Uprated engine mounts?

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Re: Uprated engine mounts?

Post by Bigblueknight3k »

I agree also

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Re: Uprated engine mounts?

Post by warpc0il »

Did the dealer reset the front geometry, using the correct equipment?

I'd bet that your front camber has been left at random angles, which would explain why it's not handling as well as before.

Very few dealers have got access to the required kit, as virtually every other car they deal with only has toe-adjustment.

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Re: Uprated engine mounts?

Post by Freeman38 »

warpc0il wrote:
Sun Mar 31, 2019 3:52 pm
Did the dealer reset the front geometry, using the correct equipment?

I'd bet that your front camber has been left at random angles, which would explain why it's not handling as well as before.

Very few dealers have got access to the required kit, as virtually every other car they deal with only has toe-adjustment.

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Unless you have fitted poly bushes your talking from no experience on the RX8. If it hadn't been an improvement I would have called it out as I have with some of the other changes. I had my aliginment checked by wheels in motion to my settings from Centre of Gravity. Both highly reputable and experienced outfits.
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Re: Uprated engine mounts?

Post by warpc0il »

It's the design and not just the materials that differentiate the eom bushes from polybushes.

An oem bush is a single unit comprising multiple layers of materials bonded together, such that movement is controlled/allowed in different directions, up/down, side/side, rotation and tipping, by the stiffness of those materials in tension, compression and torsion, as a single component.

A polybush is an assembly of multiple elements of different materials, fitted with a lubricant between the surfaces. The aim is the same, to control those movements by just the compression of the resilient material, there being no tension or torsion.

There are multiple designs of polybush and an infinite variation in the stiffness of the materials chosen, so the results can be equally different.

The RX8 suspension includes multiple bushes and these are subjected to widely different loads, through the weight of the car on the suspension, and the forces induced during corning, acceleration and braking. Most are key to maintaining the required wheel geometry in the required way, and not always by being as stiff as possible; the movement created by lateral loads on the rear suspension provide a small element of rear-wheel steering and assists turn-in, but I digress.

An ideal polybush can provide the same, or better, lateral control as the oem, usually at the expensive of increased resilience in the other planes, which increases NVH (noise vibration and harshness). This may be a compromise that you're willing to accept, especially on a track-orientated car.

A poorly designed polybush can provide both less control, either through the wrong materials and/or too much clearance, and still increase the NVH.

The impact of time and usage are very different between the oem and polybush components. A poor choice of materials and/or insufficient lubrication can mean that a polybush that was good when first installed can become wrecked within a relatively short time.

Add-in the variables such as road grit and salt, pressure washing, steam cleaning, chemical attack from solvents, rusting of steel, corrosion of aluminium, electrolytic effects between metal, and polybushes can age prematurely quickly.

The eom bushes age too and the "rubber" can harden or soften and will eventually start to crack or tear.

Incorrect reassembly, especially of the front arms can result in the bushes being clamped with the suspension fully extended such that there is a permanent torsion on the bushes when the weight of the car is applied. This will cause premature failure of the bushes and means that the car sits higher than it should. This should be obvious when just replacing the arms - though many dealer have got this wrong in the recent round of recalls - but might be less so when fitting "lowering springs" as there will still be some drop compared to before. Polybushes have the advantage of being immune to this effect.
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Re: Uprated engine mounts?

Post by Dr. FrankenRex »

I'm gonna have to disagree Dave. For a stock car, being used primarily for road use then you are probably correct, the OEM mounts provide a nice mix of flex with a good solid core to provide rigidity, but for something that is being used for hard launches, flat out track work and consistent competitive driving then a polybush will be firmer.

It's horses for courses and, whilst the OEM fit a nice broad sub-set of courses, they aren't for every horse or course.
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Re: Uprated engine mounts?

Post by warpc0il »

So which part of this...
warpc0il wrote:
Mon Apr 01, 2019 8:43 am
An ideal polybush can provide the same, or better, lateral control as the oem, usually at the expensive of increased resilience in the other planes, which increases NVH (noise vibration and harshness). This may be a compromise that you're willing to accept, especially on a track-orientated car.
... are you disagreeing with?
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Re: Uprated engine mounts?

Post by Dr. FrankenRex »

warpc0il wrote:
Sat Mar 30, 2019 7:19 am
That could be the problem, as polybushes are a downgrade, when compared to the oem design.

viewtopic.php?f=6&t=78199&hilit=polybush
This bit :)
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Re: Uprated engine mounts?

