NVH - over the edge

[jcmGT]

Knew it would come.

Really liked the smoothness of the g8. Over time I installed cradle bushings, new trail arms with poly bush and diff poly bush. While change was not significant, it was present and acceptable. I played with exhaust, eventually fabbing my own with muffled xpipe, enlarged resonators and rotated between mufflers (OEM GT, Super turbos, ultra flows and my GT Bi Modals). My favorite to date is the ultra flows with the downfalls being the annoyance of when 4cyc mode. None of the muffs "droned" enough to comment on.

So, last weekend, in went Xa's, new toe rods (poly bush) and Poly bushes in rear LCA. That did it. Local roads are fine, highway, not so good. While road feel is great, seemed to have picked up much more road noise- not loud, but subtle. This new chassis noise combined with exhaust noise - well pushed me a bit to far such that the highway is no longer pleasant, but annoying -like grain of sand in the shoe.

So, before forwarned - too much poly may not be good. I'll play with the Xa settings, but the vibrations felt, I suspect are due to the additins of the poly bushing. I'll be messing with the Xa settings, but suspect the frequency may be to high for the shocks to react to. And back to be Bi-Mode exhaust, see if that calms it.

Always something.

[Napalm]

I'm glad to see someone admit it.

Interesting is you have pedders stuff I assume you have a pedders strut top bush also. is it harder (physically harder) than the OE one. I think they are by a bit.. might consider 2 things to take some noise out.

what all do you have?

Might you need new tires?

[todds87ss]

I've heard similiar complaints by coilover users. I am interested to hear what happens when you adjust them softer. I suspect you will be happy. Most folks love the stance; hate the NVH (or have a really high tolerance for NVH).

[jcmGT]

FWIW:

BMR: toe links arms, cradle bush, diff bush, sway bars
Spohn: trailing arms, sway bar end links
SuperPro: rear LCA bushes
Pedders: coilovers

Not a tire issue as they don't change over night and are in same locations. Strut top is pedders, I do have a new set of GM, they appeared and felt the same to the hand (texture / flex) with a little different mold design

Have already swapped out the exhaust, but not driven it much. My next planned interstate travel is two weeks. I'll be able to do some sorting out them.

I must say, with the settings 16 front and 12 rear, very much a toad.

The positive side, the extra NVH brought back memories of riding in my brother's '71 boss 351 back in '72

In general, I don't think what I'm getting is unexpected, no blame on any parts from a quality/expectation perspective.

[GT Drew]

I have wondered/worried about the stiffness of the poly bushings. The poly can be produced in any level of stiffness, measured with a durometer. There are also different ways to regulate the stiffness. Pedders puts small voids in the rear diff bushings for the street version. BMR has 2 different stiffness polys, one for street, one for track for the diff bushing. Of all the brand, who's poly is the softest and street friendly????

[G8V8]

I have every Pedders bushings they make. Spoon toe links, pedders super car v8 coil overs and I do not NVH issues as you describe them. This is very subjective. Pedders tested and refined their bushings during development to provide increased control without going so far that NVH suffered too much. What I have from Pedders was engineered to work as a package. I am very pleased with it. I do not know what R and D others put into their bushings designs.

Remember the new dampers will require some time to break in. The Pedders strut mounts are rubber and while harder than OEM, I believe they are more NVH friendly than the poly units from BMR.

the best bang for the buck for handling improvement without I'll effects in NVH are the Pedders rear subframe bushings inserts, front radius rod bushings and caster washers. These will tighten up the suspension without adding NVH issues. Next, the street diff bushings.

[jcmGT]

all the bushes are "street" when offered. Front Xa's have <10K, rear Xa's are virgin. It may be a simple as rear Xa few clicks less. I'll find out in week and half

[Napalm]

I have always wanted to know what the HSV cars come with and why can't we get those types of parts over here.

I would love to have a solid rubber sub frame bushing, althought I like the poly inserts.

Have Solid rubber replacements for the front and rear LCA's etc etc.