On Nov 1, 7:15*pm, (Larry W) wrote:
In article ,Robato y wrote:

...snipped...

I personally witnessed:
Run the engine up to temperature on a wheel-driven dyno take a sample
and print.
Without delay, change to synthetic.
Run the engine up to temperature on same dyno, half hour later, sample
and print.
...snipped...
133 HP to 137 HP.
I doubt it would show up on the quarter mile time, but hey, I was
surprised.

There may well be something to that, but it would not be unusual to
have a 4hp variation between runs even if NOTHING changed.

On tech offered the idea that less restriction in the new oil filter
could even make a 4 HP bump.