4 replies to this topic

[.Jack.]

Looking at moving on from my standard 1275 SPI. I would like to know how reliable the 1380 is on all the standard SPI setup? If it is unreliable then does anyone have any experience of a 1293 with flat top pistons on the SPI setup?

Thanks

[MiniElliott]

Hi, i'm not sure on the SPI setup but why do you want to go 1380 ? Save the block for further rebores down the road by keeping it standard overbore sizes i.e 1293, 1310 or 1330

[KernowCooper]

Difference in power will be a little in outright power and maybe a couple of lbs/ft in torque, so unless its a block thats already built as a 1380 then sleeve it back to 1275

[.Jack.]

Was only thinking of going 1380 because I thought that was the best size to go to get the most power whilst still looking standard under the bonnet. I was going by the "no replacement for displacement" theory but does anyone know the differences between power from a 1293 with flat top pistons to up the compression ratio or a 1380 running lower compression?

Thanks

[Cooperman]

It's best to use dished pistons in all 1275 and larger engines and get the C.R. correct by making the combustion chambers the correct size. That's what all the competition Minis have and they work well. The 21253 is regarded as very good.
AS for going to 1380, that effectively 'scraps' the block when the next re-bore is going to be , and high-power Minis don't last forever. The 1380 bores have to be 'offset bored' to obtain sufficient clearance between the walls of cylinders 2 & 3 and this can leave very thin walls. So when a re-bore is needed, special sleeves have to be machined, the block bored a bit more, the sleeves pressed in, then bored back to 1275. This is very expensive and the alternative is to scrap the block and find another. But if this continues blocks will become scarcer and much more expensive.
In terms of power it is not critical unless you are going to race, hill-climb or rally the car.
It is always best to get the better power by having a really good and well gas-flowed cylinder head, a good induction system with either twin HS4 or a single HIF44 carb, a really good exhaust system at 1.75" internal bore and a better cam, such as a Kent 266 or MG Metro. Set the C.R. to around 10.2:1 and use 35.6 mm inlet valves and 30.5 mm exhausts.
That is the best way to preserve the classic Mini and to enjoy classic car motoring.