rabinaba

For my '81 LS/T56 swap, I'm doing full poly upgraded suspension components, a stiffer composite leaf spring, Bilstein B6 and B8 shocks, and RideTech DualRate springs. All that is to say, the suspension will be fairly stiff (or at least stiffer than stock). This will be a street car, I don't plan on tracking it, so I figured it might be a good idea to go with rubber engine and trans mounts in the hopes that it'll make the ride a little less harsh and prevent vibrations.

Any thoughts? Is my thought process solid, or am I missing something here?

Also, I know ES is the way to go for poly, but does anyone have recommendations for good rubber mounts? Seems people tend to go poly, so finding info on rubber mounts is a bit more difficult.

Edit: I should mention I plan to use the Dirty Dingo Slider Adapters.

Bikespace

There are no good rubber engine mounts. Use Moroso solid engine mounts. Always. Every time. No exceptions.

A poly or rubber trans mount is the correct pairing for this.

rabinaba

Ooh that makes me nervous. I’m trying to minimize the shake and harshness, would solid mounts not cause vibration through the cabin/cause the shifter to shake?

71 Vert LS1

I don't agree with the solid mounts. I've used rubber mounts engine/trans on all my LS swaps. Mine haven't been 1000 hp projects.
Never had a rubber engine/trans mount fail. My 98 Wrangler with a LS6/4L60E swap has 15 years on it with zero issues in regards rubber engine/trans mounts.

rabinaba

Yeah, I mean I’ll be topping out at 400 hp on a good day. I won’t be making massive power.

Which rubber mounts did you use? Stock?

Bikespace

I had a failed rubber mount in a 190 hp car.

rabinaba

Hmmmm maybe I’ll meet in the middle and just go poly then.

Bikespace, how’s NVH in your car? I think I remember reading somewhere that you have a full poly suspension as well, or am I misremembering that?

Bikespace

It's a sports car. I can't hear any noise over the sidepipes, the windows are down, and the T-tops are always off. I have some tire-induced vibration, but nothing from the tired engine (just turned 120K miles), at least above the rather high NVH floor.

I have (Energy Suspension) poly everywhere, except the trailing arms (new rubber) and strut rods (heim joints).

If you look on the Forum, you'll find a counter to every good idea. I had a failed rubber engine mount that I replaced with Moroso solids. I've heard anecdotes of poly motor mounts failing due to heat. Any solution probably works just fine for most folks. I chose solids, and I have another set of solids ready for my pending LS swaps. Moroso also sells solid mounts in three heights, which may give some flexibility for the final engine mount location (with shims), though I'm hoping not to have to find out. And perhaps it is purchase rationalization, but I have not heard anyone complain about engine vibrations who has switched to solid engine mounts. There's still lots of flex in our frames.

rabinaba

That’s right, I forgot that poly engine mounts have a tendency to melt. From what I’ve read, more people seem to complain about that than NVH from a solid mount. I guess I could always do solid mounts and then go rubber for the trans for a bit of extra flex.

Yeah, definitely a sports car and I want a sports car drive…I just don’t want the whole car to shake aggressively when you’re sitting in it idling. And I remember reading somewhere that TAs are the one place not to use poly, probably from you on another post. Good thing I already bought a poly rear rebuild kit 😅

SteveG75

Go solid. I have a 496 big block that idles at 900 rpm with sidepipes and have zero vibration issues with the solid mounts. As a plus, your engine now ties the two front frame rails together, helps to prevent flex in the front suspension.

Also, the Ridetech Dual Rate springs are not a good match with a stiffer composite spring. Just get a good set of 550# F-41 coils and be done with it. I would also look into upgraded upper control arms to allow more caster.

And don't put poly in the trailing arm bushings. The trailing arms twist as they move up and down and the poly will fail in short order.

rabinaba

Interesting, what makes you say the front springs won’t match with the leaf spring? I called up RideTech and they didn’t think it would be an issue, but it’s entirely possible they were just saying what I wanted to hear.

71 Vert LS1

I use NAPA rubber trans mount. Never had one fail. Engine rubber mounts came with the LS swap mounts. May have been poly but I don't think so.

SteveG75

Why would they give up a sale?

The front and rear springs should complement each other. The only composite rear spring they sell is a 200# TRW spring clone. If that is what they matched their front coils to, then they won’t work well with your “stiffer” rear spring.

For reference, I used to run 460 coils cut 1/2 turn with a 330# TRW rear spring. Now I run 550# coils matched with a custom 400# rear spring from VBP (before they closed doors). The rear is also 1/2” shorter on each end to help with clearance.

Bikespace

Yuck. Really?

OP, get a low-arch composite spring from Van Steel. They bought the VB&P tooling.

I have 550 springs in the front, 385 VB&P spring in the rear (also shortened), and the rear is not quite stiff enough. YMMV, but give Van Steel a call.

rabinaba

I bought the springs like a year ago, so there was no chance I could return them, but I get your point. Great, now I have to look into springs again.

Or maybe I’ll say screw it and be everyone’s guinea pig, what’s the worst that could happen 😂😅

rabinaba

I actually already bought VanSteel’s low arch 360 spring. When I called VanSteel, that’s what they recommended - they said they usually recommend 400 if you’re racing, which I won’t be.

Sounds like my RideTechs aren’t going to work, that sucks. At this point, I guess I’ll go with either a 460 (cut one coil) of 550 (not cut).

I’m fairly certain full length 550 springs lower the car, I just don’t know if it’ll be enough with the lighter LS.

Bikespace

I have the 550s (not cut) and with the L48 still in there, the front end is just a bit too high. I'll upgrade to semi-coilovers at some point. The 360 rear spring will be great.

rabinaba

If that’s the case, then I’ll probably go with 460 and cut a coil. That should bump up the spring rate a bit as well. I’d rather do that than cut a 550 spring and risk it being too harsh.

Bikespace

That would be my second suggestion. My first suggestion is semi-coilovers.

SteveG75

I would send you my 460s (cut 1/2 coil) for the cost of shipping but I gave them away years ago. :-(

Good luck