Post by PeteH »

I think there is an element of "inventing a disagreement" here! And we are moving quite a long way from the subject of uprated engine mounts....

Dave an I are both from the automotive industry, where polybushes are generally laughed at. That's why we are both of the same mind on this one. Polybushes are very compromised. They have their uses, and I should declare that I have polybushes on the front of my race car, but I did it with my eyes open. These are the pros and cons as I see them:

Pros:
- They are much cheaper, easier to source, and easier to replace, than OE bushes.
- They are generally "hard", and that an make the car feel "sporty".

Cons:
- They are not developed. They are just designed to fit in the available space. The design is dictated by the space the OE manufacturer chose to use for the OE rubber bushes.
- They are all made in the same grades of polymer. Only a very restricted range exist (e.g. 'black' or 'red' grades, etc.)
- Polymers have almost no damping, compared to rubber bushes, which means they don't damp vibrations and noise, and can set up nasty resonances.
- The manufacture put huge effort into designing the overall compliance modes of the suspension to give a very specific set of "kinematics and compliances". This was done specifically to improve the safety of the car, by inducing a safe set of toe, castor, and camber changes in response to all the various inputs the car might see. Polybushes throw all of this careful tuning out of the window. The kinematics and compliances are now a random hotchpotch of behaviours that no-one ever tuned, or even bothered about.
- They can't be designed with interleaves, pockets, oil-filled damping chambers, sophisticated snubbing elements, multi-compounds, or any of the many other design elements that OE engineers can design into rubber bushes to makes them do really clever things.
- They have moving bits, so they wear out, and require constant maintenance to keep them clean and lubricated. When car manufacturers had these sorts of designs they used to incorporate grease nipples.....
- Because they have moving parts they can make squeaking and graunching noises.
- Because the inners slide (instead of being bonded like a rubber bush) the ends of a polybush have to include "snubbers". These restrict the longitudinal movement of the bush. This is forced on the design of the polybush, and prevents the car's suspension from complying in the way it was designed to.
- Polyurethane is not very resistant to most forms of oils and petrol. It is not at all resistant to brake fluid.
- Because the components they are put in were never designed with pu bushes in mind they can substantially increase the stresses in the components. An example of this is the Range Rover leading arms (the "hockey sticks"). If you polybush these and drive the car off road a lot you are at high risk of snapping your axle in half. The compliance of the OE bushes was tuned to limit the torsional stress on the axle, and provide a known amount of roll stiffness. Polybushes transfer all the torsional load into the axle casings.

Polybushes can be suitable for some situations. They can be good in kit cars, where the loads are so much lower, and the refinement isn't important. They can be good on competition cars, where you don't care about what the car designed wanted to achieve, you only want the most rigid mounting for the wheel. But they are massively compromised, and will significantly change the behaviour of the car.

When I went from rubber bushed rear links to Japspeed balljointed links the car lost all its throttle adjustability. You won't be particularly aware of just how much the bushes are contributing to the safe feeling of your car, but when you accelerate in the middle of a turn the rear bushes toe the wheel inwards, and cause the car to understeer a little more. If you start to run out of road, and have to lift off a bit, the bushes will cause the car to oversteer just a little bit, which will tighten your line, and keep you on the road. My track car doesn't do this. It relies on the driver getting it right, and isn't at all forgiving.

When I went to polybushed front links I didn't notice any improvement in the lateral behaviour. The car became noisier, harsher, and the ride was poor, but the basic handling wasn't improved at all. Why did I do it? The longitudinal movement was eliminated, which meant that I could brake into bends harder and later without the car changing it's line, and the steering stayed heavier, which gave more feel on turn-in. I wouldn't want to drive the car on the road, because the steering is so heavy that it is a constant effort to get the car to go where you want it.

Each to their own. And do what you want. But don't imagine that a generic set of injection moulded polybushes can even get close to matching the sophistication of the carefully designed, tuned, bonded, damped, elastomeric set of OE rubber bushes.
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Re: Uprated engine mounts?

Post by Goobie »

Excellent posts from Dave and Pete above.

Back to engine mounts, lol.

I fitted RX Performance to my R3, I like the more solid feel they give and the sharper clutch bite sensation from less engine movement personally. It suits my driving style more. There is more cabin vibration, but nothing really worth mentioning as so little and only on pulling away from stand still.

Anyway, I will be swapping them out as I have a set of Carl's mounts (Ryan Rotary Performance), these are a thing of beauty! I believe they are a very soft ish polly mix? There was a lot of testing till he released the final version I think?, this was some time ago now so don't quote me on that.
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Re: Uprated engine mounts?

