Modern trailing arms for the 914?, 986 carriers/calipers/e-brake, more adjustability, more tire? |
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Modern trailing arms for the 914?, 986 carriers/calipers/e-brake, more adjustability, more tire? |
horizontally-opposed |
Jan 26 2021, 12:21 PM
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#1
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Advanced Member Group: Members Posts: 3,431 Joined: 12-May 04 From: San Francisco Member No.: 2,058 Region Association: None |
I've been reviewing past discussions on these (links below) off and on, having test fit a 215/60R15 Pirelli P6000 on a 911R wheel into both rear fenders of my narrow-body 914. It seems doable, but it's going to take some massaging on the outer fender, custom spacers, and—maybe—narrowed trailing arms. Which got me to thinking about the current state of the 914 trailing arm, which is the same it's been since 1970.
Basically, those heavy, non-adjustable steel trailing arms are one of the very few things on the 914 that hasn't been addressed or evolved by the aftermarket. I'm running PMB-rebuilt trailing arms with PMB-rebuilt calipers, and can redo them again with reinforcements and/or some reshaping, but I wonder how hard would it be to do blade-type trailing arms of similar strength with less weight and/or more adjustment. Could a 911 spring plate, or a triangulated or otherwise reinforced version of it, be adapted? Looking at the basic design of the 914 arm, it doesn't look all that complicated, but I'm no engineer. EDIT: Possible use of a machined 986 wheel carrier, an aluminum casting by Brembo that incorporates the 986 e-brake and 986 four-piston caliper mounts, comes up later—a very interesting idea from @Chris914n6, particularly as the castings are available for $100-200ea used or new from Porsche. Bolting that carrier to a new steel trailing arm with a lower damper mount seems viable to me, but here to learn. The custom work to narrow factory 914 trailing arms looks extensive, but has been done by both @914timo and @sixnotfour as well as, it looks like, Rich Johnson. I could see doing it in the process of moving to 911 e-brakes and 986 2.5 brakes, maybe, but I wonder if a group buy might attract a 914 vendor we all want to support? Relevant threads: http://www.914world.com/bbs2/index.php?sho...p;#entry1247827 http://www.914world.com/bbs2/index.php?sho...ailing&st=0 http://www.914world.com/bbs2/index.php?sho...238144&st=0 http://www.914world.com/bbs2/index.php?sho...234391&st=0 |
914forme |
Jan 31 2021, 08:03 PM
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#2
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Times a wastin', get wrenchin'! Group: Members Posts: 3,896 Joined: 24-July 04 From: Dayton, Ohio Member No.: 2,388 Region Association: None |
I have been thinking about this a lot, and came up with several solutions but they achieve nothing. As just posted there are a bunch of issues with the rear arms on both the 911 and the 914.
