Not sure which fan those CFM numbers are for - there are multiple factory mechanical fan options. I have been informed some L29s came with a 5 blade fan, although I've not seen one. The 9 blade fan that came stock on some (most?) of the L29 engines moves about 4,100 CFM at 1,500 engine RPM when the clutch is engaged and around 500 CFM when coasting at idle, which explains why the AC sucks when you park at a stoplight. 10,000 CFM wouldn't be reached until around 3,600 engine RPM with the clutch engaged.
I would be very interested to see one of those Trailblazer electric fan clutches retrofitted. If the programming would allow it that should be the best of both worlds.
500 cfm is way lower than anything I have measured with a wind speed meter. The clutch would have to be defective to allow an engine that is up to operating temperature to slip enough to spin the fan that slowly.
Some of the L29s had the a 5 bladed fan with blades 2x the width. Same blade was used on some of the TBI 454s as well as the 8.1 and finally on the 4.3 HO CPI engines in the Astro/Safari from about 93-95.
The numbers I quoted were for the Duramax blade on the Express van. I tested a later 5.4L Ford fan on the van and it pulled a bit less airflow but still cleared 8,000 cfm @ 2,500 and about 4,500 cfm at 750 rpm idle speed, ~550 rpm at the fan. Clutch engages initially on a cold start and the condenser heats the thermostatic coil quickly with the ac on which keeps the fan engaged.
Moving a ton of airflow even at idle
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It was ~100F and about 70% humidity when I did this P/T test on my AC system. As you can see very little difference in pressures, but at the higher compressor speed the compressor naturally moves more BTUs. My ac pressures are over 100 psi less than the service manual suggests for that temperature and humidity. Service manual also suggest a center vent temp of 76F is appropriate and it was blowing ~40F. I could see how some feel the ac lacking at times with the stock system, but these systems have other issues that make a bigger difference in idle cooling. Mainly the orifice tube is too large for good idle cooling and the OE condenser is terrible compared to the microtube parallel flow replacements on the market today. I had my doubts on the replacement condenser since it is literally half the thickness of the OE, but it has proven to work fantastically well. I had good luck using the Red/Orange Ford orifice tube with its 0.057 or 0.062 orifice diameters (much better idle cooling and no loss that I noticed at highway speeds) but I feel the Variable outperforms either. When I put the 87 G20 back together it too is getting a variable orifice and a more powerful Genuine GM Express blower motor. That van is front ac only, so I will get a better idea of how the singe evaporator system performs with the modifications I made on my 97. I may fit my Tahoe with an Express van blower motor as well, the 97 van blows much more strongly out of the front vents than the Tahoe does.
Idle
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1,150 rpm
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