Corvair engine compartment airflow

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morevair
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Corvair engine compartment airflow

Post by morevair »

Hey All,

Another newbie question... What are the air flow characteristics of the Corvair engine compartment ? I'm trying to understand how the airflow works in the Corvair (LM). Looking at the blower fan, it doesn't have much pitch (if any) on the blades, and the fresh air intake looks to be in a "vacuum" area of the back glass... I've seen "Stinger" mods where the hood lift ports are added, but does that really have any effect ? I'm just trying to figure out how the air moves... Plus if I ever add additional accessories (possibly A/C, external oil cooler) it would be nice to know where they could take advantage of the best flow... I'm tempted to put small ribbons all over the engine compartment, place my phone in there on video, close the hatch and see what's really happening... Plus I've heard that if A/C in put in, you benefit from removing the lower shrouds ( I live in Phoenix... 120 degrees, don't need a heater)...Would that change the airflow or just allow for more radiant exchange...

Any insights are appreciated..
Jeff M. in Phoenix, AZ
1966 Corsa 140 4-speed
Jerry Whitt
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Re: Corvair engine compartment airflow

Post by Jerry Whitt »

The fan produces centrifugal force. That force blows the air down over the cylinders, the thermostats then allow the air to flow out thru the shrouds when the engine is warmed up. As the air moves down and out, a low pressure area is formed above the engine, then allowing the higher atmospheric pressure to push air into the engine area.

These air cooled engines run at a temperature much higher than most liquid cooled engines. Many liquid cool systems are designed to run around 200 degrees F. These air cooled engines will run 350 to 400.

I live in Hemet California, where summer months are well over 100, and as yet not found any reason to remove the lower shrouds. In winter months, the temperature here can be below freezing, and the heater works pretty good.
Jerry Whitt
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65 Monza, purchased new
65 Corsa convertible
morevair
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Re: Corvair engine compartment airflow

Post by morevair »

Thanks Jerry... sound simple but effective...
Jeff M. in Phoenix, AZ
1966 Corsa 140 4-speed
66vairguy
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Re: Corvair engine compartment airflow

Post by 66vairguy »

morevair - For decades folks have argued about Corvair cooling. Lots of OPINIONS.

Bottom line --- Chevrolet tested Corvairs at there desert testing facility in summer conditions and the cooling system worked. In fact you rarely hear of an overheated Corvair unless the fan belt came loose or there was an obstruction in the cooling system (shop rags, animal nests, etc.)

Is the system perfect, of course not. At high engine RPM the fan uses more horsepower than folks would like, then again how much time does your engine spend above 4,500RPM?

GM found that at wide open throttle in 4th gear the turbo charged engines would overheat after a couple of minutes, but of course you can reach the top speed (over the legal limit) in well under a minute so that's hardly a practical or everyday type of condition. Driven at legal speeds there is no issue.

Removing the lower shrouds will probably let the engine run cooler under racing or high load conditions, but GM never tested for this and most statements are based on anecdotal evidence. Also keep in mind that the Corvair engine was designed to work with thermostats to bring the engine up to NORMAL operating temperature and keep it there!! Running an engine too cool results in out of tolerance dimensions and moisture in the oil.

If you are going to run A/C then you can run a up front trunk condenser and fans or the engine bulkhead unit. With R134a you need electric fans on the condenser because R134a temperature rises considerably with increased heat, more so than R12. That why R134a systems use over pressure shut down switches to protect the compressor.

If you are going racing, then that's another issue requiring modifications to suit the type of racing.
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Allan Lacki
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Re: Corvair engine compartment airflow

Post by Allan Lacki »

As Jerry mentioned above, the Corvair engine fan is a centrifugal fan, not an axial fan. Their blades can be either forward curved, backward curved or straight, the latter being the type you have in your Corvair.

All other things being equal, a centrifugal fan is more efficient than an axial fan. Although the racing guys often criticize Corvair fans for consuming too much horsepower, centrifugal fans deliver more air flow at higher pressure while consuming less horsepower at high RPM in comparison to axial fans.

