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There is not much discussion in the 997TT section about upgrading the stock engine mounts to semi-solid versions so thought I would quickly summarize my experience with the Rennline tunable engine mounts http://www.rennline.com/Rennline-Tun...oductinfo/M18/
There seem to be four main choices for this upgrade - the Rennline adjustable kit, RSS, Wevo and Function First's modified OEM mount which has been drained and filled with urethane. On my 996 C4S, I purchased and installed the Function First mounts and really liked them. I finally got around to upgrading the mounts in my 997TT and this time I chose the Rennline offering, as it's the only product that allows you to adjust the stiffness of the mount.
Unlike all other mounts, when you purchase the Rennline kit, you receive completely disassembled engine mounts which means you need to have some basic tools to complete assembly ie ratchet, wrenches and torque wrench. You pick which insert stiffness you're going to use and then put it all together. When you buy the engine mounts, you're supplied with three different sets of urethane bushings to choose from:
Yellow (street) 75A durometer - these are same durometer as the RSS and Wevo products
Blue (sport) 85A durometer - stiffer than 75A
Red (track) 95A durometer - stiffest
As you go up in durometer, the mount absorbs less of the engine noise & vibrations and instead passes them through to the chassis. I felt that the Rennline kit offered the most value as it allows you 9 different levels of stiffness (by swapping or mix & matching the urethane bushings) to fine tune to your liking.
Pre-assembly is simple as long as you have the most basic of tools, some locktite and a torque wrench. Rennline supplies instructions for assembly which includes torque specs for each nut & bolt on the mount as well as on the car. Pre-assembly takes 15 minutes or so.
I chose to start off with the yellow street inserts. Installation is super simple on the 997TT and does not require the car to be put on stands. The only thing you need to remove from the engine compartment to allow access to the mounts is the y-pipe. The airbox does not need to come out (just the front cover which pops out simply by pulling up on it, no tools required). A floor jack with a hockey puck or 2x4 is placed under the center of the motor where the two halves meet and is jacked up only far enough to simply provide support to the motor - the motor doesn't need to be raised. The two oem mount bolts underneath the car are easily accessible without jacking up the car, even on a lowered car. As you're not jacking up the car, and the jack you're using is only supporting the motor, not raising it, no safety concerns to worry about.
Swapping the mounts takes ~10 minutes per side, once you're removed the y-pipe and placed the floor jack. Two small 13mm bolts on top of each mount, one large 18mm bolt underneath the car to remove. Once those three are removed, the mount slides right out. Rennline mounts go in, reinsert the two top bolts, re-use the factory 18mm nut on the underneath side, torque, done. Very simple. Perfect fit & finish as well.
So I started with the yellow inserts just to see how much NVH would be passed through to the cabin with the 'softest' (but still as stiff as all the other aftermarket mounts) inserts. First drive confirmed a MUCH improved manual shifting experience, very slight increase in in-cabin volume from the engine and exhaust - but with completely different sounds and tones coming through. A much more mechanical, sport-oriented sound in the cabin without being much louder. I was worried about vibrations and rattles on a 10 year old interior but I am pleased to report there is absolutely no added buzzing, rattling, or vibration to speak of. It's hard to describe what the oem mounts feel like in terms of the engine moving around - but once you go to a semi-stiff mount, it is very obvious that the rear of the car 'stiffens up' even if you can't explain it in words. I won't try to find the words to describe the feel of the engine weight transfer before and after, I'll just say it's a very obvious improvement in feel even at normal street speeds.
As the yellow 'street' 75A inserts proved to be so compliant on the noise side, I decided to swap to the blue 'sport' 85A inserts. Definitely a step up in overall engine noise passed through to the cabin. Still no buzzing or excessive vibration. Just the same overall tones and noises from the yellow inserts just at a marginally higher volume. I could not discern any difference in shifter feel or engine movement over the yellow inserts. I am leaving the blue 85A inserts installed as I am completely satisfied with the sound level they're producing.
