Octane Level's

lowest octane rating that does not ping

 

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

 

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?

 

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

 

ummm ya well...

kinda sounds like

ping ping ping

oh heck i do not know... 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

 

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.

 

I'll stick to 87 octane.

 

lower compression under high load and high compression under low load, it automatically strives to get the most power out of the engine under all conditions. Also the knock sensor will retard the timing if it detects spark knock (detonation) occuring.

 

I suggest to you, if your up to the test is to put 85 in your Prius and do the mileage test and see if your mileage remains the same as 87 with no loss of power. If the answer is yes, I'd use it. If all of your driving is in Denver or a mile up your probably a prime candidate for 85. Then if your going on a trip and it'll take you down to breathable altitude I'd fill with 87. No sense spending more for octane your car doesn't need.

 

It's the higher altitute. The same gasoline tested at 87 octane at sea-level will test at 85 octane or lower at higher altitute. No big deal.. ust the lowest octane you can buy and the Prius will be happy.

 

the rule of thumb for many modern car, Prii or otherwise that have computer controlled ignition is to use the lowest octane gas possible - there is absolutely not benefit to using higher octane gas - just cost more and make the electronics adjusting the engine work harder.

If it pings, maybe go to the next higher level - but first have the timing and engine control modules checked.

 

http://www.caranddriver.com/article.asp?se...article_id=9752

Unfortunately, most of the tables and charts from the print version of this article aren't available online:
http://www.caranddriver.com/article.asp?se...article_id=3604

 

anything over 87 can cause starting problems with long term use. (from the toyota hybrid diagnosis training manual)

i suggest you do a search on "octane" because this has come up many times before.