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Question about EFI cold start AFR

General engine tech -- Drag Racing to Circle Track

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Rick!
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Re: Question about EFI cold start AFR

Post by Rick! »

ptuomov wrote: Wed Nov 11, 2020 10:32 pm
Orr89rocz wrote: Wed Nov 04, 2020 7:44 am Also note it is very common to add 2-4 deg timing during this time and idle speed demand being set few hundred rpm higher. Warm idle 25 deg and 800 rpm, cold starts may be better at 27-28 deg and 1000 rpm until it warms up
Here’s a question. I can see why adding timing in cold weather makes sense if the ability make air flow adjustments is limited. However, just from theory perspective, wouldn’t it make sense to retard timing when cold and increase the air flow to compensate for the power loss due to late timing? This way, the engine would heat up faster. Does this make sense?
That's how diesels (used to) do it. Diesel tuners may advance the timing a tad when cold and let the engine merrily ping away at low loads for the trade-off of sportier cold driveability.
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Re: Question about EFI cold start AFR

Post by Belgian1979 »

Try both approaches and see what works best.
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Re: Question about EFI cold start AFR

Post by Orr89rocz »

ptuomov wrote: Wed Nov 11, 2020 10:32 pm
Orr89rocz wrote: Wed Nov 04, 2020 7:44 am Also note it is very common to add 2-4 deg timing during this time and idle speed demand being set few hundred rpm higher. Warm idle 25 deg and 800 rpm, cold starts may be better at 27-28 deg and 1000 rpm until it warms up
Here’s a question. I can see why adding timing in cold weather makes sense if the ability make air flow adjustments is limited. However, just from theory perspective, wouldn’t it make sense to retard timing when cold and increase the air flow to compensate for the power loss due to late timing? This way, the engine would heat up faster. Does this make sense?
Im sure you could try it but more air and less timing being cold seems to me it wouldnt run very smooth. Fuel isnt atomizing well hence the additional amount of fuel needed to run and more timing to light it off and keep engine stable. Retarded timing would put more heat in the exhaust and maybe good for cats getting up to temp? But leaving heat in the cyl should transfer to head coolant.
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Re: Question about EFI cold start AFR

Post by ptuomov »

Orr89rocz wrote: Fri Nov 13, 2020 8:41 am
ptuomov wrote: Wed Nov 11, 2020 10:32 pm
Orr89rocz wrote: Wed Nov 04, 2020 7:44 am Also note it is very common to add 2-4 deg timing during this time and idle speed demand being set few hundred rpm higher. Warm idle 25 deg and 800 rpm, cold starts may be better at 27-28 deg and 1000 rpm until it warms up
Here’s a question. I can see why adding timing in cold weather makes sense if the ability make air flow adjustments is limited. However, just from theory perspective, wouldn’t it make sense to retard timing when cold and increase the air flow to compensate for the power loss due to late timing? This way, the engine would heat up faster. Does this make sense?
Im sure you could try it but more air and less timing being cold seems to me it wouldnt run very smooth. Fuel isnt atomizing well hence the additional amount of fuel needed to run and more timing to light it off and keep engine stable. Retarded timing would put more heat in the exhaust and maybe good for cats getting up to temp? But leaving heat in the cyl should transfer to head coolant.
Maybe right, I don’t know, but my understanding is the best torque timing heats the cylinder head less than retarded timing for the same amount of crankshaft torque. More energy goes to turning the shaft and less to heat, so less air and fuel needed and less heat to the head. Contrast with retarded timing, more air, and more fuel, later burn and less shaft torque, more heat to the head. Of course, silly retarded might not even ignite, but within reason.
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Re: Question about EFI cold start AFR

Post by David Redszus »

ptuomov wrote: Fri Nov 13, 2020 8:58 am
Orr89rocz wrote: Fri Nov 13, 2020 8:41 am
ptuomov wrote: Wed Nov 11, 2020 10:32 pm

