Mercruiser 140 Points to Delco EST results in low RPM at WOT

[Tail_Gunner]

If I set my static timing to 4* my total timing ends up being ~28*, and my max rpms are ~3600-3700 rpm, which makes sense when I look at the spec on timing for a below 0C856558 serial number motor. The boat runs fine just doesn't have any top end.

What I really would like to know is why is there such a big difference in the called for timing on early 140 motors vs late motors? My gut feeling here is the Delco EST just doesn't have the timing advance range needed to have both good timing down low and enough timing for 4000+ rpm for the early model 140 engines.

If that is the case it is fine I just want to know that is what caused my motor to go from 4400 rpm at WOT to 3600 RPM at WOT when the only change was the Delco EST and base timing set at 1*.

I am going to play with it more and see if I can find a happy place without knock and still having some top end.

Be inquisitive, start a 4 degrees and work the timing up slowly until the "marbles" start. That is detonation and you engine will not withstand that. Timing and carberation go hand in hand. Because your advanced timing cured a bog I highly suspect you have a carb problem.

The timing setting discrepancies are due to compression ratios or head design. I believe Achris has pointed that out.
And your prop size, that cam be quite a thing with boats, it could very well be the entire problem.

 

[me78569]

that's my plan, ill report back

 

[me78569]

Well I am not convinced it is detonation for a couple reasons, or at least detonation due to timing. I made a mistake earlier, i had timing set at 8* base not 12*

1. setting timing at 8 vs 4 vs 1 vs -1 makes zero difference on the noise and what rpm it happens.
2. doesn't matter load or no load then noise is the same at the same rpm.
3. the noise occurs at 2700-2900 rpm in all situations
4. the timing jump from the EST occurs right around 1500-1600 rpms and no noise exists.


Not sure what to make of the noise at this point. I am going to check plugs and put some new gas in it and see what happens.

 

[Scott06]

Not sure what to make of the noise at this point. I am going to check plugs and put some new gas in it and see what happens.

3.0's are not the quietest engine may be valve train noise

Those plugs look rich so likely getting decent fuel supply

 

[me78569]

Its not a normal 3.0 noise, it's not a good noise I am just not sure it is knock. It almost has a harmonic rattle as if something is loose and shakes at a specific RPM.

Dunno I am gonna check more or blow something up looking for it.

 

[Scott06]

or blow something up looking for it.

Well that will solve the timing issue...

 

[me78569]

sad but true, . I've been telling the wife we deserve a new boat. However she tells me " it's not as fast as it used to be" is not a good enough reason.

I set timing back to 8* and I will spend some more time looking for the issue as I can. The boat is just an "upstream boat" anyways we can always float home.

 

[Lou C]

I was thinking about this very same issue, on my old 4.3 V6 the Prestolite points distributor that was standard then had only 12* of advance at 3200 rpm, plus the 6* of base timing, for a total of 18*. One reason why I hadn't upgraded to the Delco was that I wasn't sure what the advance curve was for the 4.3 V6 versions. I never did fully understand why the 4.3's were set up for significantly less total timing advance than the V8s. I'm guessing (could be wrong) that the later Vortec cyl head design can tolerate more spark advance than the old Pre Vortec heads. It would be interesting to see what the total timing advance specs are on the Delco units for each engine, 3.0, 4.3, 5.0 and 5.7. Might make a nice sticky for those who want to upgrade their old engines to modern igniton systems...

 

[me78569]

Well to update more, I am happy to report that the noise I was hearing was not in fact timing knock, it was the u joint wearing out. went up river today fishing and it lost power to the prop. The marble sound I heard was a bad ujoint, which now that I think about it is the right sound for what I was hearing.

Floated home and now I have to figure out how to make it to the landing.

 

[me78569]

Replaced the u joints and I am happy to report I am noise free. I'll start playing with timing again to see where the limit is at idle to get 30-32* up top and hopefully see full rpms again.

I can %100 confirm that setting base timing at 1* results in a rpm limit of 3600 rpm. 8* base timing gets me to 4100 rpm.

Obviously this is only for early 140's that are spec'd for higher timing and the points have been replaced by the Delco est ignition.

 

[dubs283]

Replaced the u joints and I am happy to report I am noise free. I'll start playing with timing again to see where the limit is at idle to get 30-32* up top and hopefully see full rpms again.

I can %100 confirm that setting base timing at 1* results in a rpm limit of 3600 rpm. 8* base timing gets me to 4100 rpm.

Obviously this is only for early 140's that are spec'd for higher timing and the points have been replaced by the Delco est ignition.

Glad you got it figured out.

To answer your question as to why the difference between base timing/total advance for different vintages of the 3.0L engine is mainly due to the deterioration of the GM casting. The 2.5/3.0L castings are from the 60's and AFAIK haven't been updated since. Millions of blocks produced since then have left the castings in rough shape.

Mercruiser discovered this when 3.0L engines were blowing head gaskets at 8 degrees initial timing so over the years they've dropped the spec to suit casting issues and ignition system styles making up for top end rpm through valve timing and fueling

IMO the 3.0L is one of the greatest engines GM ever produced. Great power to weight ratio and gas gotten many a common man on the water

 

[me78569]

In theory what would have to be done to make the 140 turn rpms like a 3.0 with less timing?

I am assuming when you say valve timing there are cam differences. what differences are there in terms of fueling?

 

[Scott06]

In theory what would have to be done to make the 140 turn rpms like a 3.0 with less timing?

I am assuming when you say valve timing there are cam differences. what differences are there in terms of fueling?

Earlier in thread achris mentioned cam is the same since 1968..
Heads changed around 1990 ish if I recall my folks had '91 Sea Ray with a 3.0LX - this had DDIS and 135 hp, base engine in boat was a 115 hp 3.0L (no x..) I thought difference was head that the non LX version used the old 2.5 head on 3.0 block... I just recall seemed like a lot of HP variations for same engine