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Engine Mounting and Rotation Angle Design Considerations

Engine Mounting and Rotation Angle Design Considerations

Engine Mounting and Rotation Angle Design Considerations

I hesitate asking about this but I can't find anything meaningful about this. Beyond Neutral, right hand rotation and left hand rotation which is obvious with a simple measurement if not observation. Over the years there have been some engines commonly known rotation angle and in the 70's it was typically humorous to hear something like 10 consecutive identical cars coming off the assembly line will have 10 different rotation angles. Accepting humor like this is based in some measure of truth, there must not have been a lot of concern about it.

I'm asking now because I am currently building a 1999 F150 with a modified chassis, frame and suspension, and a new drivetrain. The original engine had no rotation angle. The new engine is a 2013, NOS crate Mustang GT, 5.0 Coyote. The engine is a Modular engine. Modular refers to the production process and has nothing to do with the internal operation of the engine. Before making any changes to the chassis I installed 5.0 in to the truck and the rotation angle was 3 degrees to the right from the front or 3 degrees to the drivers left. I'm using right here so the driveline isn't split front and back from the flywheel.

One of the characteristics of the modular is every modular block is machined with either 5 or 6 identically located points for locating the motor mounts. Anyone familiar with Ford engines understands, what took them so long to figure this out? Anyway, differences in what hangs off of the engines like the headers instead of a manifold meant I couldn't use the original modular mounts. Getting working mounts was no problem and the engine sits with the 3 degree rotation.

The problem is I can't verify if the 3 degrees is correct or not because the engine wasn't available in 99. Being Modular the mounts fit but that doesn't make them dimensionally correct and using the 2013 mounts for reference doesn't work because although they fit the engine, how the mounted to chassis is very different. To compound the problem, in 2013 the Mustang GT's with the engine had both 0 and 3 degree rotation and I cant find anywhere or from anyone an explanation to why that was. Furthermore as I said, I can't find anything about engine design considerations for using different rotation angles. There's all kinds of information about driveline angle considerations though.

When I build a car I don't want to wing anything. I want to know why and to be able to explain the decisions and choices I've made. I would really appreciate any educating, advice or experience anyone can share about this. I also hope I didn't put anyone to sleep with this. I wanted to make sure I didn't leave anything out. Thank you.

RE: Engine Mounting and Rotation Angle Design Considerations

I know it's only been 24 hours but I had hoped to hear something so I could use the holiday to get the engine in and permanently in and located so I could start working on other things that need to get done.

I spent a couple of hours this afternoon searching the internet some more and again the only thing that came up was this post of mine here. Typically the most I might get from the mechanics side is engine bay interferences and fitment. That may come in to play at times but that's not what it's about. After graduation I had a ten week wait for OCS so I picked up an early 60's F350 to do some travelling. I don't remember the year of the truck or what engine was in it but it had a straight 6 and there was enough room in the engine compartment that I could stand in it and work on the engine doing maintenance getting it ready to travel. That engine was at an odd angle rotation. More than 5 degrees and there was no interference with anything.

I assumed it had something to do with drivetrain gearing, engine torque, weights including tow weights since it was a pickup, CoG, CoM, along with all the other suspension tuning concerns? But, if that were true it seems like there would be available information about factoring in engine angle rotation considerations in designs. I also assumed whatever the issue and design consideration could be, since it was being dealt with an engine rotation angle rather than somewhere with chassis and\or suspension tuning it might be because of a reversing effect along the driveline? Similar to the effects of reversion. Maybe something with vibration and harmonics? There's nothing to be found with anything like this either? I also understand what "assumption" can mean to some!

Maybe I'm concerned about nothing and over thinking this? If that's true why did this same engine come in the same year's Mustang GT with two specific and consistent rotation angles of 3 and 5 degrees? No one can or will tell me the answer to that. The car was available with a number of different diff gear ratios along with a variety of different wheel and tire sizes. The standard stuff decided upon when buying a new car. But than again, it seems something would be available about that if true?

Anyway, I wish everyone a good holiday weekend and be safe.

RE: Engine Mounting and Rotation Angle Design Considerations

It's hard for "the rest of us" (like me) to understand what you mean by "rotation angle".

