Timing curve for the 5.7L ecm conversion 807264A01-gctid375931

[Guest]

Does anyone know the degees of advance for this conversion module (807264A01)it's for the 5.7L alpha.I'm getting 36 degrees tat in normal mode with 8 degrees initial in base mode.It's all out at 3500rpms. I converted to a vortec motor with 4bbl.The original was a 97 5.7l alpha

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dolphin1 wrote:
Does anyone know the degees of advance for this conversion module (807264A01) it's for the 5.7L alpha. I'm getting 36 degrees tat in normal mode with 8 degrees initial in base mode. It's all out at 3500rpms. I converted to a vortec motor with 4bbl.The original was a 97 5.7l alpha

Tom, I don't know enough about this particular ignition system to comment on what/when and how it is advancing.

I will tell you that 36* TA is a recipe for Detonation ..... and in particular with the GM engine using the full dished pistons..... Vortec or no Vortec.

When you are setting BASE advance, are you putting the system into BASE mode?

Looks like you are.

When you are looking at the TA @ 3.5K rpm, is this with no load?

With no load, the system may be advancing to this degree. If loaded, I'd have to say that this is a very risky TA.

Even with a good quench build, 32* TA @ 3.5K rpm is about the limit, IMO.

Are you using a digitally advancing timing light in that mode?

Try marking off your balancer, and using your timing light in Std Mode.

.

[Guest]

Hi rick

Thanks for the response I'm using timing tape and a snap-on digital light that shows advance and rpms side by side. It's being checked under load but seemed kinda high to me also, I'm not up on the t-bolt V curves.I have another spare module with the same ta.What do think about dialing back the initial timing to reduce the ta.With the initial at 4 degrees in base, the t-bolt 5 may compensate for the low base. I'm wondering if I need to give It a few minutes to stablize before I check the ta.

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dolphin1 wrote:
Hi rick

Thanks for the response I'm using timing tape and a snap-on digital light that shows advance and rpms side by side. It's being checked under load but seemed kinda high to me also, I'm not up on the t-bolt V curves.I have another spare module with the same ta.What do think about dialing back the initial timing to reduce the ta.With the initial at 4 degrees in base, the t-bolt 5 may compensate for the low base. I'm wondering if I need to give It a few minutes to stablize before I check the ta.

I think that if this was truly receiving 36* @ 3.5k rpm and while under load, it would be detonating.

Detonation is not necessarily as audible as is Pre-Ignition.... in fact, sometimes it can be difficult to hear.

Is it possible that the timing degree decal was for a larger diameter harmonic balancer?

If it was, the actual markings would be incorrect.

With the known balancer diameter, you can lay this out on paper by drawing a same size circle.

Divide the circle into degrees from zero to 30* .

Use a divider at the circumference, and set it to the distance from zero to 30*.

Compare this distance to the zero to 30* markings on the harmonic balancer degree decal.

As for the digitally advancing timing light, after you varify your crankshaft degrees, try using the timing light in standard mode.

This will eliminate any glitch or error with the digitally advancing system.

See what you come up with.

Like I mentioned earlier, 36* TA @ 3.5k rpm is very risky, IMO.

.

[nottingham88]

Wouldn't a MC 5.7L vortec come stock with a knock sensor ? In a perfect world the Tbolt V sytem would monitor the voltage from sensor and reduce timing should knock be sensed. Conversely the MC 5.0L does not use a knock sensor, that part of the circuit is looped back on itself at the control unit.

From what I've found the TBolt V system uses several different auto modes, allowing the ecu to control timing using logical conclusions derived from RPM and other engine data. I think it's high is around the 34-36 BTDC mark if all conditions are met. They don't share too much info on those expensive black boxes! It would be nice to know the max advance and at what RPM it should be in by.

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nottingham88 wrote:
Wouldn't a MC 5.7L vortec come stock with a knock sensor ? In a perfect world the Tbolt V sytem would monitor the voltage from sensor and reduce timing should knock be sensed. Conversely the MC 5.0L does not use a knock sensor, that part of the circuit is looped back on itself at the control unit.

