Fiat SOHC head variations

[Abarthnorway - Remi L]

HI!

I am quite unexperienced with the Fiat SOHC engines and its variations. It seems to be a bewildering amount of differences between them, and they span quite a few years from the 128 to the Tipo/Punto incl turbo.

Some of them:

Valve sizes
Head bolt sizes
Series 1/2/3...(?)
Compatilbility between different models/blocks ..?..

I would very much appreciate to get the differences and similarities clarified by someone of You out there.

Thanks in advance & best regards

Remi Lovhoiden

[Guy Croft]

Remi, hi

that's quite a task, and whilst some bright spark may have this to hand it would be a rather pointless exercise to try and write it from scratch. Unless you're starting a factory doing it - inwhich case you can buy the lot and figure it out yourself!

Perhaps you could tell me (us?) what you have in mind here to start with. I mean the fundamental decision has got to be 'which block' and 'what cubic capacity'. The head follows the block, not the other way round. You can do pretty much the same type of mods to all the X19, 128, Uno type heads and end up with a good race head - sure there are variations in valve size but cam layout and port orientation are the same. FWIW I think the X19/Ritmo 1500 is the one of the best around. Or maybe an Uno or Tipo 1400.

I don't think Fire blocks will marry to anything except Fire heads. And in my view the heads to steer clear of really are the Punto 'Fire' type heads - 1108, 1242, 1372 - not good heads to work on.

I did one of them recently for a trials car, and was singularly unimpressed with the head as core material for tuning. Which is of course a non-issue to a car manufacturer ...

GC

[Abarthnorway - Remi L]

Hi again!


First thank You for an informative reply!

To be more consise the key questions are:
1: What cylinder heads fits the Fiat 128 1290 cc block with little or no mods?
2: Of these heads, which one is best suited for a "budget" raceengine?

Background:
I have just been given the task of building an engine for a budget 128 race car in something called "Corsa Italiana" - a just for fun race series located in Norway - with possible Swedish participation from next year. Cars minimum 15 years old.

Engine regulations for the class are simple - max 1300cc original displacement (overbore allowed) naturally aspirated.

The base engine will be a 1976 128 1290 cc engine. All I know is that the engine was running OK. It will be dismantled in the weekend, and plans/budgets will be made.

This engine has 36/31 valves and 12 mm head bolts, 15 mm(?) OD guides in its standard form. Bore is 86mm stroke is 55mm - some potential for high revving here....;-)

My initial idea is to check the possibility to get hold of a head with bigger valves standard. I have heard that heads with bigger valves might be a direct swap - but till now its all just rumours. A Punto 1600 head supposedly has 39,5/33 mm valve combo, and some models has 37.5 mm inlets. I am considering this as an alternative to installing bigger seats/valves in the 1300 head. Combustion chamber volume/design, compression ratio, piston valve cutouts etc will need to be considered as well, and it might not be worth the hassle...
But I want to figure out the options, even if it turns out its only use will be knowledge of what does not work;-)

Anyone with experience with swapping heads on a 1290cc block - any help greatly appreciated!

The specs/budgets are not yet finished, but some hardware are already planned:
A pair of non emission 40 DHLA are on their way
Head, cams, pistons, guides and valves, manifold will be dealt with the next weeks.

I am not fond giving promises - so I wont - but I will do my best to post some photos of the car / engine as we begin working on it.

Thanks!


Best regards

Remi Lovhoiden

[Guy Croft]

Remi, hi

I think that the only head you can use readily is the original 128 one for that motor, the later SOHC heads all went to 10mm head bolts (the early 12mm setup gave a lot of problems because the 12mm fixings used to 'weld' themselves to the heads, I have actually seen 128/X19 1300 engines were the heads were stuck so tight to the 12mm studs you could not separate them at all.

Once I got so annoyed with one of those motors I had the car lifted with a crane, the chain bolted to the head and hit the car with a very big sledgehammer to get the head off. Came off with a heck of a bang, but we got the motor out..

GC

[Acki]

The Punto/Tipo head have a other thermostat and the water channel for the heating in not on the right side.

Uno 1.5 SPI is a good head for turbo's because this heads aren't cracked between the valves (normally this cracks are no problem).
I use this head for the 1.6 ohc engine of my brother and for my turbo.
Inlet valves from tipo 1.6 (39,5mm) and exhaust from 1.5 spi or 1.3/1.4 turbo.