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98 5.7 EFI timing - precise timing question

J

jid

Contributing Member
Remanufactured 5.7 EFI (not MPI) in my 98 Chapparal Sunesta 232 w/ a bravo 3 outdrive. Delco EST ignition.

Before i learned to properly set base timing at 8 deg I set timing by listening to the motor. It would run 44mph on GPS with just me and a full tank of gas with 24* props at about 4400rpm.

Starter installed by a shop was the wrong one so it eventually chipped off flywheel teeth. New flywheel and starter later I get the boat back and timing needed to be set. I set it to 8 deg BTDC w a digital advance light. Now the motor won’t rev as high as it did and won’t hit the same speed. I’m down to 39mph and motor won’t rev over 4200rpm. Changing props to 22* I pick up 200rpm but lose speed. Motor sounds good but just stops pulling as the RPMs cross 4000ish

so my question: given the Delco EST ignition curve, if I know I’m not going to rev to max RPM of this motor (either with 24* or possibly the stock 26* props), can I add a degree or 2 of timing without hurting anything?

In my quest to find the lost power, I have changed plugs, wires, cap, rotor, and even swapped out the distributor just to see if I had an gremlins in the old one. So far it hasn’t helped. I did find a missing ground strap from when the shop had the motor apart so that fixed a high-end miss I was getting (and the motor leaning out). But even still, I’m down power on a motor that has less than 20 hours on it. Oh, compression check showed all was well (all cylinders within 5% of each other).

Ideas? Figured I’d ask before trial-and-error time...

Some other random info: fuel filter was changed. Fuel has been fine. Fuel pressure is verified stable at 30psi throughout the RPM range (and WOT) as specified in the manual. I know timing is advancing (verified w light while under load). IAC, MAP, and TPS all replaced as part of my exercise. Ignition coil as well. No change in performance.



JD
 
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I suspect your timing indicator on the damper pulley may have shifted. I'd find TDC with a hard stopper (bolt threaded into an old spark plug to stop the piston near TDC in two directions) and see where TDC actually is. While you're at it, you could apply a timing tape to the damper pulley (hot rod shop item) and time the motor at high rpm. That eliminates a bunch of gremlins.

Jeff
 
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jid said:
Remanufactured 5.7 EFI (not MPI) in my 98 Chapparal Sunesta 232 w/ a bravo 3 outdrive. Delco EST ignition.

Before i learned to properly set base timing at 8 deg I set timing by listening to the motor.
FYI....... that is extremely risky for a Marine Engine!

It would run 44mph on GPS with just me and a full tank of gas with 24* props at about 4400rpm.
That would be your WOT RPM....... an RPM that should NOT be sustained for any duration. It is a test RPM ONLY!

Starter installed by a shop was the wrong one so it eventually chipped off flywheel teeth. New flywheel and starter later I get the boat back and timing needed to be set.
I wonder why the timing would have changed during a flywheel and starter motor replacement! I find that to be strange!

I set it to 8 deg BTDC w a digital advance light.
Unless you own a very high quality one, I would toss that digitally advancing light in the recycle bin. Or.... use it in Standard Mode only with your harmonic balancer fully marked off.

Now the motor won’t rev as high as it did and won’t hit the same speed. I’m down to 39mph and motor won’t rev over 4200rpm. Changing props to 22* I pick up 200rpm but lose speed. Motor sounds good but just stops pulling as the RPMs cross 4000ish
Nothing regarding a flywheel and starter motor replacement should have caused any change to performance.

so my question: given the Delco EST ignition curve, if I know I’m not going to rev to max RPM of this motor (either with 24* or possibly the stock 26* props), can I add a degree or 2 of timing without hurting anything?
Here's the deal.
GM builds their Marine version SBC using their GM style full dished pistons.
These pistons cannot possibly offer a Quench area. In fact, the full dish gives the flame front a place to hide, often causing Detonation if/when the spark lead is too great.
So...... I would say NO....... do not add 2* unless you know exactly what you are doing and will be looking for.

