Removing lower shrouds for headers?

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68ragtop
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Joined: Fri Aug 15, 2014 9:15 pm

Removing lower shrouds for headers?

Unread post by 68ragtop » Sun Oct 22, 2017 11:01 am

I have a set of headers that requires cutting (or removing) the lower shrouds. Will running the car without lower shrouds have any ill effects, such as running hot?

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bbodie52
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Re: Removing lower shrouds for headers?

Unread post by bbodie52 » Sun Oct 22, 2017 12:22 pm

Removing the lower shrouds (or cutting them) does not reduce the cooling capacity of the cooling system on the Corvair engine. The cooling fan and upper shrouds are all still in place and conducting cooling air across the cylinder head and cylinder barrel cooling fins, and through the oil cooler. Removing the lower shrouds and the associated thermostats has a similar effect to removing the thermostat in a water cooled engine. If anything, there is too much unrestricted cooling — not too little.

The thermostatically controlled air restriction that is controlled by the lower shrouds, thermostats, and control doors serves to assist in bringing the engine up to normal operating temperatures more quickly. When the engine reaches normal operating temperatures the thermostatically controlled doors open and normal engine cooling continues. The cooling capacity that is built into the air cooled Corvair engine is great enough to adequately cool the engine even when it is running at consistent highway speeds on the hottest days in the desert. The Corvair engine will seldom overheat unless the fan belt breaks or the cooling fins become clogged with debris, which sometimes happens when small animals crawl into the engine cooling area and build nests from twigs, leaves, etc. The accumulation of such debris can cause hotspots to form around the Corvair engine. Similar hotspots can form if air leaks form from areas where the spark plug boots, dipstick tube seal, or upper passenger area heater ducts are allowed to deteriorate, which can prevent cooling air from flowing across the cylinder heads and cylinder barrels as intended by the design engineers. The development of hot areas in the cylinder heads may even cause damage such as loose valve seats or burned valves. But removal of the lower shrouds essentially only removes air restriction after the air has passed through the engine and performed the necessary cooling action.

The elimination of the thermostat control of the cooling air can also cause the engine to take longer than normal to warm to full operating temperature. This may cause the automatic chokes to remain partially closed for a longer period of time than normal, which may cause some deterioration in gas mileage efficiency. In cold winter months the loss of the restricted airflow may also reduce the availability of hot air to heat the passenger compartment and to defrost or defog the windshield. The exposed hot exhaust tubing may also be subjected to rain water spray that may be kicked up by the rear tires. Water spraying on the underside of the exposed engine can cause steam to form, some of which may be drawn into the passenger compartment and may even fog the windshield.

:cool: Those who live in a generally warm, dry climate such as Southern California or Arizona will likely not have a problem with removing the lower Corvair sheet metal shrouds. Corvair owners live in cold climate areas with rain or snow may have more problem with slow engine warm-up times and with less passenger compartment heating and defrosting capacity. :doh:
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible

68ragtop
Posts: 20
Joined: Fri Aug 15, 2014 9:15 pm

Re: Removing lower shrouds for headers?

Unread post by 68ragtop » Sun Oct 22, 2017 1:12 pm

Brad,

Thanks much for the very informative answer.

I live where the winters are mild. My Corvair is garaged year round and I never drive it in the rain, snow, or on wet roads. It's strictly a 'Sunday' driver. So, I don't think I should have an issue except for longer warm up times. Also, I drive the car less than 1000 miles per year, so fuel efficiency may not be much of an issue.

Thanks again!

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