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.
------------------ " 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" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
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).
...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.
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.
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.
On the GT the other 3 mounts, if stock, would be rubber. Two on the trans(manual), and one under the front of the engine. Guess you might want to go poly all the way around if trying to get more power to the wheels. With a poly dog bone the torque twist goes elsewhere considering the other mounts are stock rubber.
Originally posted by Kevin87FieroGT: With a poly dog bone the torque twist goes elsewhere considering the other mounts are stock rubber.
Yep. The next component to look at would be the rear tranny mount. It's compressed under acceleration. So a mount with better compression resistance would reduce drivetrain movement. That should also balance out the torque twist under acceleration.
[This message has been edited by Blacktree (edited 07-02-2018).]
I plan on solid mounts for my engine swap. I like engine vibration... My 63 Nova had solid mounts all around, the vibration was great from the 350 mouse motor!
...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.
Not only vibration you feel... Solid engine/trans mounts and "dog bones" can break the car. Is like hitting w/ a sledge hammer to entire car. Something has to give from torque/suspension/etc loads and if not then will break whatever is weakest... Sheet metal or spot welds, aluminum trans case, even cast iron/steel engine blocks.
And that's ignoring everything expanse/shrinks at different rates for heat cycling for engine heating, weather, etc.
ETA--> Many use chain/cable to limit loads on engine/trans mounts. They go tight only for launching to protect the mounts. Many mounts are built so this is not needed for most cars. polly mounts/dogbone and auto trans can shake the car at idle too. I hate polly DB in duke w/ auto but saves breaking exhaust and intake parts and that's w/ solid rubber engine and trans mounts. See my Cave, Torque Strut (OE engine mount is liquid filled and doesn't last more then 2-3 years.)
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
[Not only vibration you feel... Solid engine/trans mounts and "dog bones" can break the car. Is like hitting w/ a sledge hammer to entire car. Something has to give from torque/suspension/etc loads and if not then will break whatever is weakest... Sheet metal or spot welds, aluminum trans case, even cast iron/steel engine blocks.
Sledgehammer?
The 2.8?
It doesn't seem likely this engine has the cojones to break anything.
I had the poly (TFS) dog bone to replace the rotted rubber stock one. I decided to replace the polyurethane dog bone back to stock, since I was worried that too much vibration would be transferred back to the engine and mounts. At least, that's what I learned from following PFF. b
It doesn't seem likely this engine has the cojones to break anything.
I know some people who can tear up a crowbar in a sandbox.
All kidding aside, there are cases of people tearing the front tranny mount out of the cradle with a 2.8. 88s seem to be especially susceptible to this, due to the lighter cradle.
Issue I’ve seen with two 2.8L (‘86 & ‘87) was the mushy OEM rubber mounts. Though I did put in poly dog bones, I replaced the engine and trans mounts with OEM style rubber mounts. The engines seem to be very secure and tight with the fresh mounts. The poly bone does transmit some vibration, but it’s minor and before you know it you don’t even notice it anymore. After 7 yrs with one of the cars new mounts there appears to be no abnormal wear with the rubber mounts, or poly dog bone.
Not sure why the factory rubber mounts were so mushy. On removal there was no oil on them just basic road crud ( prob oil based crud). Neither car was over 50,000 when I replaced the mounts. Fresh mounts do make the car feel tight though, well worth doing, and easy.
Sport bikes(from the factory) have solid motor mounts. The 4 cyn engine is bolted directly to an aluminum frame. Redline at 16,000 rpm. Only rubber is the tire and a cushion in the wheel between the sprocket and the wheel itself.
I've posted it a few times but my experience with the dogbone on a '85 2.5 auto is this:
Replaced the bushings on my original one since they were shot with prothane red poly. Drove around with that for quite a few years but the vibration in D at idle was teeth removing.
Decided to finally ditch it for a new rubber one and the difference was night and day. Didn't notice any real torque steer issues. Just the vibration went away so yeah. No poly there for me. I do have poly in the suspension all around though and the cradle bushings are poly for quite some years now. No squeaks, no worn bushings so far.
A) The original engine mounts were not that soft...I decided to replace mine in 2000 with "Genuine GM parts!" and the ACDelco mounts were so soft that I could twist the trany mounts so that the tab was hitting the surround...The originals (With 130,000 miles and 16 years on them) were much stiffer. I found later that the Anchor brand replacements were much stiffer- more like stock (But the metal is thinner)
B) On my 85 SE w/3.4 F-body long block and 88 rear cradle, I swapped in poly on ONE side of my dogbone- left the other end rubber; limits movement but almost stock vibration isolation.
[This message has been edited by cvxjet (edited 09-11-2020).]
I had a poly dog bone in my 3800 Fiero for about 3 days. Couldn't believe how much Noise/Harshness and Vibration it introduced. For a drag car - sure. For a somewhat daily driven car, I would go crazy. My 2 cents.
------------------ 84/87 NB, 3800SC, E-85, VS Cam, 2.8 Pulley, 4T65E-HD, HP Tuners, AEM Wideband, Regal GS Gauges, S-10 Brake Booster. 1/4 mile -11.85 at 114mph
Yeah, going poly or solid shakes the whole car, especially at lower engine speeds. Not for a daily driver! If you trackday the car then having less drivetrain mouvement helps alot with handling. For the torque at wheels question, I would say that it doesn't change that much. It's just how quick the energy is applied to moving the car forward. With the added risk of breaking/shearing a component! Look how drag cars have soft(ish) suspension and how their tyres crease up on launch. All that in order not to loose grip. They apply torque progresively.
