5.5 Head Spark Advance

[nkaminar]

Knock sensor is a good idea for us old farts who cannot hear worth a damn.

I read somewhere the Motometer was designed to sense temperature by vapor heat transfer, like a heat pipe. The vapor (steam) is condensed on the bulb which heats the bulb. I think the original Motormeters were designed to work like that but the reproduction ones may not have the same MO. But I also think Brent is right that more coolant flow will raise the temperature reading in the Motometer. I see that in my car.


Getting back to the original discussion: A high compression head with a combustion chamber that is designed for added turbulence will need less spark advance. I think that searching for the sweet spot is a good method of setting the spark advance. 28 degrees may be too much, leading to the rod bearing failure as reported.

[alexiskai]

Originally Posted by BRENT in 10-uh-C

No, not at all. A stock head does not necessarily run cooler than a H/C head. For the sake of this discussion, the piston is likely going to draw the same amount of air/fuel no matter which head is used, so the BTUs of the fuel mixture is comparable, however several things play into this such as latent heat when the combustion is made which changes because a higher compressing of air increases its heat value. That alone coupled with the burning fuel makes a higher BTU value. Therefore a higher compression head runs hotter inside of the combustion chamber.

Here's what I don't get about this version of events. Let's say for purposes of comparison that the airflow constriction of the carb/intake is not a factor – let's say we're comparing engines at low rpm. To move a car down the road at, say, 30 mph with 0 acceleration takes a set quantity of energy per unit time, a certain number of watts or horsepower, to overcome friction/drag.

So the engine has to put out, let's say, 20 HP to maintain a car going 30 mph (just to use round numbers). Now, the rpm of the motor is fixed for a given road velocity, let's say 1800 rpm. So a stock engine and a HC head engine are both turning at 1800 rpm and both putting out 20 hp to move a car at 30mph with 0 acceleration. We know they are both putting out the same hp, because if the HC head motor were putting out higher hp, that car would be accelerating, and in this thought experiment, it isn't.

We know that the displacement of the engines is similar. The HC head has slightly lower displacement because the combustion chamber is slightly smaller. But we also know that the HC head has a higher power output per unit of fuel/air mixture burned. My understanding is that the power output goes up faster than the displacement goes down, i.e., the HC head has higher hp per ci.

So if the HC head is putting out more hp per ci than the stock head, but in our scenario both engines are putting out a constant 20 hp at 1800 rpm, what variable is different? It seems like it must be the fuel/air volume, or in other words the throttle position. A HC head can output 20 hp with the throttle position more closed than the stock head. The carb passes a smaller fuel/air volume to the cylinders. Because the quantity of fuel is reduced per power stroke, relative to the stock head, less waste heat is produced. Therefore the HC head runs cooler.

I'm not saying the higher coolant volume over the combustion chamber doesn't also play a role, but to say that the increased combustion efficiency has no effect on waste heat, or that it's somehow canceled out, doesn't square with my understanding of the physics.

[alexiskai]

Originally Posted by katy

I'm considering putting a knock sensor and an indicator light on my CCPU.

Is this even possible? What would you use to interpret the knock sensor's output? I thought their output was typically read via an ECU or oscilloscope or something.

[AzBob]

All I can say is I have installed high compression heads on both a Model T and a Model A and in both cases, the engines ran cooler and both got better fuel economy. This includes lower coolant temperatures as well measured by thermocouple. This tends to back up alexiskai’s thought experiment.

[Jack Shaft]

When you can hear 'ping' it's too late,detonation can occur whether you hear it or not.

Engine heat..ever wonder why a stock A engine has exhaust gasket/ manifold issues?threads on here almost daily..its from the lack of combustion effciency..the horse power theory above is relevant in one way,as engine demand goes up the heat created by inefficient combustion increases.the threshold the cooling system has can be exceeded quicker with a less efficient use of combustion..basically you use less of the cooling systems heat exchange capacity when you use the heat to create power by raising combustion effciency.

[Model A Ron]

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Originally Posted by AzBob

All I can say is I have installed high compression heads on both a Model T and a Model A and in both cases, the engines ran cooler and both got better fuel economy. This includes lower coolant temperatures as well measured by thermocouple. This tends to back up alexiskai’s thought experiment.

I am still new to the Model A but looking at my moto meter I see a drop in coolant temp. The car drives better with the 5.5 head and she likes the spark advance at 3/4 down when doing about 45.

[AzBob]

Originally Posted by Model A Ron

I am still new to the Model A but looking at my moto meter I see a drop in coolant temp. The car drives better with the 5.5 head and she likes the spark advance at 3/4 down when doing about 45.

I seldom see any red at all in the motometer. Only on the warmest of days. I do run a 160 deg. thermostat and Apco temperature gage.

