New engine mounts = more traction?

[pokeybritches]

I finally replaced my engine mounts on my G-Power car with Vibra Technic mounts. It was possible to do the job without removing the manifold. Total time charged was a little under four hours. I'm aware of how easy it is to do on a naturally aspirated car. The supercharger meant doing things differently, and space was tight. My old mounts were trashed.

Initial impressions after 5 miles: Replacing the mounts has opened up a few new sounds. Whether they were there beforehand and I couldn't hear them due to NVH, or something was altered while replacing the mounts, remains to be seen. One sounds like either a boost leak or the supercharger itself. The exhaust doesn't sound quite as mean or loud. This may be due to there being less vibration and therefore less of a raw feeling.

It feels like I lost a bit of power. However, the boost gauge still reads 6-7 psi at 5k rpm in 70 deg weather. It's harder to spin the tires. This may be due to less flex in the drivetrain resulting in more traction. Even in damp weather, I was able to put the power down in second gear. The car has been tamed (somewhat). The new whine from the blower makes me wonder if the added traction is from less power, and a boost leak is present.

The vibration from the G-Power manifold is still there. I'm going to make a sincere effort to get rid of it this winter.

Overall there is a big difference with the VT mounts, like I took 50k miles off the car. Next I will replace the transmission mounts to hopefully make the car feel new again. Every M approaching 100k miles needs new mounts, and track/supercharged cars need upgraded mounts sooner rather than later.

[inTgr8r]

That's a bit of a surprise, I would have expected less traction as torque is more directly applied to the wheels.

[GuidoK]

Sounds to me that an issue with engine power is more likely.
I don't see how engine mounts influence traction or power. A shot engine mount may let the engine move for an inch or so, which is probably less than a degree. add that to the huge gearing 1:15 or so, and there is a 1/15 of a degree flex on the wheels on initial power. That's nothing.
If any, a little bit of flex should result in power putting down more gradually, which would result in breaking traction less likely, so quite the opposite effect.

[dc_wright]

This is all theoretical without any of us being able to take measurements, but it's a fact of physics that when you put a step input (like a clutch dump) into a system you get the systems characteristic response. An undamped system (like taking the strut/shocks off your car) will have oscillation or ringing around what would be the average response characteristic of an optimally damped system. It's possible that's what was happening with the trashed motor mounts, in which case you'd get some short duration high/low torque peaks/valleys as the drive train reacted. It would be the equivalent of stomping on and releasing the accelerator very rapidly. This would certainly feel more raw and would tend to break traction more easily. With the new mounts in place the system is more optimally damped and you're now getting smooth application of torque which is why less break in traction.
As I said at the start, just a theory.
Ideally it would have been great to have made some 0-60 runs before the mount change and then some after just to get a rough performance comparison. Then you'd know for certain you haven't a coincidental performance issue crop up or it's just the butt dyno giving you bad feedback.

[GuidoK]

Originally Posted by dc_wright

Ideally it would have been great to have made some 0-60 runs before the mount change and then some after just to get a rough performance comparison.

I don't think 0-60 will give an accurate idea.

If I do 0-60 runs over a period of time (say installing mounts) I'm happy if I get the times within 0,2 sec or so. (I time with a 10hz gps, so none of that unaccurate obd2 stuff).
Especially with FI cars (and this car has considerably more power than mine), throttle in 1st is so incredibly delicate. Too little you loose time, too much... you loose even more time. Once the rears light up ever so slightly (which is no problem at all), you loose almost a second or so. Temperature, moisture etc probably also has a deal in that.
A dodgy engine mount is then only one of the multiple factors, not even considering the driver.

If you want to know if you loosing power (without a dyno), do 60-120 or so, and carefully record the circumstances (temp, wind etc)

Just my 2ct

[Beedub]

i can confirm myself this had no bearing on traction levels or changed the sound at all, I'm very sensitive to changes on this car , I've owned it from new, and i can pick up on the slightest of changes.. I know her well Sound to me you have another issue elsewhere or have damaged something during the install.

all i felt with the engine mounts changes was a better control of the car and the way it moved around on a tight circuit ( the mass is controlled better) , gear changes felt more positive and when revving the crap out the car it all just felt smoother. Traction issues were the same as before, sound hasn't changed, but i do get alittle shimmy at idle but that seems to have gotten better as the material has bedded in. I went with the competition spec mounts.

i only got the mounts as i was approached to test them by VT, but as i was seeing/ feeling lots of engine movement under hard acceleration i though it can't hurt to try them, on installing them i literally couldn't believe the difference they made to the car. My stock mounts only has 9k miles and were split and visually damaged.

[dc_wright]

Originally Posted by GuidoK

I don't think 0-60 will give an accurate idea.

