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MG MGA - cc after +40 rebore

Hi all,
I can't lay my hands on a workshop manual to get bore and stroke dimensions and someone has contacted me to ask the cc of their 1600 Mk11 after a rebuild to +40. Could someone please tell me what the resulting cubic capacity is?

regards
Colin
Colin Manley

1622 standard bore is 76.2mm, stroke is 89mm, overbore is 1.016mm
Dominic Clancy

here's the WSM entry


Dominic Clancy

1667cc
William Revit

My 1800 MG-B was bored + 30. Curious to know what it is now.

Cheers
Gary
79 MGB
gary hansen

William is spot on with his calculations

The volume of each cylinder can be calculated by using the formula Pi x R squared x H. R being the radius of the bore and H the stroke
If the std bore is 7.62 cm, then add the 0.1016 cm overbore so the bore is now 7.7216 cm. Divide by 2 to get the radius 3.8608 cm. 3.8608 squared is 14.905.
Multiply by Pi 3.142 x 14.9 = 46.833
Multiply by the stroke 8.9 cm
=416.822 cc
X 4 =1667.28 cc.

Using the same formula, plus an overbore of +0.030" (or 0.076cm), the bore becomes 7.696 cm.

So working it through, the capacity with the 0.030" overbore becomes 1656 cc.

Gary, the MGB std bore and stroke is 8.026cm by 8.9 cm which gives a capacity of 1799 cc.

With a +0.030" rebore (0.076 cm), using the same formula, the capacity becomes 1802 cc

Cheers
Colyn
Colyn Firth

Thank you Colin.

Cheers

Gary
79 MGB
gary hansen

Hmm
I get----1836cc
William Revit

Well maybe at 10.30pm on a Saturday night, trying to use a calculator with a glass of scotch in the other hand, didn't help William 😃.
At least my formula was correct!

I will make another attempt this morning after a cup or two of coffee.
I'm pretty certain you are correct again William.

Colyn

You got me thinking of the Morcambe & Wise quote William
"I pressed all the right buttons, but not necessarily in the right order"!
Colyn Firth

Ahh---too many gigglebites on the calculator, enough to confuse the best of keypads---

lol
Cheers Colyn
willy
William Revit

I have a table of common overbores / compression ratios here - https://octarine-services.uk/bore_capacity_CR.htm
Chris at Octarine Services

This thread was discussed between 03/07/2020 and 05/07/2020

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