Why did I fit polyurethane engine mounts? Many reasons. The flex in the drive train has long been an issue. Very soft engagement of the clutch, massive amount of wheel hop in slippery conditions or during committed standing starts. Another problem has also been the cracking open of the exhaust manifold joint where it goes from 4-2. This is probably down to the engine moving so much and the fact that the aftermarket manifold only has a small spiral connector.
Please bear in mind that the comparisons between the engine mounts made here are between the black compound Prothane 14-504 and 200,000 mile old original engine mounts.
Primera P11 GT/G20 – Polyurethane Engine Mounts
I used Prothane bushes 14-504 to change the front and the rear engine mount bushes. These are a direct fit. I was considering changing the left and right motor mounts as well but I couldn’t find any of a suitable size, this turned out to be a blessing.
Fitting of the engine mount bushes was a snap because we used our friendly garage! But seriously, the mechanic said it was a straightforward job. If you have changed bushes before then you can change these bushes.
The first thing I noticed was the extra vibration coming into the car, I have had the bushes on for 3 days now and either we have got used to the vibrations or the intensity has dropped, a bit of both I think. Pulling off, you can immediately feel there is less play in the drivetrain and there is a small amount of vibration as the clutch engages. Unpleasant to start with but we are learning to drive around it and also the bushes have softened up slightly reducing the effect.
Stop Start Traffic
An unforeseen benefit of fitting the bushes has been much smoother gear changes. Whereas before it was very difficult to make a gear change without it being felt in the cabin, now gear changes are imperceptible even if you are not trying to make smooth shifts. Like I said this is not something I was expecting but it is a welcome change.
The smoothness can also be felt when you are in stop start traffic, where you are in-between slowing down with the engine and giving the engine a little bit of gas. Before there was a bit of kangarooing going on, this is all but eliminated now.
At 4000rpm and above the vibration inside the car is much much more noticeable. To the point of being unpleasant. This is the worst aspect of the change so far.
Wheel hop has nearly been completely eradicated, the difference is more than I was expecting. You can still feel the wheel hop wanting to start but the vibrations never develop into anything meaningful, unlike before when it could get so bad you thought something was going to fall off the car.
Changing the front and rear bushes with the black compound is as far as I want to go on a car that is used on the road. If I had changed the left and right bushes I would consider changing back to the old engine mounts.
Summary – Polyurethane Engine Mounts
In summary for the truly committed I would recommend changing the front and rear bushes for the red racing compound. For the committed black bushes front and rear are more than enough.
For those who want to keep the civility but want to get a bit more tightness in the drive line I would say changing either the front or the rear bush on their own would be enough to get the effect you want.
As a side note I have just wired in an AEM Fuel Ignition Controller (FIC), the 8 channel version for its boost control feature. Considering we are running a standard SR20DE ECU from a P11 GT, the mixtures at cruise are almost exactly 14.7. We will be tuning the FIC over the coming months to see if we can increase the already good fuel economy and also get a bit more power.