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Old 02-19-2013, 04:46 PM
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etduc etduc is offline
MC Fanatic
Join Date: Jul 2004
Boat: Mastercraft Prostar 205
Location: East Texas
Posts: 910
Originally Posted by kjohnson View Post
My MC manual requires 89 or higher. Does anyone know if a lower octane (87) gas will have a negative impact on the engine or just have slightly reduced performance?
No reduction in performance. Gasoline is a mixture of chemicals. Octane is included to prevent pre-detonation. (pinging) You know, that rattling noise, some engine will make. If that is happening, it will ruin your pistons.

Simple rule, higher compression ratio, higher octane. Older engines, under 10:1 can typically run 87. If there no engine issues, and gas is of good grade.

I typically run 89, in my Expedition and boat. Both will run will on 87. My MC 205 is a 9.5:1 engine. I usually run 89. I figure 89 is the most sold product, so in theory, could be a more consistant quality.

Also, gas in Oklahoma seems to work better, and usually cheaper, than East Texas. Go figure.

1994 RED Mastercraft 205, Chevy 5.7 TBI. FOR SALE
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