Ur20v

I look forward to seeing what improvemets you get with your gear change, its a very common 'fault'! Who's engine mounts are you going with?

Turbo/SC cars are set to run more sensitive to nock than NA cars due to the protential to over boost, I am sure you won't see any difference between your runs - are you going to do the runs hot (no or low cooling aids) to maximise thermal loads as you aren't dynoing for power.

Tom@TPC Racing

Here's the step-by-step on replacing the trans mount bushings.

With the trans mount removed from the car I used a 20-ton hydraulic press that we have at the shop to press out the OEM rubber bushings with ease.



Here's the mount with the bushings cleanly pressed out.



Back on the hydraulic press to press the new stiffer bushing in.



Here's the finished mount.



It was kind of a PITA to have to use a screw jack to "walk" the mount on at little at a time, one side at a time, especially at 11:30pm when I realized the can of spray lube sitting on the shelf is empty. In desperation, as this is my ride home, I sprayed Simple Green cleaner on the mating surfaces as lube.



With a little patience, one side at time, inch by inch, using the screw jack, the mount lined up to the transmission perfectly.



These particular bushings fit tightly so if you want to do this its probably a good idea to have a shop do it using hydraulic press and screw jack while the car is on a lift. And make sure they have a can of lube that's not empty.

Ur20v

Tom, sounds like the bushes may have been 'over snug', It should slid up with just a little resistance then the bolts finalise the fit.

Tom@TPC Racing

The transmission mounts are Cantrell Motosports 85A durometer stiffness. I ordered tune-table engine mounts from Rennline that includes three different durometer inserts but the mounts are on back order so I'll have to wait for them to do phase two dyno.

I agree 100%. The cars that I've seen ignition pull from stiffer mounts have been turbo cars. As you have stated about knock sensitivity, some aftermarket ECU tunes increase the sensitively over the already more sensitive OEM turbo knock table. And then of course, increased power and the quality of the fuel comes into play when running near the edge of the ignition table.


Hots runs no fans. Just two pulls and then shut it down.

Tom@TPC Racing

Good news. No change in timing and virtually no change in power. Two runs with OEM rubber trans mount bushings and two runs with 85A bushings. All runs were made at same engine coolant & oil temp, on the same tank of fuel, at very similar ambient temp, using SAE(Society of Automotive Engineers) correction factor for the comparison.



I can tell the improvement in shifting immediate making a left turn out of the shop parking lot. But man, the stiffer mounts are loud as F*CK! My car with RS flywheel sounds exactly like a Cup car inside the cabin. I could get use to the racy sound.

I'll be dyno testing the tune-able engine mounts next week. In the past, we recommended and installed many OEM 964/993 RS engine mounts and OEM 997 GT2 engine mounts as they are stiffer than our original mounts; We cannot in good conscience recommend to customers other mounts that might cost power and increase heat from ignition pull. It'll be interesting to see how the Rennline engine mounts will fair out. Stay tuned for that.

Tom@TPC Racing

Oh, I forgot to mention while the transmission mount was out I replaced the shift cables. I am in a fortunate position that at my job I test drive a lot of cars with a lot of different combinations of parts to develop my subjected feel and preferences. From what I have experienced and for my preference, I choose OEM .2 cables because I personally like the feel; positive feel yet not bolt rifle action positive. I find that with a more deliberate shift action during heel & toe I tend to drag the brake more than I need to in order to time smooth clutch release, thus slowing down the car a few mph too much at corner entry- That's just me. I suppose I could force myself to adapt but I prefer not.

Interesting fact on OEM shift cables- the .1 cars have 996 GT2 cables that have joints constructed of metal outter casings with rubber inner bushings. There is flex within the metal casings.





The .2 cables have joints constructed of hard plastic inners and outters. Perhaps that's the reason why I like the feel over the .1 cables.



Just for fun, comparing the .1 and .2 cables the are the exact same length.







For even more fun, I did a Cup cable conversion for a customer this week. Metal joints at both ends.



Cup cable conversion at the shifter end for a customer.

FLT6SPD

^^thanks for the informative post. How to you feel about the shifter assembly itself between the .1 and .2?

