(T) changing the head

what the hell does "changing the head" mean?

whats involved?

(car related!)

my mate did it to his 1.2 nova and it made it alot quicker

can it be done to a 1.0 uno?

cheers.

Ummmm... I'm not sure where to start?! Please excuse me if some of the following is too basic for you...

The cylinder head ('head') is the casting (usually aluminium) that bolts onto the engine block. It seals off the cylinder bores, by means of a head gasket (which sometimes fails due to overheating/warping of the head). The head gasket has to be replaced whenever the head is removed, and it is a good idea to replace the bolts too on modern engines because the bolts are designed to stretch during tightening.

As you probably know, the head also has valves to let in the fuel/air mixture and let out the exhaust gases. These valves are operated by the camshaft which is usually mounted on or in the head for car engines since the '70s-'80s. So, the camshaft drive (usually a toothed belt) also has to be removed before the head can come off.

The cylinder head usually needs to be removed these days to repair the head gasket or to replace bent valves (being the aftermath of a camshaft drivebelt breakage).

In the olden days (the '60s and before) the cylinder head used to be removed quite regularly (50,000 miles?) for a 'decoke' and valve grind (the inferior quality of petrol and oils used to give a heavy carbon buildup that impeded efficient combustion, and engine valves and seats were made of a less durable material that could become pitted and not seal correctly).

Apart from these 'repair' operations, other cylinder head work is sometimes done to enhance engine performance:

'Planing' the head removes material from the surface that meets the block, bringing the combustion chambers closer to the pistons and thereby increasing the compression ratio. More compression = more bang = more power.

Enlarging the valves allows the fuel/air and exhaust to flow more freely. More fuel/air = more bang, etc.

Enlarging or smoothing the ports that feed the valves removes various imperfections left by the manufacturing (casting) process. Larger, smoother ports = more fuel/air... although in some cases the smooth low-speed running can be compromised if the port diameter is too large.

It is important to note that all this work is not free (fitting larger valves is particularly expensive) and in many cases, a transplant to a larger engine (or a turbocharged engine) will provide more power for less money.

In my personal opinion, there is not a lot of point modifying the FIAT FIRE engine cylinder head. Being a modern crossflow design, it is already capable (I think) of more flow than the (very de-tuned) camshaft profile can allow for (that is, the valves are not open long enough to allow very much mixture in/out). I think you would modify the cylinder head once you have larger carburettors/fuel injection, manifold, and a 'performance' camshaft. How many of these things does your friend with the Nova have?

Hope this helps... also do a few archive searches for smokeme's turbocharged FIRE conversions...

To return to your original question, a long time in the past people used to take the head off the 1116cc FIAT 128 engine (the same engine is used in the 1984-89 FIAT Uno 55/60) and fit it to the 1290cc engine of the FIAT 128 Coupe. This was a cheap performance tweak because the smaller combustion chambers of the head from the smaller engine gave a higher compression ratio when fitted to the larger engine. Maybe this is what your friend with the Nova did? I don't think the same trick would work with the 1301cc Uno engine, because I think the head is already the same as the 1116cc engine and the pistons are a different shape instead. Though, I could be wrong. And anyway, this has got nothing to do with the FIRE engine. I just mentioned it because it was the one time I could remember where 'changing the head' made a difference!

Cheers,
-Alex

Couldn't have put it better myself Alex!

I would point out though that we say 'skimming' rather than 'planing' the head in the UK. Must be a Kiwi expression you're using

No idea as to what changing the head on a Nova (pardon my language ) did to up the power, but it was either skimmed to raise the compression, ported to allow better gas flow or maybe from a 1.0 litre Nova that possibly had smaller combustion chambers to achieve the same effect. It could also possibly have had a different 'higher lift' camshaft in it to allow better breathing.

It could also be something simple like the original head was knackered - blown gasket, burnt valves, worn camshaft/ followers, and that putting a good head on simply restored power back to normal giving an impression of power gain.

One of the advantages that the Nova/ Corsa lot have is that the basic 1.0/ 1.2/ 1.6 standard engine is the same family as the 1.8, 2.0, and 2.0 16V (and turbo!) engines as well. So dropping in a big engine into a Nova is very easy, though most of the turbo/ 16 valve conversions have serious problems with actually getting the power down on the road...Wheelspin abound!

As to the 1.0 litre FIRE engine, the biggest restriction is the camshaft. It's designed for maximum torque and economy, which is why it doesn't like to rev to the redline. Basically the engine doesn't breathe well at high revs.

A simple way to up the power is to fit the Panda 4x4 camshaft which will liberate an extra 5bhp. Or fit a Punto 75 camshaft which apparently will take the 1.0 litre up from 45 bhp to nearly 60 bhp! So I've been told...

To go further you need to fit the head from a Punto 75 MPI engine, as this not only has the hotter camshaft, but also bigger valves. I think I am right in saying that the valve sizes on the SPI 999cc, 1108cc and 1242cc heads are the same. Only the MPI 1242cc has bigger valves allowing greater gas flow.

I'm hoping to try some of these mods myself, once I get the time and money to do so. Would be nice to add a little more pep to my lil' 1.0 litre FIRE

Might even be an idea to visit the Cinq/ Sei section on the forum, because asides from the 1242cc conversion some of the member have also fitted the Punto 75 camshaft to a Punto 60 head. And there's a guy in Denmark (I think?) called Tricker who also enlarges the Punto 60 throttle body and has a rolling road print out of over 90bhp from a Punto 60 1242cc engine!

I must start saving some of my student budget so I try these mods out for myself...

wow both very detailed! thanks for your help!

i asked the guy with the nova and he said he put on a head from a 1.4 SR. this sounds like what your talking about with puntos and 128s.

if an engine conversion would be cheaper then i dont think i will be going there

will just save and get a UT engine in there eventually.

its a shame because it sounded like a cheap(ish) mod and insurance companies wouldnt notice

BUT i definitly WILL look into changing the camshaft to a panda 4x4/ punto 75 item. 60bhp does sound VERY tempting!
any ideas of the cost of this? i doubt id be able to fit it myself.

You might need to buy some shims for this. One other modification, which a few people have done is getting a twin choke carb from the 1301 engine, make an adapter block on top of the inlet manifold and flow the manifold.