Hi, i know this maybe isn't the best ideia, but i wanted to know the tecnhical and parts difference betwen an A12 and an A15, I thinking if i can turn my A12 into an A15 with the same block.
Wanted to know what i had to change...

Thanks

everything is bigger to take an a12 to a 1500 would be almost imposiible and you would be better off trying to source an a15!

Sounds like a good question to me.

You can make an 1400cc A12, by boring out the cylinders, and machining the crank. Then use A14 pistons and crank.

So can you do similar to make an A15? Pistons are the same, but the crank throws are a lot bigger. I think no on has tried.

Jeff Taylor has fitted A15 cranks into A12 blocks.

really?
so you're saying that simply changing crankshaft and pistons and i have a A14... and the conrod?
sorry but i'm portuguese so please explain things clearly and the correct names for the parts, so i can understand.
But in the end, turning it to a A14 is simpler and better?
Just want to know the changes, because the 1171cc is kind of week, and here in portugal we can't change engines to an 2000cc for example... not even to an A14, so i think this would be a great way!
And what about the head? circle ports are ok?

Thanks

The differences in an A15 include
Taller block [+15mm]
Larger bore [+3mm]
Longer stroke crank [+12mm]
Shorter piston deck height.

Fitting an A15 crank into a 1200 or A12 block is not a practical, but a popular conversion is to use the A14 crank.

You need
1200 or A12 block
A14 crank [+7mm over 1200]
Late A12, or A12A, or short stroke A13 Rods
A15 pistons [not flat tops] These have a lower crown height than other A series pistons.

Bore block to 76mm, or 76.5mm, or 77mm
These are stock A15 sizes. At 77mm you are pushing your luck, but several engines have been built with this bore size & are running fine. 76mm is safer & will make the engine the same as an A14 capacity.
[My 1200 engine is currently at 76.5mm]

Bore late A12 rod to take larger A15 piston pin.
A12A & A13 rods have the right size small end. Early 1200 & A12 rods have less meat at the small end & are not the best choice.

At BDC, the piston is pulled down into the crank counterweight, so machine the crank in a lathe to reduce the diameter of the crank by a small amount to clear the piston.

To measure the amount, just place an old 1200 or A12 rod & piston on the A14 crank & rotate it around the crankshaft. It will hit on the counterweight. Place crank in lathe & machine off 2mm & retest. Machine more untill piston & rod can rotate around crank with about 1mm clearance.

You will need to machine a small amount from the top of the A15 pistons, so either do the math, or assemble one piston & rod [no rings] & do a trial assembly to measure how much that the piston rises above the deck of the block.
I think it's about 0.5mm.

Use an A14 or A15 head if you can for the larger ports & valves.
Please note that the rod length to stroke ratio is not good & the rod angle at half stroke gets pretty severe, causing some accelerated bore wear, but for racing applications, or relatively low mileage street use it will be fine for years.

With a 77mm bore & the 77mm stroke, you get 1434cc

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what about slapping a turbo on the side that will make your 1171cc weak engine into a brute.

again the same problem... illegal... here in Portugal they are very strict

now that sux..... I thought we had it bad.... seems like we are the lucky ones around here...

loool not even the tires.... if we have 165/12 on the registration, we can't have a 185/12 on the car...