In my quest to find the lost power, I have changed plugs, wires, cap, rotor, and even swapped out the distributor just to see if I had an gremlins in the old one. So far it hasn’t helped. I did find a missing ground strap from when the shop had the motor apart so that fixed a high-end miss I was getting (and the motor leaning out). But even still, I’m down power on a motor that has less than 20 hours on it. Oh, compression check showed all was well (all cylinders within 5% of each other).
I have to ask....... did this shop do anything to the Engine while they were replacing the flywheel?

Ideas? Figured I’d ask before trial-and-error time...

Some other random info: fuel filter was changed. Fuel has been fine. Fuel pressure is verified stable at 30psi throughout the RPM range (and WOT) as specified in the manual. I know timing is advancing (verified w light while under load). IAC, MAP, and TPS all replaced as part of my exercise. Ignition coil as well. No change in performance.

Read Jeff's post below.

JD
Click to expand...

fastjeff said:
I suspect your timing indicator on the damper pulley may have shifted.
Jeff is talking about the outer ring of the harmonic balancer unit.
This ring is where the ZERO TDC mark is.
The ring is a press fit onto the inner hub, and is dampened via a rubber unit between the two.
Occasionally the outer ring will slip on the inner hub.
When/if this occurs, the TDC mark is no longer accurate.
When we use this inaccurate mark for ignition timing, the timing also becomes inaccurate.

I'd find TDC with a hard stopper (bolt threaded into an old spark plug to stop the piston near TDC in two directions) and see where TDC actually is.
That would be a PPS (positive piston stop)
PPS tool.jpg
You will need a 360* wheel and a temporary wire pointer.
You will use the PPS to gently stop the #1 piston @ approx 30* BTDC in one direction.
You will then reverse direction and again gently stop the #1 piston @ 30* BTDC.
Do this several times until you see an equal spit....... can be 27* or it can be 31*....... you decide.
When you come up with an equal split in either direction, the PPS will be removed.
You will now rotate the crankshaft until the pointer is aiming at the ZERO.
This will be your TRUE #1 TDC.
Make the correction to the OEM marks, and there ya go!

While you're at it, you could apply a timing tape to the damper pulley (hot rod shop item) and time the motor at high rpm. That eliminates a bunch of gremlins.
Yes...... this is the correct method for ignition timing.
NOTE: the decal will be specific to the diameter of the outer ring. In other words, if the outer ring diameter is 8", you will need the 8" decal.

timing decal 8 inch diameter.jpg

Now you will be able to time your engine dynamically using a standard strobe style timing light.



Jeff
Click to expand...
 
Thanks for the great feedback y’all!

I already have the timing tape on (neglected to mention) but like you I’ve suspected the original timing mark to be ‘off’. I will check that.

I agree that absolutely nothing should’ve changed from the time the motor was out for the starter and flywheel work. I’m pretty sure they moved the entire motor back to get to the flywheel ring which really should not of impact anything.

I have an old-school timing light and my $130 timing light from Amazon... I’m getting consistent readings from both. So at least that is good.

Time to triple check top dead center.


Thank you all for your help!


Joseph
 
If the advance is controlled by the EST module (no computer involved), I prefer to just set it to full advance at 3400 RPM and just live with whatever the initial timing is.....if the computer controls the timing, best to follow the factory service manual's procedure....
 
According to the EST timing curve, max advance doesn’t happen until 4400. Ish. So why the 3400?
 
Of course I can’t find it right now. LoL! Had it up a few days ago from a google search. I’ll find it and post it. Just need to sharpen my google foo!
 
OK...... even while you may know much of this, let me give you the Dummy 101 explanation.
It is hard to condense this into a short explanation...... so bear with me!

Combustible Gasoline/Air does not explode within the cylinder....... it actually undergoes a burn.
Since it burns, there is a duration for the burn that begins at ignition, and ends somewhere during the power stroke.
The goal is to create the Max burn at a certain crankshaft angle.

Many Engineers have determined that this crankshaft angle should be 12* to 14* ATDC.
This is referred to as LPCP, or Location of Peak Cylinder Pressure.
Max expansion @ 12* to 14* ATDC gives each piston/connecting rod the greatest advantage over the crankshaft.... I.E., best torque!
Baring that all else is correct, the ignition advance is given the last word regarding the LPCP.

