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MG MGA - Grille open area?

Does anyone know or have they calculated the open area of a standard MGA slat grille?
Mike
Mike Ellsmore

Good question, I've wondered about the wire mesh grilles at times, there must be probably around 10% loss with all the wire plus the blocking/buffering effect that you get from wire mesh
It'd be interesting to get both in a wind tunnel
willy
William Revit

From a post by Ian Cowan on MGAGuru:

"The frontal core surface of the original radiator measures 11.5" X 18.5" = 212.75sq". The grill opening in the body measures 20" X 7.5" = 150sq". Fitting the anti aerodynamic grill to the aperture with slats, reduces the 150sq" to less than half, but say a generous 75 sq". The air flow is further impeded by the poor shape of the grill slats, so in effect the radiator core surface of 212.75 sq" receives a restricted air flow through the inefficient grill opening, of something less than 75 sq"."

Link to full article is below:

https://mgaguru.com/mgtech/cooling/cool_209.htm
Nick Kopernik

I am not sure if there is an answer as I understand some owners “twist” the slats to increase the open area and hence the air flow.
I can’t comment on the open area, but I did some experiments myself several years ago, and found a definite drop in engine temperature by replacing the slatted grill, with a mesh grill. I still have it on the car as I also like the look of it.

I constructed the grill very cheaply by buying a piece of mesh online.
Graham V

Not entirely answering your question Mike, but from an article published by a highly respected author ( ;) ) ten or twelve years ago:

Getting the air to the radiator:
Surprisingly, the MGA grille has a LARGER cross sectional aperture area than an MGB! Looks clearly can deceive! A chrome bumper/chrome grille MGB has a grille aperture of 83cm x 12cm (Cross sectional area: 996 sq cm).
An MGA grille aperture measures 53cm x 20cm (Area: 1060 sq cm!!!).
So what else is going on? Firstly, I’d suggest that the shape of the grille blades (broader and partly angled against the oncoming air), especially in the 1500 and 1600 MGA, tends to at least partly deflect the airflow up and over the bonnet, rather than through the grille to the radiator. The 1600 Mk2 grille, with its recessed vertical grille bars would likely capture the air flow better, but better yet is the MGB with its vertical AND narrow cross section bars facing the oncoming air, which would tend to pass virtually all the oncoming air flow through to the radiator (+/- oil cooler) behind.
T Aczel

Thanks Tom,
Not sure where that highly respected author go the MGA grille aperture area from but it seems a little large! See my trace of the half grille opening attached. I am currently having a friend run it through AutoCad to calculate accurately (a bit easier than finding a planimeter these days or counting squares on graph paper). From my rough estimate I reckon the percentage projected open area of a standard MGA grille is around 33%. More to come.
Mike
Mike Ellsmore

"Thanks Tom,
Not sure where that highly respected author go the MGA grille aperture area from but it seems a little large! See my trace of the half grille opening attached. I am currently having a friend run it through AutoCad to calculate accurately (a bit easier than finding a planimeter these days or counting squares on graph paper). From my rough estimate I reckon the percentage projected open area of a standard MGA grille is around 33%. More to come.
Mike"

Mike, I simply used a tape measure to get the dimensions off my own MGA and MGB. Perhaps not highly scientific, but I thought for my purposes at the time, it was close enough.
I certainly was surprised at the time to find that the MGA was the larger of the two!
T Aczel

Sad news Tom, my calc for area of the two openings in the MGA grille frame is 960 sq cm so if your calc for the MGB opening is correct, it is larger than the MGA grille!

My calc. also shows the projected open area of a standard grille is 313 sq cm (33%). For the MGA racer grille (every second slat removed) is 685 sq cm (71%) - around that of a mesh grille depending on the wire size and aperture selected.

I'll send my findings and calcs off to Barney for him to check my arithmetic and logic (my wife says I have too much time on my hands with these Covid lockdowns, now our 5th in Victoria)

Mike







Mike Ellsmore

Hi Mike
I'm surprised my measurements for the MGA were so far off yours.
From memory I just ran a tape measure from one lateral edge of each grille opening to the opposite, and again from top to bottom. Using my Mk II grille made the MGA vertical measurement easier than with the non-recessed types. I certainly didn't measure the two apertures for each grille side separately. But your measurements for the MGA grille are clearly vastly different to mine.
I'm certainly happy to be corrected. We'll see what "The Guru" comes up with.
T Aczel

This thread was discussed between 19/07/2021 and 24/07/2021

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