Racecar Project - New Bottom End Build
12-21-2008, 05:39 PM
#1
Nordschleife Master
Thread Starter
Racecar Project - New Bottom End Build
I now have all of the new parts to put the engine together up to the pistons and cylinders which are currently in the deisgn and manufacture process.
My old crankshaft was a 996 GT3R crankshaft, installed without modification. When removed, there was no measurable wear and has now been reused in another project. The new crankshaft improves upon the 996 GT3R design and has a larger oil drilling through the center for improved oiling to the #2 and #5 rod bearings. Although the 996 Crank did not show signs of oiling issues, this should ensure that there are never any issues at high rpm. In addition, the oil feed holes at the ends of the crankshaft are now drilled at an angle to the centerline of the crankshaft to aid in oiling and to align with the thrust of the crankshaft and orientation of the forces on the crankshaft. This crankshaft has an unspecified stroke with an unspecified weight but uses the same 996 GT3 size journals. The counterweights have been designed to work with the ligher recipricating mass of my new engine.
I've gone through and measured all of the rod journals (main, rod, #8 main), have measured all of the rod bearings, and all of the connecting rod big ends. I'm using GT3 Race bearings which are coated and the tolerances are tighter than a street replacement bearing. Part of blueprinting an engine, and why a performance engine build takes roughly 20 hours more than a "throw it together" engine rebuild (I hesitate to say street rebuild because we only put engines together with careful measuring) is due to this measuring. I've included some pictures of an old GT3 connecting rod to show you the process and I've included the actual values from my new connecting rods ready to be installed. (I had done this a week ago and was bored with the snow today)
1) With the new connecting rod bolts, I've captured the starting bolt length measured with a micrometer. This will allow me to have a baseline on the bolt so when the engine is disassembled for inspection, I can see if the rod bolt has stretched (ie no good). Possible reasons would be an overrev or a bolt simply worn out.
2) Once you know the starting value, you can use a rod stretch gauge and set to 0 at the untorqued rod bolt length. Then, you begin to tighten the rod bolt and check the stretch as you go along. The picture here shows the rod bolt has stretched .0070". The method I use is that I have a digital torque wrench and can see the rolling torque. I usually torque them in stages. On my new bolts, the torque range is 60-95nm with a stretch of .0078" +- .0005". The importance here is the stretch of the bolt, not the torque value and you can see that there is a wide range of torque that is acceptable. On my old Carrillo rods, they torqued between 61 - 77ft/lb to achieve the .005" stretch required. I also measure the beginning length and stretched length and that will verify the stretch gauge as well as keeping a record of what has been done.
3) Once the rods are torqued, you can measure the bore diameter. In this picure, the bore gauge was zeroed at 2.2050" and this rod was measuring 2.2053"
4) To measure the bearing shells all you need is a bearing micrometer and it is straightforward. Even with the tight tolerances of the GT3R Race bearings, the shells varied one tenthousanth (.0001). This allows me 3 different sizes to work with to obtain the clearances I need.
You can see by the specifications on my build sheet that I was able to mix and match rod bearing shells to obtain my desired connecting rod clearance. Had I not done these measurements and simply installed the parts, I could have run into an issue on one of the journals which would have had a clearance .0002" too tight and that may have caused issues with premature wear on one rod. So, even though we are using high tolerance parts, they still need to be checked and assembled in a manner that works with the specifications. This is one aspect of blueprinting.
Over the break, I'll finish clean the case and crankshaft and assemble the bottom end.
Enjoy...
My old crankshaft was a 996 GT3R crankshaft, installed without modification. When removed, there was no measurable wear and has now been reused in another project. The new crankshaft improves upon the 996 GT3R design and has a larger oil drilling through the center for improved oiling to the #2 and #5 rod bearings. Although the 996 Crank did not show signs of oiling issues, this should ensure that there are never any issues at high rpm. In addition, the oil feed holes at the ends of the crankshaft are now drilled at an angle to the centerline of the crankshaft to aid in oiling and to align with the thrust of the crankshaft and orientation of the forces on the crankshaft. This crankshaft has an unspecified stroke with an unspecified weight but uses the same 996 GT3 size journals. The counterweights have been designed to work with the ligher recipricating mass of my new engine.
