I have done a lot of reading and have not quite been able to find a good consensus so I would like to throw this out for some advice or someone to point me into the right direction.
Very new to this so take it easy on me.

3800 sc , 88 gt cradle, 4t65e-HD trans for the swap.

This is my understanding:

I will need custom brackets, 1 for the engine and two for the trans.

I also have the option(?) of replacing the motor and transmission mounts while I am at it.

Even lets say if I wasnt doing the engine swap, I could opt for new mounts. Is this true?

The reasoning for changing to poly mounts is for increased durability to accomodate the additional power of the higher HP motor?

The custom brackets are not optional because, well you have to mount a different engine and trans.

I have seen a lot of posts about the vibration caused by the poly mounts.

Comments on above appreciated. Specific questions below:

Can the 3800 swap brackets sold on this forum be used with either Aftermarket Poly mounts OR original rubber mounts (Possibly aftermarket rubber mounts) , or are some / all of them designed specifically for use with poly ?

Is it feasible at anytime to perform the 3800 swap with rubber mounts? Is there any combination of poly trans / rubber motor or vice versa that may work?

The rubber on my cradle is not beautiful but still looks functional, if I continued swap with rubber mounts, can they be replaced ? I see a big difference in the price for OEM vs Aftermarket. Any insight?


Thanks for your thoughts and feedback .. Please let me know if i seem to be misunderstanding something somewhere.

[This message has been edited by 88GaTa (edited 06-10-2016).]

I have an 88GT with a 3800SC and 5 speed. It has all poly mounts (i.e., transmission, engine and dog bone.) A lot of vibration is transmitted in to the car from the frame. I don't drive it that hard and maybe having some it mounted in rubber would reduce the vibration.

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88 GT 5 Speed Black with gray interior
3800 SCII Swap Complete.
Paint Complete
Detailing in Progress

IT RUNS!!
IT'S QUICK!!

"Real integrity is doing the right thing, knowing that nobody's going to know whether you did it or not."

Go to GMtuners.com website for info about dodge truck mounts. Fierorog on this forum sells custom 3800 swap brackets for use with stock or aftermarket mounts (Rodney Dickman)
I wouldn't use 30+ year old stock rubber mounts on a 3800 swap as you are asking for trouble. Save yourself some time and trouble and buy the hard stuff that works like mounts and wiring harness and then fab up the other 100 small custom stuff that is needed.

Use poly engine mounts, cradle mounts and dog bone mounts on my 3800. More vibration can be felt at idle but not when the car is in motion. With poly its a trade off. You do give up some comfort for superior handling qualities. Since I highway drive my Fiero most of the time, holding the road takes precedence over comfort.

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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"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Did my swap with all new rubber mounts. I don't like vibration. With good dog-bone mounting it has been great. I used aftermarket mounts for engine and trans and GM for cradle.

quote Originally posted by larafan: Did my swap with all new rubber mounts. I don't like vibration. With good dog-bone mounting it has been great. I used aftermarket mounts for engine and trans and GM for cradle.

If you like it smooth and soft all around rubber is the better choice. No question poly gives more vibration at idle but less powertrain, cradle and wheel movement. Its really a toss up and there is the third option; poly cradle mounts and rubber elsewhere.

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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"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Have done 2 3800 swaps. Both, I used Poly on the Cradle (so it cannot MOVE) and rubber for the Engine/trans Mounts and control arm bushings.
Sway Bar to frame (rubber) and Poly for the end links. This way you isolate vibrations and restrict Excessive "Movement".
For the trans, I used '98 Trans Sport 4t65 trans BRACKETS and stock rubber Fiero trans Mounts. Engine, again stock Rubber Mount.
When the engine "Torques"/Twists under acceleration, it tries to LIFT on the side of the engine/trans under the rear window. Besides the Dog Bone, I bolt a Chain from the Block to the Cradle Cross Member with about 1/4" of "slack", it will Never Brake the mount and pull loose,

My 3.8 sc car is mounted with poly, and the cradle is stock rubber. Vibration at idle is likely to vibrate your fillings loose. So at a stop I put it in neutral and the vibration stops. No noticable vibration while driving. My V8 car has same setup, no vibration at all.

Recently replaced all the control arm bushings with rubber and noticed an improvement in ride quality particularly given the bushings up front at least needed to go long before they did. The cradle mounts are all poly, as stated above they don't move. Vibration in excess of stock that doesn't increase the power output on a regular driver isn't worth it at least in my opinion. Bushings don't generally wear out very fast and I doubt having a 3800 SC will make much of a difference. I've also read complaints about possible noise associated with poly in some instances in addition to the vibration penalty.

By far, the strongest mount bushing with the best vibration absorption factor I've used in swaps to date was the OE 84-87 Fiero front cradle mount bushing. I used to be able to get these directly from GM, until they went out of the book, then the Fiero Store; but now the Fiero Store doesn't sell them anymore either. Below are 2 pictures of custom motor/transmission mount I built using a new OE-replacement Fiero cradle bushing for a 3800 SC swap:





These are bullet-proof as they cannot be pulled apart, so power-handling isn't a concern. But as I said, you can no longer buy these cradle bushings - at least I have been unable to find a supplier. The next best "bushing" to use is a rubber control arm suspension bushing, but those are made of a considerably harder rubber compound that is nowhere near as soft as the Fiero cradle bushing material was. So you lose a measure of vibration isolation with the harder compound. That being said, poly is worse than rubber and offers almost NO vibration isolation in comparison.

Years ago I tried the Dodge Truck mounts but found they could pull apart at high power levels. I recently bought a set of LS1 Corvette hydraulic motor mounts (like the ones pictured below) but I haven't tried them yet to see how well they would work. The Corvette mounts are very large so where they will fit and can be used is limited.



-ryan

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