My Snyder’s 6.0 head likes 28 degrees advance at 45 and above. As setup on my A, this is with the spark lever halfway down or 9:00. My car is relatively quiet and have never heard any pinging.

[GeneBob]

Alex, in your post (#22), you state the displacement changes with the HC head. The displacement does not change, the piston diameter and stroke are unchanged so the volume of gas brought into the cylinder is the same. The difference is at TDC, the combustion chamber volume is less so the compression ratio is higher.
Your thought experiment works as you stated since the higher compression makes the engine (a little) more efficient so you would actually maintain the 30 mph speed with slightly less throttle opening.
I would not rely on a moto-meter for exacting results for any efficiency testing, but it gives an indication that something improved.
Of course, it is entirely possible that Ron has more water in his radiator after replacing the head on his car.

[alexiskai]

Originally Posted by GeneBob

Alex, in your post (#22), you state the displacement changes with the HC head. The displacement does not change, the piston diameter and stroke are unchanged so the volume of gas brought into the cylinder is the same.

You're correct that the displacement doesn't change – "displacement" technically is only a measure of the cylinder volume. There isn't really a term for what I meant, which was the cylinder volume plus the chamber volume. That sum does decrease slightly, and consequently the 3D volume that the carb has to fill with FAM is slightly smaller. But it's not smaller enough to explain the overall reduction in fuel use and waste heat per hp output, which was the point.

[Model A Ron]

I did change out the coolant and flush out the block but it did not look all that bad. I filled the radiator to the baffle same as it was.

[nkaminar]

There is one problem with Alex's thought experiment. The guy with high compression head would be going 45 not 30.

One other comment: The low compression head has more exhaust gas in the total volume of the head and cylinder when the intake opens. The amount of air/fuel that enters is the same as the high compression head. This is the same logic as raising a boat in a lock. It takes the same amount of water to raise a large ship as it does to raise a small boat. I know I am going to get an argument on that because on first look it does not seem logical. If you draw the diagram, remember to include the water under the ship that is needed to raise it.

[alexiskai]

Originally Posted by nkaminar

There is one problem with Alex's thought experiment. The guy with high compression head would be going 45 not 30..

Read it again. Both cars are going 30, that's the starting condition for the experiment.

[Jack Shaft]

or as they say,"you never know who's swimming naked till the tide goes out"

[nkaminar]

Alex, I think my attempt at humor must be too subtle.

[Model A Ron]

Originally Posted by Jack Shaft

or as they say,"you never know who's swimming naked till the tide goes out"

This is a new one to me and I like it.....thanks

[GeneBob]

Originally Posted by Model A Ron

This is a new one to me and I like it.....thanks

Once the tide is out, you may not like it!

[GeneBob]

Originally Posted by nkaminar

There is one problem with Alex's thought experiment. The guy with high compression head would be going 45 not 30.

One other comment: The low compression head has more exhaust gas in the total volume of the head and cylinder when the intake opens. The amount of air/fuel that enters is the same as the high compression head. This is the same logic as raising a boat in a lock. It takes the same amount of water to raise a large ship as it does to raise a small boat. I know I am going to get an argument on that because on first look it does not seem logical. If you draw the diagram, remember to include the water under the ship that is needed to raise it.

Sorry, I don't buy it.
It may take the same depth of water but not the same volume of water.

[Model A Ron]

Originally Posted by GeneBob

Sorry, I don't buy it.
It may take the same depth of water but not the same volume of water.

It would be much more water with the small boat

[Model A Ron]

Originally Posted by GeneBob

Once the tide is out, you may not like it!

The fact that we are driving antique 90 + year old cars would make a lot in society say we are swimming naked. If we weren't all crazy, we'd just go insane.

When I think about it my Grandfather was 17 when my Phaeton was new.....very cool in my opinion that I am experiencing the same Model A's that a man born in 1912 did. This also proves the fact that Henry Ford built one hell of a car back in the day. I think Henry would be surprised to see so many of his cars still around in 2021.

[GeneBob]

Alex, last night I finally realized what you were saying in post #22.
The percentage of fresh air mixture is slightly higher with the HC head.
At 4.2 compression ratio, the TDC volume is about 12 cu in.
At 5.5 compression ratio, the TDC volume is about 9 cu in.
Therefore, a fresh air mixture brought into the cylinder by the piston stroke would be:
81% of the total volume of the 4.2 compression head + stroke, and
85% of the total volume of the 5.5 compression head + stroke, so,
on a percentage basis, you get more fresh air mixture with the HC head. This would result in less recycled spent mixture still in the cylincer adding to the level of wasted heat.
OHHHhhhhh, now I see what you mean. Yes, I agree with you. A small factor, but a factor none the less.
Thanks.