Solid Motor mounts? Any options? Any interest?

[Paul Workman]

Originally Posted by 5ABI VT

As far as I see it a stiffer mount will take twist out of the c beam where it is connected to the rear end.

Considering the stock (rubber) mounts are just fine on some of the nastiest LT5s in FBI land, I'm struggling to see the need - other than for a repair/replace item.

Solid (steel) mounts bring back some unpleasant memories from my early track car days. Never again. A little rubber is crittically essential, far as vibration/shock/fatigue goes. JMO.

[5ABI VT]

Originally Posted by Paul Workman

Considering the stock (rubber) mounts are just fine on some of the nastiest LT5s in FBI land, I'm struggling to see the need - other than for a repair/replace item.

Solid (steel) mounts bring back some unpleasant memories from my early track car days. Never again. A little rubber is crittically essential, far as vibration/shock/fatigue goes. JMO.

I fully agree that they are good enough I don't ever hear of anyone talk or mention the need to change them. For me , it's about turning the ZR-1 into my vision of what I feel it should have been which is more responsive and engaging.

The feel is there from the interior , for the most part I've addressed the floating mushroom/ flat tire feel of the stock suspension on the 17" balloons (my opinion of course ) and it will get sharper once I can change the rack and do full poly bushings throughout, the noise is definitely there with the LT5 'asking unparalleled noise when uncorked. I just want a little more response and feel and I feel the motor is too isolated and soft when giving it throttle. I can only imagine the rubber is as soft as mounts used in cadillacs and buicks.

[Hog]

Originally Posted by 5ABI VT

I was actually thinking more about a poly mount and not a solid metal mount. I did find a few websites that appear to make them for any application so it shouldnt be impossible. I isn't search enough to be sure if the engine to mount bracket is the same as the LT1 or if the mounts are the same but it appears one of the two are interchangeable.

As far as I see it a stiffer mount will take twist out of the c beam where it is connected to the rear end. I've been in a few cars with poly and they do vibrate some more but they also make the motor feel much more direct and responsive which I like. Worst case I can put them on my 93 LT1 car. With a .700+ lift solid roller cam and tight leave and 370s duration it will already vibrate so some poly mounts shouldn't be noticeable lol!

Your LT5 is loud, I swear I can hear you from my house when you do your sweeping on ramp entries. I like it!

Stiffening up with urethane will give you the "feel" you are after, and I think it would suit the partivular character of your car.

I was involved in a project for engine mounts for the V8 Northstar engine. Compared to stock they certainly changed the NVH(Noise Vibration Harshness) characteristics of the car. My particular car was the 1st year of the more rounded body of the STS being a 1998, and the engine was the 300hp @ 6000rpm/295 lb/ ft torque @ 4400rpm torque with the shorter 3.71 gearing while the base engine made 275hp @ 5600rpm/300lb/ft torque@ 4000rpm with its higher 3.11 gearing.

These Northstars were mounted transversely and used the 4T80-E transaxle. In stock form with stock PCM calibrations, they were notoriously soft shifting, in fact it was more of a slide during upshifts, esp. at any TPS(Throttle Position Sensor) setting other than WOT.
However, if you placed the gear selector in 2nd gear and then accelerated at WOT from a dead stop or low speeds, the trans would shift into 2nd gear with 100% line pressure and a WOT 1-2 shift would bark the front tires.

Now how this all relates to a urethane engine mount. With the stock engine mounts, this 1-2 bark was not as pronounced as it was after the urethane engine mounts were installed. The shift after install felt more direct, less sloppy, and the tire spin was exaggerated.
I'm guessing that people who were used to the NVH characteristics of a Cadillac might not enjoy the new characteristics, but performance minded folks like myself, and yourself 5ABI VT, would enjoy them greatly.

[5ABI VT]

Originally Posted by Hog

Your LT5 is loud, I swear I can hear you from my house when you do your sweeping on ramp entries. I like it!

Stiffening up with urethane will give you the "feel" you are after, and I think it would suit the partivular character of your car.

I was involved in a project for engine mounts for the V8 Northstar engine. Compared to stock they certainly changed the NVH(Noise Vibration Harshness) characteristics of the car. My particular car was the 1st year of the more rounded body of the STS being a 1998, and the engine was the 300hp @ 6000rpm/295 lb/ ft torque @ 4400rpm torque with the shorter 3.71 gearing while the base engine made 275hp @ 5600rpm/300lb/ft torque@ 4000rpm with its higher 3.11 gearing.

These Northstars were mounted transversely and used the 4T80-E transaxle. In stock form with stock PCM calibrations, they were notoriously soft shifting, in fact it was more of a slide during upshifts, esp. at any TPS(Throttle Position Sensor) setting other than WOT.
However, if you placed the gear selector in 2nd gear and then accelerated at WOT from a dead stop or low speeds, the trans would shift into 2nd gear with 100% line pressure and a WOT 1-2 shift would bark the front tires.

