Modern-day Miura

[C5GTO]

Miura powertrain phase begins!

I’m now embarking on the powertrain phase for the Miura project. I’m doing this prior to completing the chassis and body phases as I want to prove out that I can make various aspects of this very unique transverse engine powertrain approach actually work. My experience from the computer software industry is that when venturing into the unknown or risky territory, it’s much better to “fail fast”, innovate and recover than to attempt a “big bang” from which failure is most often fatal for the project.

In preparation for the powertrain phase, I moved the Miura chassis outdoors for some “big picture” viewing and to take some progress photos.







And here’s the part that makes me most nervous as it relates to powertrain. The engine, transaxle, and drive axles all must fit into this relatively small compartment in the chassis.



The first thing I want to prove is that the intended powertrain will actually fit. So here’s some pieces that arrived this week.





It’s a Ford 5.0 L Coyote engine from a wrecked 2017 Mustang GT with 15K miles on it. I chose the DOHC Coyote engine as the original Miura had a DOHC engine and anything less wouldn’t feel right. My first impression is that the Coyote is a very wide engine at the wide part of the “V”. I sure hope it fits. :-)

I bought it as a “Master Kit” which by the 1653 lb. shipping crate weight includes about half of the original car by weight. I don’t anticipate using all those parts in the Miura but I figured that given all the electronic wizardry involved, it’s better to have the whole engine/transmission/wiring harness setup and whittle it down to what’s actually needed for the project.

After 3 years in the making, I also picked up the Pete Aardema inspired and designed transaxle this week as well. Kevin Braun is the master machinist who machined/carved the aluminum billet into a precision transaxle. The cast aluminum bit in the middle is a Tremec TKO 5 speed transmission.





Now comes the job of mating the engine and transaxle up and do a trial fitting into the engine compartment. If it fits, then it’s on to fabricating mounting brackets. If it doesn’t fit, hopefully it just a matter of trimming off some spare chassis material … or time to innovate.

[C5GTO]

Engine/transaxle Fitment to Chassis

…Drumroll please…

Now to the big question: will that big, wide V8 engine and it’s transaxle fit in that tightly constrained chassis engine compartment?

I decided to use the core engine for the first trial fit exercise because it had already been prepared to accept the transaxle. After some head scratching to work out the needed mid-air engine hoist gymnastics to drop the assembly in there, IT FITS!!





BUT…as I anticipated, there are fitment issues that will need to be addressed:

1. Insufficient CV/axle clearance under frame rail
2. Engine when in mid-air during installation will not clear the main cabin bodywork (when the bodywork is actually in place) and a risky engine/transaxle assembly rotation from horizontal was required in mid-air to get the transaxle to clear a cross member.
3. Insufficient clearance between damper pulley and frame rail. Core engine has single belt damper pulley that cleared fine but Coyote has a 2 belt damper pulley that will not.

Here are pictures that show the clearance issues.







The root cause of the CV/axle being too high is that the engine/transaxle assembly will need to be located 3 inches higher than originally planned to provide clearance where the transaxle sits directly above the drivers side rear lower A arm front pivot point on the chassis. The upper A arm pivot limits the side to side placement (thus the damper clearance issue) and the lower A arm pivot limits the vertical placement.





If we’d have done a full CAD design of powertrain and chassis together, we probably would have foreseen these clearance issues. But at the major component level, this project is closer to back of the napkin engineering, so these issues come to light during trial assembly exercises. Not to worry, I have a workable answer for each of these issues.