At idle speed, the ignition lead (spark advance) is approx 8* BTDC.
Although not critical at idle speed, that 8* spark lead creates Max expansion at somewhere in the 12*/14* ATDC range.

As RPM increase, the spark lead must also increase, as shown in your OEM EST advance curve. Again, this "spark lead" is to allow for the burn to create Max Expansion @ 12* to 14* ATDC.
A lazy ignition advance makes for a lazy LPCP, and consequently less torque.
Conversely, an aggressive ignition advance makes for an aggressive LPCP that may be dangerous to the engine.


Note that when looking at the advance curve, BASE or Initial Advance is omitted from the vertical scale.
See the notation to the left of the graph!
This means that the curve graph gives reference to the EST advance ONLY. (EST = electronic spark timing)
When doing the math, BASE or Initial must be added to the value in the line graph!
Example:
Look at the Max curve line (high octane fuel) @ 2,000 RPM.
The vertical scale shows approx 20* of EST advance.
Now we must add BASE of 8*.
With the 8* BASE added, the engine is actually seeing 28* @ 2,000 RPM (very aggressive in my opinion)

Now, when strobing the timing marks dynamically, we can't help but to see the BASE advance included in with the progressive advance.



Now look at the advance curve graph line @ 3,500 RPM.
The MAX line (high octane fuel) shows approx 22.5 * of EST advance.
Now add 8* of BASE, and you have 30.5* advance (spark lead) @ 3,500 RPM.
Again, the goal is to place the LPCP at 12* to 14* ATDC.

For me, 3,200 to 3,500 RPM is a critical RPM due to the possibility of Marine Load Detonation.
Add to this the GM Full Dished piston that is used in the Marine version SBC.

Now on to your question:
According to the EST timing curve, max advance doesn’t happen until 4400. Ish. So why the 3400?
Click to expand...
Your Cruising RPM will hopefully be the 3,500 RPM range. We don't care much about any spark lead that occurs past our cruising RPM. The engineers simply allowed the curve to continue up to 4,400 RPM.


Merc 5.7L EST ignition advance curve.jpg


can I add a degree or 2 of timing without hurting anything?
Click to expand...

This engine really needs a quench effect built into the combustion chamber in order to safely do that.
The Max curve graph that you posted is rather aggressive, in my opinion.
GM uses the Full Dished pistons in this SBC Marine engine.
The full dished pistons cannot possibly create a quench effect.
This means that Marine Load Detonation is of greater concern.

So..... in answer to the above question, I would suggest that you NOT do that!
I would stay within the OEM curve, and use high octane gasoline. :D


BTW, the only goof-proof method for determining whether or not the TDC markings are correct, will be to perform the PPS procedure. There is no short cut to this!



.
 
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All makes perfect sense! Thank you for the detailed explaination! I do not plan on pushing any limits with this motor. I do, however, plan on finding TDC to make sure the timing mark is in the right place. Then I can safely set the timing.

Thank you all for your help and guidance!!

JD
 
My interpretation of the OP's use of "EST" is the Delco Voyager EST distributor.

What increases the odds for fuzziness, is in the late 90's, Mercruisers used TB-IV, TB-V, and EST ignitions. The factory manual shows all of the EST applications using a MEFI controller to drive the ignition module (timing)...maybe more details are in order????
 
Joseph, we can make this very simple.
Get your PPS TDC verification out of the way.
Connect up your strobe light, start the engine and take progressive advance readings at increments of 250 RPM up to 3,500!

Plot this out in graph form and post it for us.


.
 
Based on post #18, your timing advance is controlled by the ECU and the only adjustment you have is the initial timing....and you need the timing plug or a scan tool to do it correctly....That's what Chris was getting at early in the thread....
 
I have the timing plug which is just a jumper for 2 pins. I’m comfortable setting base timing and then verifying it. I just want to make sure I’m getting optimal timing is beyond what the factory manual says... 8 deg BTDC.
 
Update : did NOT get a chance to do this. I’m out of town for a week so I’ll revisit on the weekend!
 
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