After installing your new Poly motor mounts, there is no longer a need for any type of engine restraint. They are merely a band-aid fix for the softer and weaker factory motor mounts. Whether you have a pair of Poly motor mounts or just the drivers side, the need for any additional restraint is not needed. These restraints put excess stress on the alternator, accessory brackets, and other areas which were never designed to handle it. As always, it is up to you whether or not to use one, but we have found no need for them to be used with the Poly mounts, at ANY HP level.
There are many cars running 10 sec. 1/4 mile times without any type of engine restraint. This is all with the production 3.8 block, and some even using a Trans-brake. My car was used in the design/testing stage, running 10.70's without any Tie-down strap, with many mid/low 1.4x 60 foot times. There is at least one car that we know of going high 9's with Poly mounts, a production block, and no Tie-down strap. There are also many 9 sec. and 8 sec. cars with stage II blocks using our mounts, some without a mid-plate or engine restraint. Ski (Frank Wilczynski) runs his low 9 sec. street car this way, and even launches it with his T-400 equipped with a Trans-brake at 20+ psi. We have found that an engine Tie-down strap will cause problems and damage parts at higher HP levels, and is not recommended on any car.
With the Poly mounts, the motor will look almost motionless at an idle compared to the shaking around noticed with the stock mounts. On my 10.70's GN, the motor torqued over 75% less at a 5 psi boost brake-torque test than with the stock mounts. This will keep the headers and down-pipe from hitting the chassis, and other components from being damaged from excessive movement. The Poly bushing material is much stiffer than the stock rubber, which keeps things where they belong.
As with practically every upgrade possible, if it increases the performance of a vehicle, there is usually some kind of compromise experienced. Luckily, with the addition of the Poly motor mount, the drawbacks are very minimal compared to all of the great benefits. There will be a slight increase in vibration felt from inside the car, and we have found this to vary from car to car. This vibration is from the natural imbalance of the V-6 and the Poly mounts holding it firmly in place, letting you know the power will be transferred quickly . This vibration can be best described as "noticeable but not excessive", and in no way should be considered annoying. We do not recommend installing them on a 14 sec. 100% daily driven car, because that is not what they were designed for. Most people that ride in a car with Poly mounts installed do not even notice anything. On a back to back test, we noticed a slight increase in vibration, but after driving it for a few days, it was barely noticeable. Also, the Poly mounts will actually reduce the vibrations compared to solid mounts. To date, we have had 99%+ satisfaction with many great responses from our many customers, both racing and street driving.
We have had no response at all that the stiffer Poly mounts have "set off" a knock sensor. As mentioned above, the 99% customer satisfaction to date actually accounts for every issue pertaining to the Poly mounts. The Poly mounts are much stronger than the typical solid mount, but still flex just enough so that it doesn't transfer any chassis vibrations, never contacting metal to metal. The only responses we have received pertaining to setting off the knock sensor are the people that are thrilled to have eliminated the "false knock" that they had. With the stock mounts, the motor moves so far that eventually something contacts metal to metal. Not only does this damage something, but it will also cause false knock. With the Poly mounts, this possibility is eliminated.
We have noticed that most street cars and street/strip cars down to approx. mid/upper 11's should only need the Poly drivers side installed. This is also assuming that the passenger side stock mount is a GM unit in new or good condition. Faster than that, or if you race more than drive it on the street, a pair of Poly mounts is recommended. Other circumstances where we would recommend upgrading both mounts would be if header/down-pipe clearance is limited, maximum performance is desired, and if the car is launched hard. With a pair installed, the motor will not move around as much, retaining any valuable clearance that you have.
We have based our design from OEM GM dimensions as best as possible. After checking several sets, both new and low mileage units, we found that there was a wide variance in dimensions. Because of the input from many people in the designing stages, we kept the engine towards the high side of this variance for header and down-pipe clearance. Our dimensions are well within the factory dimensions, but because of this wide variance, the new mounts may be higher than before. Also, if your stock mounts are worn or broken, then the new Poly mounts will lift the motor from it's sagging position to it's correct location. Any difference noticed is usually very slight, and does not effect installation or performance. We have actually "tweaked" the dimensions slightly to make this difference less noticeable. For most cars, any added height is actually a benefit.
Our first design fits PRODUCTION BUICK 3.8's ONLY, and is available for either side separately or as a pair. Our second design will fit Stage I and II, production 4.1's, 3.8's, and all GM V-6's as well. The second design is available in pairs only due to the higher HP expected from the Stage II engines. The only difference between the two designs is that the second design has added clearance machined into them. This added clearance is to clear the thicker castings on the outside of the blocks, which allows the mount to contact the block in the correct area. Otherwise, they are virtually the same mount, and both designs have the same construction, stiffness, strengths, and HP capabilities. If you have a production 3.8 currently, and the possibility of a block upgrade is in your future, it may make more sense to get the second design now.
The machining is done on a precision CNC horizontal machining center, and must be in a certain area only. The actual width, depth, and shape of this added clearance is done in a special process so that no strength is lost. There is virtually no way that this could be duplicated by someone else without the possibility of removing too much material and making it weaker. Because the demand is so great for the Poly mounts, it would be better to sell your current pair and purchase the second design to replace them. This operation is also done before assembly, which makes it almost impossible to do after assembly. Any grinding would also create a lot of heat, possibly damaging the Poly bushings.
Depending on your header/down-pipe/intercooler combination, installation will vary. Usually, it is not very difficult or involved, and takes less than an hour for the drivers side and about two and a half hours for the pair. The drivers side is a cinch because of the extra room on that side to get the mount in and out. The passenger side is a bit trickier because of the down-pipe and header being in the way. A 3/8" hex bit driver for your ratchet is the only special tool required to install, which fits the supplied socket head cap screws (Allan bolts). We have also made this available through us as a convenience in case you do not currently have one. The link to the installation page at the top of this page contains very detailed instructions so that even a beginner should understand each step. A copy of the instructions is also included with every Poly mount purchased. There are a few helpful points that even those of us who don't look at instructions should take a look at before doing the swap.
Depending on your header/down-pipe/intercooler combination, installation will vary. Usually, it is not very difficult or involved, and takes less than an hour for the drivers side and about two and a half hours for the pair. The drivers side is a cinch because of the extra room on that side to get the mount in and out. The passenger side is a bit trickier because of the down-pipe and header being in the way. A 3/8" hex bit driver for your ratchet is the only special tool required to install, which fits the supplied socket head cap screws (Allan bolts). We have also made this available through us as a convenience in case you do not currently have one. The link to the installation page at the top of this page contains very detailed instructions so that even a beginner should understand each step. A copy of the instructions is also included with every Poly mount purchased. There are a few helpful points that even those of us who don't look at instructions should take a look at before doing the swap.
Poly mounts are planned for several other applications. Plans include the '89 TTA's with the turbo 3.8 engine, several of the bigger Buick musclecars with 455's, and more to come. Check our "Future Products" section also for more details, and visit us in the future for updates for any new products available.
Please send us any other questions you might have so that we can help you and better serve our future customers. If you have already installed the Poly motor mounts and have any helpful tips, ideas, or if you had any difficulty with any part of the installation, please pass them on to us. We would like to make sure that every product we make fits perfectly and can be installed easily, and also provide everyone with any helpful tips to make it easier.