I'm no expert but if you had to put 89 in, just keep the motor out of boost. If the engine isn't making boost then detonation is much less likely to occur. If I'm way off then say so but I don't think I would do the octane boost on merc engines. Just take it easy when you're in a bind.

That's actually what my mechanics told me on my last 500 EFI's that we turned up. However, the engine builder nearly threw a rod when my mechanic said that!

Bottom line, I tend to agree with you... it's just a good insurance policy (if you get the right stuff), and let's me run a bit harder if necessary (ie: If I get caught in rough water and need to run the outside to get back before dark etc....).

I have had great results with Torco.

phrangle, as a matter of fact I raced marathons for years on AV gas. My foot was on the floor for miles, 12 lbs boost, 5500 rpm + + +. As I said, only additive was Marvel Mystery Oil and my motors always torn down with little wear. I can't swear it was the fuel, hopefully it was my engine man. But a lot of us on the left coast run AV gas, the next step up is 110 race gas at 1 1/2 times the cost. As someone above pointed out, the best insurance for high dollar motors is good fuel. You don't want to spend $50K per motor and use crap for gas. And when was the last time you heard of a small plane falling out of the sky because it had bad fuel.

What ratio were you mixing the Marvel Mystery oil?

http://stason.org/TULARC/vehicles/ga...omparable.html

Aviation gasolines were all highly leaded and graded using two
numbers, with common grades being 80/87, 100/130, and 115/145
[109,110]. The first number is the Aviation rating ( aka Lean Mixture
rating ), and the second number is the Supercharge rating ( aka Rich
Mixture rating ). In the 1970s a new grade, 100LL ( low lead =
0.53mlTEL/L instead of 1.06mlTEL/L) was introduced to replace the
80/87 and 100/130. Soon after the introduction, there was a spate of
plug fouling, and high cylinder head temperatures resulting in cracked
cylinder heads [110]. The old 80/87 grade was reintroduced on a
limited scale. The Aviation Rating is determined using the automotive
Motor Octane test procedure, and then converted to an Aviation Number
using a table in the method. Aviation Numbers below 100 are Octane
numbers, while numbers above 100 are Performance numbers. There is
usually only 1 - 2 Octane units different to the Motor value up to
100, but Performance numbers varies significantly above that eg 110
MON = 128 Performance number.

The second Avgas number is the Rich Mixture method Performance Number
( PN - they are not commonly called octane numbers when they are above
100 ), and is determined on a supercharged version of the CFR engine
which has a fixed compression ratio. The method determines the
dependence of the highest permissible power ( in terms of indicated
mean effective pressure ) on mixture strength and boost for a specific
light knocking setting. The Performance Number indicates the maximum
knock-free power obtainable from a fuel compared to iso-octane =
100. Thus, a PN = 150 indicates that an engine designed to utilise the
fuel can obtain 150% of the knock-limited power of iso-octane at the
same mixture ratio. This is an arbitrary scale based on iso-octane +
varying amounts of TEL, derived from a survey of engines performed
decades ago. Aviation gasoline PNs are rated using variations of
mixture strength to obtain the maximum knock-limited power in a
supercharged engine. This can be extended to provide mixture response
curves which define the maximum boost ( rich - about 11:1
stoichiometry ) and minimum boost ( weak about 16:1 stoichiometry )
before knock [110].

The 115/145 grade is being phased out, but even the 100LL has more octane
than any automotive gasoline.

Lucas oil octane booster.you can get it at most autozone stores.about 8.00 a bottle.

Where do you buy Torco?

800-678-6726

Gotta ask Joe - why not have it delivered to you? I used to have fuel delivered daily for heavy equipment. They will sell you 93 or maybe 91.

Something I never see anybody talk about when it comes to boat fuel - does anybody run "off-road fuel"??? Off-road fuel has a red dye in it so it can be recognized. It is highly illegal to run it in road cars or trucks, but it is not taxed like road-fuel you get at the pump. Used to save me 40 cents per gallon! I ran it in my f350 also. It seemed to actually run better on it (again, illegal ). What do you guys say??