From what I've found the TBolt V system uses several different auto modes, allowing the ecu to control timing using logical conclusions derived from RPM and other engine data.

• 1 wrote:
• I think it's high is around the 34-36 BTDC mark if all conditions are met.
• They don't share too much info on those expensive black boxes!
• It would be nice to know the max advance and at what RPM it should be in by.

I know very little about Merc's TB EST system, other than the basics of the controller performing the actual spark timing (EST), rather than a mechanical device performing it.

• 1 wrote:
• I've included a link to Merc's ignition timing information that may help explain this.
• NO.... that's for sure! Perhaps these are built in Area 51!
• Hopefully the Merc curves in the pdf file will help you.

Tom, earlier you mentioned [COLOR]"#0000FF" wrote:
36 degrees tat in normal mode with 8 degrees initial in base ..... all out at 3500rpms.[/COLOR]

I don't know if you have verified your degree decal or not, but I think that would be important for you to do.

Nottingham88, Progressive and Total Advance numbers typically don't mean a whole lot to us until we associate an RPM with them.

Here is a link to Merc info via boatfix.com in PDF format that will give you a starting point.

http://www.boatfix.com/merc/Techbk/95/95HGB4.PDF

Look at pdf pages 14 and 15 (actual pages 4B-12 and 4B-13)

NOTE: the MCM 3.0LX with EST curve on 4B-9 includes BASE advance.

[SIZE]1 wrote:
[COLOR]"#0000FF" wrote:
Don't become confused on this...... the two that we're going to look at two do not (as most do not).

see the notation at the left side of the graphs: Total Spark Advance Minus Initial Timing[/COLOR] [/SIZE]

This means that BASE must be added when we do the math for curve plotting, etc.

However, BASE will always be included while we strobe our timing marks, as I'm sure you know.

The 36* total advance mentioned must have an RPM # along with it, or we can't do much with it.

I realize that 34* and 36* numbers are used, but look at the RPM where these numbers occur. The TB systems carry the progressive advance out further than most.

Keep in mind that the 32* TA shown in 4B-13, is @ 4,800 RPM. They are apparently delaying this (carrying it out further) due to the GM engine combustion chamber design, and in order to prevent detonation.

With a quench build, this same 32* could likely occur closer to 3,500 rpm.

Point being, we need more extensive info on the engine build in order to play around with TA numbers. If the engine is OEM, then the Merc numbers will work as they should.

But use caution, and DO NOT allow a TA to come on too early with this engine.

With a conventional Non-EST system, the progressive is rather linear, and typically limits out at/near 3.2k rpm or so.

If it were to continue, it may look very similar to the TB curve.

I will say that with the knock sensor as part of the system, and the ECU's ability to cut back timing, it will usually prevent detonation.

Not sure if this helps any.... hope so!

.

[Guest]

It's critical to understand whether this unit uses vacuum (manifold pressure) as an input to the total advance.

In cars, it's not unusual to see max advances in the 45 degree range, given the right circumstances (IE: Light load high rpm, etc).

If it does use vaccuum and you're at part throttle at 3500rpm, the module could surely be giving you this output. With our old junk (rpm based only) the advance acts like we have full throttle all the time to keep it simple and safe, at the cost of efficiency.

I'd like to know if it comes down at full throttle (max rpm+max manifold pressure). This should mimic the top end of our our old school curves.

Chay

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cfoss wrote:

• 1 wrote:
• It's critical to understand whether this unit uses vacuum (manifold pressure) as an input to the total advance.
• In cars, it's not unusual to see max advances in the 45 degree range, given the right circumstances (IE: Light load high rpm, etc).
• If it does use vaccuum and you're at part throttle at 3500rpm, the module could surely be giving you this output. With our old junk (rpm based only) the advance acts like we have full throttle all the time to keep it simple and safe, at the cost of efficiency.
• I'd like to know if it comes down at full throttle (max rpm+max manifold pressure). This should mimic the top end of our our old school curves.

