Quote:
Originally Posted by Meph
i was looking at chevys website out of curiosuity of the new new engine specs, there 2.4 and 3.0 run on 87 oct with 11.2:1 (maybe even 11.7:1 if I remember correct). I don't know if thats useful at all but I found it interesting.
In theory your pulling timing because of pre ignition, as the higher compression ratio will burn faster you need to reduce the ignition point to keep the burn at an optimal point in the cycle. following this theory when you reduce timing to compensate for higher compression your not doing anything negative that would reduce power, just keeping it at the optimal point.
The second thing to consider is detention where the fuel self ignites from another source, as u raise the compression the pre ignition temp in the cylinder can raise to a point where it will ignite without a spark. This higher temp is what calls for a higher octane fuel.
hope that is kinda useful info to you
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I think you have to be careful comparing new engines to oler engines CR with octane rated .Many new engines use variable cam timing so they can adjust overlap and timing at low rpm/part throttle to give EGR affect and still run higher CR for same low 87 . Also ECU are faster so they have better chance to set up knock sensor to pull back or advance depending on fuel quality .
Here my 08 Accord 2.4 has 10.5 CR for 87 fuel, the Acura TSX 2.4(same engine but with 11.2) runs on 91 .
Both of these (K24Z3) have VCT . note i read some do use 87 in TSX and it does work but not as good (performance) .
I think your at a good value now for octane .