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Lower Engine Mount Development

18980 Views 43 Replies 14 Participants Last post by  Markus
In preparation of making a new engine mount design, I am modeling and analyzing the factory engine mount.

I have performed a few FEA (finite element analysis) evaluations of the mount based on different directions of applied load and applied materials.
While I myself do not have the original design documentation for the mount itself, my rough reverse engineered interpretation has given me a good idea how this mount behaves under certain loading conditions.

Here is an example of the different types of conditions I'm evalustaing. Mount is assumed fixed at the subframe face connection, and a 300 lb*f load applied through the bolt sleeve.

As far as I can tell, this is what we are looking at with the factory mount:
- Investment cast aluminum alloy - not 100% on this, although the surface finish and clean edges and inside radii make it seem that way
- not sure on the alloy, I have access to a Niton metal analysis gun and I'd like to see what it's made of
- still trying to nail down bushing rubber type and durometer. I should just buy a durometer tester :) I won't look too much into this though as I am researching bushings to use right now.

If we assume one of the cheapest and weakest alloys was used, the aluminum structure of the mount still has a good factor of safety at our 300 lb*f load.
I will be designing our new mount with much higher loads in the computer, and will also have a large factor of safety built in.

Right now, expect a billet aluminum body with high quality bushings. The mount will also have some adjustability for axle alignment.

I will update this thread as things progress.
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Hey Uhm dumb question but what's the point of this?
Hey Uhm dumb question but what's the point of this?
I am designing a new engine mount that will help put more power to the ground. To have a better understanding of what I should design around I am evaluating the factory mount, just like I evaluated the factory intake system.
Long story short, factory motor mounts are designed to safely hold the drivetrain in place while transferring as little noise and vibration from the drivetrain as possible.

When you have a soft mount that dampens all the vibrations, the trade off is deflection. Too much deflection under sudden force (read: launching, shifting gears fast) and you get things like wheel hop and a rather sloppy feeling when the next gear is engaged.

Most of the time, the factory mount can be upgraded in a couple different ways:

- replace the dampeners in the mount (currently some members have replaced the rubber in this mount with stiffer urethane inserts)
- Redesign a new mount, that uses stiffer dampening and possibly relocates the dampeners to an optimized location
- In our case, the mount is located in a placed where if we make it adjustable in a certain way, it can have the ability to keep our cv axles straight, resulting in better launches and gear engagement.

This would be for those that don't want to lose engine torque by wasting it in the engine compartment by limiting engine movement and forcing the torque to go to the wheels.

To add to that how long do you thing the factory mount will last once it starts seeing 250+ WHP vs the 165-175 WHP we have stock? I would say it would fail rather quickly. IMHO
It's hard to say since I do not know exactly what aluminum is used. Stresses from the model are about 8-10% of the yield strength of some of the casting aluminum alloy specs i found.
With that, it's a rough estimate but fatigue failure with that would take millions of cycles with full load on the aluminum.

I would say the rubber would break down far before that just to do with climate conditions. You'd have rotted and cracked rubber portions of the factory mount far before the aluminum fails.
Now, replace the factory rubber with the polyurethane inserts I've seen for the mount, and the stresses through the mount will increase due to the reduced deflection of the bushings. Failure due to fatigue would still take a really long time, and my guess would be longer than the life of the car anyway.

Now if we double the factory output, that's a different story. I will be designing my new mount with this in mind.
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I was thinking about the lower mount when i was installing my green rev motorsports bushings tonight...

I would love to see a "progressive" type mount... where it can soak up the idle vibrations, but then as soon as the motor starts twisting, the more it twists the firmer the mount gets...

Rev motorsports has a green set of bushings and a "race" red set... i wonder if this can be somewhat acheived by mixing a red and green one together...?

but i do like the idea of the progressive style, kinda best of both worlds
Here is a preview of my first design. Dual bushings with adjustment feature.

I am still running all the numbers for the design, and will evaluate the model through different conditions for applicable forces.
I will have an assembly 3D printed for fitment testing if the numbers and the stress results come out favorable.

Design may or may not change much depending on results. Please keep that in mind, this might go through some revisions.

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Looks pretty cool. What would the need be for adjusting length?
Looks pretty cool. What would the need be for adjusting length?
We are lucky that this mount (due to the way it connects with the transmission and mounting location) that if you make it longer or shorter, the result is adjustment of axle angle between the transmission and wheel hubs.

The straighter the axles are, the easier it is to get power to the ground.
Sign me up! I want one!
3D printed prototype just finished.

I am going to install tomorrow and take some notes. Will update on the design in the next couple days.

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Wow that is badass! What is the price point going to be on this?
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Wow that is badass! What is the price point going to be on this?
Not sure yet, depending on how this fits and when I finish all my notes I need to source urethane and machining. That is going to take a couple weeks so I should have a ballpark on this design by the first of the year. The goal is $200 max.

Isn't that a aeronautical book, that's the way to make the car go faster lol
It's my Fluid Mechanics textbook. I've been using it for reference with designing our intercooler kit.
I didn't have a textbook to reference but with this link it gave all the info I needed and of course a little direction from a engineer that specializes in fluid dynamics for NASA.
That is a good lecture on that specific topic of friction losses in rough/smooth pipes. I have taken in other topics such as velocity changes due to pipe bends, diameter changes, cavity changes and some other areas.
so do we have an ETA on the Mount yet..?
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Right now, late Feb early march.

I am still going through design changes to help manufacturing costs. I'll make an official update this weekend with some more details and pictures.
Whats up with that amigo? :)
We are getting closer. I don't have a prototype ready but I am heavily working on getting the aluminum processed for the prototype and polyurethane bushings have been sourced. It's coming soon I promise. I'll update again next week when I get some more answers.
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Prototype has been submitted for production. Assembly will be ready by the end of next week. Pics to come when finished and installed.
I will put some hard miles on the mount and update ASAP. :)

I think you guys will be happy with what you see and the price I will be able to offer for the best mount your money can buy!
are you able to compare cabin vibrations to the green and red poly inserts that are on the market?

for me i am looking for something that controls the large movement of the engine under acceleration, but i dont want the added vibrations, so im looking for something along the lines of a progressive mount, like the little "shocks" that hondas usually use on their shock towers
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Well I have a set of reds you can use to compare and a set of modified greens but would need something to install in their place (hint hint ;))
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I can testify that those little shocks don't work well. They still add vibration into the car and really don't "lock" the motor into place. It only bolts onto one side and still has movement on the motor. I have had a few on some of my past cars because I thought they worked good. I just ended up getting the polly motor mount inserts and the dogbone bushings instead.

Your probably still with this mount going to have the vibration since it is holding the motor tight and making it so it really doesn't move. I always say you have to sacrifice one thing to get another thing.
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