Tom@TPC Racing

You're welcome. The .2 shifter is better constructed than .1, with the difference being the axial bushings are aluminum instead of plastic. As far as I can tell the throw distance are the same. I did installed the .2 shifter on my previous car(997.1 Carrera S) and it felt good. I think if a driver puts a lot of force to the shifter lever then the aluminum axial bushings would become a better choice by resisting distortion. On my GT3 I used the .1 shifter because at the time I bought a lot of parts, the extra 200-some bucks for the .2 shifter would have been over my credit card limit. The .2 shifter is very nice but I have no regret in this matter because I don't force the shifter lever.

C4SGRPDK

Is it possible for you to make a video to show us the sound of those mounts?

I have been on the fence of doing stiffer mounts and numeric cables but can't find any video online of the type of sound it would make.

Thank you

Spyerx

i have LWFW, cup cables, cup shifter, (full interior), Cantrel 'softer' solid mount, wevo engine mounts. it's not that loud. But it's loud in a good way.

My buddy had the same setup with a GMG I think mount (its REALLY hard rubber/urethane) and his setup was waaaaay louder than mine.

Tom@TPC Racing

Sure. I'll do it after I put my roll bar and rear carpet back in next week. Having my roll bar re-painted.


Actually the noise seemed to have subsided when I drove in to work this morning. Maybe the new bushings settled in after couple days or it just seemed louder at first when I drove it after midnight when there were fewer ambient noises. Or I have gotten used to it. Anyway, its not a bad noise, it adds character like the distinctive sound of the Ducati dry clutch with open cover.

Tom@TPC Racing

Just delivered. Will be installing them tonight with the Red (95A) inserts and then dyno.

Tom@TPC Racing

I was eager all day to install the new engine mounts so as soon as soon as I shut things down at the shop this evening I was on it.

A little bit of weight savings so I can eat a porterhouse steak for lunch and still weight the same.



Before and after shot.



Being the obsessive-compulsive person that I am, of course I would measure the height of the engine relative to the body of the car before and after using a telescopic gauge and a dial caliper. The measuring point I chose was as close to the middle of the engine as possible; on top center of the throttle body.

The engine does sit 1mm higher with the new mounts, but it is highly likely that the original mounts with over 50K miles has 1mm of sag. Anyway, I don't think 1mm will make a difference for doing HPDE/track days.


And the dyno... Unfortunately the testing condition isn't the same as previous dyno sessions. The last two dyno sessions were made at mid-40F degree ambient temperature. This evening the ambient temp was in the low-70F. I used fans due to the increased ambient temp.



Despite the hotter temp I am happy to report there's no loss in power and ignition timing. Even gained a horsepower or two with the fans at full blast.



My butt feeling... driving spiritedly the new engine mounts definitely make the car feel different. Different in that according to my butt, having no "engine suspension" the vehicle suspension does take more of a "single" set now that the unitized mass is heavier(as oppose to a double set during corner entry with the softer rubber mounts that cause momentary oversteer result of two masses moving independently). It didn't upset the car at street pace but the suspension definitely moves a little more as a result of the heavier unitized somewhat single mass. I may end up tweaking the damping values with the DSC tuning software and/or go one step stiffer springs. Or swap out for one step softer engine mount inserts. So many choices! But I'll drive around more before I make any changes. I know, I know most people think I'm crazy, I suppose I am, but I test drive a lot of cars and I feel these things and I just want my car's suspension to be the way I like it regardless if it produce better track lap times or not. Some very good drivers that I know just man handles any car to get best out of it, whereas I am a more technical guy and think too much about how the suspension is working while I drive...which is probably a bad thing but I can't help it.

Lastly, the stiffer engine mounts didn't add any more noise than the transmission mount bushings already did. Here's a short youtube video. The carpet over the ECU is off. Sound like a loud diesel truck in the video, really sounds like a Cup car or GT3R in person.

PS- the stock 997 GT3 engine mounts(even with 50K miles on them) are still stiffer than stock 997 Carrera, Carrera S, and Turbo, and various stock 996 mounts. So for those who aren't ready to go with aftermarket mounts on non-GT cars, I think the stock GT3/GT2 mounts make a conservative upgrade that might be worth a consideration.

FLT6SPD

17mpg?!? How do you manage that.

I'm lucky if I see 10

Tom@TPC Racing

Haha. I'm not that far off. Only time I see 17mpg is right after reset which is necessary after dyno.