This engine, the 2.3L, the compression ratio is 12.3, much higher than the normal engine which is between 9.5 - 10.5. Doesn't higher compression ratio require higher grade of gas such as 89, 91 or 94 Octane rating? Did you ever feel engine knocking using regular 87 gas?

 

It doesn't on the hybrid. Its an atkinson cycle engine not an otto and that changes things significantly. The valves are left open during a portion of the compression stroke so that the expansion stroke is EFFECTIVELY longer than the compression stroke. Something that is not done in a Otto Engine. Means you get more energy out of the expansion, but loose low end torque (which the FEH uses electric motors to compensate for--they are excellent at low RPM torque).

Its hard to say what that 12.3 ratio means in reality.... when you valves are open... you aren't compressing... is the 12.3 measured from when the stroke starts, or when the valves close.

In any case... you don't use higher octane fuel its a waste of money in this engine... you won't hear knocking under load. The engine is designed for 87, just like the manual says.

 

Given that this is an implementation of the Atkinson engine concept I think we can be pretyy certain that 12.3:1 is the ACTUAL cylinder compression ratio and it is very likely that the EFFECTIVE compression ratio is below 10:1.

 

Oh I see, seems you guys are all car experts.

 

Well as far as whether it requires 89 or higher octane...I...um..read the manual Just teasing... no one reads them it seems... I usually don't but for this beast I did.

Other than that... alot of it comes from reading the forum and picking up stuff from others. I can't say its **MY** expert opinion.... but I'd say there are several experts out there.

 

I believe I read on this list somewhere that lower than 87 will slightly increase mpg... a search is in order.

AH, here it is!

("In my FEH, when I get 85 octane in the Rocky Mountain states, I get better MPG than 87 octane in other states. One time I put 93 octane in mine, and got 30 MPG over the highway where as 85 octane gives me 36+ over the highway."- John/GPSMan1)

 

It's not the octane, it is the altitude. I have gotten better MPG at high altitudes (5000 + ft) with every car I have owned. I used 89 octane, because the owners manuals all say 87 is the minimum.

 

All FEH/MMH have a compression ratio of 12.3 to 1 which is reduced by the Atkinson Cycle. The '09 Owners Manual states Ford does not recommend using lower octane found in that high altitude areas. The manual now states that 87 octane is required, and warns against higher premium unleaded.

Here is a copy of the '09 owner's manual and you can look on pages 289 & 290:
http://www.motorcraftservice.com/pubs/content/~WO9HEV/~MUS~LEN/41/09hevog1e.pdf

GaryG

 

All very interesting, but they DON'T SELL 87 octane at those altitudes. My choices were 86 or 89. Since my owner's manual (2003 CR-V) specified no less than 87, I went with the 89.