Let's talk cranks, trannies (the metal kind), and diffs - Miata Turbo Forum - Boost cars, acquire cats.

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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 04-13-2007, 06:39 PM   #1
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Default Let's talk cranks, trannies (the metal kind), and diffs

I'm rebuilding a 1.8 block for boost from a dead '96 miata using parts purchased from Belfab. I know that the power output in the rebuilt block is going to lay waste to my stock drivetrain, so I'm looking into alternatives that can handle 275-300 whp. I'm going to be hell on the car, so overengineering the drivetrain is the name of the game. What are you high HP guys doing on your Miatas to handle big FI power?

Cranks - never heard of anyone chewing up their stock crank yet. So I'm not to worried about this right now.

Trannies - I predict that the stock 5 speed is going to scream like a bitch for about .001 seconds after I lay my foot into the loud pedal. Then it's going to eat itself. I've heard of guys using the 6 speed with good success, but I don't have much confidence since the number of people using it isn't very large. I've heard of FC3 manual tranny swaps, but it is something that takes some *inguneering* and fabrication to do right (read: no kits available). I've emailed Martin (of v8miata.com fame) to see if he'll sell the T-5 transmission/7.5 IRS parts of his kit separately (which CAN handle serious power). That would make for a nice solution.

Diffs - I'm reading that the miata torsen unit is capable of doing the job with little muss and fuss. It's not cheap, but it's plug-and-play. The downside is the craptastic gearing if you're using the miata 6 speed. I've read threads recently of people using the diff out of a 79-82 RWD 626 with good results (and the 3.6 gearing matches up well with the 6 speed). Others have bolted in the FC3 turbo II diff...but that also requires a good level of engineering and fabrication to do properly.

OT: Jim's (of Belfab) customer service is every bit as good as his prices. I'm looking forward to getting my parts in the mail soon!
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Old 04-13-2007, 07:27 PM   #2
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For a Plug and Play Ring and Pinon Set:
The 3.909 came on the 99+ 6-speed Miata.

The 3.636:1 came on the 2001+ Austrailan 6-speed.

The 84-85 RX7 GSL is a 3.909.

The 84-85 RX7 GSL-SE is 4.08.

I don't suspect I'll run more than 250rwhp anytime soon, so my stock 1.6 tranny and 7" rear upgrade will be enough.
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Old 04-13-2007, 09:10 PM   #3
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6 Speed and 3.636 is how I went. 300 RWHP, handles the drag strip fine.

Mark
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Old 04-13-2007, 10:55 PM   #4
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I contacted FinishlinePerformance last summer about the 3.6 rear end, and they said they could get it for something like $750.

-Mike
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Old 04-14-2007, 12:46 AM   #5
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I think the RX7 ring and pinon would be a good compromise, considering they can be picked up for very cheap from various sources. I just sold a 3.909 set for $75 to y8s.


http://cgi.ebay.com/ebaymotors/Mazda...spagenameZWD1V

call these guys, always has lot of parts on hand.
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Old 04-14-2007, 05:42 AM   #6
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Does anyone make a bellhousing to fit a Muncie trans to the miata engine? I'm thinking back to my Chevy Monza v8 swap days and I put 400hp thru one of those transmissions. It's an aluminum trans but only in 4-speed that I know of. The Monza had a bar running from the rear axle to the tailshaft much like the PPF in the Miata. It would be easy to adapt the Monza/Muncie tail to the Miata PPC. The shifter/linkage should be easy as well since it's side mount linkage to the Muncie trans. Any aftermarket manual shift lever could be bolted to the Miata tunnel. Any opinions?
What other transmissions bolt up to the Miata engine without an adaptor plate?

