Hybrid Car – More Fun with Less Gas

better mileage with higher octane? - Page 4

register ::  Login Password  :: Lost Password?
Posted by 51_racing on January 8, 2007, 8:17 pm

Eeyore wrote:

Absolutely could not be more WRONG here.
I race(d) in a class that limited compression to 9.5:1.
We could run any fuel we wanted, and time after time, people would put
race gas (Sunoco 110 or Turbo 110) then have to crank their ignition
timing way up only to come close to getting the same performance that
they did using 92 octane pump gas.

Posted by Eeyore on January 8, 2007, 11:35 pm

51_racing wrote:

That's hardly typical though. I thought we were talking about road cars ? Also
modern cars don't have manual timing adjustment., the ECU does it.


Posted by Bruce Richmond on January 9, 2007, 2:25 am

Eeyore wrote:

His point was that if the engine was optimized for lower octane fuel
then you have to resort to work arounds like bumping the timing way up
with little if any bennefit.  There are no absolutes but it has been my
experience that the higher octane fuel has a slower flame speed for a
given temperture/pressure.  Increasing the compression ratio will
increase the temp/pressure.  Without the compression increase you
resort to advancing the timing to get the temp/pressure back up where
you need it.  But that works against you because the engine has to
overcome the rise in cylinder pressure before the piston gets to TDC.
So even if the ECU advances the timing to take advantage of higher
octane you get little if anything extra for your money.  If you have a
turbo you can crank the boost up and make more power, but that's not
the same thing as mileage, which is what this thread is about.


Posted by TE Chea on January 2, 2007, 5:27 pm

| The octane rating is, just as I said, a number related to antiknock
| properties.

Wikipedia says lower octane petrol usually produces less heat
, this I find true in BP's RON92 compared with RON97 :  both
my mitsubishi 4G15P & honda F20A ( original cr 9.2 & 9.6,
both have improved cooling via copper wires ) can use RON92
, esp in humid air here & on flat land ( no towing / climbing ),
but RON92 produces less heat ( & so torque ), so its 1.56%
lower price cannot justify 2-4 % less torque.  My brother's
mitsubishi 6G72 ( cr is just 9 ) needs just RON92 per owner's
manual, but he buys RON97, & I agree as wise.

Posted by CJT on January 2, 2007, 5:33 pm
 HLS@nospam.nix wrote:

Precisely.  Just think about it -- at one time, octane was increased
by adding lead compounds.  Why would lead increase a fuel's energy?

The e-mail address in our reply-to line is reversed in an attempt to
minimize spam.  Our true address is of the form che...@prodigy.net.

This Thread
Bookmark this thread:
  • Subject
  • Author
  • Date
please rate this thread