Anyone out their have a suggest regading what is the upper end for a engine running 89 octane gasoline ? Are the N.A. or blower engines in the 650 HP range good on 89 octane ?

How does one really know what octane to run in a custom build engine ?

ed

depends on how much comp your motor has, & how much boost your pushing, & timing. Theres dozen of other factors also. W/ a blower its all about heat & detonation.

89 octane...9.3:1 comp , pumps 180/185 , aluminum heads , 35* total timing and 637 hp and 680ft lb torque

My builder recommended 91 octane for my motors. 540 CID NA, 9.75 to 1 compression, iron heads, roller rockers, 1050 dominator. Approximately 650 HP. Seems to run great.

I am running a 540 EFI with FAST injection and a Holley 1050 intake at 9.2:1 compression, 611 hp on the dyno. It was designed for 89 octane. It runs great, and has no problems sustaining full power. Mopower's sounds pretty close to mine, just another point on compression and maybe a little head work. Probably shouldn't push too much harder than that on 89. If fuel consumption and price, factored in with motor cost and service life are high on your list of objectives, motors such as these probably represent the best bang for your buck. When you drop down in the 500 hp range, you don't really save any significant amount of money, and as you go higher, they get expensive real quick, and the useful life drops from 600 hours right down to 100 or 50 hours.

I have not seen anyone with a blown motor running less than 92 or 91, although the new generation of Merc motors can limp home on 87 with the knock sensor going off the whole way...