What octane gas to use? 87,89?

[foilled]

old manual for 1987 omc 5.7 says to use either 87 or 89 octane depending on what engines timing is set at. I don’t know the timing of engine so what should I use? The omc engine was rebuilt by Jasper though. Not sure if I should still follow manual recommendations or not? Either way which octane should I use? (Chevy 350)

 

[foilled]

Correction manual says 86 and 89 AKI

 

[superbenk]

I would run plain old 87 unless you have a reason to do otherwise.

 

[Redrig]

I don’t know the timing of engine so what should I use?

Knowing the timing is pretty dang important considering it will change as your points wear (assuming you still have the points ) I would have someone check that out sooner rather than later .

 

[HT32BSX115]

I would run plain old 87 unless you have a reason to do otherwise.

I wouldn't run the engine until I knew for sure that the timing is correct for the fuel used. Using 87 octane fuel in an engine timed for higher octane increases risk of detonation.

Time it for 87 octane unless you plan to always run premium fuel. Many lakes only carry 87 and some have higher octane.

 

[foilled]

I wouldn't run the engine until I knew for sure that the timing is correct for the fuel used. Using 87 octane fuel in an engine timed for higher octane increases risk of detonation.

Time it for 87 octane unless you plan to always run premium fuel. Many lakes only carry 87 and some have higher octane.

ive been running 89 to be safe ill have to look into timing. 8 on the timing tab is marked in white

 

[foilled]

Knowing the timing is pretty dang important considering it will change as your points wear (assuming you still have the points ) I would have someone check that out sooner rather than later .

My timing tab and harmonic balancer have multipme numbers. Should i have both matching a 8 to get 8 degrees or should one be 0 and the ther be 8?

 

[Redrig]

Sorry budder I am not much help on Chevy timing process, I have Fords. Someone can fill you in on that exact number for a 350

because like HT and I said , having the proper timing set is way more important than what octane you are running , if it is just a few degrees off you can ruin your nice new Jasper

Do you or the nieghbor Flanders have a timing light ?

 

[HT32BSX115]

Correction manual says 86 and 89 AKI

Be careful with what is called Octane and AKI. Many fuel retailers are somewhat "loose" with those terms and some are outright wrong! And no one ever tests or proves what they have.

Almost ALL newer cars and many marine engines have knock sensors that will automatically control(retard) timing to prevent "Knock" (pre-ignition detonation)

Wikipedia has a pretty good description of Octane, AKI RON, MON and the history of it.

[h=3]Anti-Knock Index (AKI) or (R+M)/2[/h]
In most countries in Europe (also in Australia and New Zealand) the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2. It may also sometimes be called the Posted Octane Number (PON). [h=3]Difference between RON, MON, and AKI[/h]
Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity,[SUP][5][/SUP] and is not typically published for those countries that use the Anti-Knock Index labelling system.

See the table in the following section for a comparison.

I guess my point is, don't put a LOT of faith in Octane listed at the pump.

Unless you're running 100LL Avgas, or "Trick Fuel" etc.....plan for the lowest common denominator , don't use timing settings from anywhere EXCEPT the OEM OMC service manual so you use whatever you get from the "pump"

Cheers,

Rick

 

[foilled]

Be careful with what is called Octane and AKI. Many fuel retailers are somewhat "loose" with those terms and some are outright wrong! And no one ever tests or proves what they have.

Almost ALL newer cars and many marine engines have knock sensors that will automatically control(retard) timing to prevent "Knock" (pre-ignition detonation)

Wikipedia has a pretty good description of Octane, AKI RON, MON and the history of it.




I guess my point is, don't put a LOT of faith in Octane listed at the pump.

Unless you're running 100LL Avgas, or "Trick Fuel" etc.....plan for the lowest common denominator , don't use timing settings from anywhere EXCEPT the OEM OMC service manual so you use whatever you get from the "pump"

Cheers,

Rick

Omc manual says 5degrees btdc. Mines at 4. Theres also a white mark on the harmonic balancer at 0 and a white mark on timing tab at 8 degrees. Thing is motor was rebuilt by jasper so im not sure what timing to set it at?

 

[Scott Danforth]

Buddersnaps you realize you have two threads going on the same topic.....

 

[searsfisher]

Whoever installed the engine should have set the timing. 8 degrees sounds high for static timing IIRC.

 

[foilled]

Whoever installed the engine should have set the timing. 8 degrees sounds high for static timing IIRC.

It was built years ago and hasn’t been driven for multiple years as well. I was doing a tune up. But original old manual says u can advance up to 13 degrees if you run the higher gas. Given mine has been rebuild by jasper and is not stock anymore the marine tech at jasper said 8 to 10 degrees was good and he timing mark on my engine is also marked in white at 8 degrees. So that’s where i set it

 

[HT32BSX115]

It was built years ago and hasn’t been driven for multiple years as well. I was doing a tune up. But original old manual says u can advance up to 13 degrees if you run the higher gas. Given mine has been rebuild by jasper and is not stock anymore the marine tech at jasper said 8 to 10 degrees was good and he timing mark on my engine is also marked in white at 8 degrees. So that’s where i set it

Any time you have an engine rebuilt by a respected overhaul facility and they recommend a particular timing setting, I would use it.........BUT only if they rebuilt the engine as a marine engine and say as much.....

I would NOT use a timing setting for an engine rebuilt as an automotive engine because they may recommend a timing that is more advanced (which could result in detonation)

In that case you might be in "no-mans-land" because you might have higher compression and/or camshaft overlap etc meant for a NON-wet-exhaust applications.

Jasper builds marine engines.......if it's a Jasper Marine engine, and they suggested a timing for it, I would use it.

 

[foilled]

Any time you have an engine rebuilt by a respected overhaul facility and they recommend a particular timing setting, I would use it.........BUT only if they rebuilt the engine as a marine engine and say as much.....

I would NOT use a timing setting for an engine rebuilt as an automotive engine because they may recommend a timing that is more advanced (which could result in detonation)

In that case you might be in "no-mans-land" because you might have higher compression and/or camshaft overlap etc meant for a NON-wet-exhaust applications.

Jasper builds marine engines.......if it's a Jasper Marine engine, and they suggested a timing for it, I would use it.

yes marine engine