Question about solid dogbone engine mount. (Page 1/3)
RayOtton JUL 01, 09:10 AM
Over on one of the Fiero Facebook pages a couple of people were touting the solid dogbone mount for the ability to increase torque to the wheels.

Another guy mentioned the poly mount as another option that transmits less vibration but still increases torque.

Thoughts?
olejoedad JUL 01, 09:44 AM
Poly dogbone is great!
Dennis LaGrua JUL 01, 10:50 AM
My 3800SC swap uses two dogbones, one at each end, as installed in the GTP. They are metal with poly inserts. The powertrain moves little. To answer the question, a solid dogbone mount is not necessary and will only further increase felt engine vibrations at idle. For better torque control, I would not use anything more than poly. One will work but IMO as GM did it on the 3800; two are better.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
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Blacktree JUL 01, 11:16 AM
I don't think a stiffer dogbone will increase torque to the wheels. However, an engine with more torque output may necessitate stronger mounts (including the dogbone).
Patrick JUL 01, 12:04 PM

quote
Originally posted by RayOtton:

...a couple of people were touting the solid dogbone mount for the ability to increase torque to the wheels.



...and the ability to increase vibration to the cab.

I noticed when I installed the poly dogbone in my Formula that the added engine vibration at idle from the 1.6 rockers became quite evident. I don't mind it, but I suspect I wouldn't like even more vibration being transmitted through a solid dogbone.
fieroguru JUL 01, 01:13 PM
It is a transient state issue.

For the split second the axle torque is rotating the driveline (compressing the mounts, dogbone or otherwise), it isn't delivering 100% of the available toque to the wheels. Once everything compresses, you see 100% of the available torque to the wheels (assuming the wheels don't spin).

Some drivetrain movement isn't necessarily a bad thing, as it softens the impact loading on the clutch, transmission, axles and tires and helps improve durability, reliability and launch traction. Like everything else, it is about balance... too much drivetrain movement can lead to wheel hop, which will quickly snap axles and break transmissions. So ideally you want it somewhere in between.

To mount all my drivetrains I use 4 rubber control arm bushings placed about 24" apart (front to back or in the direction of drivetrain rotation). They are rubber, but quite stiff and the 24" spacing gives them quite a bit of leverage to resist drivetrain rotation. This makes the drivetrain quite firm, but gives it some compliance at high loads (@ peak torque in 1st gear my combo tries to put 3902 tq to the ground - prior to the 3.09 final drive swap it was 4483).

The other thing to think about with the pre-88 cars and the rubber mounted cradles... all engine/transmission mounts attach to the rubber mounted cradle and the dogbone goes to the chassis. So axle torque being resisted by the dogbone creates a load between the cradle and chassis (trying to push the passenger side of the cradle forward) which isn't ever a good thing. The more you stiffen the engine/transmission/dogbone mounts, the more impact loading (and more deflection) there will be between the cradle and the chassis... so the first thing to stiffen should be the cradle mounts, only after that should you move on to stiffening the dogbone mount.
Blacktree JUL 01, 01:52 PM

quote
Originally posted by fieroguru: ...so the first thing to stiffen should be the cradle mounts, only after that should you move on to stiffening the dogbone mount.


I agree. If you have a pre-88 Fiero, put solid cradle mounts in it first. And if you still feel the need to stiffen up the dogbone mount, try urethane or hard rubber first.
RayOtton JUL 01, 01:57 PM
Thank you for the input.

I should have said up front that it is an '88 Formula with 60K miles and just about all the recommended mods, including the 1.6 rockers.
Tony Kania JUL 01, 03:31 PM
Only comfort would be lost if you went with a solid mount. No gain IMHO. Like stated, vibration would increase.


Edit: I would be interested in letting go of a few of my "Guaranteed 10 HP" stickers if you are looking for cheap fun?

[This message has been edited by Tony Kania (edited 07-01-2018).]

BillS JUL 01, 03:55 PM
The solid plastic mount didn't add significant vibration to my 88 but it did keep the engine from thrashing around.

No idea where your informant came up with the unusual idea that the mounts affect torque to the wheels - silly and untrue.