1. Re-angle or re-clock if you will the transaxle final drive case relative to the transmission. In other words, if you think of the transmission output shaft as center pivot on a clock face and the inner CV/axle center as the pointer on a clock hand, shift the clock so it reads more like 7 o’clock rather than the 8:30 position it’s currently at. Pete Aardema (transaxle designer) and I think this is doable but more to come I’m sure as it unfolds. A side effect of re-clocking the transaxle is that it reduces the front to back length of the engine/transaxle assembly by about 1 inch such that the engine can be moved rearward from firewall by that amount. When the distance from the valve cover to seatback is about 4 inches, every inch counts!
2. Convert the chassis rear cross member from being “fixed” to chassis and make it a bolt in removable cross member. Installing the engine separate from the transaxle is a non-starter given the tight clearances on all 4 sides of the assembly. But once the cross member is removed; the engine/transaxle assembly can be lowered into the engine compartment in a straight vertical line thus not hitting the cabin bodywork. Once engine installed, re-install the cross member and full chassis strength is restored.
3. Rework the engine accessory drive belt to a single serpentine belt instead of a 2 belt system. As used in the 2017 Mustang GT, the Coyote engine has a belt that drives only the A/C compressor and a second belt that drives water pump and alternator. Power steering must be electronic as there’s no P/S pump on the engine. I should be able to redesign this into a single belt system such that a shorter damper pulley can be used.

There’s my plan anyway. This project is never boring :-)

[Bloozberry]

Two awesome posts in a row! You're going to overload our sensors. It's finally nice to see an overall shot of the chassis... it makes it a lot easier to visualize some of the sheet metal fabrication you've done which until now have been only in close-ups. The Strickland chassis with your sheet metal mods looks amazing.

The part which interests me the most is the content of this last post though. For starters, that transaxle is just plain crazy! I've always tried to think outside the box, but that thing is out of the ballpark. I've never seen anything like it before. There seems to be a lot of moving parts, but I'm sure you'll be able to make it fit, and that it will work well. Countering the torque reaction through the case might prove to be a challenge... have you decided if you're solid mounting the drivetrain yet, or will you be using rubber mounts?

The photo with the drivetrain in place makes it appear as thought the engine will be mounted quite high up in the chassis. Is that just the angle of the photo or will the valve covers be about the height of the passenger's heads? You said you're limited in the vertical plane by the height of the lower A arm pivots... when in the lowest position, how much clearance does the oil pan have before it sticks below the chassis? If you still have lots of room before the oil pan is level with the bottom of the chassis, you may be able to re-engineer the control arm pivots to drop the powertrain lower more easily than having to re-clock the transmission. That would cure the frame rail interference with the output shafts, and achieve a lower CofG for the powertrain.

[Don]

Wow these last two posts take the project to the next level Joel... Amazing work and ingenuity.

Don

[C5GTO]

Two awesome posts in a row! You're going to overload our sensors. It's finally nice to see an overall shot of the chassis... it makes it a lot easier to visualize some of the sheet metal fabrication you've done which until now have been only in close-ups. The Strickland chassis with your sheet metal mods looks amazing.

The part which interests me the most is the content of this last post though. For starters, that transaxle is just plain crazy! I've always tried to think outside the box, but that thing is out of the ballpark. I've never seen anything like it before. There seems to be a lot of moving parts, but I'm sure you'll be able to make it fit, and that it will work well. Countering the torque reaction through the case might prove to be a challenge... have you decided if you're solid mounting the drivetrain yet, or will you be using rubber mounts?

The photo with the drivetrain in place makes it appear as thought the engine will be mounted quite high up in the chassis. Is that just the angle of the photo or will the valve covers be about the height of the passenger's heads? You said you're limited in the vertical plane by the height of the lower A arm pivots... when in the lowest position, how much clearance does the oil pan have before it sticks below the chassis? If you still have lots of room before the oil pan is level with the bottom of the chassis, you may be able to re-engineer the control arm pivots to drop the powertrain lower more easily than having to re-clock the transmission. That would cure the frame rail interference with the output shafts, and achieve a lower CofG for the powertrain.

Thanks Bloozberry!

One of the things I still need to do is tie the final drive case back to the engine block. In the original Miura, the engine block and transaxle were all a single casting. I'm looking at bracing the final drive case back to the bolt holes on the engine block where the motor mount is normally attached. This should unify the two and give a good rigid transfer of torque reaction back to the engine block.

