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11 replies to this topic

#1 terronj

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Posted 09 March 2011 - 06:15 AM

So I'm in the middle of mating a single rotor 13b Mazda to my 84 hatchback. I'm shooting for 150 hp from the modified 650cc engine when its all said and done. However I'm concerned that I may suffer in the low end torque department and it probably won't start to pickup until higher rpms. My synchros are shot in third in the 4spd that's in it right now so the transmission has to go anyway. So my question is this, taking into account that I have a lot going on with the engine build, is it worth it for me to put a 5spd in my car? What would be required? And what kind of car does the 5spd come out of?

#2 el_freddo

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Posted 09 March 2011 - 07:18 AM

Sounds like a good project with a lot of potential!

I'd recommend looking at an AWD gearbox, this way you've got maximum traction to get all the power to the road without the wheel spin.

To change the gear ratios in the gearbox for the best low 1st gear can be a bit of fun if you're up for the task... The only issue is that with this method your 2nd, 3rd and 4th gears also become "shorter" thus requires the engine to rev faster to maintain the same speeds as it would have before any modifications. 5th gear is independant of 1st - 4th gearsets so you can find your desired ratio and fit that for highway cruising.

Best bet would be the 3.7 diff ratio'd AWD gearbox that would be found in most bog standard legacy's (liberty in Oz). Find one of these then go hunting for either another gearbox or just the ring and pinion for a 4.11 or 4.44 (hard to find in Oz, dunno about the US though), fit this to your 1st gearbox that was 3.7 diff ratio standard and you'll have effectively lowered your 1st gear's ratio for a better take off. Run a legacy size tyre diametre and you'll be apples.

Someone will be able to shed more light on this I'm sure.

Cheers

Bennie

#3 WoodsWagon

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Posted 09 March 2011 - 10:42 AM

A 13b is the equivalent of a 1300cc 6 cyl engine, each rotor displaces 650cc's on it's 3 combustion chambers and there's 2 of them in there. Having ripped around in a 84 GSL-SE in highschool, I wouldn't be too worried about lack of torque. Be more worried about a good oil cooler and watching oil consumption. They're old engines at this point and most were abused ruthlessly.

Are you trying to keep 4wd or do you plan on going Rwd? You could probably use the RX7 transmission and make a custom driveshaft to the rear. Someone else on here is doing a rotary swap, with just RWD.

Edited by WoodsWagon, 09 March 2011 - 10:44 AM.


#4 terronj

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Posted 09 March 2011 - 12:40 PM

No I plan to keep the hi-lo 4wd. I was only concerned about the drivability of the high revving single rotor. Also people around here always say that the 5spd is better than the 4spd but I never hear them say why? Is it just that drivability, or is it mechanically superior in some way?

And the oil cooler is on the way.

#5 WoodsWagon

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Posted 09 March 2011 - 02:22 PM

The 4spd has a crappy shift linkage that tends to lead to people trashing synchros and grinding up reverse. I think it has a smaller clutch than a 5spd d/r too.

What is this single rotor 13b? 13b's were all twin rotors.

#6 pickstock

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Posted 09 March 2011 - 04:00 PM

yeah 13B refers to it being a 1300cc twin rotor if i am correct =/
ie each rotor is 650cc and theres 2 of them

unless your making a 650a? thaty would be cool hahah

#7 Mazdax605

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Posted 09 March 2011 - 06:49 PM

How are you going about mating up the 13B to the Subaru transmission?

Being a Mazda rotary guy that is in the process of buying my first Suby this intrigues me. Any details would be great. I have several 13B,and 12A's laying about.

Chris

#8 NoahDL88

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Posted 09 March 2011 - 08:05 PM

There is a RX-RX floating around out there, I don't know if he used the suby tranny or the RX-7 one though.

As far as tranny ratios go you're going to want to go high, 4.11 from a legacy or impreza because the higher rear end ratio will serve the higher revs of the 13B better and get it into the powerband faster.

#9 terronj

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Posted 10 March 2011 - 04:29 AM

I'm having a speed shop modify the eccentric shaft so that it only has one rotor journal and moving the front key-way to the other side. Then hardening and balancing and bolting it together with one rotor. Port both the primarys (because all it has are primary intake ports) Custom intake manifold and exhaust, tiny turbo, inter-cooler, Mega Squirt fuel injection and to handle the ignition and maybe the metering pump, adapter plate, oil cooler, custom motor mounts. I still haven't sorted out the clutch yet. And then you get a single rotor 13b Subaru, or Rutaru, with 650cc's of furry.

#10 Mazdax605

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Posted 10 March 2011 - 07:12 AM

Why a single rotor? Won't the stock 13B fit in the engine bay? What sort of adapter plate are you using,custom made,or some sort of off the shelf VW type adapter?

#11 pickstock

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Posted 15 March 2011 - 06:32 PM

so its a 6.5a?

#12 el_freddo

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Posted 02 April 2011 - 08:50 AM

So what will you be filling the rest of the engine bay with??? Sooo much room if you've only got effectively half a stock rotary in there!

The gearing will be interesting to work out - really need to know how this rotary performs on the street to get any idea of whether or not the stock subaru ratios will work with this engine.

As for the 4 or 5 speed question - 5 speed has a much better "step gap" to the top gear by splitting it with another gear. I've had loads with the 4 speed that bogged the EA81 going from 3rd to 4th unless you really flogged the engine to "jump" the gap in the revs between the different gears.

The 5 speed is generally nicer to drive, feels better in the gear changes unless the 4 speed has new gear lever bushes installed. The L series 5 speed is basically the same as the EJ/Legacy 5 speed, well over here it is as we've got the dual range function on the EJ/legacy 5 speed gearboxes where as I believe that you missed out on this in the US.

Hope this gives you something to think about/research.

Cheers

Bennie




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