Originally posted by heinzboehmer
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Sorry for such a late comment. I don't spend much time on the forums these days so I'm a bit slow to messages and tags. Sorry if you've tried to contact me here.
Saw I was tagged here so figured I'd add some comments.
One thing I wanted to mention to this part of the discussion, I've very recently released some adjustable camber arms of my own design for those looking to purchase the CMP subframe raising bushes.
Hope you don't mind me plugging it but, felt it was relevant. https://cmpautoengineering.com/colle...le-camber-arms
Originally posted by heinzboehmer
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Also, thank you for all the amazing support for my products. I appreciate that very much! I'm glad to see you guys are enjoying them as much as me.
My take on the does solid make cracking issues worse is that in theory, there's less dampening to driveline impulses loads (clutch kick/dumps, sudden off and on throttle, launches etc) not static loads like cruising as once the rubber flexes sufficiently to transfer the force (like a spring) the magnitude is the same. I feel not many guys are launching their cars too often and even then, with sufficient reinforcement this is a mute point.
On the other hand, as the rubber deteriorates it will allow excessive flex eventually causing the steel hoop inside the bushing (to make it stiff enough for a press fit) to lunge into the chassis. This happens on even brand new bushings however, gets much worse over time. The major issue here being that there's two lobes on the stock bushings that sit proud that the steel core is in which exerts a lot of force in a very localised space. This is the causing of cracking on the front right subframe mount 99% of the time.
I have seen cars that have been reinforced with the old style turner plates that were very thin and stock bushing and have managed to deform even the plated surface. Some even cracking beneath the plates however, I cannot say this is entirely because of the bushes as I've seen plenty of dodgy repairs although, the plate deformation can't have been helping. I would personally suggest as other have, a very hard subframe bushing and stock diff bushings.
One thing to be mindful of is how the bushings retain themselves on the front studs. I've seen some cheaper options have a small hole for a snug fit on the stud on one side and a larger hole (like the rears) on the opposing. This essentially means that if the clamping force on the stud isn't sufficient the subframe can pivot around that front stud under cornering forces as well as the one snug fit stud is bearing the entire cornering force of the rear wheels. It can be tight to fit at times however, this is why I went with a snug fit on both front studs to prevent this and do what I can to insure the force is spread evenly over both.
I've looked into UHMW plastic and it's got pro's and cons. It's a self lubricating material generally used for chain guides etc or other low pressure rubber surfaces from memory. Technically there will be more flex however, IMO so minimal that there's nothing to gain however, the two piece construction eliminates the possibility of doing a raising design so there is something to lose.
I won't shoot it down and acknowledge it can be used in places such as this and possible diff bushings provided it doesn't deform like most poly's do under the pressure (as it's not as strong) although, have considered it for insert in a spherical bearing for a FCAB however, I believe there are stronger and more durable grades of plastic. Yet to get very far on that.
I personally went poly after my car was reinforce the first time and now suggest the combination of solid & stock as if done correctly gets the best of both worlds although, it is a balancing act of compromise so it's entirely down to your own preference.
A quick comment on NVH. You've got noise, vibration and harshness.
Noise is pretty basic. It can be caused by the engine, the trans, the diff which shouldn't be heard on stock bushes/mounts. Engine being injector, valvetrain, accessories and hopefully not knocking. Then you've got other factors such as induction & exhaust which are mostly desired noises and lastly environmental like tyres in motion, wind around the car, rain on the body and interior squeaks, rattles etc. Keep stock engine/trans and diff and essentially the ones you don't like that you can control won't change. I found poly subframe/diff to be much worse and can say the same for engine/trans.
Vibration is essentially a product of things that produce vibration. The biggest cause and almost the only is the engine with the gearbox and diff technically producing very very small amounts. That should be it unless you've got something rotating out of balance or alignment.
Lastly, harshness. For something to feel harsh it's generally the product of an impact (like a pot hole) this is generally related to whatever prevents the wheel from moving forward or backwards in the guards (RTAB & FCAB) or up and down (shocks & springs). I can report that the RTA bushes will make impacts harsher although, just like the subframe bushes, only when they happen.
If you are just driving down a normal section of road and not over pot holes, reflectors, speed bumps etc, nothing is pulling on the wheel and therefore you wont notice a difference at all. A bearing type RTA bush will not suddenly add vibration to the car, it just reduces the elastic dampening to impulses. On the plus side you gain quicker inertial response (like how a car will have less body roll with stiffer springs).
Upgrading subframe and control arm bushes to bearings (in the context of cornering forces) should make negligible change to NVH as cornering forces are not impacting and build up slowly by comparison as you wind the wheel around and the body rolls loading up the springs and thus pressure on the contact patch. This is where M3's had 2 of the 4 bushes mounted on ball joints joints compared to just the 1 of 4 Non-M's had. CSL's went a step further by having only a single piece of rubber in the upper in arm as they use different camber arms with the same ball joint. The advantage of doing this is more consistent camber geometry due to greater link stiffness.
In short, keep engine/trans/diff/FCAB & RTAB stock and it should feel as soft as a stock car. Everything else can be upgraded with negligible compromise. Note: Not talking about prop donuts, CSB etc. Keep those stock.
If you want to do better and have more consistent toe geometry (=stability/predictability) consider monoball RTAB's followed by bearing type FCAB's.
Hope that helps with your decision making and sorry for the long comment. Didn't mean to blab on but it keeps happening.
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