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suspension engineers, what happened???? by fieroX
Started on: 10-03-2003 01:45 AM
Replies: 3
Last post by: Darth Fiero on 10-03-2003 12:55 PM
fieroX
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Report this Post10-03-2003 01:45 AM Click Here to See the Profile for fieroXClick Here to Email fieroXSend a Private Message to fieroXDirect Link to This Post
Ok something happened. Nothing bad, but something extremely good that can probably benefit others on this board.
So lately ive been having problems with an engine mount i made back in the day when I first did my swap, and its coming apart. This is it so I decided to redesign a new and better mount, and the one I came up with is a total freak of nature. See heres the problem I was having. My engine is torquing so hard that my cv boots are hitting the cradle, popping off, grease flys everywhere, my alternator pulley hits the strut tower, and all mayhem occurs. This is with the dogbone installed. The engine torques so hard that it bent my trunk front wall support brace back 1". See my engine sits about 2" lower than the WCF mounts. My engine clears all hood springs, and such, even with a 2" supercooler under the supercharger.
So I built this new mount. I dont have any pictures of it yet, but visualize this. Its made totally of 1/4" plate steel, a plate that bolts into the block where the other one did, but has 2 brackets that come off with 2" holes drilled in each one. A 2" pipe that is 3" long goes through both of them and welds completely around. Then 2 polyurethane leaf spring bushings go inside the pipe, with a grade 8 spacer and grade 8 bolt and nut holds it to a piece of 3/16 steel bracket that welds to the cradle. This babys is crazy. I even preloaded it foward with a porto power before I welded it just to make sure I had the extra 1/2" of slack pulled out before I released the mount.
So I used the porto power to push my bent wall back into place (which is soon to be replaced by something wickeder, pics to follow), and I took it out for a drive.
And heres what you all have been waiting for. heres what happened. I pulled out on K42 in front of the shop where I work (and work on my car), I punched it from idle and the car launched like it was at the track on nice warm drag radials. The pavement was even a bit damp in spots as it sprinkled a few hours earler, and it was about 49 degrees outside. This is on street tires, with an estimated 475 ft lbs of torque. figure this one out! So im thinking of how ladder bars work on front engine rwd cars. When you launch, something about how the rear end pitches causes the ladder bar to push up on the leaf spring, this causes it to try and lift the front of the car, but in turn puts weight on the rear axle. (something like that anyway). So heres my hypothesis on what is happening with my car. All of that torque is being stiffled by that mount that is so ridgidly mounted to the front of my cradle. In turn the engine is trying to lift the front of my cradle, while it torques rearward. This in turn tries to lift the front of the car and puts the added weight from the torquing action on the rear tires. Is this possible? Sorry for the novel, I just wanted to expain fully because its kinda strange and I wanted to share all the details. Any opinions? Other hypothesis'?
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Darth Fiero
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Report this Post10-03-2003 02:41 AM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
I really wish I could see the other side of your cradle. I am not sure what you have going on elsewhere but I will tell you what I did.

I have all 4 corners mounted via rubber mounts to the cradle in addition to a dog-bone mount in back. Check out this to see how I mounted the pass side of things:
http://www.l67swap.com/phpBB2/viewtopic.php?t=335

As you can see, I used 2 Dodge Truck V8 mounts at each location which still allow for some vibration dampening and I think they are much stronger than a single trans mount like you have shown in the pic above. ALSO, the front trans mount I am using, from a 94 Bonneville, has a miniature shock absorber built into it that also helps absorb the shock of launches and such.

Also in that link you will see what I did for a bog-bone mount, which is centrally located in the back of the engine/trans. Of course, I am not pushing the torque you are and perhaps I need to think about reinforcing my back trunk wall as well.

Something we all need to keep in mind about torque. Assuming you hook and your engine is producing 475 ft-lbs of torque with a 4T60-E and a final drive of 3.33 gears, you have a lot of torque trying to rip those mounts apart. Here is the equation:

475 (eng torque)
x 1.5 (torque converter multiplication)
x 2.92 (first gear)
x 3.33 (final drive)
x 0.85 (to account for 15% parasitic loss)
= 5890 ft/lbs of torque trying to twist on the centerline of the cv axles. Now, since your front motor mount is located approx 2' from the CV shaft centerline, then you can figure your powertrain is only trying to pull up on that mount with about 2945 ft-lbs of force. For the rear mounts, because they are right on the centerline, they will be the pivot point for the torque and should only bear the full amount of force.

Obviously these values should be used as a reference only because without accurate measuring equipment, it is difficult to ensure exact values. Remember that shock is one of the biggest killers of mounts which is why I try to say away from solid mounting anything to the body or cradle. Perhaps even poly is too hard for your engine/trans? Just a thought.

------------------
1987 Fiero Coupe 3800 Series II Intercooled Turbo (12.79et @ 106.6mph)
1987 Trans Am GTA 5.7L Superram 4L60-E (13.1et @ 109mph)

http://dtcc.cz28.com
GM EFI chip reprogramming & 3800 Fiero Conversions

[This message has been edited by Darth Fiero (edited 10-03-2003).]

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Philphine
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Report this Post10-03-2003 06:02 AM Click Here to See the Profile for PhilphineClick Here to Email PhilphineSend a Private Message to PhilphineDirect Link to This Post
darth, do you think those mounts would work with a manual 4sp set up? i guess i mean assuming the tranny was mounted in it's stock position with stock mounts?
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Darth Fiero
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Report this Post10-03-2003 12:55 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
 
quote
Originally posted by Philphine:

darth, do you think those mounts would work with a manual 4sp set up? i guess i mean assuming the tranny was mounted in it's stock position with stock mounts?

The beauty of the dodge truck mounts is their compact size. You could build custom brackets for the trans as well allowing you to lower or raise it along with the engine, if you wish.

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