If you hear no audible knocking then you are not doing damage to the engine. There is no difference in the cleansing capacities between different grades of fuels so don't buy into that argument either. Lower grades will not clog your fuel injectors.
I also have a 93 ls400 and ever since i've had it, i've put premium (91). The manual states: "premium unleaded gasoline with a research octane no. 96 (octane rating 91) or higher. gasolines with an octane numberas low as 91 may be used if premium unleaded gasoline cannot be obtained." I'm in California and premium is 91.
Premium fuel is required for the high compression engine. The higher temp burn reduces carbon build up on the cylinder heads, valve stems, valves and exhaust ports. The way I see it the engineers that build these engines know what they are doing and I will pay the extra $10-15 a month for the premium.
Just my .02 worth
if the prices for premium go over 270 then im switchin back to regular
its like 265 right now
1. Black on Black 1999 LS400 PM-spec
-Maya-Megan-Magnaflow-LSportline-Xenondepot-PPE Engineering-Duce-Platinum VIP-Figs Engineering-R1Concepts-
2. 1989 Toyota Supra white package
Current Status: -500 Internal System Error-
3. Black 2004 IS300 -Manaray-HKS-Eibach-
4. Ebony Teal 1995 LS400 11-8-06