In side view, it is very common for rear axle drive vehicles to have the powertrain slightly angled "nose up tail down" by a few degrees, and for the rear axle to have a matching "nose up" pinion angle (possibly slightly corrected to allow for driveline slop and deflection being taken up, "axle wind-up", when the powertrain is delivering "normal road load"). The reason is generally drive-shaft clearance. In the old days, combined with hypoid rear axle gears that have the input shaft positioned below the centerline of the axle, it allowed the drive shaft to be mounted lower in the vehicle and thus allowing a smaller central drive-shaft tunnel. The engine has to be mounted with its centerline higher in order to avoid having the oil pan dragging the ground. The easy fix ... is to orient the whole drivetrain nose-up a few degrees. That's still the case, for the few remaining rear-axle-drive cars in production.

In front view, Chrysler 225 Slant Sixes are slanted over 30 degrees to the right side of the car. Is that the angle you mean?

Normal powertrains sit nominally straight up in front view, but it wouldn't surprise me one bit if they tilt a few degrees, possibly by design for clearance reasons, possibly by tolerance stack-up in the engine mounts (which are generally not high-precision, the front subframe is "welding tolerance", not "CNC-machining tolerance"), in an older vehicle very likely because the bushings in the engine mounts are knackered. And given that "road load" inherently means these loads are biased to one direction, it would not surprise me one bit if the left and right engine mounts get differently knackered over time, because they're differently loaded! Or maybe ... something's bent. If the vehicle has been crashed at some point, all bets are off!

Some rear axle drive cars/trucks don't even have the engine/transmission on the exact center-line of the vehicle! They can be offset to one side by design. Weight distribution, clearance, who knows.

Here's another question for you. "So what?" What does it matter to you, that perhaps the engine is a smidge off center or a smidge angled, regardless of whatever the reason might be?

RE: Engine Mounting and Rotation Angle Design Considerations


Thank you for your response. I tried and thought I addressed some of your comments in my first post and realize now I didn't do as good of a job at it as I hoped. I understood everything I wrote and accept how much value that's having. [upsidedown] I considered using pitch, roll and yaw as a reference to what I was asking about. Maybe I should have?

Trying to not over think or complicate this.

The "Y axis" is through the entire truck referenced to the crankshaft centerline to the pinion centerline.
The "X axis" is through the entire truck referenced to both the flywheel and harmonic balancer mounting points. The plane of both the flywheel and harmonic balancer mounting points for the truck need to be parallel to each other and obviously both need to be perpendicular to the Y axis.
The "Z axis" for a perspective of "Engine Rotation Angle" and for visualization of all of this I'm thinking of the old drafting visualization method of sticking the thumb up, pointing the index finger and pointing the middle finger perpendicular to the index finger. Using this, the engine rotation angle would be any perpendicular rotation of the thumb around the index finger.

I expect for explaining this I didn't need to use anything more than the hand method but since you pointed out the shortcomings in my previous attempts to explain what I'm asking about, the additional information\explanation may be useful to someone else? I probably could have also said, "Think about an engine on a standard engine stand. The engine rotation angle for the stand would be any spin of the engine on via the stand's engine mount." Again though, that may not give a complete picture for everyone of what locating an engine in a vehicle is referenced to.

""Some rear axle drive cars/trucks don't even have the engine/transmission on the exact center-line of the vehicle! They can be offset to one side by design. Weight distribution, clearance, who knows.""

The Ford F150 driveline is offset from the chassis centerline and it's been consistent for years but for the life of me I can't remember what it is at the moment. Duh.

Also, in 97 I worked with Jim Thornton for a while. Jim was the Head of Chryslers racing and performance department in the 60's. He was also the principle driver for the Ram Chargers, Chryslers drag racing team. I can tell you some about the slant 6 which was actually based on a Mercedes engine from the early 50's with the same 30 deg design. I'm sorry I don't remember the specifics of why but the slant 6 design offered improved airflow, VE and torque or HP and there were no noticeable efficiency losses from the intake and exhaust ports being on the same side of the head. IIRC, the design improved the CoG in the car. What I remember most though was, "It's basically the Mercedes engine for the obvious reason." Regardless, I understand how someone can view the engine as being "rotated" and lead to an instant understanding of "engine rotation angle" but it's really not. It's orientation in the car is what it was designed to be excepting for some potential small degree of rotation like I'm trying to get an understanding of which get's to this.

""Here's another question for you. "So what?" What does it matter to you, that perhaps the engine is a smidge off center or a smidge angled, regardless of whatever the reason might be?""