• 1 wrote:
• It may, but when manifold pressure is high (vacuum), we don't have heavy engine loads. This is simply a result of physics.... (i.e., pistons wanting to pull large volumes of air in/throttle plate position restricting incoming air)
  
  When we open the throttle plates for more fuel/air (power), the restriction decreases...... therefor manifold pressure also decreases.
  
  So if the ignition is advanced during high manifold pressure...., there are usually no issues.
  
  It's excessive ignition advance while under heavy loads (low manifold pressure), where detonation issue occurs.
  
  Short of low oil pressure and/or high temps, detonation is one of the Marine gasser's worst enemies.
• Yes, you nailed it! No heavy loads when this occurs!
  
  In the Marine environment, there is also no advantage to high ignition advance during these conditions ... other than emission control.
  
  In the Automotive world, there are great advantages regarding emission controls.
• At 3,500 rpm under Marine loads, we'll typically be working the engine.
  
  Throttle plate position, at this RPM and load, does not allow for much manifold pressure.
• I suppose if you were up on plane, and then reached that spot where the load became reduced, you may see an increase.
  
  Throw a vacuum on your engine, and give it a try.

[Guest]

" It may, but when manifold pressure is high (vacuum), we don't have heavy engine loads. This is simply a result of physics.... (i.e., pistons wanting to pull large volumes of air in/throttle plate position restricting incoming air)

When we open the throttle plates for more fuel/air (power), the restriction decreases...... therefor manifold pressure also decreases.

So if the ignition is advanced during high manifold pressure...., there are usually no issues.

It's excessive ignition advance while under heavy loads (low manifold pressure), where detonation issue occurs.

Short of low oil pressure and/or high temps, detonation is one of the Marine gasser's worst enemies.

Manifold pressure is high when vacuum is low (IE: the engine is working hard). I'm not sure if this is what you meant or not. I agree that when the manifold pressure is low (vacuum is high) the engine is lightly loaded. The throttle plate is a variable restriction; agreed. Another way to look at the throttle plate is a variable pressure loss. When we close the throttle, the pressure loss increases, and we loose manifold pressure. Open it, we get more manifold pressure.

RPM affects pressure in that at higher rpm (to the max volumetric efficiency point) will consume more air at a given pressure.

If I understand what you are saying correctly, where we disagree is where you believe that we are at full manifold pressure at less than wide open throttle. This is not correct. The pressure loss caused by a partially closed (Correctly sized) throttle plate will cause a pressure loss (Or in other words, some vacuum). In the case of non wide open throttle operation we can advance the timing to a point where we don't yet have detonation, but increases efficiency occurs. This is more than just emmsions control, it's real power.

At 3,500 rpm under Marine loads, we'll typically be working the engine.

Throttle plate position, at this RPM and load, does not allow for much manifold pressure.

I just disagree completely with this statement.

I suppose if you were up on plane, and then reached that spot where the load became reduced, you may see an increase.

Throw a vacuum on your engine, and give it a try.

As I've said before, I can cruise between about 10 and 5 on my vacuum guage on the palne by adjusting the throttle. WOT is of course, 0 Vacuum. 0 Corresponds to 100KPA pressure(14.7psi or so), 0KPA is a perfect vacuum, which doesn't occur.

The formula for converting kpa to vacuum guage readings is:

KPA = (29.9216-vac guage reading)/.29529, so at 10 on my vacuum guage, I'm at 67Kpa, or 9.9psi in the manifold. The computer can pickup this difference and change the ta based on it quite easily.

Chay

[Guest]

There seems to be some confusion with regards to the definition of intake manifold pressure and intake manifold vacuum. Perhaps this link may clear things up.

http://www.engineeringtoolbox.com/vacuum-converter-d_460.html

Standard atmospheric pressure absolute is usually expressed in kilopascals (KPA) or inches of mercury (In Hg) being ~101.4 KPA or ~29.29 In HG.

Vacuum is defined as air pressure below atmospheric. In North America manifold vacuum is usually expressed in inches of mercury.

