Fiat SOHC differences

[sumplug]

Can someone put some answers to my question?
On the "128 type" engine, it came in 3 generations with diffrent capacities.
1st generation
Bore Stroke
80 x 55.5 = 1116cc
86 x 55.5 = 1290cc

2nd generation
Bore Stroke
same = 1116cc
80 x 63.9 = 1299cc
80.5 x 63.9 = 1301cc
86.4 x 63.9 = 1498cc

3rd generation
Bore Stroke
80.5 x 67.4 = 1372cc
86.4 x 67.4 = 1581cc

The question is, i have heard that the last generation of engines are not as strong as the first two especially the 1581cc engine. Is this true or not?
My asking is due to me thinking of uprating a 1600 engine, or to use say a 1400 uno/punto [prefer punto] turbo block with piston oil sprays and swap crank and rods to bring capacity up.
As charlie with his supercharger on his X1/9, the idea is to install a charger on this engine.
Would i be better using an earlier engine from an X1/9 for example with 1498cc? Any ideas?? :)

[SteveNZ]

The block was significantly changed for what you refer to as 3rd generation. These blocks tend to crack. I believe this is a result of the revised design, they have a semi open deck. Early blocks have a closed deck.

You could add a 4th generation, SOHC blocks 1994+. These were improved over the early ones. e.g. I've seen a lot of Uno 1.4T blocks that have cracked but never any Punto GT blocks.

The 86mm bore engine may not be as strong because of the closer bores. There is not as much strength in the block as there is simply not as much metal between the bores. An open deck design is going to be worse again. Maybe the reason Fiat only turbocharged the 80.5mm design.

My asking is due to me thinking of uprating a 1600 engine, or to use say a 1400 uno/punto [prefer punto] turbo block with piston oil sprays and swap crank and rods to bring capacity up.

Uno/Punto 1.4T has the same crank and rods as the 1.6 engine. The 1.6 engine has oil jets anyway. To get capacity around 1600cc you need an 86mm bore block,

You can use with the early (strong closed deck) 1.5 block and swap a 67.4mm crank into it to get 1600cc.

[Acki]

The rods are the same?!
But early OHC shall have better rods?! The Uno Turbo WITHOUT CAT has rods which are "easier"?! 40-50Gr...

Ahh by the way, I'm searching a 1116cc crankshaft :D

@Guy: Do you have pictures of cracked 1.4T blocks? I've never seen yet :(

[Julian]

The Punto GT blocks are definitely stronger, the obvious difference is the plate on the end of the block which is missing on the GT block when compared to the earlier 1.3T and 1.4T blocks. This was the source of many a leak so at the very least it is one less gasket that needs regularly replacing.

[Acki]

Do you have a picture of the plate you mean? Because of this plate the block is stronger? Or what is the reason?

[SteveNZ]

No the plate is just a difference. It does not add strength IMO. It is located behind the flywheel. There is also something similar on the front of the block