Today I finally answered the 6L80E floor cutting question. If you lift the engine up in the chassis an thereby lift the engine /trans centerline, you will need to cut the floor. If you leave the engine /trans centerline in the same position as original, no cutting required. If you think about GM Design goals, they want to use various engines and trans in various platforms with minimal changes. If they have a platform using 3 different transmissions, all platforms must accept any trans without basic engineering changes. No relocating engine/trans centerline, drive angle changes or other major mode. An example is the late Suburban/Yukon/Escalade. My 2015 Escalade has an 8L90E trans. There is about 2" vertical clearance above the trans to tunnel. This platform, using the same floor has had the 4L60, 4L85, 6L80E. 6L90E, 8L90E and 10L90E.
Statements on 6L80E trans with LS engine. 1) Centerline of engine and transmission are the same on LS block and all trans that mount to it. 2) Trans vertical position is the same on 200-4R,700R4,4L60,4L65,70E,6L80E. 3) 6L80E with fixed output flange is about 2 1/2" shorter than 4L60E and about 3 1/2" shorter than 200-4R. 4) All of the bell housings are very similar in size. 5) If the LS engine is kept at existing clamshell mount position, longitudinally, horizontally and vertically the 6L80E transmission fits easily with over 1" clearance from all areas of the standard El Camino tunnel. 6) The shaft vertical/horizontal position of the output is exactly the same as a 4L60E.
We are in the process of installing a 5.3L with a 4L60E into a '86 El Camino. We set the 5.3 long block in place with the 4L60E attached. The mount position was in exactly the vertical position as the 200-4R. Driveshaft had to be shortened 3 1/2". We removed the 5.3/4L60E and swapped the 4L60E for the 6L80E. We then installed the 5.3/6L80E combo into the exact same space as the 4L60E. We even used the same crossmember by moving it forward a couple of inches. This apples to apples comparison leads me to these conclusions: 1) The 6L80E will fit in a G Body with no floor mods if you keep the engine vertical position the same using LS mount plates mounting the clamshell small block parts, as well as the original frame mounts to match the clamshell engine mount. 2) All of the engine trans combos have the same vertical position, 3) 6L80 is shortest of the normal transmissions used in the El Camino. 4) Install LS in original position and relocate the trans mount fore and aft, modify the driveshaft as required and you are done.
Statements on 6L80E trans with LS engine. 1) Centerline of engine and transmission are the same on LS block and all trans that mount to it. 2) Trans vertical position is the same on 200-4R,700R4,4L60,4L65,70E,6L80E. 3) 6L80E with fixed output flange is about 2 1/2" shorter than 4L60E and about 3 1/2" shorter than 200-4R. 4) All of the bell housings are very similar in size. 5) If the LS engine is kept at existing clamshell mount position, longitudinally, horizontally and vertically the 6L80E transmission fits easily with over 1" clearance from all areas of the standard El Camino tunnel. 6) The shaft vertical/horizontal position of the output is exactly the same as a 4L60E.
We are in the process of installing a 5.3L with a 4L60E into a '86 El Camino. We set the 5.3 long block in place with the 4L60E attached. The mount position was in exactly the vertical position as the 200-4R. Driveshaft had to be shortened 3 1/2". We removed the 5.3/4L60E and swapped the 4L60E for the 6L80E. We then installed the 5.3/6L80E combo into the exact same space as the 4L60E. We even used the same crossmember by moving it forward a couple of inches. This apples to apples comparison leads me to these conclusions: 1) The 6L80E will fit in a G Body with no floor mods if you keep the engine vertical position the same using LS mount plates mounting the clamshell small block parts, as well as the original frame mounts to match the clamshell engine mount. 2) All of the engine trans combos have the same vertical position, 3) 6L80 is shortest of the normal transmissions used in the El Camino. 4) Install LS in original position and relocate the trans mount fore and aft, modify the driveshaft as required and you are done.
