Ignition timing vs engine torque

[tbug]

Hi all,

I am currently testing a ford escort 1100 cc petrol engine through a water break dynamometer. I carried out steady state tests for 0, 4 and 12 BTDC through an RPM range of 1500 to 4000, in steps of 500. the total torque for O degree timing was low compared to 4 and 12 degrees. I was thinking that the reason for this may have been due to misfiring and knocking.

Am I right?

and another question. I noticed that for 4 and 12 degrees the torque readings were very similar to each other (almost on the same line on the graph).

Is this normal? I mean I would have expected greater power developed at 12 BTDC.

Thanks

 

[GregLocock]

Please post your results in tabular form.

Cheers

Greg Locock


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[patprimmer]

The results are unexpected. Was there a misfire. Could you hear a knock. I would not expect knock at that timing unless something was seriously wrong in compression vs octane, cam timing or head temperature.

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Pat
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[tbug]

Yes I heard some misfire at 0 BTDC but not that much. Attached you may see my tabulated results.

Cheers
tbug

 

[Tmoose]

Was the stated timing fixed through the rpm range, or a static or idle rpm setting that was then modified by mechanical or electronic "centrifugal" advance?

 

[tbug]

yes the timing was fixed for each test. the butterfly was left wide opened for the whole duration of the test, and the rpm was varied through computer control for each timing setting.

Thanks

 

[HRHtex]

That is what I was wondering - 12 degrees is not much advance for 4000RPM - 30 or so would be more appropriate.
Maybe when you don't have enough advance it doesn't matter much whether it is 4 or 12 degrees?

 

[GregLocock]

Thanks for the data. The difference 0 to 4 looks far too great, and difference 4 to 12 looks suspiciously non existent.



Cheers

Greg Locock


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[patprimmer]

How did the computer control the rpm?

Regards
Pat
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[GregLocock]

Heywood fig 9-3 shows a 10% fall in torque from mbt over about 15 degrees

Cheers

Greg Locock


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[evelrod]

Sorry...Perhaps I'm just getting old, but I'm having some degree of difficulty in determining what the OP is after, given such limited specs. I don't know which particular 1100cc Ford is being tested (tested for what?), there have been several over the years. Still, I'm confused!

Rod

 

[tbug]

Pat, the RPM was being controlled from Labview, by varying the load on the engine by the dynamometer.

Greg, thanks for that chart, I found some good examples in heywood.

Rod, I wasn't actually testing the engine. it was used for commissioning a new water brake dynamometer. However, I was surprised with the results. I wasn't expecting the optimum timing to be at 4 btdc.

Thanks
tbug

 

[patprimmer]

OK

With the almost bizarre results I was wondering if you had constant load and a computer was controlling the throttle or something equally ridiculous.

4 deg seems unbelievable. I really wonder about your timing marks or if the spark is strong enough to fire under load or you have an ignition system that retards as you think it advances.

Regards
Pat
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[gruntguru]

Must say the results look bizarre. If they are accurate, my best guess is the zero degree result is seriously affected by misfire due to lack of ignition reserve and consequent inability to fire the plugs at the higher cylinder pressure at TDC. Having said that, 4 deg BTDC should have almost identical cylinder pressure.

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