Performance dogbone engine mount idea

[weba]

This subject was previously discussed on bstuff, but since it's gone now, really short brief here:

92+ drive train mounting was re-designed by GM to reduce NVH (Noise, Vibration, Harshness) allowing the engine to rotate along it's "natural torque axis".
That new design ruined the drive ability specially on manual transmission cars and is prone to create side issues like wheel hop and restless behavior in heavy accelerating\braking or just spirited driving. Some of us may want use all the engine's power to rotate the wheels, instead of first rotating the engine, so i have been trying to find way to fix this issue.

Just to clear possible misunderstandings, there are upgrade mounts available for 92+ style mounting, those will firm up things some, but they all run short of actually fixing the issue.

Here is an example of one, for those who may not know:


Performance dogbone engine mount idea for 92+ cars

Mind the Paint drawing, this is purely for illustration!

Here we have the dogbone

And the shape under it represents where it mounts on the car's subframe. That part of the body has 2 bolt holes, M for manual transmission cars, and A for automatic ones where the drivetrain sits more forward.


This is what the standard dogbone looks like when it's mounted. Front of the car would be right side on this picture.


And this is how the mounts reacts to the engine. The bolt where it's mounted to the subframe acts as pivot point and the mount as a shaft.


Top engine mounts allows the rotation by it's design. Poly inserts and glues there may help, but the flaws of this center mount location design cannot be overcome that easily.

So, here's what I'd like to try (next).


Custom dogbone that mounts to both, A and M holes, depending of the bushings stiffness, this should seriously hit the rotation issue. This would have to be different length for manual and automatic trans cars.

Anyhow, that's my newest idea of this never ending battle of stop the drivetrain shaking issues my car has been suffered from the day i did the 5spd swap... Next step would be getting the the custom mount machined then.

[Chad91GTZ]

Might need to add some welds to the mount box, thats a lot of stress to be dumping into that. As it is now, it simply rotates.


I think with a stock engine, it would be fine. But with a more powerfull powerplant, it might crack.

[dhenderz]

Weba - interesting idea, but I don't think it will provide the improvement you seek. For my reasoning go to your first picture showing the torque reaction arrows. They are not correct. In fact the engine is what rotates about its axis. The torque strut (dogbone) damps that torque and provides a max degree of rotation (when the rubber inside the dogbone bottoms out against the aluminum dogbone casting). The chassis end of the dogbone, where the 2 bolt holes are, does not see a rotational force. The dogbone does rotate a few degrees at that bolt location, but that is simply to accommodate the rotation of the dogbone as the other end (hooked to the engine) is moving is a true arc. I think you will see little if any change in engine movement. And in time I think you will simply shear off one of the 2 bolts that are 'doubled up' in your pic.

You want to use the dogbone as a strut to stop the engine roll - eg: use its inherent strength as a member put into tension, not use the shear strength of 2 bolts spaced so close together. Knowing what you are attempting to accomplish, I would recommend what GM did in their higher HP FWD applications. Use more dogbone struts to further restrain the rotation movement of the powertrain. If you compare a standard 90’s Grand Prix to a turbo GP, you will find that the dogbones were doubled (at least I don’t recall the base engine having 2 – but the turbo surely did). Ditto for the 3.4L DOHC V6 installed in FWD GM cars.

So, I would look for solid locations on either the top or bottom of the powertrain (engine and/or trans – likely at least one on each) where you can fab up some brackets and attachment points for additional struts. The run those added struts to a solid spot on the chassis/BIW.

[pazzy]

I have the same wheel hop that i'm trying to get rid of i figured it was a bent axle, but would putting a performance dog bone on the top of the engine and at the bottom make a difference?? I know that my 2.8L cutlass has 2 dog bones on the top but not on the bottom

[woody90gtz]

Weba, I'm running two dog bone mounts (one engine side and one trans side) and I get no rotation. There is some vibration in the cabin due to this, and you'll want to loctite your bolts because it will loosen them over time...but the engine does not rotate.



That's a 91 central trans mount and dog bone, and a 95 central engine mount and dog bone. You will need the driver's (trans) side 91 subframe & bracket and a pass (engine) side 92 subframe & bracket. Mine is actually a 92 subframe and 95 3X00 bracket, but you get the idea.

[Barry]

Yes and no.

The 92 and 93 5-speed berettas got the different trans mounts that do what your idea does, but much more effectively based on the fact that the mounting points are much farther apart to reduce the leverage.

But on the automatics, hell yeah. That mount makes a ferris wheel out of the whole situation. It is really crucial to upgrade your engine side mounts with a auto, or pre92 5-speed.

[3400beretta]

I have to agree that this would not solve the issue. The engine does not rotate enough, if it all, like you show in the picture to make two bolts in the lower dogbone improve anything. All the dogbone does is stop the lower part of the engine from pulling away from the front of the car if you will.

I have a FFP dogbone, an insert in the upper mount, and shore 94a tranny mounts that I poured myself, and my engine does NOT move PERIOD. I took a 5ft prybar to it and I could barely get it to rotate a few millimeters on its axis. And I compare this to Eric's car, who also has a FFP dogbone (but nothing else), and his engine jumps around like theres no tomorrow.

[weba]

woody90gtz, thanks for posting that picture up, looks like my memory served me wrong, I was thinking all the time that the subframe had the 2 bolt locations, and the engine bracket had one.. but it's the opposite as it seems. then my idea wont work ! Doh. !

The chassis end of the dogbone, where the 2 bolt holes are, does not see a rotational force. The dogbone does rotate a few degrees at that bolt location

I actually placed my car on the stands and took the wheel off to see what happens there, it does have quite a much rotation down there, even without load (tires touching ground) the other end of the stock dogbone moved up & down bit under 1". I am thinking that my idea would be a direct hit to the issue since it would stop that movement. But since i mis-remembered the bolt hole locations, it cannot be done this way.

It might have actually provided less stress to the dogbone bracket than the current setup with FFP dogbone. Just think about it, the current setup 'Runs into the wall' and the custom dogbone would had just pushed against the wall, imagine what hurts you the most

you will find that the dogbones were doubled (at least I don’t recall the base engine having 2 – but the turbo surely did). Ditto for the 3.4L DOHC V6 installed in FWD GM cars.

Those cars also had the dogbones much more effectively installed, they were mounted to the body on front of the engine, facing to the back of the car, so they naturally didn't let the engine rotate that much. Since making our radiator bracket load carrying part would mean serious changes around the engine bay and add much weight where it's less wanted, I do not want to go to this direction.


I don't think adding additional transmission side mounts wont help anything on my case, remember that i have 92+ transmission mounts where i had the rubbers replaced by with hardened steel, and a really tight bushings with minimal play.

Top engine mount has gone thru 3 evolutions, currently it's 95+ mount filled with glue, has poly insert and 92 manual transaxle T-piece with correct offset. FFP does the dogbone's job.

I also have fifth experimental engine mount installed just next to the alternator, it made the shifts smoother but didn't reduce the issue enough to accomplish what i hoped.

And 3400beretta, my car suffers serious drive train rotation, if you don't believe it, you are welcome here to try it

[woody90gtz]

Weba, I drilled the 2nd hole in the engine bracket, it was not there from the factory. The subframe only had one hole also.