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Old 06-09-2018, 06:02 PM
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heinke heinke is offline
MetalShaper of the Month Jan 2018
 
Join Date: Nov 2009
Location: Prescott, AZ
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Post What engine/transaxle to use?

Absent other constraints, I’d use a V12 for this project. Given the original Miura had a V12, the smooth exhaust note of a 60 degree V12, and the distinctive scream at revs, I was really hoping I could make a V12 work. So what realistic choices of V12 engines are out there?

Using an original Miura engine is out of the question as they’re just not available. That’s too bad because they are very unique in that the engine and transmission are cast together in a single alloy block.



So while finding a workable V12 is already hard, finding one that can be hooked up to a transverse transaxle makes the level of difficulty go up considerably.

Of the modern OEM made V12s, the BMW M70 engine is still readily available and makes decent power. The downside is that the engine is fairly long at just over 29 inches, rebuilding costs can be high, and adding horsepower over the 325HP it came out of the factory with is quite expensive. The chassis I was evaluating (more to come on this later) has an opening 33 inches wide where the engine will go. 4 inches of space for a bellhousing, etc. was just not enough space to work with. The Jaguar and Mercedes V12s were even less amenable for various reasons. In addition, I’d like to choose a power plant that has a large, active community of people using and modifying it as well.

Hmmm…so after a few weeks of research, the V12 route wasn’t looking very promising. In addition, I needed to take into account the mating up of the engine with a transaxle. I really like the notion of transverse engine transaxle package because all the rotating parts, from engine out to wheels, are operating in a parallel plane. There is no power loss from needing to turn the rotation 90 degrees like in a standard hypoid differential. Also a transverse engine is needed to fit the spirit of the Miura.

So I started to seek out options for factory built cars that have transverse engines (both front and rear wheel drive). Transverse engine packages in front wheel drive cars and Fieros are common but almost all are either v6 or inline 4 and fall short on the power criteria (i.e. must push a 2,800 lb car at least 172 mph). I looked at Fiero V8 conversions using the F40 manual transmission but these make for a wide engine transaxle package given the transmission is basically inline with the crankshaft. Yes, people make this work in a Fiero chassis but that’s not the chassis I’ll be using for this project. I looked at racing oriented, sequential transaxles and the $16-20K price tag quickly scared me off.

The next path of investigation was to use a V8 along with a custom built transaxle. I have a friend, Pete Aardema that is a diehard DIY car guy with a soft spot for mid-engine transverse platforms. Pete had already built a couple street rods with transverse V8s in the back seat so he has both the interest and experience. Pete teamed with master machinist Kevin Braun to build the Chevy LS3 SOHC conversion on the engine in my GTO so I know they have the knowledge, experience and machinery that surpasses most prototype machine shops. Pete cranked out a pencil drawing with the concept and offered to scout up an engine for mockup purposes. His question back to me was, “What engine do you want to use?”

So what V8 both fits to the spirit of a Miura and is short in length? Well it needs to have alloy block/heads and overhead cams just to equal the 50 year old Miura technology. The Ford 5L Coyote has this plus 4 valve heads so some advanced technology to boot. The BMW and Mercedes V8s are also technically advanced (more even than the Coyote) but don’t appear to be separable from their OEM ECM/PCMs. I’d really like to emulate the Weber carbs visible through Miura back window with an 8 stack EFI system so this brings an aftermarket ECM into the picture. I checked and yes, there’s an 8 stack EFI for the Coyote that uses very realistic looking Weber like throttle bodies.

So there you have it, the plan is to use a Ford 5L Coyote engine, most likely a new Ford Motorsports crate motor as they look reasonably priced. The factory output of 435 HP with 400 ft lb torque should propel a Miura up to 172 mph and beyond. For the transaxle, we’re mocking up a custom bell housing/transfer case mated up to a Tremec TKO600 with a shortened output mated up to a Super 8.8 limited-slip differential carrier from a 2015+ Mustang IRS all these components meshed up with custom made helical gears. Ok, so I’m sure your heads are spinning from that last sentence. I’ll be posting pictures for the transaxle mockup after answering the chassis question in a subsequent post.
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