The MGA With An Attitude
Drilling out the two rearmost water holes in the top of the engine block
to improve water flow through the cylinder head.

At 11:04 AM 7/14/02 -0400, Chris Chandler wrote:
>"I was browsing on the Chicagoland MG Club web site and they have a great section of pictures of them doing various work on their cars. In the section on replacing the head gasket (which I'm doing to my car) they show a picture entitled 'drill out the rear water holes'."

That page would be here:
And yes, I did take the pictures and post that web page.

>"Two questions:
1) Why?
2) What size? "

Shucks, this one is easy. From the MGB Special Tuning Booklet, under Stage 4 procedures:
"To Increase water flow through the head, drill out to 9/16 inch (14.29mm) diameter the two water holes at the rear end of the cylinder block face."

Now bear in mind that Stage 4 is preparation for a very serious racing engine where you may be nearly doubling the power output over the stock engine setup (and the related heat output). In that case the cylinder head can use all the cooling help it can get. For a mild mannered street engine this may be a moot point, but if you intend to run it near full throttle for extended periods of time, maybe it's a good idea.

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