Solid engine mount and trans mounts...?

[Strychnine]

And lastly, as if you needed more non-answers, here's what my copy of Allison's transmission mounting document says about three point automotive systems:

• The preload force at the transmission rear support must not result in a negative bending moment at the engine/transmission interface which exceeds the maximum bending moment limit for the engine.

• The rear mount should provide sufficient flexibility to permit frame flexing and power pack roll without imparting rotational stress on the transmission. This is frequently accomplished with a leaf spring or spring-loaded cross-member reacting to the vehicle frame

• The rear mount should be isolated from the frame with isolation pads, biscuits, or bushings – to reduce shock loads and the transmission of vibration and noise between the powerpack and the frame.

No word on what will happen without that, but you can use your imagination.

[aggie97]

Semi-related. You've been racing that car for quite a while with a big cage and stuff in it. Have you ever gone over the car inch by inch and looked for small cracks or other signs of stress?

Just curious - I'd like to know how much abuse they can take before they start to show some signs of hating life.

it was hating life in 2009! LOL! Front frame/unibody beneath the fenders started showing signs of cracks a long time ago. drilled the ends of the cracks and honestly have just monitored them. too lazy at this point but with an extra 100-120rwhp on tap, there is more cage planned this offseason. Honestly couldn't tell you how stiff the structure is, but it will be getting a serious upgrade with some of the cage additions I am planning.

If anything the driveshaft is 1/2" to 3/4" too short.

Something else to consider are the track loads. The transitions into Turn 1 and turn 15 are pretty violent and are doing all kinds of damage to stuff. I regularly check the K-member which has a bash plate that hits the surface constantly in a pancake impact. I also had a pretty bad off at a race in Utah back in 09' that could have started the crack and may have just been getting worse since then.

I'm going with the stock trans mount and monitor it again. I think the points of the chassis flexing could be important in the grand scheme of things given this tub has been a race car now going on 8 years. Since I am going on a "cutting more weight out" scheme, it will be a good time to go over it with a magnifying glass and look at how the uni-body is doing....I might not like what I find! Luckily the car only had 22k street miles on it when I started so it wasn't already worn out from 150k miles of street duty.

[fastwhite99gt]

Dammit boy and I thought I was rough on my car with 4500rpm 2step clutch dumps!

[otrtruckpro]

On our dirt cars we always ran solid motor mounts and rubber trans mounts.

That always works,street, strip or oval

[danielhv]

What do solid motor mounts feel like? Lot of vibration?

[bird_dog0347]

My car needs new motor mounts bad, they are trashed... But my trans mount I discovered is solid... Should I just put poly's on the motor and leave the trans? It's gonna be 95% weekend street car, with an occasional track day taking it kinda easy.

[aggie97]

My car needs new motor mounts bad, they are trashed... But my trans mount I discovered is solid... Should I just put poly's on the motor and leave the trans? It's gonna be 95% weekend street car, with an occasional track day taking it kinda easy.

personally I would go solid engine and soft trans. Keeps the torque managed especially on downshifts and upshifts so the shifter isn't moving around too much and shifts are clean. I prefer things to not be moving so I am not having to drive around any slop.

[Grape]

Front motor mounts, rear block mounts and no transmission mount at all is the proper way.

[Strychnine]

Front motor mounts, rear block mounts and no transmission mount at all is the proper way.

I get that you work on shit that's not typical around here, but are you really recommending a cantilevered trans setup in a mustang?

Anyone know what the RFOB bending moment limit is for a 4.6 block?

[Grape]

I get that you work on shit that's not typical around here, but are you really recommending a cantilevered trans setup in a mustang?

Anyone know what the RFOB bending moment limit is for a 4.6 block?

Yes, all cup, busch, truck stuff is done this way.

[Strychnine]

Yes, all cup, busch, truck stuff is done this way.

Did not realize that.

Well... carry on! We do stuff like that on the thingsI do at work, but I'd never think to do it in a track car. Need to think outside the box more I guess.