If centrifugal fans are so great, then why do air-cooled Porsche 911s have axial fans? I can't speak for the engineers, but a couple of things come to mind. In the Corvair's case, the engineers chose to use the more-efficient centrifugal fan, but to do it, they had to resort to the unusual "mule drive" fan belt to make the cooling system fit inside the engine compartment. In the Porsche's case, they used a conventional fan belt, but they had to resort to a sophisticated fan assembly that cost much more to manufacture. A stock engine cooling fan for an air-cooled Porsche 911 goes for $500, maybe more at a Porsche dealer.

There is a lot of literature about centrifugal fans on the internet. Here is a link to the article where I copied the diagram.

http://www.reitznorthamerica.com/what-i ... fugal-fan/

::-):
Attachments
A simple diagram showing the 3 types of blades.
A simple diagram showing the 3 types of blades.
centrifugal_fan_blade_types.jpg (31.55 KiB) Viewed 2475 times
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Allan Lacki
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Re: Corvair engine compartment airflow

Post by Allan Lacki »

Trivia: When Chevy designed the experimental OHC Corvair engine, they managed to get away from the mule-drive fanbelt, but to do it, they equipped the engine with three(!) centrifugal fans! More complexity - and who knows if it actually worked?

According to the literature, it was intended to be installed in the Astro I concept car, but if so, it never powered the car in motion. According to Pete Koehler's article in the April 2016 CORSA Communique, the Astro I was a "pushmobile" - it never actually ran. Peter wrote, "In fact the shift lever that was supposed to move through the gears was just glued to the fiberglass floor of the car’s interior. Nothing underneath that floor connected it to anything but air. I remember that the steering was hooked up and the special “wheel” was connected to the front tires, but you could only rotate that wheel through a small arc. The turning radius must have been measured in yards, not feet!"

Maybe that OHC engine was installed in some other vehicle, but there doesn't seem to be any literature suggesting that Chevy had actually done real-world testing of it.
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The experimental OHC engine.  3 centrifugal engine cooling fans in a row.
The experimental OHC engine. 3 centrifugal engine cooling fans in a row.
66vairguy
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Re: Corvair engine compartment airflow

Post by 66vairguy »

Allan - Sorry I don't recall the reference material source, but the OHC Corvair engine had the capability to develop more power at higher RPM due to the valve train. Testing found the three fans consumed excess HP at the higher RPM in effect negating HP gains at higher RPM. No doubt it could have been improved, but the program was cancelled.

Yes the Corvair fan design is basically the most efficient, but elaborate housings with improved clearances could make it better (AND MORE EXPENSIVE). This reminds me of alternator upgrades. The Delco 10DN and 10SI alternator fan was designed to cool adequately up to about 65Amps (80Amps in moderate tempertures). The 12SI unit had a revised fan and housing to improve air flow per RPM (note the 12SI fan won't work on the Corvair due to the reverse rotation). When I hear folks running modified 100Amp 10SI units I just say "Works if you don't exceed about 80Amps".

All the above in interesting, but the stock Corvair cooling system works adequately for the STOCK motor. Note that fan height to top shroud makes a difference - it's in the manual.
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Allan Lacki
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Re: Corvair engine compartment airflow

Post by Allan Lacki »

Hi 66corvairguy,

Yes, I agree, the stock fan works fine on a stock Corvair engine, except for the fact that Corvairs with the stock fan have a reputation for whipping off fanbelts, especially on the track. Not because of the fan, but because of the 90 degree mule drive fan belt setup needed to drive it.

I've attended NECC track events for many years and have seen it happen several times. My Corvair did it too during autocross. And I think it's reasonable to assume that all of those folks built their engines with the factory-recommended clearances between the fan height to top shroud. That's why some of the Corvair racers, like Bob Coffin, Michael Leveque and others run vertical fans with axial fans from Austins. But the vertical fan setup is not recommended for street use. And perhaps that's why Chevrolet came up with the three-fan arrangement on the experimental OHC engine.

You mentioned, "Testing found the three fans consumed excess HP at the higher RPM in effect negating HP gains at higher RPM." I don't doubt it, but I haven't seen any documentation of tests on the experimental OHC engine. If you've come across it, please share it. Let's keep this discussion going. This is an interesting topic!
caroseiii
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Re: Corvair engine compartment airflow

Post by caroseiii »

Bob Helt wrote about this in his Corvair Secrets book. I wrote to him about the source of the information but he wouldn't tell! However, he may have forgotten about my request. The upshot is that the turbo always put out more power more cheaply than the experimental OHC and fuel injected engines and that there was no cost benefit reason to do the hardware upgrades before Corvair development was discontinued. The fan power consumption issue presented in any high rpm power production alternative.

