JMortensen Posted January 13, 2007 Share Posted January 13, 2007 So I'm getting ready to paint the whole underside of my car pretty soon here (currently stripped bare), and I'm looking at the trans tunnel and the ears for the transmission. My original intention was to leave the engine placement alone, but I know I'd be back in here cutting the "ears" out of the trans tunnel in a couple years, so I'm thinking that now might be the time to do this.Eventually I'd like to do an LS swap, but for right now I'm going to stick with the L6, at least until I can blow it up and justify the swap. I was thinking that I might like to change out the trans mount to make it attach to my subframe connectors, then I was thinking that if I did that I almost might as well set the damn engine back and improve the PMOI. I've seen cars with this done but never really paid attention to how this is done. Without messing with the firewall other than cutting the hood latch off, I think you can move the engine back about 4". I guess the question then becomes how do you mount the engine? I suppose a setback plate would work, although 4" of setback would have me worrying about the plate breaking. It might be fairly easy to box the stock "towers" on the crossmember and then run a diagonal brace from the boxed section up to the plate to reinforce it a bit. I think I need clinical help to cure me of the while I'm at its... In the meantime if anyone has any pictures of engine and/or trans mounts for L6 cars with the engine setback that would be great. Or if you just want to talk me out of it, I'm listening. Quote Link to comment Share on other sites More sharing options...
mrcheeze36 Posted January 13, 2007 Share Posted January 13, 2007 Hey Jon, Ask Johnc...I believe The ROD's engine was moved back and lowered. He may still have his mounts available. Here's a pic of johnc's motor from the betamotorsports site. Looks like the hood latch may need to be removed: Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted January 13, 2007 Share Posted January 13, 2007 As Eric said, JohnC has posted on this before, which I assume you've seen. Otherwise I would have to say ``the search button is over there.''. Let us know how you do it as I want to do it at some point. Dave Quote Link to comment Share on other sites More sharing options...
Boy from Oz Posted January 13, 2007 Share Posted January 13, 2007 Jon - Just a thought, but could you mount a second cross-member back 100mm from the existing one. Remove the engine mounts bits from the existing one and remove the suspension bit from the new one. After some consideration about forces, etc, you may consider some other lightening. This is very much off the top of my head - it's just an idea not a recommendation Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 13, 2007 Administrators Share Posted January 13, 2007 Jon - Just a thought, but could you mount a second cross-member back 100mm from the existing one. The problem with this is that it will put ALL of the loads of the engine through the frame rails/structure, whereas stock, it does not. If a person did something like this, serious consideration to structural reinforcement would be highly recommended. At least, thats how I see it... Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted January 13, 2007 Share Posted January 13, 2007 what if you made a bracket that bolte to the stock engine mounts and went straight back about 6" and then down to the frame rails? That way you distribute the forces to the frame and stock mounting position... Maybe made of some square or round steel stock Quote Link to comment Share on other sites More sharing options...
Boy from Oz Posted January 13, 2007 Share Posted January 13, 2007 The problem with this is that it will put ALL of the loads of the engine through the frame rails/structure, whereas stock, it does not. If a person did something like this, serious consideration to structural reinforcement would be highly recommended. At least, thats how I see it... If the cross-member is presently bolted directly to the frame rails isn't it already bearing all the weight? I have measured the mounting hole distances and they are 90mm, perhaps a completely seperate second cross-member would be too far back. As an alternative could you marry a second to the original using the rear mounting hole of the existing one as the front mounting hole for the second. It would envolve scalloping away a portion of the second member and welding it to the first. You could then reposition the engine-mount bracket so that it straddled both members. You would remove the steering rack mount on the second. You could also reduce the height of the engine-mount bracket before reattaching them which would lower the engine giving you perhaps even more clearance at the firewall. All theory you understand. Quote Link to comment Share on other sites More sharing options...