I intend to use rubber mounts for the engine and transaxle. I'm told by Pete Aardema (the transaxle designer/builder) that when he made a similar setup for his 1937 Ford he put mounts at the front of the engine, by the bellhousing and at the rear of the final drive case. So 3 mounts total and it worked great for him. I've been looking at rubber doughnut heavy machinery mounts from McMaster-Carr that I think will work. Do you have any other suggestion on sources for motor mounts that might work botter for this application?

The motor isn't actually sitting all that high but you are close as valve cover is just about driver shoulder/neck height. It's a relative thing because the drivers seat bottom is only about 6 inches above the ground and the picture is deceiving as it's a high back seat. Yes, it's an extremely low profile seat but needs to be that way as the overall car height is only 43". My original intention was to have the bottom of the oil pan even with the bottom of the frame rail but it is now about 3" higher than that so about 8 inches above the ground. Changing the vertical height on the A arm pivot would take major re-engineering of both the chassis and A arm itself. At the current pivot height, the A arm has a slight downslope to the upright. In other words, just as it should be. When I look at an original Miura, the engine also sits about this same height so I should have expected it would work out this way.

[C5GTO]

Wow these last two posts take the project to the next level Joel... Amazing work and ingenuity.

Don

Thanks Don!!

[Kent50]

The metal work and craftsmanship on this car is unbelievable! You are a true artist. Many props to you.

[Bloozberry]

I intend to use rubber mounts for the engine and transaxle. [...]. I've been looking at rubber doughnut heavy machinery mounts from McMaster-Carr that I think will work. Do you have any other suggestion on sources for motor mounts that might work better for this application?

Personally I think it's a really good idea to use rubber or flexible mounts for several reasons. The car will be be significantly less fatiguing to drive with reduced Noise, Vibration, & Harshness (NVH), plus the shock loads to the powertrain from quick accelerations will be will be reduced and better damped. My Fiero-based 308 replica with a hard-mounted SBC is fun to drive, but it's numbing to drive it for more than a couple hours. The trick is finding mounts with the best compliance. It's an area I have little experience in, though I know from researching mounts for my Northstar project car that today's powertrain mounts are pretty sophisticated. I decided to use the OEM mounts for two reasons: 1. they represent the state of the art using internal hydraulic fluid chambers and 2. I had enough room to use them... they are somewhat bulky. I used two on the engine and a third one (same part number as the engine mount) on the F40 transmission. Because so much goes into the design of these mounts nowadays, I'd recommend you try to using the Coyote mounts if you have the space. It shouldn't matter that the engine orientation is different in your car... the engine still reacts to the torque the same way.

The motor isn't actually sitting all that high but you are close as valve cover is just about driver shoulder/neck height. [...] My original intention was to have the bottom of the oil pan even with the bottom of the frame rail but it is now about 3" higher than that so about 8 inches above the ground. Changing the vertical height on the A arm pivot would take major re-engineering of both the chassis and A arm itself.

Well that sucks... 3" is a lot when you start looking at all the kinematics that are affected by changes in the height of the CofG. The only other alternative I can think of is stretching the wheelbase enough to move the lower control arm pivot rearward. A longer wheelbase always makes a car look lower and sexier... and since your car already isn't 100% true to the authentic dimensions, it might be something to consider if it only meant having to stretch the chassis an inch or two. Now would be the time!

[C5GTO]

The metal work and craftsmanship on this car is unbelievable! You are a true artist. Many props to you.

Thanks Kent!!

[C5GTO]

Well that sucks... 3" is a lot when you start looking at all the kinematics that are affected by changes in the height of the CofG. The only other alternative I can think of is stretching the wheelbase enough to move the lower control arm pivot rearward. A longer wheelbase always makes a car look lower and sexier... and since your car already isn't 100% true to the authentic dimensions, it might be something to consider if it only meant having to stretch the chassis an inch or two. Now would be the time!

