It is arrogant, and inappropriate for you to make an assumption about a car you have not seen. The problem with this car ABSOLUTELY is the mounts. I know this because the vibration was not there, then the mounts were replaced (by a competent mechanic), then the vibration was there. I have owned, built, and raced several rotary powered vehicles for 27 years. I know a little bit about what I am saying .

What you have failed to consider is the level of vibration. What I consider to be a horrible vibration, others may consider to be a relatively minor vibration. Either way, the solid poly mounts are ABSOLUTELY to blame.

 

No, they are NOT.

Let's get this straight, motor mounts do not vibrate. Something else is vibrating and the mounts are transferring that. The stock mounts are so soft that they can easily mask a problem that is not apparent until they are replaced.

I really do not care about how "tender" you are, the fact is that motor mounts are not the cause of any vibrations. It is exceedingly arrogant of you to tell people that "Your entire car will vibrate. They directly transmit every engine vibration to the frame. Trust me, you will HATE it!!!!" , when you really know absolutely nothing about motor mounts or how they function. Additionally you refuse to consider that something else is doing the vibrating. All of your statements thus far in this thread have been "total bullshit"

I have personally installed hundreds of set of mounts and have first hand knowledge of how much vibration they transfer and how quickly it dissipates with break in.

 

i just wanted to mention the op of this engine mount discussion wanted to know how to install mounts, how hard etc, i find no real good info on a couple of guys going back & forth arguing about mounts, imo just cloging up what could be a good post with good info for when a noob is searching engine mount swap?

 

Second that...I just turned some mounts down on a lathe, only cost me about 20 bucks in material and was the best upgrade. However, I havent driven my car in over a year so I dont remember all that well. It wasnt bad though. Now all I need is engine torque brace and I should be set for spring time!

 

adam c think of it this way, if your friends car was not running there would be no vibration whether it has solid mounts, no mounts, or rubber mounts. Most rotaries are so well balanced that they run this smooth. The solid mounts can't transmit a vibration that isn't there. Now if you have an engine and one rotor was half a pound heavier then the other, the engine would shake like hell and have serious vibration. The solid mounts would transmit this vibration, the rubber mounts would mask it. Engine mounts will only transmit what the engine is doing. If you held a solid mount in your hand it wouldn't make your hand vibrate. It is impossible for an inanimate object to be the cause of vibrations. So the engine is the source of the vibration indicating something is out of balance. Maybe a lightweight flywheel without the counterweight or something.

 

adam c, stop while youre ahead.

yes there MAY be added vibrations when you are replacing soft spongy rubber engine mounts for a hard piece of urethane, the stock mounts are designed to absorb vibration. in contrast urethane mounts are designed to improve feel and performance, they do that well.

if you dont like the way the feel, dont get them, plain and simple. most fd owners are willing to sacrifice a little comfort for performance gains.

 

You are correct, motor mounts do not cause vibrations. I never meant to say they did. However, they can/do transmit vibrations. The only real question is how much. Obviously, solid mounts will transmit more vibrations than stock mounts. Some people don't care about about it. Others do. I don't like vibrations, and my friend doesn't like them in his car either. When he gets around to reinstalling his stock mounts, his vibrations will be gone. Just like the car was before he installed them.

You are a fool to think that solid mounts transmit no vibrations. If they didn't transmit any vibrations, solid mounts would be OEM equipment. The Mazda engineers knew better, but apparently you don't.

 

The point isn't whether solid mounts transmit more vibrations then stock. It's that their shouldn't be any noticeable vibration to begin with. If there is, there is something wrong (that needs to be addressed) no matter what it.

thewird

 

Give it up pal. You have already proved beyond a shadow of a doubt that you are the ignorant fool. Are you just arguing for the sake of trying to convince someone (or yourself) that you are right? I will not be responding to any more of your posts in this thread as they are not constructive, good luck with your crusade...

Mazda engineers developed an aluminum arm bonded rubber driver's motor mount that ruptures almost instantly, I do not put too much credence in their motor mount development skills. They even wrapped them in a steel band because they knew how quickly they would fail and had to have something there to stop the engine from just bouncing around in the engine bay.

 

This statement is meaningless until you define exactly what you mean by 'vibration'.The issue for all automobiles is usually lumped together as 'NVH"--noise,vibration and harshness.All rotary engined cars have there own particular issues when it comes to NVH and if you read the history of Mazda's rotary engine developement there were NVH issues to overcome.

Anyway the fact that Mazda chose to use 3 liquid filled mounts,two at the rear and the left front,demonstrates that there are NVH issues to control in the drivetrain.Not just the engine!

The performance advantages of solid mounts have been demonstrated,but obviously the comfort factor must and does deteriorate.Then this all becomes subjective,and a matter of personal taste and hierarchy of needs.

My main point here is to absolutely contradict those who say that rotary engine and drivetrain does not have vibrations,because it does!

 

All mounts transmit vibration. It's simply a matter of how much.

Dave

 

Just about any rotary engine will have some vibration at idle. That's when my friends vibration is at its worst, because of the solid mounts. With a ported motor, the vibration (at idle) will be worse. The bigger the port, the worse the vibration will be. Many of us daily drive our cars. With solid mounts, that means sitting at stop lights at idle with a vibrating car. For me, that is unacceptable.

The guy who is on the track at high rpm isn't likely to feel anything. Some guys don't care if the car vibrates a bit at idle. Solid mounts may be perfectly acceptable for those people. Most of us don't track our cars, and don't want a vibrating car at idle.

