I brought a car the little old lady PO never went anywhere with and went there on cheap gas. It sounded like a muffled alarm clock when driving over 50 mph.

After a tune up, filter, three cans of treatments, replaced knock sensor and a few tanks of high test, I gave up and water boarded the engine followed by an Italian tune up, twice!

It was draconian and took a few weeks but within a month, the engine ran like a sewing machine and the kids use regular gas again.

To be fair, I understand this can be very hard on an old HG and I was prepared to pull the head as the method of last resort as mentioned above.

However, most shave the head as part of the rebuild which I would think actually increase the squish thus offsetting the gains in loss of carbon deposits, but the idea is only theoretical and I’ve never heard it from a credible source.