If I do 0-60 runs over a period of time (say installing mounts) I'm happy if I get the times within 0,2 sec or so. (I time with a 10hz gps, so none of that unaccurate obd2 stuff).
Especially with FI cars (and this car has considerably more power than mine), throttle in 1st is so incredibly delicate. Too little you loose time, too much... you loose even more time. Once the rears light up ever so slightly (which is no problem at all), you loose almost a second or so. Temperature, moisture etc probably also has a deal in that.
A dodgy engine mount is then only one of the multiple factors, not even considering the driver.

If you want to know if you loosing power (without a dyno), do 60-120 or so, and carefully record the circumstances (temp, wind etc)

Just my 2ct

0-60, 60-120, whichever will give the most consistent data points for the given car, just so that there's some actual data, because unfortunately the butt dyno can be very inaccurate. 10 runs (5 each direction to account for wind, slope, etc.) generally is sufficient, but one does need to look at the confidence interval of the before and after data to make certain there's no overlap to know there's been an actual change. In this case there's no "before" data unless PB has some previous baseline he can use.
Interested to see what the final outcome of this is!

[pokeybritches]

My thinking is that in extreme circumstances, driveline flex leads to wheel hop. A fractional amount of flex would result in one wheel being less weighted than the other, which may be enough to break it loose (or result in a speed differential that causes traction control to intervene). I recognize that the twisting of the engine is supposed to be axial, but with worn mounts and more torque, I wonder if the axial movement can be so great that there is also an element of lateral movement. This movement could be translated on down the line until it makes a minute change in distribution on the wheels.

For reference, here's a video my passenger took of roll-on throttle, second gear. Traction control comes in immediately. The road was dry and temperature was 57 deg F. I had been driving normally for about 10 minutes, so the tires were neither warm nor cold. Tires are <3k mile PSS 265/35/18.

[pokeybritches]

Originally Posted by Beedub

i can confirm myself this had no bearing on traction levels or changed the sound at all, I'm very sensitive to changes on this car , I've owned it from new, and i can pick up on the slightest of changes.. I know her well Sound to me you have another issue elsewhere or have damaged something during the install.

all i felt with the engine mounts changes was a better control of the car and the way it moved around on a tight circuit ( the mass is controlled better) , gear changes felt more positive and when revving the crap out the car it all just felt smoother. Traction issues were the same as before, sound hasn't changed, but i do get alittle shimmy at idle but that seems to have gotten better as the material has bedded in. I went with the competition spec mounts.

i only got the mounts as i was approached to test them by VT, but as i was seeing/ feeling lots of engine movement under hard acceleration i though it can't hurt to try them, on installing them i literally couldn't believe the difference they made to the car. My stock mounts only has 9k miles and were split and visually damaged.

The differences I've noticed (but you didn't) might be because you had 9k miles on your mounts, and I had 120k miles on mine (20k supercharged).

Since replacing the mounts, coins in my change tray don't chatter every time I get on the throttle. The exhaust is quieter inside the cabin.

I put another 15 miles on it today. It still feels very strong, but less like the torque is overwhelming the chassis. The bypass activates when it should, so I don't have a major boost leak. I've found the source of the vibration in the manifold, but I don't know how to fix it. If I could wedge a small piece of rubber between the supercharger and air intake, it would solve it. I'd rather have a more elegant solution, so I'm going to keep digging.

[pokeybritches]

Originally Posted by dc_wright

0-60, 60-120, whichever will give the most consistent data points for the given car, just so that there's some actual data, because unfortunately the butt dyno can be very inaccurate. 10 runs (5 each direction to account for wind, slope, etc.) generally is sufficient, but one does need to look at the confidence interval of the before and after data to make certain there's no overlap to know there's been an actual change. In this case there's no "before" data unless PB has some previous baseline he can use.
Interested to see what the final outcome of this is!

I have some third and fourth gear pulls I might use. I may end up hitting the dyno again, since I (embarrassingly) figured out during my last runs that the coolant lines to the manifold had cracked, running it dry.

[pokeybritches]

Circling back to this....

After 100 miles, I can say with absolute certainty that I have more traction. One possibility is the old mounts were so worn that they weren't providing any damping. A step input on the gas pedal translated directly into the engine rotating to the solid frame / mount bracket, and essentially providing a step input of its own.

The supercharger whine is only present from 2800-3400 rpm, and it's most apparent as the revs fall when upshifting. It's unrelated to the engine mounts, but it might be from an undiagnosed issue (like a boost leak) or worn supercharger bearings. The whine is faint and nothing like the fire truck sound my Vortech emitted when it needed a rebuild.

Overall I'm happy with the switch to the VT mounts. The car feels solid, controlled, and generally better than when it left the factory 9 years ago.