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Index > Engine/Drivetrain > Thread: Transmission differences
Thread: Transmission differences
Philthy


Newbie
Posts: 3
posted February 06, 2004 10:27 AM

Transmission differences

Anyone know where to find the differences in transmissions offered behind rotarys? All I've found so far is posts saying there are differences, but no specifics. Basically, I'm looking for the lowest 1st gear 5 speed that can bolt up to a carbed motor. I'm not too concerned with tranny length but it would be nice if it also happened to be short. And available in the US and easy to get parts for and cheap and all the other things. I'm gravitating toward a truck tranny instead of a car, because, I assume they would be stronger. Anyone agree with me?

Thanks.
____________
Troy
Senior Test Pilot
www.AbusiveMotorSports.com

         
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nwaco


Redlining
Posts: 407
posted February 06, 2004 10:49 AM
Edited By: nwaco on 6 Feb 2004 10:50

This is a decent site.....

with lots of information.

http://members.ij.net/mrmazda/interchange.html

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Klaus43


Rotorhead
Posts: 1259
posted February 06, 2004 11:55 AM

At this point in time

the benefits of an early ('74-'78) 'ribcase' transmission, in terms of strength, might be eclipsed by the relative inexpensiveness/greater availability of 1st-gen rx-7, if not 'turbo 2' trannies... unless your engine's output requires the more extreme strength... though, apparently, the earlier synchro's aren't as good... you might end up wanting to use a 'ribcase' bellhousing with a later transmission.
Making a rotary rockcrawler, Philthy? Could be really cool, if geared to the rotary's powerband!
For reference, first gear in a '79/'80 rx-7 trans. is almost too low for the street, when hooked up to a '74 REPU rearend...

       
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Philthy


Newbie
Posts: 3
posted February 06, 2004 12:23 PM

Yeah, a rock or two. I've been wanting to turbo the stock Samurai 1.3l for some time now (65 HP @ 5500 RPM and between 60 and 70 lb ft at 4500) but I started wondering why I don't just skip all that (plumbing, intercooler, fuel injection, oiling, blah blah) and go with a 13B. I think the 13B also has around 100 HP and 100 lb ft, which is right about where I want to be anyway. And if I'm not wrong, they have better apex seals than the 12As but are like 2 inches longer or something. I have a divorced transfer case, so I will use a the rotary's tranny and can move the transfer case around to where I need it. With 32 inch tires and 4.10 R & P I'm running around 5000 RPM at 70 mph, so, with 35 inch tires and 5.29 R & P, I should be just shy of 6500 RPM at 75 and right in the rotary's sweet spot. As for the actual rock crawling, I've got 90something:1 in low range now and with the 5.29s should be over 100:1, so, I should have no problem keeping it in the power band there.

Sorry this is so long and off topic, but it may give someone some insight into what I'm thinking about doing and they maybe able to point me in the right direction.
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Troy
Senior Test Pilot
www.AbusiveMotorSports.com

         
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Klaus43


Rotorhead
Posts: 1259
posted February 06, 2004 01:06 PM

There's a world more technology

out there now for Apex seals alone, which you might want to research a bit... waay beyond '13B's better than 12A's' (you can build either with steel, carbon, or ceramic apexes... 2 or 3mm wide... one, two, or three-piece seals... etc., etc. ...)
You're on the right track, though! Just remember to count on investing in a Racing Beat header for your more bulletproof exhaust setup! And whatever you do, don't scrimp on the cooling--especially the oil cooler! That 1stgen rx-7 under-the-filter one might be good as a supplement, but in my book it's a joke used on it's own.
I also gotta wonder at what point of tilt a dry sump oil setup becomes nessecary... and how far over you can go before the carb. rebels...? Any of you offroad guys ever run the 'predator' carb? I've always been curious about it...

       
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Jeff20B


Moderator
Posts: 661
posted February 07, 2004 12:13 AM

quote:
For reference, first gear in a '79/'80 rx-7 trans. is almost too low for the street, when hooked up to a '74 REPU rearend...
Uh-oh Klaus, you did it again. Check this out to see what I'm talking about. http://members.ij.net/mrmazda/tranchrt.txt

All '79-'80 trannies are taller in 1st. I also noticed a difference when I went from a '79-'80 tranny to a '76 Cosmo 5 speed in my REPU. 1st gear in the ribcase trannies is a lot better for hauling and towing.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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Klaus43


Rotorhead
Posts: 1259
posted February 07, 2004 10:53 AM

OK Jeff...

...you're welcome to come on over and ID what's in my 'driver' REPU--Looks to ME to be an early 1st gen 5-speed smooth case transmission... but I suppose it could be some j-spec POS like the 4-port 13B that's in it. What do I know? Whatever the hell this tranny is, first is pretty damn low. Gotta grab second to really get very far. Nothing was cut to make it fit. Driveshaft is REPU. What else could it be?

       
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Jeff20B


Moderator
Posts: 661
posted February 07, 2004 11:42 AM

It could be, but I'm just going by the chart on Felix Miata's site and my own pertsonal experiences with tranny swaps. Sorry to have upset you.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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rotarydave


Hauling
Posts: 108
posted February 07, 2004 12:20 PM

you would also do well to check out the gearsets in other MAZDA/FORD trannys it is my understanding that there are some interesting 626 combos that go nicely into a SA tranny case (which will fit into a repu)

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Klaus43


Rotorhead
Posts: 1259
posted February 07, 2004 02:29 PM

No apology nessecary, Jeff!

I'm just getting upset at my self... and wondering what's really what, and all... certainly don't need to be mistaken about key items, on top of having no funds to do a damn thing with my little collection right now. Just makes me wanna puke, and stop making a fool of myself here.
So, are there any simple ways to positively ID transmissions, without having to pull 'em out first? Kinda like the clutch BS... Seems it could be real helpful!

       
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Philthy


Newbie
Posts: 3
posted February 07, 2004 11:55 PM

I like the 3.67 1st gear in the RX, but what really excites me is that 4.36 in the B2000. The Japanese equilvalent of a granny gear. Anyone know if it will bolt up to a rotary motor? I did some measuring today and found that a Sami tranny is around 25 inches long, so the 32 inches of an RX7 tranny will pose some "opportunities." Anyone know about how long a 13B is?

         
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