Ever wonder which LSx adapter plates you should use? Ever wonder how to chose between the various offerings? Surprise! If you look at the adapter plates for the motor mounts when installing an LSx engine in our old cars, they are mostly the same, and those that are different are easy to spot.
The motor mounts used with the SBC/BBC had two bolt holes at the top and one centered on the bottom. I'll refer to the bottom hole in the SBC/BBC motor mount as the "single" hole below.
LSx engines have a rectangular pattern for the motor mount. The adapter plates "adapt" the standard SBC/BBC motor mounts to the rectangular pattern on the LSx engines. When using these plates the triangular pattern for the SBC/BBC mount goes toward the front of the engine.
The triangular pattern is the chassis mounting point. The location of the single bolt hole for the SBC/BBC mount, as compared to the location of the nearest bolt hole in the adapter for the rectangular LSx pattern, is the key. Once you see the relationship between these two holes, you can easily determine what the differences are among the various mounts. In addition, when you see the relation of the single SBC/BBC hole to the rectangular pattern you can also determine the direction the LSx engine will be moved and by how much.
In the pictures below, the Moroso and DSE mounts locate the LSx engine in exactly the same place because, in each case, the single SBC/BBC mounting hole is concentric with the nearest hole for the 4 bolt LSx pattern.
Moroso mounts:
DSE mounts:
As compared to the DSE/Moroso mounts, the Hooker mounts locate the LSx engine farther back and slightly higher (or lower, see below) in the chassis. Look at the location of the single SBC/BBC hole as compared to the nearest LSx hole. The LSx engine moves as the 4 bolt hole pattern "moves" relative to the single SBC/BBC bolt hole.
Hooker mounts:
The Edelbrock mounts also move the LSx engine back, but not as much (measured by eye) as the Hookers and don't appear to have any impact on the LSx engine height:
The Doug's headers (PerTronix) mounts seem to be a combination of the Hooker and the Edelbrock plates, having two sets of holes for attaching the plate to the LSx engine.
This may be a pretty good option. I've got an LS1 with the F-body oil pan sitting in a '67 Camaro using the Moroso/DSE type mount and the drag link just barely hits the pan. Setting the engine back even 0.25" may provide adequate clearance. Certainly the full setback on the Doug's plates would work for oil pan clearance. However, I want to try to use a mechanical clutch linkage in this car, and the farther back the engine and headers are, the more likely I'll have Z-bar to header interference. I'll be getting Doug's headers for this swap (they appear to have the best #7 header tube for Z-bar clearance). So I'll try the "slightly back" position. If it works for oil pan clearance, I think I'll be good to go on the Z-bar. If I need to use the most rearward position, I know I'll be good on the oil pan and that the headers will fit (the plates are designed to be used with the Doug's headers) and I may still be okay on Z-bar clearance. If not, it'll be hydraulics.
A final variation on the theme is that some of the adapter plates want you to use the SBC/BBC mount upside down. If you look at the Moroso plates above they are marked "DS" and "PS" for driver's and passenger's side. In that case, the SBC/BBC mounts have to be upside down to fit the triangular pattern. With the "low/wide" SBC/BBC motor mount (so far as I can measure by eye) the upside down mounting of the SBC/BBC motor mount has no impact on the location of the LSx engine. I'm not sure if the upside down mounting changes the location of the LSx if you use the "tall/narrow" SBC/BBC motor mounts. However, for the plates that have an offset built in between the SBC/BBC motor mount position and the LSx engine mounting point, using the adapter plates upside down would have the effect of changing a slightly higher mounting point into a slightly lower mounting point.
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