Timing/dwell 350 Crusader

[RABUCK]

I have a 1983 Bayliner Explorer 3270 with twin gas engines.They were 305 and were changed out a few years back to Crusaders 350 carb.I just switched to electronic ignitions , they are Mallory Distributors.I want to insure the dwell/timing on it and need the specs. Port engine needs some adjusting. Thanks

 

[RicardoMarine]

The dwell will be pre-determined via the OEM set-up with the Mallory. Unless we mess with this, it will remain unchanged.

With regard to ignition timing, you'll want to know that we have two basic ignition advances to be concerned with.

BASE or Initial, will be what the engine fires on and idles on.
This includes ZERO mechanical advance!
While it must be within specs, it is the lessor of importance in the large scope of things.

TA or TAT (total advance timing) and the advance "curve/limit" will be your very critical numbers.
See your OEM specs for this.

With your harmonic balancer marked off, you will strobe the timing marks while checking at various RPM up to approx 3.2K rpm.
Plot this out in graph form on paper.
Compare your data to the OEM curve and limit.

NOTE: BASE advance is commonly NOT included on OEM ignition curve graphs.
So BASE/Initial must be added to these numbers in order for your "strobe" readings to be meaningful.

NOTE: if BASE must be varied in order to maintain a correct TA, it's not a deal breaker if BASE can remain fairly close to OEM specs.
TA and the limit RPM are much more critical for best performance and defense against Detonation.

.

 

[makomark]

I don't think you can adjust the dwell on most electronic distributors.

In addition to Rick's thoughts, you need the specifics of the new engines to get the correct timing values...most every Factory built Crusader engine comes with an ID plate that will have the initial timing value; the total advance number will be in the factory service manual.

 

[RicardoMarine]

I don't think you can adjust the dwell on most electronic distributors.

Mark, dwell for an electronic ignition system is controlled by the distance between the sensor and the magnetic triggering unit. Fortunately, this is factory set!
Change this relationship, and we change dwell a tad bit!
This is why I suggested: "Unless we mess with this, it will remain unchanged."

There is no changing this with a Photo Eye unit, unless we were to some how change the slots in the rotor wheel... or the distance from the rotor wheel to the sensor...... which changes the duration, which changes dwell a tad bit.
There should be no concerns with any of these if we leave them as is.

One other aspect of TAT, will be the engine build.
If the Full Dished pistons have been employed, we must cut back on TA (as seen in many OEM curves).
If a Quench Effect (or Squish style) combustion chamber design was employed, we can bump this up some.... thus better performance and reduced Detonation potential.

This is why I get so dog gone upset with GM (and most re-builders) who use these stinking "full dished" pistons in their Marine Version SBC.
Don't get me started! ...............



.