Dragonfly Posted January 13, 2007 Share Posted January 13, 2007 Well Jon, while your at it... you could make the set back plates like you had considered and then bolt an engine plate to the back of the engine between the engine and the transmission (like what Terry (blueovalz) has in his car). With that you will make all your mounting much more rigid and you will distribute the load from the engine and transmission across the tans tunnel, the frame rails and the modified engine mounts. Do some reading up on Terry's set up before you decide to take a bite out of this kind of project though. Dragonfly Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 13, 2007 Author Share Posted January 13, 2007 I really don't want to solid mount my drivetrain. I could do that fairly easily at this point, but I wasn't planning on it. Just a way to rattle nuts and bolts loose if you ask me... Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted January 13, 2007 Share Posted January 13, 2007 I am pretty sure JohnC moved his engine down as well as back. If it were me, I would cut the Datsun MM towers off the stock crossmember and just fab up some new towers that extend back and don't go up as high. I would also leave the stock trans ears alone (they shouldn't get in the way) and add some new ones however far back I was moving the L6. You are then spending a few hundred dollars for a new driveshaft and, depending on where your stock shifter came out originally, reworking the shifter hole and possibly lever. FWIW my LS swap did not require removing the stock trans ears. Another option is to find a drive shaft from a 70 240 that had the diff in the forward mounted positions. Those shafts are 35 mm shorter than the later shafts. This would give you and inch and a half rear movement without the expense of the driveshaft. With such a small set back you would unquestionably be able to use some type of set back plates on the motor mounts. You would then just need to redo the trans xmember, but might be able to get away with something that still uses the stock ears. As for a second crossmember, Ron is right in that the frame rails behind the stock crossmember are awfully thin. But I found it a simple matter to sheath the rails with a piece of 18 guage, then weld some 3/8 inch pipe through the rails to keep the mounting bolts from collapsing the rails. Quote Link to comment Share on other sites More sharing options...
johnc Posted January 13, 2007 Share Posted January 13, 2007 I boxed the existing mounts on the crossmember and then machined a chunk of 2024 aluminum that angled back from the top of the stock mount and was the 1" thinner then the OEM rubber mounts. Don't go overboard making heavy duty engine mounts because the trans mount also takes the load. With the power my L6 made I never had any issues with the engine mounts I made. Engine was set back as far as possible while still allowing head removal with ARP studs. You may also was to retain the trans mount ears in the chassis and rethink the actual mount on the transmission. I have a plate that was held in place by the bolts holding the tailshaft to the transmission, similar to an engine plate. Just reinforce the trans mounting in the chassis by runing some 1.5" square tube across the chassis in the passenger compartment connecting the trans mount to the rocker panel. You'll also need to "clearance" the front right of the driver's foot well to make room for your header. I cut the corner off and welded in some sheet metal. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 13, 2007 Author Share Posted January 13, 2007 If it were me, I would cut the Datsun MM towers off the stock crossmember and just fab up some new towers that extend back and don't go up as high. I would also leave the stock trans ears alone (they shouldn't get in the way) and add some new ones however far back I was moving the L6. You are then spending a few hundred dollars for a new driveshaft and, depending on where your stock shifter came out originally, reworking the shifter hole and possibly lever. I could do that, but I'm trying to keep it simple at this point. I don't expect that I'll use whatever mod I come up with to mount the V8, so I don't want to add another tower that I then have to cut off later. Also I have a taller than stock AZC oil pan so I really can't move the engine down too far. FWIW my LS swap did not require removing the stock trans ears. Really? Interesting. I've just seen that so many times I assumed it would be necessary. Do you think that's because the John's cars mounts positions the engine a bit more forward than the JTR? I assume there is a difference in the early ears vs the later ones, and I have the early ears, so do you know if one needs removing and the other doesn't? Another option is to find a drive shaft from a 70 240 that had the diff in the forward mounted positions. Those shafts are 35 mm shorter than the later shafts. This would give you and inch and a half rear movement without the expense of the driveshaft. With such a small set back you would unquestionably be able to use some type of set back plates on the motor mounts. You would then just need to redo the trans xmember, but might be able to get away with something that still uses the stock ears. I saw