Post by 13Black »

Words words words words words words words words words.

A video of PU engine mounts doing their thing.
Something a lot of people seem to forget / not mention / not realise is that they retain ALL of their upper rubber component which is by no means insignificant.
It's not like new PU replacement mounts for some other cars that do away with all of the rubber and replace it with 100% metal and PU. Mmmm lovely. This is probably why the BHR (and possibly RRP) mounts are that bit harsher than a PU/rubber hybrid.
I've handled some of the eBay items and they seem to be made with a softer shore PU than what these below were made with - you could quite easily dig a nail into it.




You can be fancy and use a softer shore for the upper part to help keep some flexibility and use a harder shore for lower to resist sag.
Mans also has a jig for filling them that pre-stretches the top part (so you end up with the mount's 'ledge' in the middle of the space in the aluminium bracket) as it seems that the rubber part likes to naturally 'sag' after enough use - otherwise you could fill them in that already-collapsed position and have to deal with the rubber bumpers hitting the aluminium bracket still.
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Re: Uprated engine mounts?

Post by RenesisRaceBuggy »

They still won't have the performance/NVH suppression range that that the liquid damped OE ones would have. But if you want harder mounts you have little option.
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Re: Uprated engine mounts?

Post by 13Black »

Oh no absolutely not - but is the reduction in NHV with OEM mounts worth a price tag ~4 magnitudes higher... for a lot of people, I highly doubt it.
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Re: Uprated engine mounts?

Post by Phil Bate »

When I started playing with PU filled OEM mounts I found that to have them soft enough not to buzz the car meant that the suspended drive train would resonate (wobble) over bumps. It was only a very subtle bouncing but I could feel it and knew what it was straight away. And it annoyed me. After briefly dreaming up a wild array of supplementary dampers securing the engine to the chassis, I decided it would be a project too far and happily stumped up the 200-odd quid for a new set of oil bags.

Some people won't notice it, and others will be more than happy with harder full PU mounts, but the damping was worth it to me. I've put two sets on in seven years and 50k miles, the second set seem to be lasting better (I think they were a later revision) but I'll buy a third when these fail.
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Re: Uprated engine mounts?

Post by bigpete8 »

If I could have found them for 200 maybe.... Think when I looked they were nearer 400 for the pair. (vs 99 for refurbs)
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Re: Uprated engine mounts?

Post by PeteH »

Only the driver's side usually fails though, so usually you should be able to just change one. (You don't need to do engine mounts in pairs)
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Re: Uprated engine mounts?

Post by bigpete8 »

I still have both the old ones and to be honest they seem to be pretty similar shape to me. - Can you test them off the car?
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Re: Uprated engine mounts?

Post by RenesisRaceBuggy »

Phil Bate wrote:
Mon Apr 01, 2019 11:18 pm
When I started playing with PU filled OEM mounts I found that to have them soft enough not to buzz the car meant that the suspended drive train would resonate (wobble) over bumps. It was only a very subtle bouncing but I could feel it and knew what it was straight away. And it annoyed me. After briefly dreaming up a wild array of supplementary dampers securing the engine to the chassis, I decided it would be a project too far and happily stumped up the 200-odd quid for a new set of oil bags.

Some people won't notice it, and others will be more than happy with harder full PU mounts, but the damping was worth it to me. I've put two sets on in seven years and 50k miles, the second set seem to be lasting better (I think they were a later revision) but I'll buy a third when these fail.

Maybe one for the suppliers of uprated mounts on here - but I've made OE style mounts before by just re-using the valve disc and flow channel out of the OE mounts and casting around it before, if you use a fill port you can then fine tune the damping to match your stiffer poly just by tuning the weight of the liquid (as they're only a low-speed path with high hysterisis and a floating disc to allow small HF movements through, so the fluid weight doesn't really affect the high frequency circuit much at all)
May be a pain in the ass to automate for low volume batches though.
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Re: Uprated engine mounts?

Post by Torque23 »

I read through this whole thread and found it interesting as I think my driver's side mount has collapsed slightly as it does not appear to be sitting in the middle of the slot. I get a bit of vibration from the chassis at all speeds but I also have issues with brake judder and the wrong staggered aftermarket wheels being fitted which are being changed to the PZ wheels with new tyres which should eliminate the wheel related issues. The main issue I note is going on and off power at low engine rpms, the drivetrain slightly jerks shaking the car forwards and backwards when going back on the throttle. Is this a typical symptom of a failed engine mount?

