Ignition question for motorheads

[boscoe99]

Let's say that a Yamaha Offshore model, when running at WOT at 5500 RPM, has an advance ignition timing of 40 degrees BTDC.

If there was a knob on the ECU so as to manually retard the ignition timing, (like we did in the old days using a distributor) what do you think would happen if the advance timing was retarded somewhat? Say I turned the knob to go from 40 degrees BTDC to 38/36/34 degrees BTDC. What would happen?

[99yam40]

I would think that retarding would loose some power.
they advance the timing to get as much burn time on the fuel before it leaves the cylinder.

By doing what you stated I think you would also retard the timing during all RPMS not just WOT.
Or is it just suppose to happen at 5500

[pstephens46]

Please post the complete model number. How can you expect us to help you with such vague information?

[robert graham]

Yep, I'd say you'd lose power.....what else could it do?

[boscoe99]

Updated with more information

Please post the complete model number. How can you expect us to help you with such vague information?

Sorry. You know how us damn posters can be. Anyway, here are more details.

- Model is a Yamaha F300BETX
- Serial number is 6CE X 1005487
- Motor is mounted in a test tank located within a test cell
- A test wheel is installed so the load is consistent
- The drive shaft has a torque meter installed to measure torque
- The test cell is climatically con*****ed so that everything that affects the creation of power remains constant (pressure, temperature, humidity, etc)
- The engine is warmed up and when operating at full power remains at a constant temperature
- The throttle is fully advanced
- At maximum RPM the variable cam mechanism is disconnected so that the cam shaft phase angle with the crank shaft remains constant
- At WOT the RPM is 5500
- At WOT the torque meter is indicating 296.02 pound-feet
- Calculated HP is 310
- YDIS indicates an ignition timing of 40 degrees BTDC

Question is, if the timing is less advanced a bit, say from 40 degrees to 39 or 38 degrees, what would be seen on the engine instruments?

Where are our outboard motor speciallisstts? This is not a trick question. I don't know the answer. What will happen?

Fairdeal, rodnut, sequoia, xeno,????

[boscoe99]

Guess I will go to The Hull Truth. More answers but more crap as well.

[fairdeal]

https://www.hindawi.com/journals/jc/2011/678719/

[99yam40]

I guess the cam timing would need to be set to where it would not change when the timing changed, but may be interesting to know if it would change if hooked up along with what it is set at.
sounds like another test run is needed

[boscoe99]

I guess the cam timing would need to be set to where it would not change when the timing changed, but may be interesting to know if it would change if hooked up along with what it is set at.
sounds like another test run is needed

I started wondering that myself. How and when and what makes the cam shaft angle vary.

But for now all I am interested in is how timing affects HP.

Might need to go to a motorhead forum where folks have done dyno runs and perhaps played with the distributor while the motor was running at WOT under a fixed load at a constant RPM.

[boscoe99]

https://www.hindawi.com/journals/jc/2011/678719/

A good read methinks.

[99yam40]

https://www.hindawi.com/journals/jc/2011/678719/

mind boggling , but the conclusions is all I needed to know.
not really the others were interesting.
for those that do not want to read the whole thing

"6. Conclusion

In the present work, the performance of a commercial SI engine under different ignition timing conditions was analyzed. This is in order to postulate the ignition timing for maximizing engine performance in terms of power, torque, thermal efficiency, and so forth. The following conclusions have been drawn.
(1)If ignition timing does not become advance enough, most of the combustion occurs when the piston is moving down and, in this case, the power and the thermal efficiency decrease.
(2)If ignition timing gets too advance, most of the air-fuel mixture burns before the piston rises. Additionally, the period of the time of heat loss becomes larger, then the net work and the thermal efficiency decrease.
(3)By raising ignition advance, however, an increase in temperature and pressure in cylinder happens but the power and the thermal efficiency decrease due to higher friction loss and other losses in the engine.
(4)The performance of an SI engine highly depends on ignition timing, and its optimum value should be determined for each SI engine. For this engine, the maximum thermal efficiency and net work are obtained at 31°CA BTDC."

[pstephens46]

Sorry. You know how us damn posters can be. Anyway, here are more details.

- Model is a Yamaha F300BETX
- Serial number is 6CE X 1005487
- Motor is mounted in a test tank located within a test cell
- A test wheel is installed so the load is consistent
- The drive shaft has a torque meter installed to measure torque
- The test cell is climatically con*****ed so that everything that affects the creation of power remains constant (pressure, temperature, humidity, etc)
- The engine is warmed up and when operating at full power remains at a constant temperature
- The throttle is fully advanced
- At maximum RPM the variable cam mechanism is disconnected so that the cam shaft phase angle with the crank shaft remains constant
- At WOT the RPM is 5500
- At WOT the torque meter is indicating 296.02 pound-feet
- Calculated HP is 310
- YDIS indicates an ignition timing of 40 degrees BTDC

Question is, if the timing is less advanced a bit, say from 40 degrees to 39 or 38 degrees, what would be seen on the engine instruments?

Where are our outboard motor speciallisstts? This is not a trick question. I don't know the answer. What will happen?

Fairdeal, rodnut, sequoia, xeno,????

BETX sounds foreign. You may need to check with a local dealer.

[boscoe99]

BETX sounds foreign. You may need to check with a local dealer.

You better get your hearing checked. USA American as apple pie ala modus operadi rights.

[zenoahphobic]

mind boggling , but the conclusions is all I needed to know.
not really the others were interesting.
for those that do not want to read the whole thing

"6. Conclusion

In the present work, the performance of a commercial SI engine under different ignition timing conditions was analyzed. This is in order to postulate the ignition timing for maximizing engine performance in terms of power, torque, thermal efficiency, and so forth. The following conclusions have been drawn.
(1)If ignition timing does not become advance enough, most of the combustion occurs when the piston is moving down and, in this case, the power and the thermal efficiency decrease.
(2)If ignition timing gets too advance, most of the air-fuel mixture burns before the piston rises. Additionally, the period of the time of heat loss becomes larger, then the net work and the thermal efficiency decrease.
(3)By raising ignition advance, however, an increase in temperature and pressure in cylinder happens but the power and the thermal efficiency decrease due to higher friction loss and other losses in the engine.
(4)The performance of an SI engine highly depends on ignition timing, and its optimum value should be determined for each SI engine. For this engine, the maximum thermal efficiency and net work are obtained at 31°CA BTDC."

By and large this conclusion appears as the correct answer. But what is meant by thermal efficiency and an explanation of what is the higher friction loss and other losses in the engine under (3) needs to be included for this summary to stand on it's own.

If I was to answer Boscoe's question briefly, given he quoted reduction by a degree or two or three at such a high advance, inspite of the above, I would still have said Bug.. All difference in the practical sense.

[rodbolt17]

that engine has a knock sensor and the ign timing is computer con*****ed.
backing the timing down 2 degrees most likely will have no affect.
you can disconnect the cam OCV's and all you will find is it is sluggish at midrange.
at WOT the cams are in full retard same as idle speed.