What did you do today to your 3/S?

[AdamVR4]

you can't still use it as the stock mount holes will no-longer line up.

Pretty much what I figured. You could probably slot the original mounting holes to make it go back in...

there is no need for a trans mount due to a few things...iirc the plate takes the TC strain

Huh? This plate doesn't go near the TC:

and now that the engine is unable to wobble (again, with the plate) there is no need to stabilise the gearbox end of things

People have used solid mounts for years. Why don't any of them ditch the trans mount? You really think this aluminum plate is more rigid than the stock stuff with solids?

keep in mind the weight center is pretty much 1/4 into the engine, so as long as whatever is holding everything has a very strong grip of the engine I can't see it being an issue.

The CG being in the block doesn't render the trans mount useless. It could certainly reduce the amplitude of the cyclic stress on these aluminum welds... Again, if this thing isn't heat treated post-welding, the heat affected zone around those welds will be considerably weakened. This plate surviving one or two passes down the track doesn't mean anything because regardless of the stress level, aluminum fatigues.

Don't stress, if it was a horrid idea some of the big names would have said something by now.

This is some of the most ridiculous logic I've ever heard. First of all, I hope you don't apply this logic to the rest of your life. Second, the big names avoid Nelson's shit-fest threads like the plague. Third, this is the most I've seen this plate discussed.

[i3igpete]

People have used solid mounts for years. Why don't any of them ditch the trans mount? You really think this aluminum plate is more rigid than the stock stuff with solids?

It's because our mounting system is essentially 3 point torque-roll-axis mounting system (the front and rear mounts, for calculation purposes, are considered one piece). Taking off the trans mount turns it into a 2 point TRA system - this is statically indeterminate and increases the mount stresses sky high.

see the quick primer on engine mounts here:
http://www.vecom.org/events/04Erdely...layouttool.pdf

Given where the weight is centered with the engine/tranny combo, what will likely happen is that the driver side mount will no longer support the weight of the engine upward. In fact, just from basic statics, it might actually pull downward on the engine assembly. that means the weight AND torque pulses will be taken by that plate. You better hope it's thick as shit.

on a side note, this is why it's acceptable to run with a bad rear engine mount for so long (or run without a front engine mount for some big turbo guys). As long as there is a healthy one in the front or back, all you're really doing is reducing the stiffness of the roll stop by half. It doesn't critically support the weight of the engine.

[AdamVR4]

It's because our mounting system is essentially 3 point torque-roll-axis mounting system (the front and rear mounts, for calculation purposes, are considered one piece). Taking off the trans mount turns it into a 2 point TRA system - this is statically indeterminate and increases the mount stresses sky high.

see the quick primer on engine mounts here:
http://www.vecom.org/events/04Erdely...layouttool.pdf

Given where the weight is centered with the engine/tranny combo, what will likely happen is that the driver side mount will no longer support the weight of the engine upward. In fact, just from basic statics, it might actually pull downward on the engine assembly. that means the weight AND torque pulses will be taken by that plate. You better hope it's thick as shit.

on a side note, this is why it's acceptable to run with a bad rear engine mount for so long (or run without a front engine mount for some big turbo guys). As long as there is a healthy one in the front or back, all you're really doing is reducing the stiffness of the roll stop by half. It doesn't critically support the weight of the engine.

Interesting...

Quick and dirty, please look for mistakes...


Let's pretend you're making 750 ft-lbs of torque and the center line of the crank is 18" from each mount. It's conservative to assume the torque load is fully applied to just one of the mounts, and the plate begins life as 6061-T6.

750 ft-lbs / 1.5 ft = 500 lbs on the mount. Multiply by 12+ to account for torque multiplication in 1st gear... 6000 lbs. ADD the weight of the engine to the mount that's loaded in compression. ~6500 lbs.

Whether the plate is heat treated post-weld or not, if the welds are beefy, the weakest point will be in the sheet aluminum. The Heat affected zone could have an ultimate tensile strength of 18 ksi (8 ksi yield). If the part is heat treated after welding, this jumps to 45 ksi (and 40 ksi)... Not trivial.

If I had to guess, the effective weld length looks like ~5 inches. If you assume the aluminum is .375" thick, you're talking about an effective cross sectional area in the HAZ of ~ 1.875 in^2

18,000 psi * 1.88 in^2 = 33,750 lbs required to cause fracture (safety factor = 5.2)
8,000 psi * 1.88 in^2 = 15,000 lbs required to cause yield (safety factor = 2.5)

So there are the static safety factors. Fatigue makes the problem much more interesting...

[i3igpete]

actually you don't need to multiply by the gear ratio, the ratio is applied on the driveshaft side, not the engine side.

However, what I'm more concerned about is bending moments that might occur because of the missing trans mount. Since the weight will be supported mainly by the front and rear mounting points, the rocking motion of the engine from the passenger to the driver side due to a bumpy road or cornering is a real concern. Unless you have a solid driver side mount, that is a shitload of stress you see at those joints as the rubber slack is taken up at the driver mount. let me draw a sketch, hang on.

[Sin'sVr4]

wow this has gotten a bit off topic. Well, my driver aws rack boot is leak like a siv. So, gonna drain it, then wrap a new rag around it for fri at the track. lol need to do aws delete soon.

[AdamVR4]

actually you don't need to multiply by the gear ratio, the ratio is applied on the driveshaft side, not the engine side.

Walk me through this a bit because I don't see how the torque that's applied at the tires/ground isn't applied equally/opposite to drive train and ultimately to the only part of the drive train that's constrained.

wow this has gotten a bit off topic.

There is no topic. That's the point of this fun, meandering thread

[i3igpete]

It's easier to think in terms of free body diagrams. Consider a block with a crankshaft inside floating in space. If we bolt the flywheel to a wall, it makes sense that any torque output form the engine will be spent spinning the block the opposite direction. This is the "perfect" case when it comes to engine recoil - in reality, because we are accelerating a vehicle, the actual recoil will be less.

just a disclaimer - i'm not bashing nelson at all. I just wish he would let someone DD with this thing for a bit to test it out before making a massive group buy.

[MR2]

yeah I agree that bumps on the road which have enough force to twist the end points are likely to be the biggest problem, but for $650 why not... all else fails I go back to poly mounts, besides no-one is forcing you to buy it, there will be enough people trying from the first buy to figure out if it's going to break or not.

Yes I think the plate will be more rigid than the stock stuff with solids, I agree that there will be a lot of strain, it'd be nice to see a titanium part with poly's to absorb something like a suspension bottom out.

[Chris@Rvengeperformance]

I'm not sure how much of an effect this has, but the engine is also no longer tieing the left and right frame rails together.

[DK77]

Ordered my message plates again, this time my message shouldn't be denied.