I've gone through and measured all of the rod journals (main, rod, #8 main), have measured all of the rod bearings, and all of the connecting rod big ends. I'm using GT3 Race bearings which are coated and the tolerances are tighter than a street replacement bearing. Part of blueprinting an engine, and why a performance engine build takes roughly 20 hours more than a "throw it together" engine rebuild (I hesitate to say street rebuild because we only put engines together with careful measuring) is due to this measuring. I've included some pictures of an old GT3 connecting rod to show you the process and I've included the actual values from my new connecting rods ready to be installed. (I had done this a week ago and was bored with the snow today)
1) With the new connecting rod bolts, I've captured the starting bolt length measured with a micrometer. This will allow me to have a baseline on the bolt so when the engine is disassembled for inspection, I can see if the rod bolt has stretched (ie no good). Possible reasons would be an overrev or a bolt simply worn out.
2) Once you know the starting value, you can use a rod stretch gauge and set to 0 at the untorqued rod bolt length. Then, you begin to tighten the rod bolt and check the stretch as you go along. The picture here shows the rod bolt has stretched .0070". The method I use is that I have a digital torque wrench and can see the rolling torque. I usually torque them in stages. On my new bolts, the torque range is 60-95nm with a stretch of .0078" +- .0005". The importance here is the stretch of the bolt, not the torque value and you can see that there is a wide range of torque that is acceptable. On my old Carrillo rods, they torqued between 61 - 77ft/lb to achieve the .005" stretch required. I also measure the beginning length and stretched length and that will verify the stretch gauge as well as keeping a record of what has been done.
3) Once the rods are torqued, you can measure the bore diameter. In this picure, the bore gauge was zeroed at 2.2050" and this rod was measuring 2.2053"
4) To measure the bearing shells all you need is a bearing micrometer and it is straightforward. Even with the tight tolerances of the GT3R Race bearings, the shells varied one tenthousanth (.0001). This allows me 3 different sizes to work with to obtain the clearances I need.
You can see by the specifications on my build sheet that I was able to mix and match rod bearing shells to obtain my desired connecting rod clearance. Had I not done these measurements and simply installed the parts, I could have run into an issue on one of the journals which would have had a clearance .0002" too tight and that may have caused issues with premature wear on one rod. So, even though we are using high tolerance parts, they still need to be checked and assembled in a manner that works with the specifications. This is one aspect of blueprinting.
Over the break, I'll finish clean the case and crankshaft and assemble the bottom end.
Enjoy...
12-21-2008, 09:08 PM
#2
Addict
Rennlist Member
Rennlist Member
Better than sex!!!
12-22-2008, 11:31 AM
#3
Rennlist Member
Thanks for posting. As someone who has a lot of interest in race engine rebuild, but has no aptitude for it, I find the details that go into building a blue printed engine fascinating.
BTW, I disagree with Don. Sex is still better.
BTW, I disagree with Don. Sex is still better.
12-22-2008, 12:52 PM
#5
Nordschleife Master
Thread Starter
The GT3R crankshaft will fit an early engine. However, the nose is a flat nose like a 993, not a tapered nose like the C2 (well, the 1999-2000 996 crank was tapered, but they are hard to find). In addition, the locating dowl is a different dimension and the location has changed. This requires a custom pully to be made. The connecting rod journal is smaller so you cannot use stock rods and need a custom one made. So, no modifications required to the crank.
01-13-2009, 06:12 PM
#7
Nordschleife Master
Thread Starter
I am ready to assemble the bottom end of the engine now that I have my case prepared. This engine build, I modified the case to be the same as a 993 RS / RSR / GT2 cases. The modification is the installation of an O-ring into the case in the 2, 3, 4, 5 case webs. This requires machining a pocket for the O-ring in the right case. According to Porsche Motorsport, this prevents the case thru bolts from vibrating and breaking. I don't know how much of a big deal this is as I haven't seen any broken case thru bolts in the last 10 years of engines. I did contemplate on installing ARP case thru bolts this engine build, but the $750 price tag kept me from doing that.
In the picture you can see the case modification and in the second web I placed an O-ring for reference.
In the picture you can see the case modification and in the second web I placed an O-ring for reference.
