timing.....again

So yes I have searched and read several threads about this and I have a mechanical background. Clean, (just splashed), bottom, props are perfect.
I have twin 454's in a 35 downeast style express. I have been chasing a problem of not being able to get the starboard engine to come up as high, (rpms/speed) as the port. So, we checked the timing today.
Idle-700 rpm
Port-21 BTDC
Star-was 18, bumped to match port, 20 BTDC

2500 rpm
Port- 35
Star- 35

Does this seem high? These engines start/run awesome.
Any thoughts?
Thanks

firepiper said:

So yes I have searched and read several threads about this and I have a mechanical background. Clean, (just splashed), bottom, props are perfect.
I have twin 454's in a 35 downeast style express. I have been chasing a problem of not being able to get the starboard engine to come up as high, (rpms/speed) as the port. So, we checked the timing today.
Idle-700 rpm
Port-21 BTDC
Star-was 18, bumped to match port, 20 BTDC

2500 rpm
Port- 35
Star- 35

Does this seem high? These engines start/run awesome.
Any thoughts?
Thanks

Click to expand...

Ayuh,.... Donno what ya got, but I'm thinkin' yer ignition needs to be put into base mode to set the timin',...

I'd expect to see 8° / 10° Btc,...

The Cutler fuel injection has no ties to the timing. Fuel only.

Perhaps give us some information re; your ignition systems.

Many of these systems are EST (electronic spark timing) these days.
The distributor housing is positioned to offer full advance.
Via the Ignition model, the spark lead is delayed as to give BASE advance during low RPM.
The delay is then altered as per RPM increase and other engine data.

All of this is via EST module.... (i.e., the brains of the system, so to speak).
If the brains need psychological help..... the ignition advance may be wacky.


Look up the ignition advance curve for your model number engines.
Strobe your markings from low speeds to higher speeds......., and see if the system is doing what it should be doing.

IMO.... a Full Advance (or TA... total advance) of 35* @ 2,500 rpm could be a recipe for Marine Load Detonation!

Had your TA been closer to 35* @ 4,000 RPM.... it may be OK.



Keep in mind that the TA numbers are meaningless unless associated with an RPM.


Here's an example curve only.

BASE advance is generally excluded from the vertical graphs.... and must always be added when checking dynamically.

Take a close look at the spark lead @ 2,500 rpm.
Even with a BASE of 8*.... there is no where near 35* TA @ 2,500 rpm.




.

Thanks, these engines are 1988 Crusader Model 350's, with accel elec distributors. I tore them down and the weights are fine and free. The Cutler system has no ties to timing. It's fuel only.
I was thinking that they would be 'all in at 2500 rpm, my mistake. I'll have to check it all again. I'm thinking the base timing is either very advanced or it's the timing marks on the engines that are improper or incorrect.

firepiper said:

Thanks, these engines are 1988 Crusader Model 350's, with accel elec distributors. I tore them down and the weights are fine and free.
1.... I was thinking that they would be 'all in at 2500 rpm, my mistake. I'll have to check it all again. I'm thinking the base timing is either very advanced
2.... or it's the timing marks on the engines that are improper or incorrect.

Click to expand...

1.... If all in by 2.5K rpm, you would likely encounter Ignition induced Detonation.

2.... If in question, you'll need to perform a PPS procedure. PPS = positive piston stop.


.

5 degrees too much advance, and does the STB throttle and choke plates go completely vertical at WOT? can do this with engine off.

too much and too soon, too...

And accel distributors aren't standard production...so its hard to say how they were setup ...