2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

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Nathan Atkins
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2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by Nathan Atkins »

I can find a rolled 2011 mustang with this engine/trans combo to use as a donor for $1200, but apparently this swap isnt legal in MD. Anyone have any ideas to make this happen? can i register it in another state? I'm more interested in the legal side rather than the technical side. how long could i get away with it before i have to drag the car in for an inspection? It only gets inspected when i sell it, so really no one needs to know as far as i can tell, and as long as i don't intend to sell it, which i dont. :D

Also I'm pretty keen on this combination, I know an LS swap would probably be easier to fab for. but i think that with the cheapness of the v6 donor car and the ultimate goal of having a more fuel efficient, but not overtly more powerful rx8, points to this as being a pretty straightforward affair. I'll have all the electronics i need with the donor car, its just a matter of dropping it in (easy...mostly) and wiring everything together(PITA).

Let me know if you have any sage advice or if you're interested in beer and pizza fueled engine swap weekend wrenching sessions.
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by v10climber »

You can always register in a state that doesn't have inspection (like Florida) however then you need to prove residence in Florida somehow. I thought there was a way you could tell VA that the car was garaged in a county without inspections and get around it like that. Not sure what Maryland's rules are like.

I support this idea. Therefore, I'd be down for some wrenching sessions. We going to have to do this in your driveway? :lol:
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by yardy8301 »

Id be more worried about how to pass emissions testing. I don't think you'll have a problem with inspection unless you plan on selling it.

What's wrong with your current engine?
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by Areddi »

I am in on wrenching
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by Nathan Atkins »

yardy8301 wrote:Id be more worried about how to pass emissions testing. I don't think you'll have a problem with inspection unless you plan on selling it.
I wont have problem with the sniff test since this engine will be considerably better on emissions than the renny.
As long as the swap goes well and I can get at least one of the ecu's to be cooperative then i should have any ETCs which for now is all they check for on my car, and with this swap I'll basically have the car Mazda should have made in the first place, so I dont intend to sell it :)
yardy8301 wrote: What's wrong with your current engine?
let me put it this way, with the amount of miles I drive, if I can manage the same fuel economy as the V6 'stang, then this will save me about $450 dollars a month in fuel meaning that my most optimistic estimate of the swap is paid for in 10 months to a year.

My current engine has straight-6 power and smoothness, 4-cylinder torque and V8 thirst, that and it has 100k miles on it and is argueably a ticking bomb.

the new engine gets 31mpg in a car weighing 600# more than mine, has over 300hp and 280#ft of torque, plus I think the swap will be fun to do since I like doing things like pulling my hair out
v10climber wrote:I support this idea. Therefore, I'd be down for some wrenching sessions. We going to have to do this in your driveway? :lol:
sort of, it will be between my garage and my friend down the streets garage, but the first order of business would be stripping the mustang of all it's parts, setting aside what we'll need and logging what I can sell. I'd like to get the engineering of parts to be fabbed and such knocked out without having to give up the rx as a daily driver until its absolutely necessary.

There are a ton of things to think about first though, so I'm looking into it casually for now, but once the trigger is pulled on it I want to get it done prety quickly.
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by yardy8301 »

This would ceratinly be interesting. I hope you go for it. Do you already know what parts would need to be fabbed?

I am also in to help.
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by Nathan Atkins »

yardy8301 wrote:This would ceratinly be interesting. I hope you go for it. Do you already know what parts would need to be fabbed?

I am also in to help.
Thanks! :)

As far as fab work, there's motor and xmsn mounts, rear diff brackets, mod driveshaft and half shafts, transmission tunnel modification, oil pan reshaping, custom intake plenum, fuel lines, cultch hydraulic lines, brake booster modification, comprehensive wiring reconfiguration and electronics fiddling, and if there's time, money, and desire air conditioning! :)

That's the short list, naturally it grows exponentially from there, most of the hardware will come from the donor car but I'm looking into a rear diff solution now as the v6pp 'stang uses a 3.31 diff an my rx8 diff is 4.44 much too high,

bottom line is there's a lot of planning to do before I get started. I want to have a comprehensive plan in place before I start cause I don't suspect my wife will have much tolerance for downtime
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by Areddi »

