LSD vs Welded diff
 

My friend says that a LSD that is shimmed to act almost as a welded differential will have less power loss than an actual welded differential. Is this true? Thank you

Welded diffs have no place anywhere than NASCAR, drag racing, or a drift missile.

There's no "power loss" to worry about. But any LSD is going to be easier to turn than a welded diff or spool.

Some of those monster porsche le mans cars from the 70's and 80's ran full spool. Just sayin.

They don't use spools or welded diffs in NASCAR.

And yes, your friend does not know what he is talking about.

not sure what power loss means? the diff is just along for the ride except when you're turning, and you're probably not using all the power in a turn, so it A) doesn't matter and B) the LSD takes some power, but that is how its limiting wheel spin, which is why you have it.

In drag racing, a lot of the guys who bother testing know that a spool is generally a tenth or two slower than a limited slip. Tires never have the same rollout.