EDIT - This is just badass... http://home.earthlink.net/~miatav6/id15.html
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Old 04-14-2007, 09:03 AM   #7
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a muncy would be bad *** i love the one in my chevy. They are supposed to be good for 700 hp i dunno how close id get to that though. A 7 inch rear is plenty strong for the 300 or so whp range from what i read m if you are handy with setting pinion backlash etc a rx7 internals swap with rebuilt clutch type unit would probably be the cheapest route. And fairly durable.
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Old 04-14-2007, 12:34 PM   #8
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Quote:
Originally Posted by Markp View Post
6 Speed and 3.636 is how I went. 300 RWHP, handles the drag strip fine.

Mark
I see where the 3.636 rear came in both the Ozzie 6 speed and the 79-82 626. Which did you source your rear from? Was it a pain to get the ring/pinion to fit the miata 7", or did you need to do a little grinding?
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Old 05-05-2007, 07:02 PM   #9
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I'm still going back and forth, trying to decide if I should build the bottom end, considering the trans won't take more than 250whp. I'll probably just build the bottom end so I can hope for 100k out of the motor with a conservative tune.

I found a 6-speed today for $300. I'm considering it, but don't want to be forced to hunt for an austrian ring...put another shrimp on the barbie, lol.
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Old 05-07-2007, 02:08 PM   #10
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Quote:
Originally Posted by jcochran View Post
I see where the 3.636 rear came in both the Ozzie 6 speed and the 79-82 626. Which did you source your rear from? Was it a pain to get the ring/pinion to fit the miata 7", or did you need to do a little grinding?
Ozzie 6 speed was where I sourced it. Actually purchased it new from Mazda for $270 and it bolted right in... I didn't even have to replace the crush collar (I know that was wrong of me.)

Mark
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Old 05-10-2007, 08:41 PM   #11
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what models did the 6 speed come in? all i'm seeing are 5 speeds.
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Old 05-11-2007, 01:33 AM   #12
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99 10AE
00 SE
And several of the 01+ cars including the Mazdaspeed
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Old 05-11-2007, 01:35 AM   #13
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Quote:
Originally Posted by hustler View Post
I'm still going back and forth, trying to decide if I should build the bottom end, considering the trans won't take more than 250whp. I'll probably just build the bottom end so I can hope for 100k out of the motor with a conservative tune.

I found a 6-speed today for $300. I'm considering it, but don't want to be forced to hunt for an austrian ring...put another shrimp on the barbie, lol.
The other option is the Ford IRS (the 7.5" should suffice) and the 8.8 comes with traction lock and a 3.55 gear. I have one in the garage waiting to go in the '99 should I blow out the torsen, already mounted in a spare subframe.

Mark
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Old 05-12-2007, 06:11 AM   #14
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Quote:
Originally Posted by Markp View Post
The other option is the Ford IRS (the 7.5" should suffice) and the 8.8 comes with traction lock and a 3.55 gear. I have one in the garage waiting to go in the '99 should I blow out the torsen, already mounted in a spare subframe.

Mark
I agree to this solution That's the route I'm going because the 8.8" has alot of gearing options. 3.55 would be nice for those long straight roads and considering the tiny miata 4.10 was for an n/a stock engine I don't see the torque loss being a huge issue since the car is so light. Junkyard here I come.
What year/option T-birds have the 8.8" with traction lock?
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Old 05-12-2007, 12:50 PM   #15
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Quote:
Originally Posted by lazzer408 View Post
I agree to this solution That's the route I'm going because the 8.8" has alot of gearing options. 3.55 would be nice for those long straight roads and considering the tiny miata 4.10 was for an n/a stock engine I don't see the torque loss being a huge issue since the car is so light. Junkyard here I come.
What year/option T-birds have the 8.8" with traction lock?

The 8.8" was in the IRS Cobra, not the T-bird. The T-bird has the 7.5" which is strong enough for all but the most rediculous setups.

Mark
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Old 05-12-2007, 01:03 PM   #16
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Someone wanna link me to a ford diff install in a miata? It sounds like a bit of an adventure.
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Old 06-10-2007, 11:47 AM   #17
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Old 06-10-2007, 02:04 PM   #18
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Doing some research on the Engine Conversions forum over at M.net will yield plenty of pics, discussion and kits for Ford rear-end swaps.
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