One might think so. Is this statement based on actual comparison testing or is it based on what you expect from the resilient properties of the two materials? If the former, can you describe the methodology used?

I ask b/c of Steve W's very clear statements (see above). Chuck M. also has some diagrams posted on his web site.

I'll also add that Porsche designed this suspension in the late 1950s and early 1960s. As Lou Reed once said (in a somewhat different context) "Things have changed."

Moreover, any OEM has multiple factors they optimize for -- and one is usually cost. We often relax that constraint when compared with Porsche. Then there is maintenance as a constraint.

My car's noisy enough with my sport muffler, premuffler, sound pad removed, etc. that I probably wouldn't even notice a bit of extra noise transferred, but I sure don't hear it. To play devils advocate to your premise however, how do you know that the "Poly" portion doesn't isolate/reduce the noise transfer even moreso than rubber would? That would seem to be a pretty decent sound cushion between the bronze bearing portion and the rest of the car imo. I wouldn't assume they're noisier...ride in a well sorted car with polybronze, and you'll see :)! Your point is well taken however, I hadn't considered that aspect at all.

I am reading every one of these posts, so if anyone else is out there that wants to chime in, please do. If for some reason you are hesitant about posting in this thread publicly, then please, I encourage you to send me a PM. Thanks!

I am getting ready to do these bushings on my car. That said I track my car 6 to 8 weekends a year. Not to mention I am the only one that rides in it except my son. My wife won't ride in it any longer since I put the race seats/harnesses and roll bar in it.

If my car was a street only car I probably would not go to these bushings. Not that I believe they will be too stiff or too noisy but I personally think that stock is perfectly fine for the street. I think this stuff is overkill and more costly than needed for the street.
Just my.02

Noise isolation is caused by a stiffness mismatch between the chassis / control arm structure and the rubber bushing. It's basically a 3 dof spring/mass system. It's just math, nothing new here (though obviously the torsion bar 911s did not have very fancy bushings - they do not appear to be designed specifically for isolation in any way...) Isolation gets better as the stiffness mismatch gets to be greater - we shoot for a factor of 10 when designing chassis structure. I'm not smart enough to derive the equations that prove all of this, unfortunately, but I have seen it done... maybe I can find the presentation some day.

The urethane, being thin and having large surface area, is going to be quite stiff. It will not provide much isolation.

Again, I'm not knocking PB's. My car was clearly riding on the torsion bars during bumps (as evidenced by the 1mm deep wearmarks), which is metal to metal and isolates nothing, and I didn't find the ride horrible or objectionable (though it was harsh - may have been the tbars impacting the A-arm that caused the harshness), so I believe the PB comments. But it did get noticeably better when rubber was back in the picture.

The point is simply that rubber has to isolate better than no rubber. Wether or not this isolation matters or is even noticeable? Depends on the car, the roads and the driver...sounds like for many 911 folks the answer is "NO".

So, did you do any actual comparison testing?

Also, there is no need to derive the equations -- but all mathematical models are based on sets of assumptions. We don't have the assumptions for the models you describe narratively.

I personally don't know if the polybronze reduces NVH below that of (new) stock rubber or not. I'm just wondering how this stacks up with expert opinion, as quoted above. It would be better if we had statistically valid trial data. We don't.

I find this discussion somewhat intersting but I think there are many factors (bushings, T-bar size, tire aspect and width, bump steer, corner balance, alignment, shock travel, ride height, and compression/rebound rates, sway bar size and settings, driving style, road surfaces, etc) that go into what constitues what one perceives as a good vs bad ride (ie squeeking, harshess, body roll, etc).

Without knowing the exact configuration of a given car and your personal preferences, it is very hard to tell if another person will find the ride better or worse. We can go around and around on this topic and still not know anymore than we know right now.

Ultimately, you pay your money and you take your chances.

As many of you have already seen, I advocate spending some quality time with a local shop that specializes in setting up 911's and go from there. I know the time I spent discussing my needs with Steve Weiner and Jeff Gamroth (plus repaying them by purchasing my needed goods and services from them) were well worth the effort as I like what I have now.

