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

Lou C

Lou C

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One reason I stick with the old points distributor was the advance curve specified by OMC on the pre Vortec 4.3 V6. These engines got 6* of base advance with 12* of centrifugal advance at 3200 rpm. This total of 18* is a good deal less than what you see on any of the V8s. Not knowing how the Delco EST is programmed as far as advance I decided to stay with the original set up. I could have switched to the Petronix since all it does is replace the points the simple mechanical advance remains the same.
 
achris

achris

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Lou C said:
One reason I stick with the old points distributor was the advance curve specified by OMC on the pre Vortec 4.3 V6. These engines got 6* of base advance with 12* of centrifugal advance at 3200 rpm. This total of 18* is a good deal less than what you see on any of the V8s. Not knowing how the Delco EST is programmed as far as advance I decided to stay with the original set up. I could have switched to the Petronix since all it does is replace the points the simple mechanical advance remains the same.
Click to expand...
That's where the Merc Thunderbolt system comes in. Same as OMC (they got their engines from the same place), 14 degrees of advance, with an initial setting of 8 before (total of 22 degrees of advance)...

Would be worth asking Delco what the curve looks like for the V6 dissy....

Chris.......
 
Scott06

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achris said:
That's where the Merc Thunderbolt system comes in. Same as OMC (they got their engines from the same place), 14 degrees of advance, with an initial setting of 8 before (total of 22 degrees of advance)...

Would be worth asking Delco what the curve looks like for the V6 dissy....

Chris.......
Click to expand...

Page 7 has all the EST timing curves in terms of base and all in degrees/rpm for all models
 
Lou C

Lou C

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Interesting, I looked at the specs for the 4.3 (262 cu in) and they list it at 26* total at 4000 rpm, with 8 degrees of base advance that means that 18 degrees of electronic advance versus the 12 on my mechanical advance (+ 6* base timing for a total of 18* @ 3200 rpm) Prestolite. I know that OMC and Volvo used the Prestolite BID system from '90 on up after they stopped using points before they went to the Delco, that was basically the same as the old style distributor (mechanical advance) but with electronic module spark control. However, I'm not sure if the advance curves were changed when the Vortec engines came out (1996).
I'm wondering if the difference is that the later engines using Vortec cyl heads may be able to tolerate more advance, than the older pre-Vortec design. Not sure if this really applies to the 3.0 though, did this engine get a Vortec cyl head upgrade?
I don't know that I'd be comfortable using the Delco with the 6 degrees more of built in advance on an older pre-Vortec engine. Thoughts?
 
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Tail_Gunner

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alldodge said:
Don't keep us in suspense oh e-luminous one, why can it have 36* total timing, and the newer motor cannot?
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Actually I cannot or better said will not wade into emissions and corporate ideology..well kinda that is..

Here because it can, to the point of the matter engines do quite well there. It's called combustion efficiency. Now with that being said stick to the factory settings or you will blow up your motor....Don abored such thinking..I've been admonished more than once a long time ago.

A few yrs yrs ago I resurrected a 454 smog motor, what a adventure. Today it runs like a mule..actually pulls. Timing goes as follows.

15 initial

All in at 3000 rpm..20 dgrees full mechanical advance.

15 degrees vacuum advance

And if you know what that means in the long run, yes the 454 runs 35 degrees advance at idle, when under acceleration no vacuum 15/35 degrees...Now here is where it gets crazy. At 3000 rpm and cruise it's 50 degrees...Now don't punch the monitor.

These timing settings vary from engine to engine, nor are they intended for marine use. But having 35 degrees in a 4 cyl low compression engine is not anything new.

Umm high advance in hotter cams tamed the pulses..
 
Lou C

Lou C

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achris said:
That's where the Merc Thunderbolt system comes in. Same as OMC (they got their engines from the same place), 14 degrees of advance, with an initial setting of 8 before (total of 22 degrees of advance)...

Would be worth asking Delco what the curve looks like for the V6 dissy....

Chris.......
Click to expand...
I have 2 spare Prestolite points distributors for my 4.3, one is from an OMC engine (OMC grey) one is definitely from a Merc engine (Merc black) but otherwise they appear identical. I guess that's what Merc used in the pre-Thunderbolt era.
 
Tail_Gunner

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Lou C said:
Interesting, I looked at the specs for the 4.3 (262 cu in) and they list it at 26* total at 4000 rpm, with 8 degrees of base advance that means that 18 degrees of electronic advance versus the 12 on my mechanical advance (+ 6* base timing for a total of 18* @ 3200 rpm) Prestolite. I know that OMC and Volvo used the Prestolite BID system from '90 on up before they went to the Delco, that was basically the same as the old style distributor (mechanical advance) but with electronic module spark control. However, I'm not sure if the advance curves were changed when the Vortec engines came out (1996).
I'm wondering if the difference is that the later engines using Vortec cyl heads may be able to tolerate more advance, than the older pre-Vortec design. Not sure if this really applies to the 3.0 though, did this engine get a Vortec cyl head upgrade?
I don't know that I'd be comfortable using the Delco with the 6 degrees more of built in advance on an older pre-Vortec engine. Thoughts?
Click to expand...

Vortec heads do well at 32 degrees full advance, they are highly efficient combustion heads.
 
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Scott06

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alldodge said:
Don't keep us in suspense oh e-luminous one, why can it have 36* total timing, and the newer motor cannot?
Click to expand...
I recall seeing but cannot find at this moment a service bulletin on retarding the timing on some 3.0's that were blowing head gaskets, even included a sticker to cover the timing spec on the flame arrestor. I think they moved base timing back to 1 * ATDC.
 
nola mike

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Scott06 said:
I recall seeing but cannot find at this moment a service bulletin on retarding the timing on some 3.0's that were blowing head gaskets, even included a sticker to cover the timing spec on the flame arrestor. I think they moved base timing back to 1 * ATDC.
Click to expand...
That's only 2' from original, still way different
 
nola mike

nola mike

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Scott06 said:
From the 8* BTDC listed in post #10 its quite different.
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"Base" is different than "initial". Only est had a base setting. At idle there is still advance. If they actually retarded the timing that much the engine would be significantly detuned (see the op's numbers) so we're now talking about a 110 hp motor or whatever
 
Scott06

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nola mike said:
"Base" is different than "initial". Only est had a base setting. At idle there is still advance. If they actually retarded the timing that much the engine would be significantly detuned (see the op's numbers) so we're now talking about a 110 hp motor or whatever
Click to expand...
Ok yes i used the term base instead of while in base mode set the initial to 1 deg….Still doesn’t change the fact that at one point merc used 8* initial with 36* total, and changed it to 1* initial with 23* total for some reason with engine rating at 135 hp
 
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J

j cat

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me78569 said:
will do, thanks for the help on this, Thought it might be a lack of timing, but good to see the spec agree's
Click to expand...
the engine rpm idle is 650-700 timing is 6deg BDTC ..THEN increase the rpm to 1200 rpm and its 8 deg BDTC.. I have the OEM manual.. oem distributor and the engine OEM parts in it ..
 
M

me78569

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Here is the engine plate for reference

PXL_20210512_172002169.jpg


So suggestions so far is to set base timing mode then adjust to 8* btdc and try from there? Verify total timing at wot is near 34*?
 
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