Now how this all relates to a urethane engine mount. With the stock engine mounts, this 1-2 bark was not as pronounced as it was after the urethane engine mounts were installed. The shift after install felt more direct, less sloppy, and the tire spin was exaggerated.
I'm guessing that people who were used to the NVH characteristics of a Cadillac might not enjoy the new characteristics, but performance minded folks like myself, and yourself 5ABI VT, would enjoy them greatly.

Haha thanks ! . That is very cool .. years back now we had 2 olds auroras with the smaller north star version with 250 hp. Incredibly smooth engines I loved them. Both succumbed to head gasket failure from Dexcool sadly and back then I wish I had more space and tools to just replace them myself.

But you are right and that is exactly my experience with them. They make the engine feel a little more responsive and raw. And raw is a term many use to describe the c4 and poly mounts would definitely add response. Wether it is a good thing or not remains to be seen as I know the LT5s are smooth but with aftermarket flywheels and clutches I wonder if the balancing will be the same as however the procedure was from the factory with the dual mass.

When people usually ask me about the light flywheel I try and be a little cautious in my reply. I certainly like it but I don't think they are for everyone. It depends what you want from the car and ether or not you care about what effects it actually has on the cars performance that you may not even feel (except for idle revving or rev matching in downshifts etc where it should be pretty obvious). Anyways my point about the aluminum flywheels is that I think they should be paired with a 'stiffer' material than the stock mounts to help feel the difference in flywhee weight. I always notice the engine is very responsive at idle but I can feel nothing like it is way too isolated from the pedal.

Waiting to hear back from a manufacturer that advertises custom mounts. The oem ones are pretty cheap so I may just buy a pair or 1 if they are the same part number and ship it to them and see what happens. Worst case scenario I just take them out!

[BigJohn]

One should be longer than the other?

[orthodoct]

Great old adage applies here, "if it ain't broke, don't fix it". I rebuilt top end, stainless works headers, clutch, beam plates, fixed twenty oil leaks on my '92. Pulled mounts and cleaned them up; looked brand new and work fine. Repetitive cyclic loading ( like when you repetitively bend a coat hanger) will eventually cause any piece of metal to break dependent on grain size. Crack that cast block, and you are SCREWED, my friend. They are made of "unobtainium".


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[5ABI VT]

Originally Posted by orthodoct

Great old adage applies here, "if it ain't broke, don't fix it". I rebuilt top end, stainless works headers, clutch, beam plates, fixed twenty oil leaks on my '92. Pulled mounts and cleaned them up; looked brand new and work fine. Repetitive cyclic loading ( like when you repetitively bend a coat hanger) will eventually cause any piece of metal to break dependent on grain size. Crack that cast block, and you are SCREWED, my friend. They are made of "unobtainium".


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Interesting that Ive never seen a top end get broke, or factory manifolds, a c-beam or a factory clutch? How did you manage to break them all?

[BigJohn]

It is obvious you have never raced !
As I said before you can do anything you want to your own car.
Some people just have to learn the hard way.
Best of luck to you!

[orthodoct]

I haven't broken any of them, but I am very familiar with what happens with repetitive cyclic loading. The first femoral stems for hip replacements were made of cast chrome cobalt stainless steel at least 1/2 inch in diameter. They were put in fragile 100 pound little old ladies. We found that after one million steps, they would snap and that was a piece of metal that you could tow a tractor trailer with. That is why all femoral prostheses are machined from solid forged billets using CNC machines. My point is that with the vibration from the engine being transferred to the frame with no elastomer to absorb that energy, something is going to give and it will probably be the boss on the block where that engine mount attaches.


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[5ABI VT]

Originally Posted by orthodoct

I haven't broken any of them, but I am very familiar with what happens with repetitive cyclic loading. The first femoral stems for hip replacements were made of cast chrome cobalt stainless steel at least 1/2 inch in diameter. They were put in fragile 100 pound little old ladies. We found that after one million steps, they would snap and that was a piece of metal that you could tow a tractor trailer with. That is why all femoral prostheses are machined from solid forged billets using CNC machines. My point is that with the vibration from the engine being transferred to the frame with no elastomer to absorb that energy, something is going to give and it will probably be the boss on the block where that engine mount attaches.


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I was merely taking a fun jab at the 'if it aint broke don't fix it' part and then stating all the modifications you did. The way I see if we are both on the same page here. All of those mods I have done for similar or the same reasons be it more power, durability etc. Im looking at polyurethane or another stiffer than oem material that will still allow some flex but make the engine feel more responsive than it is now.

Interesting stuff about the hip replacement stems ! Reminds me of the common issue with the e46 M3 I had where the tabs on the vanos hub break over time. Aftermarket tuners tried to make a replacement and went through many different versions and materials before finally settling on one that wouldn't shear off.