Electric fans suck!

[Supercharged111]

25,000BTU dumped into 2000cfm would yield a ballpark ~11degF heat rise, i.e., the "preheated" temperature of the air entering the radiator is increased by ~11degF. The temp rise varies inversely with CFM, e.g., at 1000 CFM the rise is ~22degF, at 10,000CFM it's ~2.2degF.

Other factors will cause this to vary but for a ballpark estimate, this should do.


Assumptions:

Ambient conditions - Dry air at or around 68degF, thereby having density of 1.29kg/m^3 and specific heat 1000 J/kg*degK.

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[L31MaxExpress]

Any idea what the heat rejection into the coolant might be for that 383 under similar conditions?

I am not sure but I can take a guess. Ball park figure, 25% into the cooling system, maybe 4-5% into the oil which a large percentage ends up in the cooling system because the oil cooler is in the driverside radiator tank. So call it 28%. Engine is burning around 1 gph at idle with the a/c on and that number jumps substantially above idle. At 40 mph, steady speed it is using 2.2 gph. Gasoline is around 120,000 btu per gallon. At idle 28% of 120,000 is about 33,600 BTU and at 40 mph steady speed about 73,920 btu at 28% of 2.2 gallons. The torque converter when it is unlocked also slips a good bit with its 2,800 stall but I do not know what kind of BTU the transmission and converter is contributing.

 

[1998_K1500_Sub]

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I'll have the Royale with Cheese.

 

[L31MaxExpress]

So 25,000 btu is high for idle, but can be reached under acceleration. When I am accelerating I am in the 2,000-3,500 rpm range frequently and the compressor is overdriven 1.36x crank speed.

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[1998_K1500_Sub]

I am not sure but I can take a guess. Ball park figure, 25% into the cooling system, maybe 4-5% into the oil which a large percentage ends up in the cooling system because the oil cooler is in the driverside radiator tank. So call it 28%.

Not bad place to start for a back-of-the-napkin analysis.

Engine is burning around 1 gph at idle with the a/c on and that number jumps substantially above idle. At 40 mph, steady speed it is using 2.2 gph. Gasoline is around 120,000 btu per gallon. At idle 28% of 120,000 is about 33,600 BTU and at 40 mph steady speed about 73,920 btu at 28% of 2.2 gallons.

Using the same assumptions I used before (which might be dangerous now but I'll throw caution to the wind), ~74,000BTU into 3000cfm would yield ~22°F heat rise. I'll let that number simmer for a bit.

Here's the budget (using your earlier numbers), just for the sake of conversation:

Source air temp: 115°F (@L31MaxExpress' earlier post)

- Heat rise, AC condenser: 7°F 25k BTU @ 3000CFM
- Heat rise, engine rejection: 22°F 74k BTU @ 3000CFM

Subtotal 144°F

I'm missing, at least, some estimate of the radiator efficiency, i.e., if the target max coolant temp is 185°F, what's the temp of the air leaving the radiator.

The torque converter when it is unlocked also slips a good bit with its 2,800 stall but I do not know what kind of BTU the transmission and converter is contributing.

I'm trying to come up with a simple estimate for the trans heat adder.

But I think you can see what I'm up to here, as simplistic and perhaps flawed as it may be: There's a certain temperature rise "budget" for the airflow, and to stay within that budget one needs to increase the CFM (or lessen the added heat). The exit temperature for the airflow I'll chose to be that necessary to maintain engine temperature at 185°F. The inlet temp, I'll use your ambient sensor's temp measurement.

I may mull this over into the evening. Meanwhile, the readers are bored to tears

 

[L31MaxExpress]

Not bad place to start for a back-of-the-napkin analysis.



Using the same assumptions I used before (which might be dangerous now but I'll throw caution to the wind), ~74,000BTU into 3000cfm would yield ~22°F heat rise. I'll let that number simmer for a bit.

Here's the budget (using your earlier numbers), just for the sake of conversation:

Source air temp: 115°F (@L31MaxExpress' earlier post)

- Heat rise, AC condenser: 7°F 25k BTU @ 3000CFM
- Heat rise, engine rejection: 22°F 74k BTU @ 3000CFM

Subtotal 144°F

I'm missing, at least, some estimate of the radiator efficiency, i.e., if the target max coolant temp is 185°F, what's the temp of the air leaving the radiator.



I'm trying to come up with a simple estimate for the trans heat adder.

But I think you can see what I'm up to here, as simplistic and perhaps flawed as it may be: There's a certain temperature rise "budget" for the airflow, and to stay within that budget one needs to increase the CFM (or lessen the added heat). The exit temperature for the airflow I'll chose to be that necessary to maintain engine temperature at 185°F. The inlet temp, I'll use your ambient sensor's temp measurement.

I may mull this over into the evening. Meanwhile, the readers are bored to tears

The obvious way to make the radiator more efficient for a given airflow would be an increase in target temperature. That being said I am cheating on pump gas and skating at the limit on both static and dynamic compression ratio. Cooler temps help prevent having to retard the timing to prevent detonation. Very crude graph but gives an idea of what happens as coolant temps and thus cylinder head temps increase. Looking back, should have used the LT1 block, snagged a set of LT4 heads and had a machine shop drill the Vortec intake pattern on the face of them. Could have been done and reverse cooling has big benifits here. Probably could have gone 11.5-12:1 with a LT1.

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