strada 105tc Head

[archigraphe]

I'm actually participe in rally regularities in Belgium and I would access to Legend 60 and 80 rally.

I've in project to update the engine of my 2l carb ( hybrid car mechanics and interior from a 76 coupé in a 84 car body).
I ve a complete 105tc engine, it has a 43.5/36 head and high dome piston ( not yet open but it seems to 8mm dome.)

The guy croft forum inform me this piston in a 2ltr make a 12:1 cr ratio expected, bad for the french unleaded fuel with the 98 octane...

So I think just use the head to benefit from the bigger valve with no modification (except deburr castings fondry..)

The first stage (expected this winter) is:

swap the head,
replace camshaft and cambox with a top distributor SM800AX on exhaust cam.
Use a 1800 beta inlet manifold with a 34 DATR (25/27 venturi ).
Baffled sump,
Mount a 1300 gearbox ( which have 20.000 km ,completely revised).

Second stage (next summer) :

Inlet manifold and 2 x solex 40addhe (from strada 130 tc).
exhaust : 4-2-1

The suspension will be all revised....

Can you inform me what torque or extra power can be expected with this simple modification?

Thank's.

[75coupe]

Hi There,

I use 105TC pistons in my 2 Litre engine, with VX head gives around 10.8:1 CR. You can also use Fiat 1800 or early Lancia Beta 1800 pistons, these give slightly less CR, around 10:1.

It all depends on head chamber volume, head gasket (there are several types and thickness).

I would fit the Solex carbs as soon as possible, they will give you at least 10-15BHP with the bigger valves.

The head alone may give you a few BHP, not sure.

[mangocrazy]

Which model of Fiat 1800 pistons would you need for this, and what CR would they give in a standard 2 litre Spider head? Also, what CR would 105TC pistons give in a std 2 litre head?

Ideally I'd like to get forged pistons for my proposed engine rebuild, but availability (or lack of) and cost would seem to be against this.

[archigraphe]

It seems to me more cheaper byiing a complete engine to take his piston than (as cast..) that bying forged Pistons...

For the CR calculation, I had to obtain the chmber volume.

[75coupe]

Guys,

These new cast pistons are available from Vickauto in the USA for $335 for a set, including pins and rings. I have used them in my race motor for 2 seasons at up to 7200rpm without problems. I used 84.8mm, but they are available in most oversizes. They are much, much cheaper than forged but not suitable for over 7200rpm.

Compression on a std 2 litre will be around 10.5 to 11:1 depending on gasket, amount machined off head, block etc. I use BP Ultimate or Shell V power 98 octane unleaded fuel without problems, and I have big Guy Croft cams in my engine, with twin 45DCOE etc.

I originally used S/Hand early Beta coupe 9.8:1 1756 pistons, these are very similar, as are the Beta 9.4:1 1585 pistons, both give around the same CR as the Fiat 105TC pistons in a 2 litre. The others you can use are Fiat 131 1585 pistons these give around 10:1 CR in a 2 litre.

Buy new pistons if you can, it is not worth the hassle of trying to re-use old pistons, the std ones are graded to a particular bore size, and it is painful to get bore claerance and ring gaps correct etc. You will end up with an engine that has blow by and not much of a performance increase....

Regards Ian

[mangocrazy]

Hi Ian,

Thanks very much for that - I think that is definitely the way to go. I'd love a set of GC's unobtanium forged pistons, but the price is just too much... I feel a call to my brother-in-law in Tennessee is in the offing...

[rossocorsa]

you are certainly right that GCs pistons are a serious investment but if you are already going to spend serious money I'd think seriously about that bit extra,the amount of thought that goes into his product and the friendly back up available could make them more than worthwhile