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Mercruiser 470 Timing and Fuel grade

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Phantomsculler

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I have seen 2 different timings recommended for the mercruiser 470 engine: 8 degrees BTDC and 4 degrees BTDC. Could someone please advise what it should be set to. My other question relates to the octane rating for the unleaded petrol that is best for this engine. I am in Australia and we have Regular (91) Premium (95) and Ultra (98). The engine has not been used for approx 19 yrs . I think that I used to set the timing back then at 8 Degrees BTDC when we used to still have leaded petrol and maybe Regular unleaded. Could the recommendation for 4 degrees BTDC be for the higher octane petrol? Any advice on this would be greatly appreciated. Dave.
 
Ayuh,.... I believe the ratings are different here in the US,.....
The 4* btc is for lower octane fuels,....
I'd try it at *8, 'n then check the plugs for detonation after a run,....
 
The 4* comes from a service bulliten.

Those engines have a lot of serious issues and with the lower octane used it was reccommended to set to 4*BTDC.

Set it where you choose 8*, 6* or 4*

but you have been informed.
 
bondo said:
Ayuh,.... I believe the ratings are different here in the US,.....
The 4* btc is for lower octane fuels,....
I'd try it at *8, 'n then check the plugs for detonation after a run,....
Click to expand...
Thanks for the reply. Please forgive my ignorance but what should I be looking for with the plugs after a run?
 
This is not any kind of special or performance engine. As long as your point dwell (gap) is set correctly and you timing is set at around 4-6* BTDC and your engine runs good and performs good and your engine temp is at specification, there is not much else to worry about.

Regarding reading your spark plugs, in a way this was engineered into the ignition specifications so you dont have to worry about it.
Use the correct plug as specified and the correct gap.
 
kghost said:
This is not any kind of special or performance engine. As long as your point dwell (gap) is set correctly and you timing is set at around 4-6* BTDC and your engine runs good and performs good and your engine temp is at specification, there is not much else to worry about.

Regarding reading your spark plugs, in a way this was engineered into the ignition specifications so you dont have to worry about it.
Use the correct plug as specified and the correct gap.
Click to expand...
Thank you.
 
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