My 26ft Tollycraft is running fine with the single Mark IV 454 on a 2:1 V-drive, but I’m wondering if I can improve performance by adjusting the advance curve on the distributor?
This is a 10,000 lb flybridge cruiser, 26’8” LWL, 10’ beam, runs at 7 knots at 1700 rpm most of the time, or 14 knots on plane at 3200 rpm when we are in a hurry to get across to Vancouver.
It has a Mallory points ignition that replaced the original distributor a while back. I am only now understanding the concept of properly curving the distributor.
With my initial advance set at 8 degrees BTDC at 800 rpm idle, I measure centrifugal advance up to 5 degrees higher than the max spec in the Mercruiser manual mostly at the lower 1700 rpm that I spend 90% of the time at.
So should I dig into my distributor and try replacing springs or just leave it alone as I am not hearing any pre-detonation?
Is there a general rule of thumb that slow heavy boats should use a slower curve, or the opposite?
1977 Mercruiser Mark IV BBC
800 hours on rebuild
Serial #5551947
2:1 Borg Warner V-drive
Mallory Points Ignition
Coil, ballast resistors, dwell all within spec
This is a 10,000 lb flybridge cruiser, 26’8” LWL, 10’ beam, runs at 7 knots at 1700 rpm most of the time, or 14 knots on plane at 3200 rpm when we are in a hurry to get across to Vancouver.
It has a Mallory points ignition that replaced the original distributor a while back. I am only now understanding the concept of properly curving the distributor.
With my initial advance set at 8 degrees BTDC at 800 rpm idle, I measure centrifugal advance up to 5 degrees higher than the max spec in the Mercruiser manual mostly at the lower 1700 rpm that I spend 90% of the time at.
So should I dig into my distributor and try replacing springs or just leave it alone as I am not hearing any pre-detonation?
Is there a general rule of thumb that slow heavy boats should use a slower curve, or the opposite?
1977 Mercruiser Mark IV BBC
800 hours on rebuild
Serial #5551947
2:1 Borg Warner V-drive
Mallory Points Ignition
Coil, ballast resistors, dwell all within spec