Stock 3800sc - Stock or Poly mounts? (Page 1/1)
bmyers JUN 23, 04:19 PM
So I need to buy motor and tranny mounts for my 3800sc swap. I am using brackets from FieroRog.

Question; can I use the stock Fiero mounts or are they guaranteed to fail. I wouldn't ask if the price difference were not so significant.

Advice appreciated.

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Brian

Dennis LaGrua JUN 23, 04:47 PM
I know a few guys who have stick transmissions behind their stock 3800sc. They have used NEW stock mounts and they seem to hold OK but I favor poly mounts and dogbone as it is more solid. The downside is that there is more roughness and vibration felt when the engine is idling. I would definitely use poly or solid aluminum cradle mounts though.

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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, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, 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 "

bmyers JUN 23, 05:08 PM

quote
Originally posted by Dennis LaGrua:

I know a few guys who have stick transmissions behind their stock 3800sc. They have used NEW stock mounts and they seem to hold OK but I favor poly mounts and dogbone as it is more solid. The downside is that there is more roughness and vibration felt when the engine is idling. I would definitely use poly or solid aluminum cradle mounts though.




Thank you. Mine is an auto so I think that will be easier on the mounts, yes?

I see the polys for $65-$90/ea and the rubber mounts for like $15-$20/ea. It's hard to ignore that price difference. Are the mounts difficult to change once the motor is in the car? If so then I just get the polys.

Thanks again.

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Brian

Dennis LaGrua JUN 23, 10:34 PM

quote
Originally posted by bmyers:

Thank you. Mine is an auto so I think that will be easier on the mounts, yes?

I see the polys for $65-$90/ea and the rubber mounts for like $15-$20/ea. It's hard to ignore that price difference. Are the mounts difficult to change once the motor is in the car? If so then I just get the polys.

Thanks again.




Stock NEW rubber trans mounts should work if you have a good dog bone to limit powertrain movement. The issue is that no one that I know of makes rubber trans and engine mounts for swaps. WCF charges about $375 for a complete set. I believe that Fierorog only makes front engine mount bracket. His tensioner bracket is also op notch and he may make a low alternator mount.

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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, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, 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 "

pmbrunelle JUN 23, 11:46 PM
I was pretty good at tearing apart stock-replacement rubber transmission mounts with a stock 2.8.

Driving is obviously an important factor here; 5k RPM clutch dumps were routine.

[This message has been edited by pmbrunelle (edited 06-23-2021).]

Dennis LaGrua JUN 24, 09:46 AM

quote
Originally posted by pmbrunelle:

I was pretty good at tearing apart stock-replacement rubber transmission mounts with a stock 2.8.

Driving is obviously an important factor here; 5k RPM clutch dumps were routine.




I would agree that for strip use, poly is best.

[This message has been edited by Dennis LaGrua (edited 06-24-2021).]

DimeMachine JUN 24, 09:47 AM
I found poly to be so annoying with noise harshness and vibration I switched everything back to rubber years ago and have not looked back.

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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

Blacktree JUN 24, 11:37 AM
Keep in mind the stock Fiero engine mounts were designed to handle the power output of a stock Fiero engine. You can expect life of the mounts to be reduced considerably, with a more powerful engine.

That said, I was able to break urethane motor mounts with a 3.4 V6. But that was 4000+ RPM clutch dumps, on a drag strip. So driving also plays a big role. So for example, if you're going to granny the car, then the rubber mounts should be fine. Just keep in mind, if you decide to get frisky there may be consequences.

In a roundabout way, I'm saying "rubber mounts for cruising, urethane for hard driving".
Dennis LaGrua JUN 24, 01:07 PM

quote
Originally posted by DimeMachine:

I found poly to be so annoying with noise harshness and vibration I switched everything back to rubber years ago and have not looked back.




I agree. That is the downside of using poly but I still use it as my Fiero is only used as a hobby car that goes to cruise nights and events. The longest trip that it sees is my home to Carlisle

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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, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, 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 "