Here’s a question. I can see why adding timing in cold weather makes sense if the ability make air flow adjustments is limited. However, just from theory perspective, wouldn’t it make sense to retard timing when cold and increase the air flow to compensate for the power loss due to late timing? This way, the engine would heat up faster. Does this make sense?
Im sure you could try it but more air and less timing being cold seems to me it wouldnt run very smooth. Fuel isnt atomizing well hence the additional amount of fuel needed to run and more timing to light it off and keep engine stable. Retarded timing would put more heat in the exhaust and maybe good for cats getting up to temp? But leaving heat in the cyl should transfer to head coolant.
Maybe right, I don’t know, but my understanding is the best torque timing heats the cylinder head less than retarded timing for the same amount of crankshaft torque. More energy goes to turning the shaft and less to heat, so less air and fuel needed and less heat to the head. Contrast with retarded timing, more air, and more fuel, later burn and less shaft torque, more heat to the head. Of course, silly retarded might not even ignite, but within reason.
Advanced ignition timing will put more heat into the head and less out the exhaust.
Conversely, retarded timing will reduce piston temperature and heat the exhaust.
That's assuming the same amount of fuel is burned.

A mixture that is either richer or leaner than optimum will require more ignition timing.

A mixture that is not fully evaporated will require more timing and more fuel.
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Re: Question about EFI cold start AFR

Post by ptuomov »

"That's assuming the same amount of fuel is burned."

A better assumption here is that the idle rpm stays the same.
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Re: Question about EFI cold start AFR

Post by Belgian1979 »

Ptuomov, I don't understand this. If you're convinced that retarding and/or a richer mixture helps you engine, you should just try that. I've had theories about a lot of things and tried them out. Some failed, some were good. The only way to really know if your idea is good on your particular engine is to try it out.
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Re: Question about EFI cold start AFR

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Belgian1979 wrote: Sun Nov 15, 2020 6:10 am Ptuomov, I don't understand this. If you're convinced that retarding and/or a richer mixture helps you engine, you should just try that. I've had theories about a lot of things and tried them out. Some failed, some were good. The only way to really know if your idea is good on your particular engine is to try it out.
I will need to wait for two about equally cold mornings and then run two data logged tests. Does retarded timing increase coolant temperature faster?

In general, there are so many variables to test, tests are so time consuming, and test results are so noisy that I think it makes sense to think about the “theory” first.
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Re: Question about EFI cold start AFR

Post by Belgian1979 »

ptuomov wrote: Sun Nov 15, 2020 7:19 am
Belgian1979 wrote: Sun Nov 15, 2020 6:10 am Ptuomov, I don't understand this. If you're convinced that retarding and/or a richer mixture helps you engine, you should just try that. I've had theories about a lot of things and tried them out. Some failed, some were good. The only way to really know if your idea is good on your particular engine is to try it out.
I will need to wait for two about equally cold mornings and then run two data logged tests. Does retarded timing increase coolant temperature faster?

In general, there are so many variables to test, tests are so time consuming, and test results are so noisy that I think it makes sense to think about the “theory” first.
I would say that no, retarded timing doesn't heat up my engine faster. Quite the contrary. Best mod I ever made on my sbc to get her warmed up was to connect the top op the waterpump to the adapter below the termostat. Never warmed up faster.
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Re: Question about EFI cold start AFR

Post by vannik »

I have no experience with such extreme cold except when we developed a vehicle for the Swedish military and it had to start, with some preparation, after soaking a night at -55C, but that was a diesel engine. Some thinking along the issues we experienced:

You seem to have two issues that has to be solved at the same time:
1. The formation of mixture and the generation of heat, probably needing rich mixture with retarded timing; and
2. Generating enough power to overcome the thick cold engine oil, probably needing advanced timing.

I think the two requirements might be in conflict part of the time. And the trade-off will be dependent on temperature. Ambient and engine.
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