Take the 1MZ-FE 3.0-litre V6 engine for example. It is tuned differently for 192 HP, 210 HP, 220 HP, etc with different grades of gas. (old V6 Camry, Sienna+ES300, RX300+Highlander)

Besides modifying the intake and exhaust, changing the shape of piston heads can change the compression ratio, thus change the octane requirement.

The bottom line is to use what the owner's manual says, and never downgrade from it. If the manual says using higher octane gas can improve performance, then make your own judgment call.

Personally I didn't notice appreciable difference in performance and gas mileage with premium gas (91), so I stick with 87 (mid-grade in Colorado.) Even though 85 is supposed to work like regular in high altitude, but there's a severe loss of power so I use mid-grade 87.

 

Let's take the 2004 - 4.7 V8 used in the big Lexus LX470 and in the Toyota 4runner V8, they both even use the same 5 speed transmission. Both applications (Lexus LX470/Toyota 4runner V8) are rated at 235 HP/ 320 TQ. Toyota recommends 87 octane for the 4runner and I believe Lexus recommends 91 Octane for the LX470. WHY???

 

The 2004 4-runner owners manual says to use 91 octane for better performance.

Before assuming the engines of the 4-runner and LX470 are exactly the same, check the emission certification sticker on some vehicles at a Lexus dealer that have freshly arrived from Japan and havn't been detailed yet. If they differ in emissions output then it means the engines are tuned differently.

Also a fairer comparison to the 4-runner V8 would be the GX470 V8 since the GX is essentially a dressed up 4-runner. Compare fuel economy ratings, emissions output and published horsepower and torque figures. Then compare what the owners manuals say about fuel recommendations.

 

so someone said " except for the ES 300" which is what i have. . . a 92 to be exact. . . can i use the cheapest gas? i think im recommended to put 89, can i put the one cheaper? itd save me a few bucks and thatd be nice. . . thanks.

 

I asked the service department at the local Lexus dealer the same question re: Toyota vs Lexus. The answer I got after passing the phone around was the emission systems are different and anything less then premium fuel will damage the catalytic converter. Personally I think that is a load of BS.

 

Never downgrade from what the owner's manual specifies.