101.4 KPA pressure absolute = 29.29 In HG pressure absolute = 0 in HG vacuum

0 KPA pressure absolute = 0 In HG pressure absolute = 29.29 in HG vacuum

At idle intake manifold pressure is at minimum, intake manifold vacuum is at maximum (not considering over run conditions). At sea level typically ~35 KPA pressure absolute or ~10.34 In HG pressure absolute, or ~19.8 In HG vacuum.

At Wide Open Throttle intake manifold pressure is at maximum, intake manifold vacuum is at minimum. At sea level typically ~100 KPA pressure absolute or ~29.53 In HG pressure absolute or ~0.6 In HG manifold vacuum.

In order to get the best performance possible out of any engine, which means best possible power at full load and best possible economy at part load it must be tuned to optimum at all points in the speed and load range. In a gasoline fueled spark ignition engine this means optimizing air/fuel ratio and ignition timing at each speed and load point. No matter what the application, an engine will go from practically no load at idle to full load. Depending on the application this can take place at a single maximum speed or at many different speeds. In between idle and the full load point or points will be many points of part load.

Not even considering emissions concerns, if there is any question about just how important additional ignition timing advance is, over and above standard RPM based advance, under anything less than full load conditions in any spark ignition engine application, I would strongly suggest a detailed study of this publication:

"Internal Combustion Engine Fundamentals" McGraw Hill Book Company

John B. Heywood

Professor of Mechanical Engineering.

Director, Sloan Automotive Laboratory.

Massachusetts Institute of Technology

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Tom, I see that you haven't been back to your thread here for a few days.

I asked a few questions early on.... were you able to verify anything?

Did the Merc ignition curves help you any?

.

[Guest]

Rick, I've bee out of state working but did make it back to the boat. I'm still in the break-in period up to 4000rpms. rechecked the timing at 3600 rpms and it was 36 degrees while running down the waterway, The chart and timing seem to be fairly close.The motor came with timing tape and I'm also using a snap-on advancing timing light. I have two modules both are t-bolt V and same model # and giving the same advance. I found another issue, the coil was leaking residual voltage to the neg side of the coil,I put a peice of cardboard between the terminals and the rpms would rise and when i moved it they would fall. I guess that why my tach These are all new merc parts with the MichMotor 290hp vortec. So I put another merc coil and wires on it and it done the same thing. Ended up coating the coil tower and neg terminal with di-electric grease. seems fine now,that was really strange.merc might need a taller coil tower,it looks like they are shortened a little.Is their a need to check the valve adjustment anytime soon during break-in.In the other posts there was a mention of vac advance,this is determined by the dist sensor.No vacuum advance,1997 alpha no knock sensor

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Well, I'm not sure what to think of your TA number (3600 rpms and it was 36 degrees). It seems aggressive for a non-quench build, but apparently the engine is not detonating.

According to Boatfix.com's PDF 4B-12, the MCM/MIE 350 CID (5.7L) shows a max of 20* (plus BASE) @ 3.6K rpm, and a max of 22* (plus BASE) @ 4k rpm.

Then if you will look at PDF 4B-13, the MCM 350 Magnum Alpha shows a max of 23* (plus BASE) @ 3.6K rpm, and a max of 24* (plus BASE) @ 4k rpm.

If using your Initial or BASE of 8*........, then the Maximum actual crankshaft advance would equal 31* @ 3.6K rpm, and 32* @ 4k rpm.

31* @ 3.6k rpm is quite different from 36* @ 3.6k rpm, IMO.

That additional 5 degrees could be an issue.

No, you won't have any vacuum advance, per 'se, such as with the old school diaphragm advance units.

I think that Chay was talking about MAP sensing (Manifold Absolute Pressure) and the influence this has on the controller unit.

As for re-setting cam followers...... if this 290hp vortec engine came from MichiganMotors, I've spoken to Phil about this before.

They use the 8 stop procedure, and if memory serves me, they do so prior to oil priming and prior to the intake manifold being installed.

This is a very accurate procedure, so I doubt that you'll need to run back through them.

If this is the GM 290hp vortec engine, I can only assume that they do the same at the factory.

If the two or three stop procedure was used (not as accurate, IMO), you may want to go back through them later on.

.