I think I'll stick to the message from this old saying, "Don't let the perfect be the enemy of the good" as it relates to engine mounting height here. Stretching the wheelbase is too drastic of a measure to lower the engine a bit.

[C5GTO]

Engine/transaxle Fitment to Chassis (cont.)

I started on the most actionable item on the engine fitment plan, which is to make the rear cross member removable. That way, I can make additional trial fitments with the benefit of a straight forward drop-in. I used 1 ¼ by 1 ¼” angle that’s ¼” thick for brackets and lots of 5/16” grade 8 bolts. The most nervous part in this type undertaking is when I break out the saw and cut through a nice, solid welded in chassis member.





The forward most bracket goes frame rail to frame rail for maximum strength. Four angle brackets in total were needed to make the cross member removable. While I was at it, I added some extra bolt-in bracing for the rear bulkhead. This wasn’t needed for making the cross member removable but should add some bonus strength into the chassis.

[C5GTO]

Engine/transaxle Fitment to Chassis (cont.)

It’s been a busy week on the Miura project and as a result there was a lot accomplished. I made a trip to San Diego, Ca (a 7+ hour drive from where I live) to visit Pete Aardema and Kevin Braun with the objective to make the changes necessary so the Coyote and transaxle combination will fit properly in the Miura chassis. The two outstanding fitment issues were the damper pulley hitting the frame rail and CV/axles hitting the frame rail.

The Coyote damper pulley is made to run a two serpentine belt system. My approach to making it fit was to convert it to a single belt by parting off the outer half of the damper. Pete chucked it up in a lathe and quickly made the alteration.



With the narrowed damper pulley, there is now about ½” clearance between it and the frame rail.



The water pump used the outer belt so that needs to be addressed. As you can see in the picture above, there is also a lack of clearance between the thermostat housing and the roll bar upright. The thermostat housing is mounted directly to the water pump. My intention is to replace the belt driven water pump with an electric water pump. This should eliminate need for a water pump drive belt and with an electronic controller the need for a thermostat. I think I’ve found a good product to do this but am still trying to verify that it will work in this application given the 8 plus feet of tubing between the radiator and engine.

Now onto the much more complicated transaxle modification to rotate the final drive case. Here’s a before picture showing the main clearance issue when final drive is rotated to the desired position. Notice the ear sticking out from middle case that hits differential housing and mounting bolts.



Unfortunately I was so busy doing other things that I forgot to take progress pictures of Kevin Braun doing the machining operations. It included CNC machining away metal on the transmission middle case to provide clearance for the newly angled final drive case, counter sinking some fasteners, drilling holes for new alignment dowels between the cases, and drilling/tapping new holes for mounting bolts. The prior holes that protruded into the middle case were filled to prevent oil leakage. Because of Kevin’s expertise and deep precision machining talents, he was able to get it done in about a day.

To prove to ourselves that the CV would have the needed clearance, the engine and transaxle was test fit into the chassis.







In addition to the above, we were also able to make a clutch shaft pilot bushing, dial-in the bell housing, positively located the clutch shaft to prevent rubbing on the transfer case, add dowel pins for positive pressure plate alignment and adapt a starter for mounting on the opposite side of the engine.



On the Coyote engine, Ford locates the starter on the passenger side of the engine. We were able to move it to drivers side of the engine block by enlarging an existing hole in the block to accept a Hitachi gear reduction starter. This starter is commonly used as an aftermarket replacement on many different engines by utilizing different adapter plates. We machined up a special adapter plate that uses 2 bell housing mount bolts extended though the threaded block holes and a third bolt tapped directly into engine block to mount the starter. We hooked it up to a battery and the starter engaged the ring gear fine and easily spun the engine over.

Well it was very much worth the 2 days of driving and 2 days of work to get all this done. My special thanks and acknowledgement goes out to Pete Aardema and Kevin Braun for helping me with this project and contributing stuff that goes way beyond my abilities.