I believe the IS250's compression ratio is 12 to 1 which is very high. Regular would be a stretch to get by without knocking.
Exactly. With the higher compression you need to have a more accurate explosion. 87 octane is more unstable as compared to 93 octane. In my Dodge Ram with the 'oldschool ' 5.9 engine, that 87 octane gas causes the valves to rattle, 'ping' exploding before the valve closes. I hate that sound, its just not right , metal against metal. 93 octane will smooth it out every time. So premium is not a question, its more of a requirement. I surely Hope the IS350 will get better mileage than a three quarter ton four wheel drive truck. It gets 16.5 on the highway, with a tailwind. About twelve and a half mpg pulling motorcycle trailer. So I won't feel too bad about using premium in IS350. You have to take care of your investment .
Oh, did I mention I pick up the car on Friday !
2006 Blue Onyx w/grey, IS 350, OEM spoiler, 49,900 miles, new air filter, original flash & Floor mats. No resonator, original owner.
(new brake pads, rotors, & rear shocks) 5 months away from the '10 year' member club.
"If it weren't for physics and law enforcement, I'd be unstoppable"
Most of the Lexus cars should be fine with regular except Lexus IS 250/350 and GS300. These three cars use dual VVT-i and have extremely high compression ratios. Whether you use regular or premium is always determined by the compression ratio of the car. Ofcourse, it would not damage the engine in most cases if you use regular, but you will get constant knocking or if you drive it hard for too long with regular gas, it can seriously hurt the engine because low Octane gas mixed with gas cannot be compressed as well as high Octane with gas and can cause the fuel mixture to explode in the cylinder prematurely, which can lead to serious engine damage.
In a nutshell, Lexus IS and GS people should follow what the manual says and put premium in order to keep the car in best shape.
2005 Toyota Corolla XRS 2ZZ GE VVTL-i
6 Speed Manual/8350 rpm/Injen CAI/Greddy SP2/MPSS 205-45-17/Megan/Koni/Cross drilled rotors/Ceramic pads/Enkei 17 x 7.5/MWR 8 lbs flywheel/ACT Stage 1/ES MM/03 XRS ECU
"The word immediate was invented for the throttle response of this car....and the steering, and...the gearbox - Jeremy Clarkson"
There is more to the required use of high octane gas then just compression. Timing advance also plays an important role. That being said, higher performance engines have more compression and timings that generally advance depending on throttle position and rpms.
Higher octane gas actually burns slower then lower octane, this is to help prevent pre-detination (aka knocking) as the air/fuel mixture is compressed in the cylinder.
Modern cars have knock sensors that can detect these pre-detinations and adjust air, fuel, and timing to compensate, but only to a certain extent.
I would never use 87, but the price difference between 89 and 91 is usually only 10cents per gallon which equates to less then $2 per fill up. Assuming you fill up once a week thats a difference about $110 over the year.
Not a matter of "If you can afford the Lexus then why can't you spring for premium? Buy a Civic if you can't afford it". There are lots of things I don't buy but could easly afford. Why pay for the premium if you don't have to. My G35 only took premium so its no big deal to me. But I may run midgrade every now and then for my 70 mile commute.
Posts like this boggle my mind. You people need to do some research... Octane ratings aren't there for fun, and they're certainly not there to add to your vague notion that higher octane gas is in some way better, but really only something you splurge on.
Higher octane exists because it detonates less easily than lower octane. High compression means higher chance of detonation, hence the need for high octane fuel.
Obviously they're your vehicles, so do what you like. But the science and engineering behind Lexus's requirement for premium fuel is there for a reason.
You can use regular but you will just loose some performance. I, myself, will be using premium. My dealer actually delivers every new Lexus on their lot with regular. Ask them next time you are there and I would be surprised if most dealers deliver their cars filled with premium.
I was actually shocked to hear my salesperson tell me that they deliver all their cars with regular, but I can see them doing this to save a few dollars per car they sell.
The dealer I bought my car from also does this but I requested they put premuim and I know the tech that filled up my car and he did put premium.
I guess. But Im cheap what can I say. I used regular in the Landcruiser for years even though it said premium. No problems there. But it is a landcruiser. Im not opposed to the idea. Just wondering if the book is always right.
that's like buying a $20k high-def plasma TV to watch low-res VHS, or feeding a thoroughbred crabgrass. No, it doesn't hurt it, but it defeats the purpose of buying a luxury, high-performance car in the first place. Basically you will lose "some" hp due to the lower octane. Occasional use is probably alright. How much money do you really save anyway, over the life span of this car, compared to the total cost of ownership?
this is an interesting question. of course most everyone will initially fill her up with the top shelf, but in a few years that may become increasingly more difficult due to gas prices. I tend to put a ton of miles on my car from a long commute. If you add those extra few dollars up over the course of a year thats pretty substantial. hence going back to the posed question "how much could it possibly hurt to use regular gas?" I think thats a tough question to answer. for now...I'm all premium until convinced otherwise.
It's funny that you say that because for as long as I can remember premium has ALWAYS been 10 cents more than mid-grade, which is 10 cents more than regular. This is the case regardless of the fluctuations in the gas prices. Even when the gas $/gal nearly doubled it was 10/20 cents more than mid/reg. So, if this holds true, you could really say that as the gas pricess rise, premium becomes MORE affordable since the premium charged doesn't rise in relation to the gas price (percentage-wise)......
Between my V8 Grand Cherokee, 73 Charger (9 miles a gallon on 110 octane), boat, commuter car, and the IS (once its delivered ) I pay out the rear for gas starting this time of the year thru October. Just one more thirsty toy in my eyes.