An interesting note I found regarding PPF alignment is found here and copied below: https://www.rx8performance.com/pages/tech-tips

MOTOR MOUNTS AND THE POWER PLANT FRAME OR PPF
The RX-8 does not utilize a traditional transmission mount, instead it uses what is called a PPF. This is a steel back bone that connects the rear of the transmission to the front of the differential. The front mounting points of the PPF are four slotted holes that are slipped over the four studs located on the rear of the transmission. When changing the clutch, flywheel, engine or transmission these four (4) 21mm nuts are usually loosened or removed.
When reinstalling the PPF after major work there is a specific adjustment range of 55 -57mm that sets the engine, differential and driveshaft angles to ensure optimum performance. This procedure is discussed in the factory workshop manual section(s) 05-11-7 (manual) and 05-13-42 (automatic). If the technician or owner was not aware of this factory alignment specification (pretty common), the nuts are likely to be reinstalled in the wrong position making the alignment incorrect. Alternatively, if these nuts were loosened and adjusted to the factory recommend settings and the OE motor mounts were worn, broken or sagging it will be out of the specified range.
After installing your new RX8Performance motor mounts take a quick look along the slots in the PPF and check for markings where the paint was scratched when the 21mm nuts were previously installed. If there is scratched paint in a different location than where the nuts are currently, it is likely out of adjustment. We suggest you take a few minutes to setup your PPF as Mazda had intended. By aligning the drivetrain components to the correct angles you will eliminate any preload on the new motor mounts and will reduce NVH throughout the drivetrain.
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Re: Uprated engine mounts?

Post by PaulAV »

I would recommend checking the differential mounts and the rear control arm bushes if your noticing a jerk going on and off power
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Re: Uprated engine mounts?

Post by warpc0il »

Does the gear lever move as you come on/off power?

If it does then it's the engine mounts.
If it doesn't then it's the diff and/or rear suspension.
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Re: Uprated engine mounts?

Post by Torque23 »

warpc0il wrote:
Wed Aug 04, 2021 2:53 pm
Does the gear lever move as you come on/off power?
I paid extra attention today and no the gear lever does not appear to be moving coming on and off power. If I mash the throttle pedal a bit quickly coming back on power, I can feel the car jerk to and fro about 2 or 3 cycles before power is on smoothly akin to say a loose motorcycle chain slack being taken up before latching properly , more so going back in throttle than coming off.
Where and how do I check for the rear diff and rear suspension arm bushes?
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Re: Uprated engine mounts?

Post by Torque23 »

PaulAV wrote:
Wed Aug 04, 2021 2:37 pm
I would recommend checking the differential mounts and the rear control arm bushes if your noticing a jerk going on and off power
After a few more drives I can see there is no real change is movement of the gear lever when going on or off power except for the usual slight wobble at all times. There is a slack in the drive train going on power which makes the chassis "chug" to and fro, more noticeable when blipping the throttle a bit enthusiastically at lower revs about 3k rpm +/- 1k rpm. It is still there at higher rpms but it happens a bit quicker so less noticeable.

How should I check the diff mounts and the rear control arm bushes? What am I looking for? And most importantly how difficult are they to replace? I found the attached diagrams.
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Re: Uprated engine mounts?

Post by PaulAV »

The rear arms are best checked with a pry bar, to try and move them so you can check for play and damage (a visual check may be enough if they are torn or cracked but not always) imagine the diff would be similar. Bushes aren't the easiest to swap and the arms can be a pain to remove as the bolts like to rust inside the metal sleeves. But at least if you find anything split it worn your a step closer
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Re: Uprated engine mounts?

Post by warpc0il »

The "problem" might be being exaggerated by your driving style.

Try driving one ( or even two) gears lower, so the revs are up above 4k rpm, and see what difference it makes.



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Re: Uprated engine mounts?

Post by Torque23 »

warpc0il wrote:
Fri Aug 06, 2021 11:34 am

Try driving one ( or even two) gears lower, so the revs are up above 4k rpm, and see what difference it makes.

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I usually drive at high revs well over 5k rpm once warmed up and I could feel the slack going back on the throttle. So I decided to 'experiment' at lower gears to intentionally exaggerate the movement to see what was happening. Are you saying this slack is normal? Never had it in any cars I have owned before. In fact Mazda seem to claim the drive train design is rigidly designed to get the feel of instant response and power transfer. Unfortunately, I am a bit tuned into the mechanical feel and noises and if something catches my attention and I have not found a satisfactory resolution, it will continue to detract my driving experience. :)