My 454 Rebuild

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L31MaxExpress

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I can tell you first hand that my ac was nearly 10F warmer at idle and low speeds with electric fans than it is with a clutch fan. I can sit in traffic with the ac blowing 40*F on a 105*F day. Clutch fan is about 6,000 cfm at idle, 10,000 cfm when reved up to 2,000 rpm.
 

Supercharged111

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I can tell you first hand that my ac was nearly 10F warmer at idle and low speeds with electric fans than it is with a clutch fan. I can sit in traffic with the ac blowing 40*F on a 105*F day. Clutch fan is about 6,000 cfm at idle, 10,000 cfm when reved up to 2,000 rpm.

I've found the opposite to be true in my 1500 and 3500. Come to a stop and the AC heats right up. 1500 had the plastic fan (now late MarkVIII e-fan) and 3500 has the old crappy 5 blade fan. Our 07 Envoy Denali does it too, but I noticed in the tune the fan clutch has a commanded duty cycle. I really need to buy a license and play with that in the tune.
 

L31MaxExpress

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I've found the opposite to be true in my 1500 and 3500. Come to a stop and the AC heats right up. 1500 had the plastic fan (now late MarkVIII e-fan) and 3500 has the old crappy 5 blade fan. Our 07 Envoy Denali does it too, but I noticed in the tune the fan clutch has a commanded duty cycle. I really need to buy a license and play with that in the tune.

I have a 25% underdrive on the crankshaft and still find the clutch fan cools better.
 

Carlaisle

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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.
 

L31MaxExpress

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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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Carlaisle

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If you checked the airflow with a handheld anemometer in front of the grill the multiple obstructions represented by the grill and everything else in front of the fan blade are all acting to artificially increase the indicated CFM via the velocity of the measured air column. The actual volume of air moved by the fan at a given speed and clutch engagement will be less. I did not put the fan in a wind tunnel - that's too much effort and expense just to satisfy my curiosity. I did a rough calc based on the OEM 9 blade fan in my possession and used typical thermal clutch values. Utilizing measured blade pitch, area, swept diameter, etc., it is mathematically impossible for the 9 blade fan to move anywhere close to 6,000 CFM at 650 engine RPM when fully engaged even after artificially biasing every assumption in the fan's favor.

The only reason I invested that much effort was because I've grown weary of losing my cool (pun intended) every time I come to a stop light. I paid a shop to work on my AC last year because it wasn't cold enough. Their work left it warmer than it was when I took it to them and now it apparently leaks, which it did not previously, so I think I will use this opportunity to make some improvements. It sounds like your investigation has produced good results optimizing the AC system. You found the same thing experimentally I found mathematically: the air moved by the cooling fan is not the handicap. Following your lead, I think I'll replace the condenser with a parallel flow and a different orifice tube than stock. Can you elaborate on the variable orifice as it would be implemented in this application? I can be the guinea pig if it has only been theorized and not actually attempted previously. I have never been impressed with the truck blower, either. The van blower does not look like it will conveniently interchange with the truck/Tahoe/Suburban version, but that is just another problem solving exercise. Have you been using 134a or a different refrigerant? What about the compressor? I miss the A6 with R12 that could turn the inside of your vehicle into a functioning meat locker. Whomever signed off on the 76 degree center vent temp as acceptable clearly did not need to operate the vehicle anywhere AC would be required.

Apologies to Spareparts for the threadjack.
 

Spareparts

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Na i don't think it's a thread jack. It all kinda revolves around the electric fans i installed compared to the 9 blade fan with HD clutch they replaced.
 

BNielsen

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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.
My truck had the 5-blade fan factory; I swapped it out for an S10 11-blade fan and a Severe Service fan clutch. My dad's old C3500 had the 9-blade. Come to think of it my truck is the only 454 truck I've seen with a 5-blade; maybe it's just an early Vortec thing.
I've been perusing the 0411 E-Fan rabbit hole trying to soak up as much knowledge as I can before I pull the trigger on anything. I know at the bare minimum doing the larger pusher fan would help my AC drastically, it blows ice cubes now but there is always room for improvement.
 

Spareparts

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So that stupid misfire is just driving me nuts trying to ignore it.
Im thinking the only thing i can do after doing all i can think of or has been suggested is take the heads off and see what's up. It's the only thing left i can do that i know of.
My stock Vortec heads have a combustion chamber that is 100CC and if i need to take em off ill just replace em. I already have all the necessary gaskets and stuff.
So im looking at These heads. Pricey and would deplete my truck play money account for a few months but it may be worth it.
Mostly considering this as i just don't know what else to do other than save up for another complete rebuild.
Would you go with stock reman heads or new aluminum heads or am i just going overboard?
 
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