Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - 1800 head thickness

I am rebuilding a 1979 1800 motor to put in my 1960 mga. the head has been milled to thickness of 3.097"by the DPO. There are eye brows cut in the block so the exhaust valves will not hit the block. Is this too much? What effect will this have on the engine performance? Will the compression be so high I will need premium gas?
Also the valves had single springs not double, is this normal for a 79 head?
Thanks for getting back to me on this. Steve Bryan
S E Bryan

3.187" original thickness -3.097" final = 0.090" removed. 0.009" is approximately 1cc reduction of chamber volume, so 0.090" would be about 10cc reduction.

Near as I can calculate, that would change compression ratio from 8.8:1 to 10.4:1. Some upgrade cams like that sort of CR. If you change dished pistons to flat tops it goes even higher.
Barney Gaylord

Later MGBs were 8:1. It really depends on which head you have as combustion chamber depths changed. I'd suggest you read here:
and here:

With those two sites you will be able to calculate your CR. I have a 5MB B engine in my 58 Coupe and it's a 9.8:1 engine. Runs very well on the remaining stock MGA pieces. I'd recommend a B flywheel and clutch while your're at it. I'm very pleased with my swap. I had to machine the back plate to carry the B oil seal, but that was the only fussy bit.

This thread was discussed between 24/02/2011 and 26/02/2011

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.