one car, not sure where, but it looked like they took the cheesy easy way out and they actually bolted to the stock motor mount, but with the front bolt in the rear hole. No setback plate, no nothing, just used one bolt instead of two. I think if I were to do that I could use the shorter driveshaft, and I know my bro-in-law Matman has about 10 of them. I'm kinda wanting to get the full effect if it isn't too hard to do though... I boxed the existing mounts on the crossmember and then machined a chunk of 2024 aluminum that angled back from the top of the stock mount and was the 1" thinner then the OEM rubber mounts. Don't go overboard making heavy duty engine mounts because the trans mount also takes the load. With the power my L6 made I never had any issues with the engine mounts I made. Yeah, I already snapped a badly modded trans mount, so I can definitely vouch for you on that part. Engine was set back as far as possible while still allowing head removal with ARP studs. You may also was to retain the trans mount ears in the chassis and rethink the actual mount on the transmission. I have a plate that was held in place by the bolts holding the tailshaft to the transmission, similar to an engine plate. Just reinforce the trans mounting in the chassis by runing some 1.5" square tube across the chassis in the passenger compartment connecting the trans mount to the rocker panel. My thought here was that the V8 guys just bolt their trans mounts to the floor, and I have the Bad Dog SFCs. So I figured I could do a simple trans mount that bolted to the SFC instead of the floor. The hope was to use it like a cross beam in the tunnel, which would be an improvement since the stock piece doesn't connect to anything structural. You'll also need to "clearance" the front right of the driver's foot well to make room for your header. I cut the corner off and welded in some sheet metal. This doesn't part doesn't phase me one bit, although I guess that is something I'd have to figure out later. It might not be necessary with my POS 6-1 header, but if it was that would be a bit of a bummer after painting everything. Maybe I'll just take a BFH to it if necessary. We'll see when I get there... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 13, 2007 Author Share Posted January 13, 2007 Looks like maybe for now I just need to cut the hood latch off... Quote Link to comment Share on other sites More sharing options...
johnc Posted January 13, 2007 Share Posted January 13, 2007 So I figured I could do a simple trans mount that bolted to the SFC instead of the floor. The hope was to use it like a cross beam in the tunnel, which would be an improvement since the stock piece doesn't connect to anything structural. That was my suggestion regarding the square tube going through the passenger floor to the rockers. The mount itself would either span the existing mounts in the tunnel or use the trans itself as a structural part. Additionally the brace to the rockers helps a little bit in a side imapact. When you remove the hood latch you create a nice flat place for triangulated strut tower bars... Quote Link to comment Share on other sites More sharing options...
tube80z Posted January 13, 2007 Share Posted January 13, 2007 The tranny mount on my car used the stock ears but hooked to where the case split rather than under the back where the normal mount is. Not sure this helps as it was solid mounted. On the front it had kind of a tripod arrangement that came from the stock engine mount towers. I'm not sure I would have done it this way myself but it was seemed to work. Let me know if you want some pics. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 13, 2007 Author Share Posted January 13, 2007 Sure I'd like pics, you know I'm a visual learner... Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted January 14, 2007 Share Posted January 14, 2007 Originally Posted by Pop N Wood FWIW my LS swap did not require removing the stock trans ears Really? Interesting. I've just seen that so many times I assumed it would be necessary. Do you think that's because the John's cars mounts positions the engine a bit more forward than the JTR? I assume there is a difference in the early ears vs the later ones, and I have the early ears, so do you know if one needs removing and the other doesn't? Mine is a 12/70 so I don't think the ears get much earlier. I had to build my own mounts. Pretty sure the reason I didn't need to remove the ears is because I used a TKO instead of a T56. There is actual a LOT of room around the trans. Quote Link to comment Share on other sites More sharing options...
wheelman Posted January 14, 2007 Share Posted January 14, 2007 This must be a later ear vs early ear thing as I had to remove the stock ears to get my T5 into the tunnel. I retained the stock Datsun crossmember by making new ears that bolted into the tunnel about 4" back from the stock location. I had to widen the tunnel a bit to get the crossmember in there but it all worked out. Not sure this helped much with your questions Jon but if you want some pictures of what I did I'm pretty sure I have some around somewhere. Wheelman Quote Link to comment Share on other sites More sharing options...
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