View Full Version : 89 Octane on 9.4:1

11-12-2010, 11:31 AM
Why does the MCX need 89 octane gas when it's only 9.4 compression? :confused:

11-12-2010, 11:52 AM
NVM, I found it on page 5.


11-12-2010, 12:19 PM
there you go! LOL
I was going to say what almost the same as MYMC said on page 5.


11-12-2010, 12:23 PM
Yeah, it seems that it's more of a performance/timing/computer issue then it is a compression issue.

That poll is from 05 and it seems it's still accurate information today.

east tx skier
11-12-2010, 12:30 PM
Engine Nut from Indmar gave a pretty simple alternative explanation some time ago. To paraphrase him, "87 Octane will run fine; 85 will not." The concern is that when you buy 87 octane, it may have aged a bit and no longer be 87 octane by the time it gets to your boat.

11-13-2010, 12:20 PM
very good alternative ETS. in the high performance auto world, we use 93 in everything. even in my 04 5.3 w/ 9.5:1 when towing in the mountains. I would get some KR with 87 with stock timing and fuel curves... Do not have that issue now though with the tune. I tuned for 89.
Its based a lot on the load the engine is under.