I may be off on this, but I thought the rebuild intervals was largely driven by the titanium rods and their tendency to stretch and/or crack. Also, solid valve lifters being another area to check and adjust. Obviously once the engine is open bearings are replaced.

 

I had my heads done by Todd McKenzie who built the heads with 9000rpm valve train. The limiting factor are the rather heavy hydraulic lifters but even street GT3s use those. We use a conservative 7500 redline and the engine pulls like a freight train all the way there. On Motec I frequently see 7600-7800 on data during upshifts. RSR/Cup motors have lightweight lifters which is one of the reasons whey they can rev so high. RSR/GT3 R motors go to 9400.

Yes, the RSR crank has a smaller diameter but greater width rod journal. The smaller diameter in turn reduces the speed between the journal and rod. The RSR crank is fully counterbalanced and several pounds lighter than the TT crank. If I recall, it was 2 lbs lighter when I compared them side by side on a scale 3 years ago when my engine was built. As I mentioned before, all the GT3/RSR cranks have dual oiling passages 180º apart on each rod journal vs. a single oil passage on the TT crank. For race motors that see sustained high rpm operation this additional oiling is paramount.

I have no hard data of the strength of the RSR v. TT cranks, but have never heard of a failure in either. I run 720 ft.lbs of torque to the wheels (probably 800+ at the crank?) though engine without issues. If anything, I have heard that the TT crank is subjected to greater loads due to the fact that it is not fully counterbalanced. I'm certainly no expert, but this certainly makes sense as my engine runs smooth as silk with the RSR crank. There is simply none of the IMS rattle nor the LWFW rattle (I run an 11lb FW) that these engines have with the TT crank. Additionally, one well respected tuner has told me that the TT crank (which is a 993TT part) is actually rather "soft" and does allow for a bit of flex. I don't know how one would measure that but bottom line he also recommends the RSR/GT3 crank in any engine build.

As far as the deciding factor for the RSR crank? Chris Cervelli built my engine and he's built countless RSR and Cup motors over the years. Chris is one of the finest race engine builders in my opinion and I left it in his hands to build the most reliable engine for my intended use. He would not consider building a high rpm race motor without using race proven crank. Personally, simply knowing that you have twice the oiling capacity makes this a no brainer in my book. Porsche has figured this out, they are not stupid.

 

I am running the stock oil cooler which is the same on all the 996 Mezgers. The 997 mergers apparently utilize a larger oil cooler but it is not retrofittable to our engines. I guess anything can be done but it would be a huge undertaking. I am in the process of modding a few items to improve the airflow through the front radiators which should drop peak coolant temps 10F or so in turn lowering peak oil temps. Should have data next weekend.

Gearbox temps are not a problem as long as you have a cooler. I have a large air to liquid gearbox cooler and temp stay well under 250F even in the hottest ambient temps. I also have another GT2 gearbox with the liquid to liquid OEM gearbox cooler and will run that next year. It will be interesting to see which set up is more efficient.

 

Makes sense. What is the difference between the different GT3 cranks? Also, did you switch to the 959 PN IMS shaft? I seem to remember the INS noise in our cars being related to the IMS gear keyway and also the gear lash between the gear on the TT IMS shaft and gear on the crank being sloppy.

 

Here is a link to the various cranks. The stock 3.6 GT3 crank has the rough textured finish. The Motorsport RSR crank has the smooth finish.

https://rennlist.com/forums/997-gt2-...next-year.html

I will be swapping in the single piece IMS shaft. There are several options, either the 959 part number IMS or the 997 part number IMS that is used in the 997RSR. We will probably swap in the RSR IMS barring an astronomical price tag from Porsche Motorsport. I'm not buying the IMS noise being caused by the stock IMS on our cars. The only way it would cause more noise is if the bolts were backed out and the IMS gear was allowed to wobble. If that's the case, catastrophic failure would surely follow. If the bolts are tight, there can be no more play than in the single piece IMS. I have the bolted IMS currently and the noise is not there. I attribute the lack of noise it to the crank and maybe different harmonics of the 3.8 engine. Just my $0.02 of course...

 

According to the 996 RSR, Cup and GT3 street parts catalogs, the crankshaft are all PN 99610202192. Guessing the weight difference is due to smaller journals and more oil passage drilling. Not sure if anyone has done it yet on our cars, but I know other 911 builds people will get their cranks smoothed, profiled counterweights, additional oil passages drilled and balanced. Of course nothing beats motorsports proven factory parts either though.

 

There are many variants of these cranks with many supercessions. I know the street 996GT3 cranks have the rough textured finish. The RSR cranks have the smooth finish and likely improved oil galleys but I'm no expert. Interestingly these cranks are still relatively inexpensive. I'm not too sure about all the modified cranks. I would stick with the Porsche Motorsport stuff. Hard to go wrong there...

 

Interesting. This is the only GT3 street crank picture I can find. Looks pretty smooth, but cannot see oil passages. I know the 996 and 997 turbo cranks look like sand cast and are extremely rough.

 

Again, many variants of these. The 3.6GT3 crank is pictured in the rennlist thread above and it has the rough finish. Don't quote me but I believe the smooth Motorsport crank is what went in the RSR and variants of it also made it into the later generation GT3s. The 4.0 has a totally different crank. Trying to decipher all the various part numbers that went into all the different cars will give you a headache.

 

I don't know, it just calls it a 3.6 crank. Seeing they offer the crank for GT2 and GT3 and without a part number visible in the pics of the 3.6 crank it is hard to say for sure. The porsche parts catalogs call the street/cup/RSR cranks to be the same up until the later 997 cups and RSR. And the -92/94/95/96 are all superseded versions of the exact same part. Without any 996 GT3 street crank pictures i would venture to say that the marketing pictures GMG provides could in fact be a turbo crank. One thing is for sure, our cranks do have much to improve upon.

 

Did a little more digging though pet. Looks like the RSR/Cup/GT3 3.6/3.8 76.4mm cranks are basically the same thing. The 04 RSR catalogue shows it as a .92. The one we put in is a .95 if I recall. That is what is listed for the '12 3.8 997Cup. It does have a smoother finish than the .92 I've seen. I'm not sure if Porsche tweaked the cranks a little or improved the oiling thought the years as they updated the last number. They may have but I have no idea. Maybe the difference in the finish is simply due to different suppliers through the early to later years? I would assume that only the last versions of the crank can be ordered now. Interestingly, the 2011 997GT3 pet shows the crank for the 3.6 as a .93/94 and on the next page for the 3.8 as a .95 which would seem to indicate some type of minor difference. Go figure.

 

When I checked with Sunset here they said that if I order a -92/94/95 I would only be able to get a -96. I am guessing a manufacturer change. The -95 appears to have been the cheapest at right around $2000 if you can find one.

 

Here is the Porsche Motorsport 997RSR billet IMS we will be installing in the engine when it goes down for a rebuild next month. This is a 997 Motorsport PN, not the 959 PN IMS which is used in the 996GT3, 996Cup, and some 997GT3 and 997Cup engines. Contrary to what is rumored, the 959 part is NOT compatible with the Turbo/GT2 engine.


[url=https://flic.kr/p/GRQaHr]

[url=https://flic.kr/p/21Nv8dF]

 

Thanks for sharing. What is not compatible about the 959 part?

 

The snub nose on the back of the 959 IMS is different. There are several versions of the IMS with slight variation in size but mainly a difference in the snub nose depending whether the engine is a 3.6, 3.8 or 4.0.