I had a set of the best arms ever made from Tangerine Racing. And they had a bit of clearance issues with 17 rears. Chris said dent the gusset he puts in there. Here is my thoughts going thiner you have to increase strength in some way. Thicker walls and internal gussets but these do nothing for the inherent geometeryissues that come with running the arms. If you want lighter get a set of arms made out of Titanium. That would also allow you to narrow them. If you really don't care what they look like under the car, a series of laser cut sections could be made and significantly reduce the thickness of the area while adding to registry. If you did this out of aluminum then you could weld on a modified 986.2 rear console and all the great bits that go along with it. Lot of TIG time to build it. In reality have someone 3D model it, send it off to be 3D printed as a sand cast mold, and then build the parts of your dream. You get one shot with the mold. But it works. |
barefoot |
Feb 1 2021, 11:45 AM
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#3
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Senior Member Group: Members Posts: 1,272 Joined: 19-March 13 From: Charleston SC Member No.: 15,673 Region Association: South East States |
I have been thinking about this a lot, and came up with several solutions but they achieve nothing. As just posted there are a bunch of issues with the rear arms on both the 911 and the 914. I had a set of the best arms ever made from Tangerine Racing. And they had a bit of clearance issues with 17 rears. Chris said dent the gusset he puts in there. Here is my thoughts going thiner you have to increase strength in some way. Thicker walls and internal gussets but these do nothing for the inherent geometeryissues that come with running the arms. If you want lighter get a set of arms made out of Titanium. That would also allow you to narrow them. If you really don't care what they look like under the car, a series of laser cut sections could be made and significantly reduce the thickness of the area while adding to registry. If you did this out of aluminum then you could weld on a modified 986.2 rear console and all the great bits that go along with it. Lot of TIG time to build it. In reality have someone 3D model it, send it off to be 3D printed as a sand cast mold, and then build the parts of your dream. You get one shot with the mold. But it works. Making trailing arms out of titanium or aluminum won't necessarily buy you anything of value. Stiffness is the major design requirement for a trailing arm and for a given mechanical design (ie the present dimensions od the 914 arm) While aluminum is only 34% as dense as steel, it's only 34% as stiff as well, so specific stiffness (Tensile modulus divided by density) is 106 for 7000 series alloys. 6-4 Titanium alloy is 56% as dense as steel boy again is only ~62% as stiff, so specific stiffness is 101. carbon steel is more dense, but much more stiff, so specific stiffness is 106. so for a given geometry you'd have to make the wall thickness much thicker in aluminum to achieve the same stiffness, same for titanium, so no weight savings. Only changing the arm geometry (like a bigger box section, or the clever tube inserts seen in these posts) can improve it's stiffness. Higher strength alloys don't improve stiffness, just allows greater deflection before permanently bending. |
914forme |
Feb 2 2021, 09:53 AM
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#4
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Times a wastin', get wrenchin'! Group: Members Posts: 3,896 Joined: 24-July 04 From: Dayton, Ohio Member No.: 2,388 Region Association: None |
I have been thinking about this a lot, and came up with several solutions but they achieve nothing. As just posted there are a bunch of issues with the rear arms on both the 911 and the 914. I had a set of the best arms ever made from Tangerine Racing. And they had a bit of clearance issues with 17 rears. Chris said dent the gusset he puts in there. Here is my thoughts going thiner you have to increase strength in some way. Thicker walls and internal gussets but these do nothing for the inherent geometeryissues that come with running the arms. If you want lighter get a set of arms made out of Titanium. That would also allow you to narrow them. If you really don't care what they look like under the car, a series of laser cut sections could be made and significantly reduce the thickness of the area while adding to registry. If you did this out of aluminum then you could weld on a modified 986.2 rear console and all the great bits that go along with it. Lot of TIG time to build it. In reality have someone 3D model it, send it off to be 3D printed as a sand cast mold, and then build the parts of your dream. You get one shot with the mold. But it works. Making trailing arms out of titanium or aluminum won't necessarily buy you anything of value. Stiffness is the major design requirement for a trailing arm and for a given mechanical design (ie the present dimensions od the 914 arm) While aluminum is only 34% as dense as steel, it's only 34% as stiff as well, so specific stiffness (Tensile modulus divided by density) is 106 for 7000 series alloys. 6-4 Titanium alloy is 56% as dense as steel boy again is only ~62% as stiff, so specific stiffness is 101. carbon steel is more dense, but much more stiff, so specific stiffness is 106. so for a given geometry you'd have to make the wall thickness much thicker in aluminum to achieve the same stiffness, same for titanium, so no weight savings. Only changing the arm geometry (like a bigger box section, or the clever tube inserts seen in these posts) can improve it's stiffness. Higher strength alloys don't improve stiffness, just allows greater deflection before permanently bending. I while I agree with you on your basics, it is the design that forms the ability to make the part structurally sound beyond the pure metallurgy, You have to know what you're doing with the Alloys to make this work. I was never implying it would have been built the same as the 914 stock steel carbon arm. But that you are limited in the design due to the factors placed onto via the chassis. |
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