get them to work but it would be more work than it's worth). I would probably use S5 N/A rotors for the higher compression(9.7:1) and they are lighter. PM Jeff20B about '74 Spec ports. You will find better results than a street port
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Old Jul 26, 2008 | 06:24 PM
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12a Irons
-SE housings
S5 NA Rotating Assembly OR RX8 rotating assembly
-SE oil Pan
Streetport

There you go. 200HP with bolt ons.
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Old Jul 26, 2008 | 09:59 PM
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question about 4 and 6 ports.

does the 4 port make more low rpm torque over the 6? and does the 6 port make more high end hp?
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Old Jul 26, 2008 | 10:52 PM
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Yes and no, and yes and no. are we talking ported or stock?


isaac
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Old Jul 26, 2008 | 10:57 PM
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Question about "bastard engines". What intake manifold do you use when you have 12a irons and 13b housings?
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Old Jul 26, 2008 | 11:10 PM
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13B intakes made for the 4 ports
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Old Jul 26, 2008 | 11:52 PM
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im using an rx4 intake iirc, the bolt spacing for the carb is bigger but the bores are the same. 4 quick drilled and tapped holes convert it to nikki spacing. If you decide to go this route let me know and i can snap you a pic.


isaac
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Old Jul 27, 2008 | 01:11 PM
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From: https://www2.mazda.com/en/100th/
Originally Posted by spottedfrog
question about 4 and 6 ports.

does the 4 port make more low rpm torque over the 6? and does the 6 port make more high end hp?
stock to stock, a functioning 6 port engine will make more low end and high end is about the same, 6 port is a little better, as its got more port area and timing.

once the 6 ports arent working, however, the low end goes away.

porting a 4 port has more gains than porting a 6 port.
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Old Jul 27, 2008 | 01:13 PM
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From: https://www2.mazda.com/en/100th/
Originally Posted by FirebirdSlayer666
. PM Jeff20B about '74 Spec ports. You will find better results than a street port
74-75 ports basically ARE a street port.
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Old Jul 27, 2008 | 02:54 PM
  #19  
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It's a different shape port than a streetport. Jeff posted a thread about it but I don't remember a whole lot about them
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Old Jul 27, 2008 | 04:59 PM
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You're right, you don't remember a whole lot.

'74 spec ports are like a small streetport. The intake opening is not changed and can allow for bridgeports if desired (I've never done any). Only the closing timing is changed; delayed a few degrees but not as far as a Racing Beat or Pineapple streetport. '74 spec is like a happy medium and gives better low end than a full streetport on the street for daily driver duties.

The next 13B 4 port I build will have an RX-4 intake manifold, jetted Hitachi and '74 primaries with streetported secondaries. Exhaust ports will close a couple degrees after T2 (for better overlap = more NA power) and exhaust opening is yet to be determined; either GSL-SE or US-spec 12A/T2; which ever gives best low end while not hurting high end.
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Old Jul 27, 2008 | 08:10 PM
  #21  
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Jeff your posts make me speechless, i dont know the right word to describe your level of intesity towards the rotary motor.
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Old Jul 27, 2008 | 08:46 PM
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Originally Posted by bstrange99
Here's your solution Richard. As a result of our MANY and LOOOONG conversations about what you want from your car, I woul sa you need the following......

6 port 13b with stock internals
Stock 12a transmission
Full racing beat street port exhaust (incl. the muffler)
2nd gen leading ignition
Stock trailing coil
Racing beat carb hat
GOOD nikki carb, possibly a sterling. (very dependable on both counts)
5 psi fuel pressure

This will put you in the 145-150 hp range. Very drivable, and still fun.
Reply
Old Jul 27, 2008 | 09:55 PM
  #23  
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Originally Posted by wackyracer

And your estimation would be?.....be careful. I may have proof and witnesses....

Last edited by bstrange99; Jul 27, 2008 at 09:56 PM. Reason: add info
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Old Jul 27, 2008 | 09:57 PM
  #24  
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feel free to prove it and be sure to read my sig
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Old Jul 27, 2008 | 10:11 PM
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13B frankenrotor.. 12A irons, SE housings, S5 rotating assembly and the RE dual Weber dcd carbs for low end torque. Mild primary streetport, Judge Ito secondary port.
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