I feel like I have the answers to a multiple choice question but with no idea of what the question is. Even worse because I'm trying to research what the question might be and can find nothing. The Ford performance PCM I have for the engine and I'm somewhat in the same boat with that. The PCM supports AiM electric steering but good luck trying to find out what "supports" means. What I've been told is it's feature a no longer available and the earlier PCM's that had it are no longer supported. I can't verify this but again, what I was told is access to the controls became too dangerous. Too many people with access thought using it was the key to preparing for Baja, Daytona or WRC. Not necessarily a problem, regardless of the manufacturer, but the vast majority of people playing with the controls were discovering what it does on cars that are also their daily drivers. That was the problem and access was drastically curtailed.

RE: Engine Mounting and Rotation Angle Design Considerations

"it was typically humorous to hear something like 10 consecutive identical cars coming off the assembly line will have 10 different rotation angles. "

Frankly, nonsense. Or if you prefer, inevitable. The build tolerance of a subframe is 1mm for critical relationships, and probably 3 for a general tolerance. The twist in the body rails in front view could be another 5mm (hopefully not). The distance between the rails on some cars was accommodated by a 25mm sliding fit in the floorpan.

You'll notice I'm talking about the body, which is made of stampings welded together. The engine on the other hand is a lump of metal held in a jig and machined in that jig. Yes there is still variation but it is fractions of a mm.

Other factors in the installation angle (which is a term that exists) is the stiffness of the engine mounts, which can vary by 15% and still be in spec, and the different accessories fitted to a given engine.


Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Engine Mounting and Rotation Angle Design Considerations


My question has taken some turns but your post is interesting and I'm not sure where to begin???

There's a "generic" reality of the post WWII auto industry with the philosophy of the US auto industry that went like this. 1.) Engineering, Win market share by building a better mouse trap. 2.) Wall Street and Accountants, Market share took a back seat to Wall Street and accounting metrics and ratios as determined by the way they take and use financial relationships and reduce them to a single "number" to define current and the future stability of profits--industrywide profit share became more important than market share. 3.) Quality and the impact of the realities of globalization.

Granted, anyone can find instances and decisions made that will question this but I defy anyone to make a good argument that will redefine the aggregate industry manufacturing philosophy as it evolved. This is also not something I came up with. This was all primarily identified and defined by Deming and his ideas. Simple ideas mostly like globally defining standards for GD&T so everyone is working on the same page. Nonsense?

When I first started working in the auto industry it was with the then loosely defined "compliance" department. Unfortunately compliance to most people means EPA and DOT Regulations when actually they were a small part of what compliance was redefining. Maybe not in terms of the impact customers could identify but definitely in terms volume.

During my first month my "place" didn't exist so I worked with people on floors. Hopefully you can imagine my thoughts at the time? We were at one of the largest stamping plants in the world and 75% of the floors were made up of oak 4x4's 2' to 5' long oriented on their ends. Why? 1910 technology. At the time the design was a good solution to the amount of oil that was everywhere. You couldn't see more than a couple of hundred feet from all the smoke that was oil looking for someplace to settle. Where the floor was concrete their condition would rival the worst roads today. There were at least a half a dozen old press pits that were fenced off because they weren't useable. Expansion was the only solution mostly because of the fear that repairs would also lead to soils mitigation. This was happening because through Deming the industry found out what those floors were costing in terms of maintenance and repairs and quality. It was eye opening to everyone. This all led to the development of floor and compliance standards for floors. This also led to the development of a new industry. Automated, laser controlled screed machines.

Why did I write this? I don't question what you wrote but I do question it's relevance. Of course tolerances as you identified are important and they aren't arbitrarily defined but there's volumes of research showing that consistency far outweighs the value of meeting tolerance requirements. When I started, as cars were assembled on the line they moved from defined stations to stations. Today, the cars are on the stations in the form of a cradle or sled and it's the cradle or sled that defines tolerances of assembly. They usually have much tighter tolerances than the vehicles on them.

Although I won't argue with your premise it's all anything but nonsense. And as far as what I wrote as paraphrased humor, remember I put it in the context of the 70's which has no relationship to todays production in the heavy manufacturing industry. I'm retired now but a couple of years ago I went through a catalytic converter production plant and it was like a clean room. The people working at the stations had their own, open air lunch\break room with potted plants. There were scaled down versions of the "lunch truck" that goes through the plant to the stations. It's not hard to see the difference in attitudes of the workers between the early to mid 80's and today. Nonsense? Not if your livelihood depends on heavy manufacturing and I'll just end it here.

RE: Engine Mounting and Rotation Angle Design Considerations


There's an old saying, anything worth doing is worth doing right. As a disabled vet I've learned that the saying is nonsense if what you're doing isn't premised on, anything worth knowing is worth knowing right.

