Building a 13B FC motor

Technical info not specifically 1st gen RX7 related.

Re: Building a 13B FC motor

Postby TOOL » Thu Oct 09, 2014 9:03 pm

Common sense really:

Image

And don't forget to shim the front reg, which is there to protect the oil cooler and lines:

Image
Now with 3 rotors
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Re: Building a 13B FC motor

Postby TOOL » Thu Oct 09, 2014 9:18 pm

As I said earlier, the S5 rotors are the same mass as FD.

The FD has much bigger diameter torrington bearings and this spreads the load on the front of the eshaft a lot better.

Image

Because the S5 and FD have the same rotating mass, you can fit FD stat gears and front counterweight with the bigger torrington bearings without the need to rebalance the rotating assembly. The stat gears are hardened and have better oil releifs, meaing when you fit the 3 window bearing, you've got greatly improved oil flow.

The S5 plates are also better than the S4 plates as they have been strengthened around the dowel holes.
Now with 3 rotors
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Re: Building a 13B FC motor

Postby TOOL » Thu Oct 09, 2014 9:27 pm

The rotor:

You can run twin side seal springs under each side seal.

You can run one piece carbon seals on NA motors. I prefer these. They are great for ported motors as well, so you don't need to worry about the corner piece falling into the inlet port. Carbon seals are also very gentle on the chrome on your housings.
You have to use the matching carbon seal springs when using carbon seals.

Solid corner seals and FD type corner seal springs. The solids don't seal as well at low rpm, but they are less prone to breaking. The rubber inserts in the keyhole corner seals turn ugly anyway.
You can get solid corner seals which are recessed too to reduce their drag on the side plates.

Rotor bearings are rotor bearings. The MFR ones are too expensive and don't do a lot.

Oil control rings. Fit new orings and springs. You can also get an MFR outer oil control ring spring. I've got some and will try them out.
Now with 3 rotors
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Re: Building a 13B FC motor

Postby TOOL » Thu Oct 09, 2014 10:21 pm

Eshafts. RX8 eshafts are cheap as chips:

http://atkinsrotary.com/store/Mazda-Rot ... ic-Shafts/

Apparently the front plate on an RX8 is thicker, so the shafts are longer. You get around it be extending the oil gallery hole in the front stat gear bearing.
They've got a tapered rear journal which is useful at high rpm to prevent the shaft contacting the bearing as the shaft flexes.

S5 shaft is good, only fractionally heavier than RX8. Fit a thermal pellet plug in the front of it or source an RX4 13B shaft.
Now with 3 rotors
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Re: Building a 13B FC motor

Postby myatt1972 » Thu Oct 09, 2014 10:58 pm

Great thread, Im taking it all in 0-0
Keith...
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Re: Building a 13B FC motor

Postby Hobbawobba » Thu Oct 09, 2014 11:07 pm

Yeah man this is a cool thread aye. Chur bro! I've nearly finished reading Street Rotary that Steve let me borrow. Learnt loads from it! They explain things really well so that even I can understand *most* of it! :lol:
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Re: Building a 13B FC motor

Postby Ghostkls » Fri Oct 10, 2014 7:49 am

TOOL wroteColonHow about these beauties?

Image

Image

Rice Racing I believe.


That is what I am talking about! Wouldn't it make more sense to taper off the top of the port for street applications, which should help reduce wear on the apex seal and increase engine life by allowing the seal to transition into the groove?

When I look at that port, at high RPM the seals are being "thrown" out the rotor so sudden end would chip the seal over time.

I must thank you Tool! You are really willing to share your knowledge and material you have! I don't have access to any information on this level here in SA and the few people who do have info just don't want to share, which is a shame with rotors becoming more and more rare....

With a little luck and the info you have provided, I will be able to build a clean simple reliable 13b that will surprise the locals at track and drag days! s(c)
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Re: Building a 13B FC motor

Postby TOOL » Fri Oct 10, 2014 8:31 am

Totally OTT those housings. This would be used for top end power only, with a massive turbo stuck on the side.

Less is more when it comes to NA motors.

There is nothing in this thread that isn't freely available out in the world if you know where to look. It's just easier when it's assembled in one place.

There's way more tricks. What else do you want to know?
Now with 3 rotors
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Re: Building a 13B FC motor

Postby Ghostkls » Fri Oct 10, 2014 9:04 am

Thanks Tool!

The more info I have to work with, the better choices I can make when building/modding the motor.

As I have more questions I will ask, for now got lots to process and work through, I think I have rewritten my shopping list at least 3 times already.... :oops:

How difficult is it to get hold of things like IDA webers on that side of the world? Here they are very uncommon....
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Re: Building a 13B FC motor

Postby TOOL » Fri Oct 10, 2014 9:54 am

Not all Webers are the same.

The old Italian built Webers are preferred, if they're not flogged out. Watch out for the accelerator pump and main spindle.

New Webers are Spanish built, and reportedly not as good.

You can buy them all day. Here's one, just throw away the A series manifold:

http://www.ebay.co.uk/itm/WEBER-48IDA-C ... 2596ca8e5b

The EMPI IDA is reported to be a nice item. I've seen one of them and they jet to your liking. Try Green Brothers in NZ.
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