Non Return flap- am I missing something?

[highlandmurf]

I am missing the passenger side non return flap, but there is no place to attach one.

See, no holes for the little wire pin:



So, Did all of the fan shrouds have a passenger side flap?

Does this look like it has been modified?

Should I worry about not having one?

Thanks

[Amskeptic]

I am missing the passenger side non return flap, but there is no hole for the little wire pin:

So, Did all of the fan shrouds have a passenger side flap?
Does this look like it has been modified?
Should I worry about not having one?

Yes, yes, yes, m'boy.

If you don't mind a little inefficiency in your heat, don't worry about it. BUT, you must have functional flaps in the heater blower housing.
Colin

[CarlosZ]

I've no heating parts, only a header to muffler. Are the two non-return flaps needed? If so, should they remain flapping open or closed off somehow? I'm under the assumption that closing them does change the air flow. I think by closing them off you get turbulence or disrupted airflow within the shroud, but more air volume/flow overall or sufficient air to keep it cool. Isn't there is a great loss of air pressure/volume/flow to the heads due to having so much air escape through the openings at the bottom of the shroud if removed or left to flap open? The heating system must have restricted the volume of flow (from the shroud exit) greater than leaving off or leaving them flapping. Keep getting conflicting advice. Just want as many opinions so I can make an educated decision. Thanks!

[Bleyseng]

On race engines they still leave em open and they run headers....

[Amskeptic]

I think by closing them off you get turbulence or disrupted airflow within the shroud,
loss of air pressure/volume/flow to the heads due to having so much air escape through the openings at the bottom of the shroud if removed.

I'd experiment. Got CHT gauge? Run them open, read gauge at specified control speed load.
Then tape them off. Read gauge at specified control speed load.
Report back.
Colin
(specified control speed load: 60 mph for 15 miles in one direction then 15 miles back, tape then repeat)