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454 timing

Andrew33764

New member
Hey guys

ive got twin 454 efi tbi fwc engines

I had throttle position sensor issues. Fixed it

im using rinda diacom software. I set the timing to 8 degrees in base timing mode

in run mode I see the advance go to 40 at high rpm but I’ve been told by someone at marine power no more than 32

so what’s the deal. Any help?
 
Just as base advance is associated with idle RPM, high speed advance must also be associated with engine RPM.

The suggested 32° advance should be occurring at approximately 3,200 RPM.
If the advance continues to 40°, it is most likely occurring at close to 4,000 + RPM.

.
 
Thank you for the rely

i was told by marine power no more than 32 ever. I was told to check at 3500 - 4000. Or when ever it stops advancing

so I’m very concerned my engines will be damaged at high rpm
 
Thank you for the rely

i was told by marine power no more than 32 ever. I was told to check at 3500 - 4000. Or when ever it stops advancing

so I’m very concerned my engines will be damaged at high rpm



The combustion process is actually a "burn" that occurs within micro-seconds.
In other words, the burn is not instantaneous as with what we may think of as an explosion.

Because it is a "burn", the point of ignition must lead the point of the piston reaching TDC and going over TDC into the down stroke.
This is what we call an advanced spark event, or an advanced point of initial combustion.

The Maximum expansion of the gasses should ideally occur at/near 12* to 14* ATDC, and is where Torque is created.
This is referred to as LPCP.... location of peak cylinder pressure.

As RPM increase, so does the need for more spark event lead (aka ignition advance)
This is referred to as the "progressive" spark lead (aka progressive ignition advance).

As the ignition spark event stops advancing, this is known as the Full In advance.
A Full In advance number is worthless without an associated RPM.

At/near 3,500 RPM, the degree of advance is critical. This is where Marine Power is suggesting 32* BTDC.

If the advance continues to increase, and if it remains linear, there should be no issues at or above 4k RPM.


I could show you quite a few ignition advance curves that show the curve continuing to climb up to and even past 4k RPM.
 
I’m about to head out of the country for three months. When I return i hope to use the boat more

i think I will record the diacom recording with my phone for you too observe

it seems to be above 32 at 3500 rpm

also thanks for the description above. Interesting
 
Marine Power typically uses the default GM configuration so I'd expect you have the early MEFI computer with the EST distributor and the knock sensor. If that's the case and they are all functional, you may see timing values that appear 'above normal' at higher RPM.....to get the 'whole' picture, you need to look at multiple parameters at the same time..FWIW, the knock sensors are pretty good at maximizing the timing while inhibiting damage.


As a general rule, the longer you run the engine at elevated RPM levels, the shorter its service life will be...75-80% of WOT is the nominal range for most....
 
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