Looking at a 2008 Lexus eg 350 with a 6cyl.engine.Why does it need hight test gas?

Two possible answers:

1. Because most Mercedes six-cylinder engines require premium fuel, and the Lexus is a wanna-be Mercedes.

2. Because Toyota is probably utilizing a higher-than-average compression ratio and/or ambitious timing to generate a reasonable amount of horsepower from this engine, and the price for that strategy is paid at the pump.

Many engines in that class will adjust their ignition timing based on the fuel used.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

...but a given octane is recommended for optimal performance.

I read a post on this forum a couple of years ago that guys were using 1/2 tank of Reg. and 1/2 tank of Prem. I have been doing that ever since with out any ping. I don't think my MB has a ping sensor.

Only you can determine if "optimal" performance is worth the extra cost.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

Will using a lower octane cause any damage to the engine?

Engines such as this have a knock sensor on them to determine if the engine is knocking. Pinging would be a better word, and the correct term is preignition.

For those that don't know a knock sensor is a small microphone bolted to the side of the engine that is tuned to pick up the rattle noise of preignition due to lower octane gas. It adjust the ignition timing so the knocking stops before you even hear it, but this will result in lower performance. It also keeps the top of your pistons from being blown apart a little at a time.

My wife has a Pontiac G8 GT that is supposed to do 0-60 in 5.5 seconds. On 87 Octane it has good performance, but on Premium she can pull of 0-60 in 4.6 seconds. And that's with the traction control on.

I think you will find that Premium is 'recommended'; not required, but I could be wrong. You might check out a few Lexus sits for more info from them what's been there and done that.

What difference does it make, its only a couple of bucks per tank, if its such an issue buy a Camry it takes regular and is the same car.

Most nicer cars with some power need 91-93 octane.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

In my old car I used to get better mileage with premium, usually it would make up for the extra cost of premium, but that was in the good ol days when gas was below $3. This got me thinking though, the M103 is supposed to have premium, yet its CR is something like 9.2:1, pretty low. Same with the M117. Hmm...

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

Thanks for all of that great info.

When I was a kid I distinctly remember gas being up at 107 octane etc. 116's and 107's etc were new cars then. Yet many are still running arount today with nothing but 91 etc available. Is there really a significant difference between these octanes? Because even if you are running your M117 on the highest octane available today it's still way lower than what was recommended when it was new.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

Peter,
Your memory is different from mine.
My first job was a commisioned island salesman (gas pump jockey on commission I made $7.40 on every $100 of gas I sold ( at 30 cents a gallon)). I sold for Esso; later Exxon. We had three grades--regualr at 94, plus at 97, and depending on the year, Golden at 101 , and later Extra at 100.
There are at least 2 methods for determining octane, and the present method averages the other 2, so variations in ratings do exist.--

Sunoco had a pump that could blend at six or seven different ratios, perhaps the highest was at 107 or so, I don't remember.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

Yes. Big time.

The knock you hear is predetonation of the fuel. It basically ignites before it can be lit by the spark plug. It is especially hard on the piston top and the cylinder walls.

If done long enough, it can actually break chunks off the metal.

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Ben
1987 190d 2.5Turbo

more importantly in the 70's gas contained lead which was there as a lubricant and a cooling agent. If you plan to run an old leaded gas engine for a daily driver, plan on hardened valve seats in your future.

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)