1989 cobra 3.0l engine swap ignition timing question

[billbr]

I recently bought a new 3.0l GM base engine from Michigan Motorz, and it came with the Voyager EST ignition module. It started right up and I set the base timing to 1 degree ATDC, per the included instructions. I'm nearly done with the break-in procedure and when I get the the boat up on a plane, I'm getting less power than the tired old engine it replaced. I think this is due to there being about 9 degrees less spark advance with the new ignition system vs. the old mechanical advance.

The EST has 24 degrees of electronic advance, and a base of -1 deg BTDC, giving a total advance of 23 degrees, while the original ignition had a base of 4 deg BTDC, and a 28 deg mechanical advance resulting in 32 deg total. As an experiment, I set the base timing of the new ignition to 4 deg BTDC and the boat had a lot more power. I didn't hear any pinging or other signs of detonation, and the engine temp was unaffected by the extra advance. I realize that doesn't necessarily mean that detonation isn't happening.

At this point, I'm tempted to rebuild the original distributor (I had already installed a Pertronix on it) and just run that. My concern is that the compression and valve timing of the new Vortec engine may not be set up for 32 deg of total advance. I don't mind running 89 or 91 octane fuel. Alternatively, I could set the base to 4 BTDC and ignore the warnings in the timing instructions.

Any thoughts on the best setup? Thanks.

 

[alldodge]

The 1 ATDC gives you 21 to 24 degrees at 2700 rpm with a 16 degree advance. The issue is the EST advances the timing between 10 and 13 degrees after the base timing jumper is removed. Check your timing without the jumper installed. It would not be the first time that a new EST module is failing to provide the advance needed. Michigan Motorz has replaced several for folks.

The original 1989 engine would have given 14 to 18 degrees advance at 2700 rpm

If I was on my other computer I could post the timing curves

 

[billbr]

No Title

This must be the problem. I set the base timing back to 0 BTDC (just to make it easy) and observed the following:

Below 700rpm, plugging in the base timing jumper had no effect. Above 800rpm the timing dropped to 0 BTDC when I plugged it in.
With the jumper removed, the timing remained at 0 BTDC until the engine reached 800rpm, where it jumped to 12 BTDC (and 1000rpm).
From 1000rpm to 2700rpm, the timing increased to 16 BTDC.
It stayed at 16 BTDC for all rpm's above 2700rpm.

I guess I'll need to call Michigan Motorz first thing Monday Morning.

I've attached the timing curve from the official OMC service manual for my engine. As you can see, they claim 28 degrees of centrifugal advance between 700rpm and 2700rpm. Even if I got the full 24 degrees from the EST, I would still have 9 degrees less advance at cruising speeds. Something doesn't add up.

If you have the EST timing curve and are willing to upload it, I'd be grateful. I've looked all over for one and came up empty.

Thanks for your help!

 

[alldodge]

Agree, here is the EST curve