My 1988 LFX F40 build. (Page 14/68)
Rickady88GT FEB 16, 08:49 PM
On my Short Star and my LS4, I did not use a dogbone. I have 5 motor mounts. The Short* used stock liquid filled mounts and the LS4 uses poly. Neither engine moved enough to contact anything. And I do not feel engine or drive train vibrations. I hated the idea of using the heads as a motor mount on the Short*.
Daryl M FEB 17, 01:16 AM

quote
Originally posted by Rickady88GT:

On my Short Star and my LS4, I did not use a dogbone. I have 5 motor mounts. The Short* used stock liquid filled mounts and the LS4 uses poly. Neither engine moved enough to contact anything. And I do not feel engine or drive train vibrations. I hated the idea of using the heads as a motor mount on the Short*.


That is worth considering, but the good news is that if the engine moves that little, having a dog bone shouldn't hurt.
Rickady88GT FEB 17, 09:19 AM

quote
Originally posted by Daryl M:

That is worth considering, but the good news is that if the engine moves that little, having a dog bone shouldn't hurt.



You may be correct?
For two reasons, I did not want to use a dog bone 1: I did not like that the dog bone mounted to the heads. I know the factory does it but they also replace head gaskets. Second: I did not like the thought of the bulkhead/firewall moving or flexing, even the slightest. Because the rear window is very difficult to replace it it cracks.
I have used the original dog bone mount of the Fiero at the strut tower location on at least one of the swaps I have done. But I had to make a new mount for the engine side of the dog bone. The factory dog bone is always on the wrong side of the engine for our Fiero swaps.
fieroguru FEB 17, 10:17 AM
I too don't have a dogbone on my LS4. I used the basic 4 corner mounting method with rubber lower control arm bushings.
1. The bushings are quite stiff and since they are round and enclosed in a metal ring, they limit available movement.
2. The bushings are spaced about 24" apart front to rear, so they have a significant amount of leverage to control engine movement.
3. The bushings at the front and rear are also co-linear, which helps balance the torque loads between the bushings.

The factory mounts that Daryl is using are probably quite flexible to significantly reduce drivetrain vibrations. So even with 4 of those, he will likely need some type of dogbone as well to limit the engine movement at WOT.
Daryl M FEB 17, 06:52 PM
The mounts I used are from a first gen Cadillac SRX. The Cadillac engine is longitudinal with two of these in front and a transmission crossmember in the rear. I'm not exactly sure how much movement to expect in my application.

[This message has been edited by Daryl M (edited 02-17-2019).]

Will FEB 19, 12:54 PM

quote
Originally posted by Daryl M:

The mounts I used are from a first gen Cadillac SRX. The Cadillac engine is longitudinal with two of these in front and a transmission crossmember in the rear. I'm not exactly sure how much movement to expect in my application.




Keep in mind that longitudinal engine mounting methods only have to deal with driveshaft torque, while transverse engine mounting methods have to deal with axle torque.
Daryl M FEB 20, 12:50 AM

quote
Originally posted by Will:


Keep in mind that longitudinal engine mounting methods only have to deal with driveshaft torque, while transverse engine mounting methods have to deal with axle torque.


Interesting you should mention that. Taking into consideration final drive gear reduction, the effective torque is about tripled but the speed of the torqing action is 1/3. How that effect plays out on mounts is an interesting puzzle.
pmbrunelle FEB 20, 12:44 PM
I would estimate three times the engine movement vs. the original application.

I took the hypothesis that the movement is proportional to the applied torque.

In your case, since you have two transmission mounts spread apart, that's not quite the same as the single mount in the Caddy.

[This message has been edited by pmbrunelle (edited 02-20-2019).]

Rickady88GT FEB 20, 08:41 PM

quote
Originally posted by Daryl M:

Interesting you should mention that. Taking into consideration final drive gear reduction, the effective torque is about tripled but the speed of the torqing action is 1/3. How that effect plays out on mounts is an interesting puzzle.



Just think about how much a Fiero fire wall will have to deal with if dog bones were yanking on it?
Not sure if you intend to use the stock engine dog bone mounts or not, but if you do want to use a dog bone or 2, consider switching them to the rear, and not on the fire wall.
Another reason to not use fire wall dog bones is for maintenance. Idesigned my engine swaps to be able to swing down the cradle easily for stuff like changing plugs. A dog bone under the deck lid could be difficult to disconnect for a cradle swing down.
Believe me, it SUX to work on stuff that can't be reached back there. Even the wire harnesses should have enough slack to flex the cradle down. OR be easily disconnected. The coolant pipes, and exhaust system should also be untouched for a cradle swing down.
Daryl M FEB 20, 09:25 PM

quote
Originally posted by Rickady88GT:


Just think about how much a Fiero fire wall will have to deal with if dog bones were yanking on it?
Not sure if you intend to use the stock engine dog bone mounts or not, but if you do want to use a dog bone or 2, consider switching them to the rear, and not on the fire wall.
Another reason to not use fire wall dog bones is for maintenance. Idesigned my engine swaps to be able to swing down the cradle easily for stuff like changing plugs. A dog bone under the deck lid could be difficult to disconnect for a cradle swing down.
Believe me, it SUX to work on stuff that can't be reached back there. Even the wire harnesses should have enough slack to flex the cradle down. OR be easily disconnected. The coolant pipes, and exhaust system should also be untouched for a cradle swing down.


I was thinking of a brace connecting the upper spaceframe siderails. Not thinking of using the firewall for support.