Technical 1.2 8v engine compression lowring, crazy thought

[MKoers]

I'm reading up on preparing and punto 75 1.2 8v engine for turboing.
Now I know I can use 12. 16v piston rods to lower the compression.
But these are hard to find.

I had a crazy thought and would like to know how you guy's think about this.
The 1.2 engine is higher that the 1.1 engine.
So why not use the 1.1 engine rods. Or would this lower the compression to far?
If so maybe it's an idea to CNC the deck until the compression is at the right level?

 

[gazzaman2k]

because the pistons are wider on the 1.2

 

[whitz]

https://www.fiatforum.com/classifieds/showproduct.php?product=20626&cat=55

have a look on there, theres some 16v piston ad rods im sure he will sell

Ash

 

[MKoers]

Ok.
But isn't it possible to place the punto 75 pistons oon the 1.1 rods.

 

[gazzaman2k]

yes but only when going back into a punto 60 or 75 engine block again as the crank is the same size

 

[craigb244]

looked into making a Frankenstein engine before.
a 1108 crank in 1242 block with 1242 pistons will make the engine low compression but most likely will be far to low.
the block will need machining down to bring the compression back up.
the cc will be down to about 1180ish but the stroke is much more square so will be better at higher rpms. but not really heading away from the turbo route as turbos tend to be long stroke engines.

if you going to the effort of machining blocks down id stay with the 16valve pistons to and machine the block to make the CR better. you then have the advantage of the better rods and pistons that the 16valvers have.

we are looking into building an engine with a old panda 850cc fire crank in a 1242 machined block, end up with the same bore and stroke as an old R1

 

[MKoers]

So the 16v pistons are stonger en better resistant to the turbo pressure.
I thought the where just bigger and shaped differently.


Tommorow morning I'm gonnan take a look at another scrapyard to see if there are car's with 1.2 16v engines.

 

[craigb244]

not sure about the pistons but mine have lasted thousands of miles and lots of events (which includes driving on the limiter and still withstanding a bar of boost...see the video i just put on my turbo thread)
has the wastegate pipe fail and hit the 2bar engine cut without any damage.

the rods are much better then the 8valve, nearly half the weight to. the engine is actually very noticeably smoother running them

the pistons are very good shape (imho) i cant imagine proper custom made pistons (££££) looking much different other then the small end been very slighly lower on the piston (so to raise the compression) and not having the 4 valve relief (which ive thought about getting welded up on the standards and then i could machine it back)

 

[MKoers]

OK.
If I have a set of 16v pistons and rods.
I wanna take them apart to renew all the pistons rings as they go into another engine.
Also the cilinders have to be honed to get them smooth again before the pistons with the new rings go in.

Will honing remove a lot of metal so the rings will be to small and the pistons won't fit anymore?
Or is honing just smothing the surface without removing any metal at all?

 

[craigb244]

honing removes minimal amounts of metal. shouldnt effect performance as long as the bores are not worn out anyway

 

[baker92]

if you still cant find any pistons and rods try goin on ebay or to a breakers and find a punto 85 being broken and ask for the rods and pistons i got my set for 45quid in amazing condition

 

[fingers99]

So the 16v pistons are stonger en better resistant to the turbo pressure.
I thought the where just bigger and shaped differently.

The pistons are no stronger in themselves. Just cast pistons -- weaker than the Mahle cast ones or any forged ones. Rods are no stronger, better finish and lighter, is all. But, together, they're a fairly cheap way to lower compression, preferable to machining the stock pistons.

 

[craigb244]

way way way way way better then machined pistons or decompression plate. with both these you loose the piston squish band which is very important for fuel mixture.

for anyone who dont know, the squish band is the flat raised ring around the top of the piston, as the piston reaches TDC this ring comes close to the head (closer the better! in very high performance engine (no production thats for sure) it is so close that at full rpm the ring can actually very lighly touch the head due to flex in parts of the engine)
this forces the fuel/air mix at very right velocity away from the cylinder walls (most the fuel near the walls does not burn 100% so it wasted) and into the centre causing a huge amount of turbulence.
this evenly distributes the air/fuel in the combustion chamber and vaporise any remaining fuel droplets (if any) also the turbulence causes the flame front to be spread faster.

 

[ycming]

craig, you mentioned that the 16v rod is lighter, could i use just the rod in a 1242 8v block then with 8v pistons??


Thanks
Ming

 

[craigb244]

the gudgeon pins are bigger in the 16valve so wont fit... maybe you can get the journal bored out to fit.

 

[MKoers]

I've been to three scrapyards this morning.
Non of them have car's with the 1.2 16v engine.
I've seen a couple of punto 60 cars and a lot of 1.4 16v engines.

Are there other cars than fiat and lancia that use the fire engine?

 

[jimbro1000]

Tata have used them in the Indica and Indigo, as have Alfa (Mito and Giulietta) and of course the new Ford Ka *but* I don't think any of these are the 1.2 16v so basically you are left looking at the Fiat range, but it is a big old range of models that used it - the bravo/brava 80sx is one of the better bets (after the Punto of course).

A lot of the 16v engines just get scrapped as they borderline reliable if ever abused (servicing wise) beyond 60k miles. Older models with shorter service intervals are more likely to still be going.