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Old 02-24-2008, 11:20 AM   #1
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Default Howdy All!!!!!!!!!!!!

Well Ive finally decided to make my first post.
I dont have a Miata yet. That said, I've found a red 2003 automatic Miata I'm interested in. I really like the look of this generation Miata with the non-popup headlights.

I know that "EVERYONE" wants a 5 speed, Well I dont.
I drive crosscounty from Laurel, Ms to Seattle, Wa and back again every 2 weeks in a semi truck with 18 forward gears and 2 reverse.

My question is: How much HP can the auto transmission in the Miata take.
I'd like to get around 250 to 275 HP to the ground with a turbo. I HAD an autotranny 71' 240Z that put down 316 rwhp with a turbo. It went up in flames last summer.

Ive done searches on this site with no real awnser found and GOOGLE searches come up with same results. Went to flyin Miata and didnt find anything in their FAQ, they did have a stock auto trans for sale tho.
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Old 02-24-2008, 12:25 PM   #2
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welcome....don't take this the wrong way, in my opinion if you don't own a miata and are looking for a 250-275 hp car with a lazy auto, just pick something else like a stock camaro or something
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Old 02-24-2008, 12:57 PM   #3
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Yeah i dont know what you can really do with an auto trans. I would be concerned that the stock ECU controls shifpoints and such.

I would get in touch with BEGI and see what they say. I want to say there was a guy with a supercharged automatic at 300hp, but i dont remember

If they say no, try calling FM.
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Old 02-24-2008, 01:01 PM   #4
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I would say do a v8 swap and use an auto tranny if you are looking for a miata that's an auto with some power.....
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Old 02-24-2008, 05:22 PM   #5
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Originally Posted by airbrush1 View Post
I would say do a v8 swap and use an auto tranny if you are looking for a miata that's an auto with some power.....
Get a third gen and paddle shifters - maybe you won't need all those ponies.

But then Ford makes some OK trannies for their V8's . . . if you got the time to make the swap.
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Old 02-24-2008, 08:04 PM   #6
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The stock ECU plays a significant role in controlling the Auto tranny, so you're stuck with it... which means it's time for piggyback. I do remember a guy working with DIY autotune for a PnP Megasquirt specifically for the auto-trans. Call DIY and check on the progress of that.

I'd grab that tranny from FM. From what I see searching the AUTO forum at, 200whp is the upper limit of what guys are running.

On the other hand, there lots of guys running both hotside and coldside MP62 kits on their autos that report huge success. There are even more guys running M45 units. Get yourself a FFS coldside and run Megasquirt as a piggyback and 200whp should be no problem and really simple.

I think you're asking a lot of the tranny in the 250whp realm... especially if you want to get any real lifespan out of it. But I think you'd be really surprised at how fast a 200whp Miata is. There's a thread at where a guy who seems to know what he's talking about says you can count the number of +200whp auto Miatas on one hand. You're in short company.

Begi is currently working on a downpipe compatible with the Auto transmission. Currently, any of the DP's at Begi or FM aren't directly compatible with the Auto-tranny bellhousing. But when Begi comes through, a Begi"S" w/intercooler, plus Megasquirt running piggyback, some 460'w, and a decent exhaust at 10psi should get you into the 200-210 area with little problem for under $3k.

To be perfectly honest though, I think 250whp+ just isn't in the cards without some serious homework and experimenting on your part. I just did some huge searching and didn't find anybody running anywhere near that kind of power through the auto.
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