RE: Engine Mounting and Rotation Angle Design Considerations

I'll answer your question.

You're overthinking it. Hook it up and run it.

Vehicles are not precision instruments.

RE: Engine Mounting and Rotation Angle Design Considerations


I agree and I was going to let this go. I'm not losing any sleep over this but I'm curious about why the same car with the same engine would come with specifically different engine rotation angles knowing it's not because of any interference issues.

I did get to speak with an engine designer for a British racing engine manufacturer who told me some interesting facts some may be interested in. In a condensed re-telling, during the late 70's and early 80's when engines designs were changing from the displacement of 8, 12 and even 16 cylinders to the displacement of 4 cylinders running at RPM's previously unheard of, design considerations drastically changed. The operating environment inside the new engines had no relationship with what was previously known to be going on. Lubrication, coolant and particularly pressure differential characteristics had to be redefined. Environmental characteristics inside of an engine that were once accepted to self correct at different engine operating speeds no longer were. Pressure differentials react very differently at 20,000 RPM than they do at 9 or 10,000 RPM because of time. All solvable problems but the internal environment at low RPM's became critical considerations because they defined what was going to happen after that speed and time threshold was reached. He said solutions to the problems began with looking back to breaking the sound barrier problems.

He further added that many of the once less critical considerations like engine rotation angle became more important considerations.

Of course this has nothing to do with my original question.

RE: Engine Mounting and Rotation Angle Design Considerations

I finally re-read post #1 and discovered that there really was a question buried in there. HINT: Use fewer words!

A 3 degree clockwise (front view) bias in the engine mounts sounds like they are counting on "road load" levelling the engine out when you are rolling down the road. There will be considerably more anticlockwise movement in the engine mounts than this when accelerating hard in 1st gear. Clockwise movement in the engine mounts implies hard acceleration in reverse (most drivers won't do that, and certainly not for long). Engine-braking (overrun/coasting) doesn't apply anywhere near as much reverse torque, even in 1st gear.

Obviously this begs the question "why was this built into the design", and then ... who knows. Maybe that engine-mount bias is necessary to avoid hitting something in the engine compartment at max forward acceleration torque with the engine mounts deflected to the max in that direction. (That's the primary reason I can think of, for why it would be done this way.) Maybe it's NVH-related, they want whatever vibration is in the engine to be oriented a specific way. (That's the secondary reason I can think of, for why it would be done this way.)

It's unlikely to be oil pick-up or drain-back issues ... the oil level in the sump goes much more askew from rounding a corner, and that oil pick-up is as close to the bottom of the sump as they can make it to avoid this ever being an issue unless the car is on its side or upside down.

I obviously don't have an answer for you. You would have to ask a Ford powertrain engineer, and that, I am not.

I also wouldn't sweat it. If it works, leave it alone. Being tilted 3 degrees to one side isn't going to make anything blow up, and if it does, it was going to blow up anyway.

RE: Engine Mounting and Rotation Angle Design Considerations


Thank you. I will think more about how I write in the future. With this question though I did use a lot of context because the question is more a design considerations than about any specific technical problem to solve.

Another speculation on the 3 vs. 5 degree angle I was given had to do with the car being available with both a live axle and IRS. The cradle or sub-frame the IRS was part of was not considered to be a great design and there were a number of issues the aftermarket focused on. It wasn't until 2015 that Ford was considered to have gotten it right. Like you though the suggestion was followed with "Who knows?"

Also buried in my question was why is there no information on engine angle considerations? There is so much so much on various design considerations that have been beat to death but there's nothing on this.

When I spoke to Cosworth my access was granted for very different reasons than these questions of mine. I just took advantage of the access and was given permission to ask my questions. Another rotation angle issue he mentioned had to do with the FWD, transverse engine orientation. Since you brought up NVH, he brought up in racing anyway (he had no information on daily drivers) the engine rotation angle can be used to mitigate NVH amplitude although it's not a solution. Research in to why this is hasn't led to consistent, reliable information. When needed this is examined on a case by case basis. He didn't or wouldn't expand on this. The same response I've gotten from Ford engineers with my questions.

I want you to know Brian and everyone else that has participated how much I appreciate the time you've taken and thoughts you shared responding to my question. It's helped identify pursuits beyond my limited interests with this question.

RE: Engine Mounting and Rotation Angle Design Considerations

In 1704 the Philosophical Transactions of the Royal Society of London printed a letter from William Cowper that contained the following:

If in this I have been tedious, it may be some excuse, I had not time to make it shorter.


Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

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