12 replies to this topic

[blacktulip]

does anyone know why a 1293cc was made/thought of? what advantage does it have over a 1275cc apart from a few cc of combustion?

[miniboo]

well when the bores wear out they can be overbored and larger pistons used.

1293 is 20 thou over standard.

1302 is 30 thou

1310 is 40 thou

1330 is 60 thou

1380 is not classed as a standard overbore size not usre what it is but it is a 73.5 mm bore

[blacktulip]

thanks for that, i always wondered how a 1293 came about, surely there cant be much of a gain in performance over 1275. is it soley for an overbore then for a worn 1275cc.

[miniboo]

yeah but the saying is: there aint no replacement for displacement.

more cc's generally means more power

thing is most people wil probs upgrade other stuff when they get an engine rebore

[liam_italian]

Is it possible to build a 1320cc engine? reason being i have just bought a mini and the original receipt from 1988 for the engine build states it an overbored 1275GT to 1320

[miniboo]

nah i bet it is a typo. bet it should be 1302.

[liam_italian]

or 1330 possible? how can i find out properly what it is?

[93-rio]

Off with the head and using some complex (could be simple) formula, measure the size of the pistons and work out chamber volume. The piston heads might say +30thou on them which would make it easier

[miniboo]

pretty sure all oversize pistons have the +... on them.

could be 1330.

but i think 1302 is more likely on a non A+ as it was used more in the past

[Sprocket]

well when the bores wear out they can be overbored and larger pistons used.

1293 is 20 thou over standard.

1302 is 30 thou

1310 is 40 thou

1330 is 60 thou

1380 is not classed as a standard overbore size not usre what it is but it is a 73.5 mm bore

1399 is 74mm bore

Odd number over sizes are pretty much unavailable now, its just the +20, +40, +60 and 73.5mm that are available now

Edited by Mini Sprocket, 13 July 2006 - 12:14 AM.

[Guess-Works.com]

in the oldern days +30 was a fairly popular bore, but as said above difficult to get hold of nowadays...

One other thin increasing the bore does, is increase the compression ratio ( given that every thing else stays the same ) this small but significant change will improve the bang as well !

[DYO776C]

in the oldern days +30 was a fairly popular bore, but as said above difficult to get hold of nowadays...

One other thin increasing the bore does, is increase the compression ratio ( given that every thing else stays the same ) this small but significant change will improve the bang as well !

Can an old newbie come in here? The real reason 1293 was popular was down to competition in the '60s, where there were classes based on engine size. Under 1300cc was such a class, and attracted other cars e.g. Ford Escorts, Cortinas, Vauxhalls, and everyone was getting every last cc possible to get just under the class limit. There were even some 'funny' bore sizes using specially made pistons that yielded 1298cc.

The same was true of the 970S......that engine was *bred* for racing in the under 1000cc class, and was popularly bored to 999cc PERFECT. Also that engine was able to rev higher than any other A series due to the short crank throw, relative to the bore size (known in old parlance as 'square' or 'over square').

[Jammy]

And just to add, I believe MiniSpares have now started selling +80 998 pistons.