*Batman*

I would either stick with 93 Octane which is what they sell here, or blend in a tiny amount of 100 Octane to get the average up to 95 octane which is what premium is in the UK and which is probably supported by the stock ECU which adjusts to Octanes from 86 to 95.

http://www.osbornauto.com/blend.htm

rjacket

Actually just interested in fuel economy and engine cleanliness.

Higher octane fuels burn more cleanly correct? So better fuel economy and cleaner engine. So my first thought was adding a bit of 100 octane.

Second question on ethanol was that I had heard people complaining about E10, on the basis that it wasn't good for their engines. On the other hand, I read elsewhere that the alcohol helps clean the engine as well as have environmental benefits.

So just curious I guess

rjacket

Interesting. However it says not to use super with any alcohol in it which is hard to find esp in CA.

ASILVER

also per batman's post make sure you understand that 95RON in the UK has nothing to do with 93 or 100 octane in the US as we use a different calculation to achieve our rating

it's similar but still not equal,

UK uses RON to calculate octane whereas the US uses AKI to calculate octane

RON = Research Octane Number
MON = Motor Octane Number

In the USA we've standardized on the AKI (Anti-Knock Index), which is calculated as (RON+MON)/2.


basically US 91 = UK 95 already, therefore if you blended any 100 US to 91 US you're already over 95 UK.

sakataj

iTrader: (182)

hahahaha thats to funny

but NOT as funny as this


i cant stop laughing at this


if u mixed 100 into 91 you would end up with somewhere around 94-96 octane which would be fine and produce some power as the ecu can compensate for this. def not cost effective on a street vehicle....get a deep wallet i drive with ALMOST 3/4 of a tank of 105 on one of my crotchrockets. its UBER expensive but my motor is a depraved thirsty *****, although my motor is built lol

*Batman*

Yeah it's closer. UK super unleaded petrol is 98 RON which is 94AKI, and BP Ultimate 102 is 102 RON which is 97 AKI

Although in my experience there is negligiable impact of any octane rating. On our ES we have tried 87 octane and 93 octane and I can't tell the difference in acceleration or smoothness. I think the engine just adjusts to the slower ignitiion timing of the higher ron fuels without creatign more power. This is why there is a 1hp difference betweent he Camry V6 which rund regular, and the ES350 which runs premium.

rjacket

So why do Lexus want us to run premium (apart from the fact the engine is tuned that way)?

In other words, why do Lexus tune the same engine to take premium?

If it's not power, it must be fuel economy.

Or for the illusion that it's a luxury car .................... (kidding, don't want to start that thread again)

rominl

iTrader: (4)

your answer is partly here

http://www.lexus.com/models/GS/detai...fications.html
http://www.lexus.com/models/ES/detai...fications.html

es350 has compression ratio of 10.8:1, gs350 and gs460 11.8:1. in general, the higher the compression, the more its requirement on the octane value. and i can tell you, 11.8 that's very high compression (you can google more on meaning of compression ratio)

on lexus cars, the ecu is smart enough to help sense the octane value in the gas and retard timing if necessary. this is to prevent any pinging issue which will be noticeable to owners as "jerkiness" or "roughness". however, over time, it could induce worse fuel economy or slightly reduced power. put it this way, between 91 and 87, you wouldn't expect drastic changes anyway.

grade of gas is especially important on FI cars. my friend with the wrx, he has chips boosting up the power more. the car becomes very sensitive to gas between 87 and 91, at 87 is a lot of pinging.

*Batman*

On some cars when you use non-premium you do get pronounced pinging - like the V-series Cadillacs. However most cars adapt so it's not pronounced. I guess there is a slight increase in roughness. I haven't noticed it in our ES350, but I do notice it in our Infiniti EX35 which also has a high compression engine. It's interesting but this explains why the same engine feels smoother in the Infiniti than in the Nissan - it's fuel grade!

So the logic is the following:

High performance luxury cars use higher compression ratios
High compression ratio engines run smoother on higher octane fuels, but most are designed to accomodate lower octanes but with a slightly roughness.
To maximize the luxury experience, the manufacturers therefore recommend premium.

Premium does not make more power than regular for the same engine, but it does allow the design of more powerful engines which run smoother with premium.

The reason that cars like V-series cadillacs and Nissan GTR struggle to run with regular whereas Lexus does not is most likely forced induction which implies compression ratios above 12:1

Bottom line for people here - paying for premium makes your car smoother, but not faster.

rjacket

Ok, but I was more refering to ES350 vs Camry

Camry: 3.5-Liter V6 DOHC 24-Valve Dual VVT-i; 268hp @ 6200 rpm; 248 lb.-ft @ 4700 rpm. Mpg 20/29 (Toyota site) 19/28 (Lexus site) Weight 3516

ES350: 3.5-Liter V6 DOHC 24-Valve Dual VVT-i; 272hp @ 6200 rpm; 254 lb.-ft @ 4700 rpm. Mpg 19/27 Weight 3605

Same engine, so same compression ratio I presume.

Using premium in the ES gets a tiny increase in HP and Torque which should give you better fuel economy, but in fact the mpg of the Camry is better.

I don't see why premium would give you a smoother drive though. If the engine adjusts it's timing, then the smoothness would be the same. It seems it's just about a slight improvement in power, and at those levels, it appears the extra cost is not worth it.

*Batman*

It doesn't. Like I said, we have an ES350 and the regular vs premium is not noticeable. In the Infiniti it is noticeable, but not in the ES350.

That small hp difference above must be exhaust or intake related.

rjacket

I think it's premium gas related. More oxygen in the fuel means more powerful explosion within the same space. Has to lead to more hp & torque. Also, you can see footnotes on the Lexus website that say the 0-60 times were achieved using premium gas.

I may move down to mid grade in my 3GS and see what happens from a performance perspective. If they have an engine which they put in a Lexus and recommend premium, which they also put in a Toyota and recommend regular, then there's some data to support the fact that the 3GS can safely run on non premium gas also.

The penalty will be less power, but very little lost. Apart from the power issue, nobody is giving me any compelling reasons to run premium eg engine cleanliness, fuel economy, smoothness etc.

rominl

iTrader: (4)

in that sense i can already tell you it will be safe, if that's what you looking for. like i said the ecu will retard the timing to match. there is no need to prove that again

LexFather

It will run fine. Shoot I've put 116 in my GS 430 at the track before. Its basically a cleaner more than anything.

Europe has higher gas standards than us in regards to Octane and Lexus sends them the same engines we have. They don't get any better MPG than we do.

Brockton

These articles say there is no difference, but still are confusing to me:

http://www.consumerenergycenter.org/...s_premium.html

http://www.scientificamerican.com/ar...tion-premium-g

http://www.edmunds.com/advice/fuelec...3/article.html