Last year when changing oil, the Kendall GT-1 that I used on anything with old seals and gaskets (synthetic seems to leak too easy), had changed from the traditional green to a typical golden color. I asked a counterman at NAPA, that runs a Super Gas car and also uses GT-1, if he had noticed the change or had heard anything about it. Last month on another web site, I came across a post were a few engine shops have had oil related failure with the new GT-1 Kendall. I relayed this info to the NAPA racer not to use GT-1 anymore. He then showed me a new racing oil from Valvoline. This is not the race oil they have had and still carry. This is 'Not For Street Use'. It has a zinc/phosphorus antiscuff additive that is not compatible with cat. convertors. This additive used to be in most oils and has since been reduced in amount to where there is only 10% of what it used to be. This should be great oil for non cat. conv. cars like our slants. Only race oils like Red Line have kept the % of antiscuff additives up. Lucas oil treatment is also supposed to have it. The new Valvoline race oil is available in synthetic and regular. And no, this is not a sales pitch!

Cecil

The additive is zinc dialkyldithiophosphate. This zinc phosphate organic salt has been in use for many years. It breaks down under extreme pressure/heat and plates/embeds itself into the opposing surfaces, minimizing wear.

Mitch

That's a mouthful! How about zi-pho for short.

Cecil

You say it's not compatible with cats, so would it likely damage an O2 sensor?

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me