I used Slick 50 in a Triumph Dolomite back in the mid 80's - and it make the car accelerate in 2nd gear as hard as it used to previously move when in 1st gear, it made an absolutely massive difference.
I later used it in a 1973 Ford Capri 1.6L and it made no difference whatsoever, so I think it matters as to how old the engine is and how it has worn.
I am positive that it can provide great results in some cases though.
However, I have no interest in using it in a modern car - I believe that the manufacturing tolerances on engines is much tighter than it used to be 20 years ago (of course!) and modern oils are far more advanced (of course of course) - so it has less of a role to play.
My grandad used to work for Ford in the UK on engine development back in the early 70's to late 80's and I clearly remembering him saying that you can only use it when an engine is correctly worn in, as if you use it when the engine is brand new it will not be able to wear in properly. I also remembering him talking about a test where an engine was treated with Slick 50 (which takes 2 oil changes and a certain amount of driving before the treatment is completed) and was then drained of oil and run without oil as a demonstration.
All impressive stuff in its day!
These days, instead of spending money on Slick 50 - invest that money in a couple of extra oil changes and the engine will be much more grateful.
