Optimum air / fuel ratio for marine engine
 

What is the optimum A/F at WOT for a naturally aspirated EFI gasoline marine engine running 87 octane to get maximum HP with out detonation? The 496 versus 502 BBC are the two engines of primary interest.

Re: Optimum air / fuel ratio for marine engine
 

From Torco Fuel's website:

Air/fuel ratios vary with load conditions (those that are ideal for fuel economy are not ideal for maximum performance). Because of small losses during the vaporization process and other losses that occur when the residual exhaust gases in the cylinder dilute the fresh incoming charge, a more realistic air/fuel ratio for maximum horsepower on gasoline will probably be a richer 12.5-to-13.5:1. When the mixture ratio strays from the optimum, either excessive air or fuel will be present in the cylinders and the power output of the engine will deteriorate.

Re: Optimum air / fuel ratio for marine engine
 

If you have aluminum heads you can get away a little leaner. But over all I like to see 12.8 to 13.2 to stay safe. we run are blower motors at 11.8 to 12.0. You could also look at cylinder temps with the air fuel to double check yourself.

Re: Optimum air / fuel ratio for marine engine
 

Thanks for the info.

How does one check the cylinder temperatures and what are the temperatures that indicate bad fair good best?

Re: Optimum air / fuel ratio for marine engine
 

You'd need an EGT to check cylinder temps. Usually when running an engine on a dyno, each cylinder can be checked because there is an EGT sensor in the exhaust of each cylinder.

Re: Optimum air / fuel ratio for marine engine
 

Livorsi makes a EGT gauge.

Re: Optimum air / fuel ratio for marine engine
 

I had gaffrig/livorsi egt gauges with temp probes on my lightning headers and they read 200-250 degrees HIGHER than actual temp,hopefully they have straightened that out but mine were about usueless,Smitty

Re: Optimum air / fuel ratio for marine engine
 

What should the exhaust temperature range be?

Re: Optimum air / fuel ratio for marine engine
 

1150 to 1250 is what I have always heard,1330 is melt down. My gaffrig egts read 1500-1600 degrees all the time on my old blower motor so it was obvious they were useless,Smitty

Re: Optimum air / fuel ratio for marine engine
 

On a closely related topic, does anyone know the formula to determine the amount of fuel needed for a specific horsepower? Trying to determine GPH of fuel pump. I have alway just gone overkill in the past.