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01-13-2009, 08:04 PM
#9
Nordschleife Master
Thread Starter
Hi Brant,
You may want to check some of the other posts on the engine project where much of the detail about the engine disassembly and the resultant parts and their condition. You'll probably find some other information of interest. The engine ran 100 hours measured by MoTeC.
The oil question is not so easy. In the past I have always used a 30 weight oil specific for break-in in every engine I've done for a customer or for myself for the last 25 years. On this race engine I did not do that, I used a standard non synthetic oil and the engine did not seat the rings properly and burned some oil until about 10 hours when I overheated the oil (270F) adjusting the throttle bodies. After that the crankcase pressure was normal and the engine finally seated the rings properly. The end result is that I will never try that again and have returned to using only 30 weight break-in oil in the engine through the first dyno session.
After that I ran Mobil 1 in the red top most of the time. For awhile I tested some Gold & Spectro non synthetic oil. I used this oil for 2 oil changes at about 12-15 hours each time. I was pleased with the Gold and Spectro, but returned to the Mobil 1 red top because I had so much of it from the stash I purchased as they were changing the formulation. I am unsure what I will run this next time around. I'm considering Elf, Mobil 1 v-twin (same as the old red top), but to be honest, I haven't really looked into it thoroughly and things seem to change every week.
You may want to check some of the other posts on the engine project where much of the detail about the engine disassembly and the resultant parts and their condition. You'll probably find some other information of interest. The engine ran 100 hours measured by MoTeC.
The oil question is not so easy. In the past I have always used a 30 weight oil specific for break-in in every engine I've done for a customer or for myself for the last 25 years. On this race engine I did not do that, I used a standard non synthetic oil and the engine did not seat the rings properly and burned some oil until about 10 hours when I overheated the oil (270F) adjusting the throttle bodies. After that the crankcase pressure was normal and the engine finally seated the rings properly. The end result is that I will never try that again and have returned to using only 30 weight break-in oil in the engine through the first dyno session.
After that I ran Mobil 1 in the red top most of the time. For awhile I tested some Gold & Spectro non synthetic oil. I used this oil for 2 oil changes at about 12-15 hours each time. I was pleased with the Gold and Spectro, but returned to the Mobil 1 red top because I had so much of it from the stash I purchased as they were changing the formulation. I am unsure what I will run this next time around. I'm considering Elf, Mobil 1 v-twin (same as the old red top), but to be honest, I haven't really looked into it thoroughly and things seem to change every week.
01-13-2009, 09:41 PM
#10
Rennlist Member
I am testing Brad Penn and Elf Competion 10w50 in the 944's this season. Running Redline 10w40 in the 964 cup as it is by far the best UOA's I've had. M1 in my case was OK but always sheared out of grade even with short drain periods. Joe Gibbs has a good break in oil as does Brad Penn. There are too many options! Find a few that work for you and your car and stick with it. I've had really terrific "luck" with my oil choices. PM if you'd like some sample UOA's.
01-13-2009, 11:00 PM
#11
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I switched to Brad Penn for last season. Prior to that I was using Mobil 1 red top. What I had left. My S2 would use about 1.5 quarts over a race weekend on the Mobil 1. Last season I used about 0.5 quarts or less for a similar weekend.
01-14-2009, 11:23 AM
#13
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If you are making a custom pulley for the GT3 crankshaft, consider having it made with 2 or 3 dowel holes and have the end of the crank drilled to take the extra dowels.
Why?
Because with the rate that this engine will accelerate, in extreme conditions it can shear the single dowel and spin off the pulley. Happened to me on track when I wrong slotted 2nd instead of 4th and buzzed the engine up to 8700 - twice in the same instance. Engine survived (how about that for the 9m high lift valve spring package and billet followers??) but the pulley came loose three bends later. Mine now has one extra dowel on a new pulley.
Why?
Because with the rate that this engine will accelerate, in extreme conditions it can shear the single dowel and spin off the pulley. Happened to me on track when I wrong slotted 2nd instead of 4th and buzzed the engine up to 8700 - twice in the same instance. Engine survived (how about that for the 9m high lift valve spring package and billet followers??) but the pulley came loose three bends later. Mine now has one extra dowel on a new pulley.
