Octane Level's

[Prakash]

I wanted to know if anybody can help me resolve this issue. I looked at the previous posts but could not come to a conclusion.. I am waiting for Toyota to email me back on
this issue.

All the 2004, 2005, and 2006 Owner Manuals state:

"Select unleaded gasoline with an Octane Rating of 87 (Research Octane Number 91) or higher"

However, in the FAQ Link posted from Wikipedia it reads:

" Fuel Type

Page 204 of the 2005 Owner's manual. The Prius is designed to run on unleaded 87 octane fuel (85 in high altitudes) (R+M)/2 method [1], and is not calibrated to derive any advantage from slower and cooler burning higher octane, such as higher MPG. The Atkinson cycle effectively prevents it, so engine deposits and higher emissions can be expected due to incomplete burn and the catalytic converter not running hot enough to efficiently clean it. "

The owners manuel recommends octane rating 87 or higher.

The Faq provided from previous post on this topic indicate that the atkinson cycle prevents any advantage from higher octane levels than 87.

i currently use exxon's supreme octane rating 93, which has high anti-knock ratings. however after reading all this information i have considered using 87. i have not used 93 for that long. plus 87 is cheaper. so if the atkinson cycle prevents any advantage a octane level of 93 it would be pointless for me to continue using it.

the owners manuel recommends 87 or higher.

so which would be the best way to go?

[DaveinOlyWA]

lowest octane rating that does not ping

[Prakash]

Originally posted by DaveinOlyWA@Mar 22 2006, 10:01 PM
lowest octane rating that does not ping

[snapback]228806[/snapback]

does the atkinson cycle prevent potential advantage from higher
octane levels than 87?

[DaveinOlyWA]

there is no need to have higher octane. it only prevent premature ignition by raising the flash point of the fuel. pre ignition can be caused by hotter than normal running engines (hard to do on a Prius since the duty time of the ICE is not 100 % like a standard vehicle) running high compression.

the reason, as the air fuel mixture is compressed, the temp of the mixture rises. the higher the compression, the hotter it gets. if the mixture gets too hot, it starts to ignite too early causing that pinging sound. pinging is basically mini explosions of the mixture before its ready to blow which causes back pressure while on the compression stroke.

the higher the octane, the higher the flash point. it provides no other benefit. if you can use 85 octane and not get ping and its cheaper, do it.
that option is usually only available at high altitudes... but for 99% of all needs, 87 will do just fine

[tripp]

Originally posted by DaveinOlyWA@Mar 22 2006, 09:34 PM
there is no need to have higher octane. it only prevent premature ignition by raising the flash point of the fuel. pre ignition can be caused by hotter than normal running engines (hard to do on a Prius since the duty time of the ICE is not 100 % like a standard vehicle) running high compression.

the reason, as the air fuel mixture is compressed, the temp of the mixture rises. the higher the compression, the hotter it gets. if the mixture gets too hot, it starts to ignite too early causing that pinging sound. pinging is basically mini explosions of the mixture before its ready to blow which causes back pressure while on the compression stroke.

the higher the octane, the higher the flash point. it provides no other benefit. if you can use 85 octane and not get ping and its cheaper, do it.
that option is usually only available at high altitudes... but for 99% of all needs, 87 will do just fine

[snapback]228837[/snapback]

So Car dudes, here's a question. I live in Denver. I use 87 octane because the dealership told me to. I'd love to use 85 octane since it's even cheaper than 87. Am I pushing it or does that make sense give my altitude?

[DaveinOlyWA]

if you can use 85 and it dont ping, do it.

[Prakash]

Originally posted by DaveinOlyWA@Mar 22 2006, 10:48 PM
if you can use 85 and it dont ping, do it.

[snapback]228851[/snapback]

can you describe the ping sound, coming from the engine

so i can detect it properly

[DaveinOlyWA]

ummm ya well...

kinda sounds like

ping ping ping

oh heck i dunno... take a screw driver and tap on the top of the valve cover about 3-5 times per second... that is close.

the best way to test, is to floor it. if its present, you will have no problem hearing it. in fact, you can usually hear it over your stereo without too much difficulty. it has a much higher pitch than anything sound your engine will make

[DocVijay]

IMPORTANT NOTES:

(Pinging, knocking, detonation are all same.)

Most modern cars today have very advanced ping sensors (or anti knock sensors). The computer "senses" the impending ping/knock then retards the engine timing to prevent it. You may never hear the noise, and won't know that the engine is doing it. The only noticeable effect is the reduced power and... MORE EMISSIONS! I know that is important to Prius drivers!

Anyway, this pinging/knocking/detonation can damage the engine, so it stops it from happening. It may not be noticable in the Prius though, as it is not as powerful as other cars.

In our twin-turbo Volvo XC90, this is very critical. In a turbocharged engine, this detonation can be catastrophic, and the computer goes to great lengths to prevent it. If you fill anything less than premium (91/93 octane), the decreased power actually can be quite noticable under acceleration. In turbocharged cars it is extremely important to use hte highest octane possible, not so much from the danger of detonation, but from the greatly hampered engine. And like I said, the emissions ususlly go up quite a bit.

As I said, in a Prius it's not so much a problem. As someone noted, sue to the intermitent use of the ICE, it rarely gets too hot, and the compression is not so much a factor either. Still, you may never knoe if your engine is pinging or not since the computer cuts it off before it happens. Best bet is to just use the recommended octane, or if you're paranoid, once step higher.

I myself fill regular.

[tripp]

I'll stick to 87 octane.