Administrators RTz Posted January 15, 2008 Administrators Share Posted January 15, 2008 Summary... If I wanted to offset the standard JTR mounts an additional 2" rearward, what is the necessary material thickness to achieve equivalent rigidity? Why... Today's EMS's commonly allow us to delete the distributor, which is the principal physical limiting factor with respect to engine location. Deletion allows a more reward location of the drive-train. Nitty Gritty... The JTR brackets offset the drivetrain rearward 3.5". If I wanted to increase that to 5.5", 57% increase center-center, I would need to increase the bracket thickness from .3125" to ??? Knowing that any material, doubled in thickness, results in 8x rigidity (increases with the cube, correct?), increasing the thickness to .375" should more than cover it with a 73% gain in stiffness... 20% greater thickness = 1.2^3 = 1.728. Am I looking at this right? Considering lateral and vertical loads, does it matter that they are mounted on a 45 degree, or is that 'no factor' in this scenario? Quote Link to comment Share on other sites More sharing options...
wrxand280z Posted January 15, 2008 Share Posted January 15, 2008 I'm no engineer but 1/4" steel is extremely strong in those short distances. If you are worried about it you could get some tempered steel. However I would have a machine shop fabricate it because its almost impossible to drill and tap. Just my $.02 Quote Link to comment Share on other sites More sharing options...
hughdogz Posted January 15, 2008 Share Posted January 15, 2008 Hi Ron, If you post up a drawing (or sketch) of the bracket and the loading conditions, I can create a solid model and run it through an ANSYS FEA solver I have here at work. ...if you're interested I can vary the thickness and give you the results respectively. Cheers, -Hugh Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted January 15, 2008 Share Posted January 15, 2008 This is an area to use "more than needed" because we are not too concerned with a pound or two extra. Also do not use a brittle grade of steel. Brittle steel (or anything) does NOT belong on cars...or bridges. You will get FAR MORE strength per pound by the SHAPE of the piece rather than the thickness of the material. ie. gussets, bosses, trusses, ribs. Common sense makes good engineering also. In order to solve the equation with a solid number result, you would need all the knowns; weights, torque, safety factor, engineering drawings, material specs, weld strengths..freebody diagrams...ughh...I am going to go with the "Make it extra strong!" solution to save the legwork. A good CAD program will do it but you still need DATA. A photo of the existing setup would help to guesstimate. Quote Link to comment Share on other sites More sharing options...
Minotaur Posted January 15, 2008 Share Posted January 15, 2008 We need a drawing in order to run it through a FEA (finite element analysis) program. We also need to know the material of construction (or asume cheap carbon steel). I would recomend whoever is doing this analysis to keep under the 1x10^6 cycles stress values for fatigue calculations. Quote Link to comment Share on other sites More sharing options...
jt1 Posted January 15, 2008 Share Posted January 15, 2008 The bellhousing bolts are the limiting factor, although the distributor is not far behind. To move 2" to the rear, you need to get rid of the distributor and cut out/major BFH the firewall. John Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 15, 2008 Author Administrators Share Posted January 15, 2008 To move 2" to the rear, you need to get rid of the distributor and cut out/major BFH the firewall. Hows this for BFH? Thanks for the offer Hugh. I'd hate to see you spend all day on something like this. I'd probably settle for sound advice, for or against 3/8" plate. Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted January 15, 2008 Share Posted January 15, 2008 Ron are you going to run a doghouse like a conversion van? lol. Wow. Evan Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted January 15, 2008 Share Posted January 15, 2008 " I'd probably settle for sound advice, for or against 3/8" plate." Ok your NEVER going to bend a 3/8" thick boxed or even correctly multi-gusseted & tig welded, steel motor mount simply because anything on the cars frame you bolt it or weld it TOO will bend first if enought stress is applied, you might also consider the potential stress and weight of the drive train are FAR below the tensile and sheer and torsional strength a correctly designed 3/8" steel mount less than 8" long will have Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted January 15, 2008 Share Posted January 15, 2008 Ron, If you had some sketches so that I could model the mounts I can run a diagnostic on it with my version of Cosmos. It's not like I'm working yet...LOL Dan BTW... Ron is aparently taking the brute force method on such a nice, calm Z... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 15, 2008 Share Posted January 15, 2008 Is that the same car that used to have the L6 mounted about 1/2 way into the passenger compartment? Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 15, 2008 Author Administrators Share Posted January 15, 2008 Ok your NEVER going to bend a 3/8" thick boxed or even correctly multi-gusseted & tig welded, steel motor mount simply because anything on the cars frame you bolt it or weld it TOO will bend first if enought stress is applied, you might also consider the potential stress and weight of the drive train are FAR below the tensile and sheer and torsional strength a correctly designed 3/8" steel mount less than 8" long will have I hear ya Grumpy... makes sense. Here is part of my concern... If the brackets are completely ridgid, there should not be any rotational forces on the crossmember. But, if the offset brackets were allowed to flex, that would putting a twisting load on the crossmeber, yes? Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 15, 2008 Author Administrators Share Posted January 15, 2008 Is that the same car that used to have the L6 mounted about 1/2 way into the passenger compartment? Stop paying attention Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted January 15, 2008 Administrators Share Posted January 15, 2008 First off, I realize you had asked for material thickness options, sorry as I do not have any answers regarding that. Though, a couple alternatives did come to mind and I hope you don’t mind me throwing them up here in this thread… Possibly use mounts off the “front” of the block, using some isolator in the OE Datsun cross-member?… Click ME for the mount below... Click ME for the mount below... Click ME for the mount below... Click ME for the mount below... Click ME for the isolators below... Some mid plate options... Click ME for the mount below... Click ME for the mount below... Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted January 15, 2008 Administrators Share Posted January 15, 2008 Or something like these options? Click ME for the eBay auction pictured below... Here is another lightweight approach. This bracket resides between the water pump and block. This approach might need a mid plate as well, or you could possibly fab some brace that also attaches to the SBC mount pads on the side of the block and ties into this bracket? Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 15, 2008 Author Administrators Share Posted January 15, 2008 Possibly use mounts off the “front†of the block, using some isolator in the OE Datsun cross-member?… Now I hadn't thought of a front mount. Hmmm... gotta look into that. This one is catching my eye... ... looks to be stout enough longitudinally as well. Thanks! Quote Link to comment Share on other sites More sharing options...
jt1 Posted January 15, 2008 Share Posted January 15, 2008 posted by rontyler Hows this for BFH? Heh heh... That will do nicely. More like BF sawzall!!!!! Looks like motor plate time to me. John Quote Link to comment Share on other sites More sharing options...
getZ Posted January 15, 2008 Share Posted January 15, 2008 Why not just cut the original motor mount brackets off and move them back 2 inches or do away with the JTR setback plates and move the original motor brackets back even further? Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 15, 2008 Author Administrators Share Posted January 15, 2008 Why not just cut the original motor mount brackets off and move them back 2 inches or do away with the JTR setback plates and move the original motor brackets back even further? I would prefer to mount the engine to the crossmember. The load paths of frame mounting don't really excite me. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 15, 2008 Author Administrators Share Posted January 15, 2008 I ordered... http://www.speedwaymotors.com/p/6725,405_1955-1994-Small-Block-Chevy-Engine-Mount.html?itemNo=chevy%20mounts At only $50.00, its not much of a gamble... we'll see how she fits up Quote Link to comment Share on other sites More sharing options...
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