While that is true, it is a misleading statement. You fail to mention that the bad aluminum OEM mount was only on the drivers side. The passenger side mount was steel, and was not prone to failure. You also fail to mention that Mazda upgraded the drivers mount to a steel mount after discovering that the aluminum mount was a poor design. You probably don't mention that to your customers either. I'm sure its much more profitable to just sell them two of your poly mounts, and charge them for installation in the process. Those same customers are probably expected to get used to the new vibration at idle

 

The poly mounts WONT make the car vibrate like crazy. They WILL result in a huge reduction in rear end wheel hop and a major increase throttle response "feel" since the engine isn't rocking anywhere near as much as the stock marshmallow mounts. I've compressed *new* FD mounts within several mm with my two hands, and installed, the stock mounts allow the engine a very surprising amount of rocking. Plus there's always the option of using just one poly mount.

 

If you are really scared of added vibration or whatever these fellas are arguing about, I would just get OEM mounts and get a solid torque brace.

 

This is too funny

The guy even quotes me in his post:

Mazda gets in excess of $250 per stock motor mount, so over $500 per pair. We change $250 for the set (Aluminum arm modified) shipped or $130 for the pair shipped if the customer has steel brackets. We make it very clear that this is an option.
http://www.banzai-racing.com/polyfd_motor_mounts.htm

 

Dude, I'm by no means an expert... but it sounds like you and your friend have overlooked this little thing good builders would take into consideration called "flow balancing"....

If the more you deviate from stock (porting) the worse the vibration gets than it seems pretty obvious that YOU are making the engine shake at idle. Don't blame the mounts for that one

 

This is correct. My race ported 13b-rew with 35R had a silky smooth 800rpm idle, with absolutely zero vibration at any RPM. We now have a similar setup in our 91 vert with an agressive SP 13b-RE w/35R and have zero vibration. I am expecting the same outcome with our new agressive SP 20B w/Gt42RS.....

 

Thank you. Anyone else bother to read this ???

 

This is probably one of the few factual statement in the whole thread. There will be NVH increase with most if not all stiffer bushings or manufacturers wouldn't bother with expensive, liquid filled bushings in various parts of the drivetrain and suspension.

 

Everyone is focusing on bashing how about we stick to more helpful info...

What exactly would cause the NVH that people might experience?

I've been considering poly engine mounts but NVH is a concern for me as I have had both good and bad experiences with poly bushings in different uses.

 

I honestly do not know what is wrong with his "friends" car. If the "entire" car is vibrating I would start with a compression test. If the engine is drastically unbalanced (example 110, 110, 110 front & 85,85,85 rear) then there would be noticeable vibration. It could be as simple as bad tuning, you would be surprised how many overly-lopey idles are a result of poor tuning and not huge ports. On the other hand if it is bridgeported it will be lopey, but that is to be expected and one certainly would not expect stock vehicle feeling from this type of port. It could also be a flywheel out of balance, this has been an issue with a few LW ACT FWs that I am aware of, or it could be an improperly resurfaced stock flywheel....the list can go on and on. However on a properly balanced, even compression engine, with stock or street porting there is little to no vibration transfer with poly mounts.

If you are looking for completely stock feeling then stick with the stock mounts, pretty simple actually. Just do not expect the car to perform as well, for instance do not try slamming 3rd in a race as you will accidently smash 5th , because of the allowed flex and you will crack the syncro...

 

^Sorry, I didn't mean about adam's friends car specifically. I also have experienced the issues you mentioned regarding bad tuning causing a bad idle lope that would cause the car to shake and vibrate.

Thanks for listing the other factors that might affect NVH. I'll keep that in mind on my next build. I'd like to use some slightly stiffer than stock mounts to decrease the amount of twist in the drivetrain on road courses provided that they don't result in annoying street driving experience.

 

I installed poly mounts on my car and they increased the vibration I felt. I didn't mind because it was a sports car and it was minimal. I drove my friend's FD with all stock engine and diff mounts, and stock twins and it was like night and day. His car was WAY quieter, WAY less vibration. We make little compromises with every modification and so with a single turbo and poly engine/diff mounts we think that we just made improvements...

When we ride in a proper car, that is stock, then we see the difference. I think the reason most people think Poly mounts don't add vibration was because they were used to the old worn out mounts. Good stock mounts do have their advantages.

I gave my poly mounts away... but, that being said, the Poly DIFF mounts are ESSENTIAL in my opinion!

The stock rubber/steel engine mounts are adequate as long as you have the rubber/steel on both sides. That AL/rubber mount was totally worthless.

 

Actually my 93 still has the original aluminum motor mount with rubber and oil.Car has about 58k miles.I don't track the car but like to drive fast,but I am gentle on clutch and gearbox(yep still original 5th syncro).

 

There is nothing wrong with my friends car. It has a low mileage engine, with a mild street port. It has a smooth idle, and a PFC tuned by Steve Kan. The only thing wrong is the solid poly motor mounts that transmit too much vibration. Several others have noted on this thread that their poly mounts transmit vibrations. Are you going to state that all of them have something wrong with their cars too????

My car has over 65K on it, and has OEM mounts. I have "slammed" 3rd gear thousands of times without cracking my syncros. I have never missed 3rd, and gone into 5th.

OEM motor mounts are supposed to have a little flex. That doesn't make them bad. In fact, for most of us, you can't do better than a good set of OEM mounts.