Crawford Rose
66vairguy
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Re: Corvair engine compartment airflow

Post by 66vairguy »

Good points Crawford.

While I enjoy the old high revving small displacement motors more prevalent in Europe in the 60's, once you look at the torque curve of a well designed turbo motor there is no contest. Basically big cubic inches torque from a small displacement motor.

Even the basic, and slow to boost, Corvair turbo engine has an impressive torque output at lower RPM vs. the normally aspirated engine - once the boost comes on.

I've read a great story (not verified, but plausible) about GM doing a turbo field evaluation on the road to Sedona, Ariz (then basically wide open). Zora Duntov heard about the test and was working with the Corvair folks on a hot version of the standard engine. Both cars showed up for the evaluation. Contrary to GM policy about NO aggressive testing on public roads, both driving teams pulled away from the support vehicle at illegal speeds. The turbo car showed up first in Sedona!!
----------
Allan - The fan belt can be an issue. Yes on high RPM fast up shifts or down shifts there is a tendency for the belt to come off, yet I've had folks say they race without issue once everything is aligned - not taking sides, just what I've read. One fellow did a CORSA article years ago and varied the fan pulley bearing height as an experiment. He stated that beyond +/- 1/8" from optimal the fan belt would easily flip off. Others have noted that pitting or rust on the pulleys will cause issues. Of course using a belt that is too wide also causes problems, a known issue since the Gates catalog specifies the incorrect belt for Corvairs (this was a number of years ago when the issue came up on the other forum).
perfectreign
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Re: Corvair engine compartment airflow

Post by perfectreign »

66vairguy wrote:While I enjoy the old high revving small displacement motors more prevalent in Europe in the 60's, once you look at the torque curve of a well designed turbo motor there is no contest. Basically big cubic inches torque from a small displacement motor.
That’s what GM and others are using now to squeeze efficiency out of every last drop of petrol or diesel. The midsize Malibu I drive has a version with a 1.5 turbo making an impressive amount of HP and torque. My beautiful young bride drives a VW Golf with a speedy 1.8 turbo.

Now wonder what would happen to my 5.3 L Avalanche if I dropped in a turbo.



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Image 2016 Chevy Malibu Hybrid
johnj92131
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Re: Corvair engine compartment airflow

Post by johnj92131 »

I purchased a new, 1969 Monza 110/4 spd that I drove for 16 years and 145k miles. About 1971, I added the full factory air set-up from a 67 Monza. I also kept the factory smog pump by using a California only high a/c and smog pump mount bracket.

Results were a car that finally blew a head gasket at 145,000 miles. Chevrolet chose to drop A/C in 1968 because both A/C and A.I.R. on the Corvair resulted in higher cylinder head temperature. My own long term results in Southern California tend to support the factory judgement.

The 69 Corvair pinged slightly on premium fuel from day one, because of the smog pump and the factory distributor curve.

But today, I would love to have a 1966 factory A/C set up with no smog pump. And I would have no worries about cylinder head temperature.

Just my experience and thoughts.
66vairguy
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Re: Corvair engine compartment airflow

Post by 66vairguy »

John - The "smog" distributor timing curve caused issues, but the open chamber heads (except 140HP engines that did not use them) also caused detonation issues. Emissions reductions resulted in a lot of compromise engineering and lousy running engines. After GM patented the catalytic converter things got steadily better until computers really advanced engine control.

The problem with bolting a turbo on any engine is the engine has to be built to withstand the extra HP, torque, and HEAT . That added expense kept the turbo on the sidelines until fuel economy regulations made the cost acceptable to the auto manufacturers. The upside is a normally driven modern turbo engine will go an easy 200K.
johnj92131
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Re: Corvair engine compartment airflow

Post by johnj92131 »

It is also true that the open chamber head and the domed pistons contributed to the pinging problem.

Besides, thinking a bit more about it - 145K miles was a good thing in 1969. Even with the added heat load of the a/c, I was always happy to have the a/c in Southern Calif.
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