Nathan Atkins wrote:As far as fab work, there's motor and xmsn mounts, rear diff brackets, mod driveshaft and half shafts, transmission tunnel modification, oil pan reshaping, custom intake plenum, fuel lines, cultch hydraulic lines, brake booster modification, comprehensive wiring reconfiguration and electronics fiddling, and if there's time, money, and desire air conditioning! :)
Don't forget rear-wing calibration to account for the increased need of downforce :D

But yeah I definitely am in to assist, have wanted to be a part of something like this for awhile. Also, I figure If I help you out now when I am ready to sway a 302 into my Ranger I can call in the return favor ;)
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by v10climber »

Nathan Atkins wrote:As far as fab work, there's motor and xmsn mounts, rear diff brackets, mod driveshaft and half shafts, transmission tunnel modification, oil pan reshaping, custom intake plenum, fuel lines, cultch hydraulic lines, brake booster modification, comprehensive wiring reconfiguration and electronics fiddling, and if there's time, money, and desire air conditioning! :)
Whoa now. That's not a small amount of fabrication. The driveshaft and halfshafts aren't exactly something you can just weld together yourself. You'll have to take them to a shop to do that or buy custom built axles/driveshaft. Do the half-shafts even fit in the RX-8 knuckles or do you have to use the entire mustang rear end and some sort of black magic to get the solid rear axle to work in a car that was originally IRS? What do people do for headers? That's typically a big issue in motor swaps because stuff like the steering shaft/brake booster is always in the way.
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by yardy8301 »

I think he could get away with just getting a custom driveshaft and using the rx8 diff/axles. Thats the way I would go. But even that can't really be done until the motor and trans are in place so you can get a good measurement.

If its going to be the daily, I would highly recommend making a/c a priority.
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by Nathan Atkins »

I think that swapping the stock rear diff gearing for one of the longer ratios and just using OEM half shafts would be best, the mustang uses a 3.31 vs. the rx8 4.44, so I'll have to look at the ring and pinions that fit my diff. The diff is used in many applications so there's a lot of browsing around to do. But this method requires less fab work.

I certainly want ac, if nothing else just so I can defog the windshield.

The Mustang's stock exhaust manifold is very compact, so I'm hoping that it just fits, (so such luxury as the GM 3.6 which has them cast into the cylinder head)

Because the renesis sits so far aft in the engine bay, many of the components that would normally be in the way, like brake booster and such are a bit less so, nobody has done this swap before so there is a lot to investigate and plan. Id like to get some comprehensive dimensioning done of both the incoming engine and the rx8 chassis. Lots to think about but it's currently a back burner project.
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by Areddi »

Nathan Atkins wrote:nobody has done this swap before so there is a lot to investigate and plan
Sounds to me like it would be more fun to just start throwing parts on and fab as we go. Measure once and cut twice!
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by Rock Star »

Nathan Atkins wrote:I think that swapping the stock rear diff gearing for one of the longer ratios and just using OEM half shafts would be best, the mustang uses a 3.31 vs. the rx8 4.44, so I'll have to look at the ring and pinions that fit my diff. The diff is used in many applications so there's a lot of browsing around to do. But this method requires less fab work.
The FD Rx-7 and Rx-8 Ring and pinions are interchangeable. I know because I am running a FD diff with a Rx-8 4.44 in my car. I still have the 3.9 Ring & Pinion out of my diff if that is long enough gearing for you, I'd be willing to trade straight up for the 4.44 out of yours.
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by Nathan Atkins »

I don't know Rock, that's 17% stouter than the engine and trans were made for, but yeah I'll keep it in mind if I can't find one closer to 3.31
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Re: 2011 Ford Mustang 3.7 V6 with 6sp manual into 2005 RX8

Post by Rock Star »

I'm not sure that there is much else available that is an easy swap in to that diff. Most of the rotary guys want more mechanical advantage as opposed to less. You should scour the V8 forums for more info, they have a plethora of torque and less rpms to work with so they often want to slow down their shifting by swapping diff ratios. Most switch to a Cobra 8.8" to keep the independent rear or just go full solid axle, neither of which help you if you are planning to keep the same diff carrier. I have heard rumor that there is a 3.73 in a hard to find MPV gearset that will work, but it still requires some custom parts and is not a straightforward swap.

Anyway, I disagree with the project seeing as it is your daily and far too exotic of a swap to go quick/easy/cheap, but good-luck I hope it goes well.
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