I track my car and plan on swapping the inserts to the red 'track' 95A units for the first PCA track weekend May 5/6, considering it's such a quick and easy procedure. It's a 1.5 hour drive to the track so will report back on what the 95A inserts feel like on the street.
Very glad I made the upgrade, and for $350 I don't think there is another modification that produces such a dramatic difference in overall feel and character - great return on investment.
Nice write up. I did the OEM and immediately noticed the change. My mounts were shot and shifting was odd. New mounts improved everything, it's like when you get new tires the best I can compare to.
I have the blue mounts on mine and really like them as well. I actually prefer a little more NVH so I'm considering switching to the red. Please post an update after you switch. I'm curious if there will be a significant difference between blue and red.
I have these as well, have been running the blue inserts since Rennline released the product and can attest to how much improvement they made when it comes to engine movement.
Recommend considering the stiffer inserts for the gearbox mount as well.
I am told by more that one shop that changing the stock engine mounts to these semi-solids can and has caused the knock sensors to pick up "false" knocks and thus retarding timing, etc.
To date I have not found proof one way or the other and if somebody can point me to them, it would be greatly appreciated.
I am told by more that one shop that changing the stock engine mounts to these semi-solids can and has caused the knock sensors to pick up "false" knocks and thus retarding timing, etc.
To date I have not found proof one way or the other and if somebody can point me to them, it would be greatly appreciated.
I read similar anecdotes about full solid mounts on the 997.1TT, but not the semi-solid mounts. The knock sensors in the Mezger motor are quite sensitive I understand.
I'm going to be doing some datalogging at the track soon with Kevin from UMW, so I am sure we will find out
I am told by more that one shop that changing the stock engine mounts to these semi-solids can and has caused the knock sensors to pick up "false" knocks and thus retarding timing, etc.
To date I have not found proof one way or the other and if somebody can point me to them, it would be greatly appreciated.
That's why I went with OEM RS-mounts, after the recommendations of Kevin among others. Have had them for about 2 years without any subjective issues but haven't done any logging to look for retardation.
That's why I went with OEM RS-mounts, after the recommendations of Kevin among others. Have had them for about 2 years without any subjective issues but haven't done any logging to look for retardation.
What were the differences you noticed after installing the RS mounts?
What were the differences you noticed after installing the RS mounts?
Most obvious difference was increased engine noise in the cabin. No drone or vibration, just louder which I kind of like but wouldn't recommend if you want to listen to the radio. Handling wise probably a tighter feel but I installed the DSC box at about the same time and unfortunately didn't have the chance to test the mounts by themself on the track.
I am told by more that one shop that changing the stock engine mounts to these semi-solids can and has caused the knock sensors to pick up "false" knocks and thus retarding timing, etc.
To date I have not found proof one way or the other and if somebody can point me to them, it would be greatly appreciated.
Wevo engine mounts on our car, no false knocks or strange timing behavior when datalogged on the dyno, or more importantly on the the track/road in motion. All knock events follow expected patterns with load/timing/fuel etc. The engine mounts still have a decent amount of flex, and added minimal NVH. The trans mount insert was much more noticeable.
Wevo engine mounts on our car, no false knocks or strange timing behavior when datalogged on the dyno, or more importantly on the the track/road in motion. All knock events follow expected patterns with load/timing/fuel etc. The engine mounts still have a decent amount of flex, and added minimal NVH. The trans mount insert was much more noticeable.
Thanks, appreciate the data point - that's good information. I'm working with Kevin to tune my car and will be data logging as well, and we're going to see if the Rennline's pose any issue with knock sensors before first PCA track weekend May 5th & 6th. Will make for good information for the 997TT community.
I just installed the OEM 964 RS mounts tonight and initial impressions are good, improved handling and less slop from the engine movements with no noticeable NVH. I also bought the ones by URO (OEM supplier) instead of Porsche brand as they are less than 1/2 the price (only $199 vs $449) and looks identical to the Porsche brand.
The installation was relatively straight forward and not very difficult. I think I spend more time researching which mounts to get (original oem vs oem 964 RS vs semi solids) and where to order from.
03-18-2018, 09:57 AM
Rennline Adjustable Engine Mounts
