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Uprated engine mounts - Lower power?


10 Jul 2015

Just wondering if anyone has come across this before, or heard similar from 996 Dyno tuning experts..


The substance of it is, that a stiffer engine mount makes the engine knock sensors believe that the engine is detonating and retards the timing, causing a drop in power.

Jake Rayby is convinced and recommends standard Porsche engine mounts as a result.

That's really interesting. Hard to argue with the data. I wasn't aware of this but happy that I used standard mounts on mine!

Jake Raby seems to get a mixed reaction on the www, but regardless of his personality or politics, I have been aware of him since his and my air-cooled VW days and he has a lot of experience and data to support his opinions.

I have heard of this before.

I think if you use a solid transmission mount along with solid engine mounts then it is a real risk. RS engine mounts are stiff enough for most people I think.

I have a set of RSS mounts waiting to go in when the car is serviced in a few weeks time. I'd been having a little buyers remorse anyway as I worried they might be harsher than I'm expecting. Hmm
I've got some new oe mounts I've bought for my other halfs Boxster. I'm tempted to swap them in to my car which has rs mounts to see if I can tell the difference.
It would be very interesting to see if someone could replicate Jake Raby's findings on a chassis dyno.

Trouble is that even altering the strapping of the car onto the rollers has some effect.

Also, not sure what fuel the Americans have access to in terms of octane levels? It could be that it's only an issue over there due to a reduced operating window for ignition advance, which isn't so much of an issue here, using 99 Ron fuels? I.e. even if the engine reduced adv due to perceived knock, it wouldn't hurt the torque curve anyway.

The other consideration is whether this is just at WOT. If the car was pulling adv all over the ignition map, even at part throttle, it would make the car markedly less sprightly than one that doesn't.

A seat of the pants evaluation would be interesting Shalmanaser. I'll bet it's virtually impossible to detect though.

Be interested to hear what Wayne from Chipwizards or DMS automotive think.

Raby's great at self promotion, but that doesn't mean he's wrong of course....
Agree It would be interesting to see if any one else has picked this up. I wasn't aware that the strapping could affect results. Every day is a school day!

In this video, Raby was opining on his experience with a few cars and not just this one, so in his opinion it isn't a one off thing. He also claims he didn't move the car off the dyno, so in this specific case the only variable appears to be the engine mounts.
Shalmaneser said:
I've got some new oe mounts I've bought for my other halfs Boxster. I'm tempted to swap them in to my car which has rs mounts to see if I can tell the difference.

Did you car have the RS (presume this is 993 RS rather than a typo of RSS?) mounts when you bought it? If not I guess you'd have noticed at the time.

I might just take one for the team here and get my RSS mounts installed as planned and see what's what both with this issue and NVH.
M444TTB said:
I have a set of RSS mounts waiting to go in when the car is serviced in a few weeks time. I'd been having a little buyers remorse anyway as I worried they might be harsher than I'm expecting. Hmm

You won't regret it. I've had semi solid mounts on both my cars. I have the RSS mounts on my current car and they are softer than the previous bushed mounts I had. A lot less vibration in the cabin.

Neither mount had the issues described, I think that it would need to be quite severe to cause this.

The RSS are barely noticably different to standard to be honest.
I have the RSS in mine and they really improved the dynamics of the car. The car feels so much tighter and the action of the gear shift is massively improved. Back-to-back I felt no power loss or change in torque - noting this is on a stock engine and stock map.

I struggle with this video as the tuner has already remapped the car very significantly away from stock and perhaps has many other variables with all their other modifications. Also who knows what beef he has with other competitor tuners?

The cup cars use completely solid mounts, the RS mounts are akin to semi solids and the standards are soft. If this claim is true that would mean Porsche gradually designed in power loss to their faster cars. Hence I'm skeptical.

As for NVH i noticed no difference to the *worn* factory mounts when using RSS.
Interesting video.

I'm not sure my arsedyno would notice a 7hp loss but I sure do value the positive affect fitting RSS mounts has on the chassis.

My OEM mounts were showing signs of wear so the affect was pronounced.
I wrote out long post but it disappeared!

Basically I've been running 964 rs style mounts from type 911. Been chasing an issue where the motor feels a bit flat, like it's pulling timing. Was thinking it might be the knock sensors and the YouTube video on the subject really got me thinking.

Fitted oe mounts, disconnected battery to reset adaptions, result is a massive improvement in power, smoothness and exhaust note!

Knock sensors are basically microphones looking for a particular frequency, in my case id say the semi solid mounts have amplified that frequency. I'm using the cheapo 964 rs copies, maybe RSS mounts are better?

Cup cars no doubt have a spec ECU with the timing wound up and the knock detection wound right down, no one is putting crappy fuel in their race car.

Anyway, big relief that the motor is back to its best!
Well well!!!!

Are we all going to be putting OEM mounts back in now?

I've got the 964 RS ones as well. The car feels very tight and together with them though...

Hum :?:
Try 997 GT2 engine mounts - sticking them on myself at the mo - not cheap at £480! :wink:
I would add a couple of caveats.

1 - my car is a very early motor (despite being W reg...) with the Motronic 5.2.2 ECU. quite likely more sophisticated ecus like the 7.XX used in e-gas cars might be able to be a bit more discerning.

2 - Amount of vibration will no doubt vary from engine to engine. Maybe mine is towards the less well balanced end of the allowable tolerances which is why I noticed such a difference?

3 - Frequency of the vibration is key here I think, maybe I just got unlucky?

I might put my 964 RS style mounts on my wife's 987 which has knackered OE mounts (and now no replacements, oops...) to see if I can sense a difference.

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