I installed rear PB bushings last winter on my 84 targa since the rubber ones were worn out. This was after reading a bunch of posts here on all the various options and pros and cons. Did it myself, working slow and it took about ten hours start to finish mostly because it was the first time I had been into the suspension of one of these cars.
I was really impressed with the quality of Chuck's product and I also wanted something that had the ability to grease as needed.
In the spring I replaced shocks and installed PB in the front with the self adjusting washers and mono ball strut mounts and plates. Also upgraded to hollow t bars. At this point, all done, including corner balancing and alignment.
Ride is slightly firmer due to slightly larger bars but certainly not harsh. The entire combination is really nice and I drive the car every day, all year, no matter what. Did all the work myself with help from all the posts here, from Bentley, and Chuck spent about an hour on the phone with me, great guy.
Karl

assumptions or principles?

It's obvious to me that burgermeister has a MUCH better understanding of the principles involved here, than most. Your labeling his (deeper) understanding as "assumptions" is pretty weak. IMO

And, what about the "logic," often thrown about here, that the PB "firms-up the pivot, but is still as compliant as stock" ? :rolleyes:

Jon

For your use (street, not competition/DE), I'd take Chuck Moreland's advice and rebush with rubber. The factory knew what they were doing in designing a sports car for street driving - good handling and control, but a comfortable ride. And 30 years is good service from a part that gets twisted every moment of its driving life.

I realized this not long after I had installed bigger bars and polyurethane bushings and lowered the ccar: I had taken a car that was fun to drive on trips and make it kind of uncomfortable. That didn't stop me from using it for street and track (daily driver), but it did make me wish I could afford two 911s, one for each purpose.

And when a guy who sells stuff suggests you buy something less expensive but better fit for your use, the advice gains some extra credibility in my books.

Walt Fricke

Isn't that what Porsche said when they went AWAY from the model-T era "technology" of messy, time consuming zirked/greased bushings? http://forums.pelicanparts.com/suppo...ool_shades.gif

I did the same, and that's sound advice for anyone. I'm not sure Steve was using Chuck's polybronze bearings at the time, but the jury was still out back then, and they weren't part of my discussions. I'm just a novice and these guys know a LOT more about these things than me, but I'm still learning, thanks all :)!

I agree. My alignment shop asked me what use my car was put to and when I said road they questioned why I had used 22/31 t/bars - I have to say I can see where they are coming from now as the (bumpy) road handling has now been compromised.

Ever notice how small, drawn-out dips in a road become big bumps, when at speed? --yep, compliance in suspension seems to really help keep the rubber on the road.

As to rubber mounts, I always think back to my motorcycle days, when rubber mounts for m/c engines became more common place. That technology made a HUGE difference in how long I could ride. Why anyone would want to go backwards with "technology" is beyond me. ...Simple, noisy, mounts are not a step forward. They provide no solution to isolate out undesirable impulses. What next, a carbon-fiber seat (no padding)molded to your naked body .... you know, for that maximum road feel? :eek:

I have a carbon fiber seat. :D I should take the padding off you say? (sorry..had to throw one in there for "island" it's been a long time since I posted on the same thread as you :D)

Please do NOT post pics of a carbon-fiber seat (no padding) molded to your naked body. Exception: attractive women.

"Albums played through tube amps" is "old technology"
"CDs played through solid state amps" is "new technology"

It's just not crystal clear to me sometimes :)

... and what really sucks is that new-tech hyper-compressed digital processor decoded and amplified thru tinny little ear-buds "i-pod/i-Tunes" thing. :D

I suppose that the key to new technology, which is worse than the old, is to package it in a shiny shiny box! ..tho' shiny shiny metal parts seem to carry a lot of 'buy' impulse too. :cool:

Island, in some strange way it's actually flattering that my products occupy so much space in your brain.

Yeah, for some reason those products that tout engineering (but miss that mark) sit awkwardly in my brain. It's the "What were they thinking" category. :confused: --lots of products in there with ya Chuck. Yours lower than so many cell phones, if that makes you feel better. :D