Fiat SOHC Turbo Race - Crank / Block options

Competition engines and ancillaries - general discussion
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Abarthnorway - Remi L
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Fiat SOHC Turbo Race - Crank / Block options

Post by Abarthnorway - Remi L »

Hi all!


After helping a few other people out with their race engines, I am now starting to collect parts for building my own Fiat SOHC Turbo for racing use only.

I was actually planning to use a 1.6 Tipo/Tempra block (86mm)...
When looking at the turbo models all run approx 80 mm bore (except some series 1 Uno T)
Is this for a good reason?

Regarding the cranks:
Are there any differences in strenght between the models?

Thanks!


Best regards

Remi Lovhoiden
GC_45
bugar

Re: Fiat SOHC Turbo Race - Crank / Block options

Post by bugar »

Many use 1,6 blok to make big HP whit turbo you look for 1,4 or 1,6? last can gave more power if you all other parts is same
Acki

Re: Fiat SOHC Turbo Race - Crank / Block options

Post by Acki »

All uno turbo's has a bore of 80,6mm. The legend of a bore of 86,4mm I have never seen.

You can use serval blocks.
I would use a 1602cc tipo block with oil sprayers.
Crankshaft from Fiat 127/128 - forged steel, not cast like the late models (I'm looking for these crankshafts... PN me when you have) but the cast also works fine (1372cc N/A and turbo and 1602cc are the same).

Which car do you want to put the engine?
Punto, Tipo? Or Uno, X1/9 etc.?
You can use different heads, with some heads it's easier for you (thermostat and 1 waterpipe).
Guy Croft
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Re: Fiat SOHC Turbo Race - Crank / Block options

Post by Guy Croft »

Crank material:
This one goes 'round and round' on every Fiat forum so once again I'm going to try and end it. I've worked on more cranks than most see in a lifetime.
The cranks on ALL the sohc units 127,128, Tempra, Uno, X19 are cast, and although I have never embarked on metallurgy tests they are most likely heat treated spheroidal graphite cast iron. Don't think this is a weak material, it's possible to get its UTS up to over 900 MPa, higher than some steels. But only the TC range had forged steel. You don't have to file the thing and inspect the shavings (If you do you'll see the steel ones are way harder and the material doesn't contain the grey, powdery & slippery graphite that exists in cast iron) the difference between a cast and forged crank is easy to ID, it comes from how they are made, see photos. I had a photo from GC client Gunter Pitzer in Germany of his Tempra 1600 crank, looked identical to the design of the X19 one. Cast cranks rarely get much machining because they are cast to adequate tolerances, whereas the surface of forgings will exhibit a mix of machining and casting. As to whether the material is a steel or simply an iron alloy it really doesn't matter, the key issue is that a forging is much stronger in all modes than a casting because it has preferential grain orientation induced by high temperature stamping. you can't develop grain flow like that by casting.

These SOHC production cranks - whatever the particular iron it's made of - is easily capable of taking double the design power and rpm way over 12,000. I say this, as usual, because I've done it. The most extreme was a Delta Turbo ie 1600 which is cast and has exactly the same design as the X19 albeit bigger bearings etc and easily accepted 240 bhp. Sure I have heard of cast cranks cracking and breaking but usually in much 4 cyl older engines without 5 main bearings and a nice stiff block and mostly the contributory cause has been bearing failure or imbalance. Steel cranks fracture too!

Uno Turbos were series 2 80.5 bore x 67.4 stroke, cap 1372cc, ser 1 80.5 x 63.9 1301cc

The Tempra is a good choice (virtually identical to an X19/128 in layout) because parts are readily aval from Fiat, yes, it has oil sprays, the head gasket will take 17+ psi boost comfortably. It is also a powerful head, see flow data, and can accept Uno Turbo sodium-cooled ex valves. The choice ultimately comes down to cubic capacity really.

GC
Attachments
X19 1500 crank, cast, GC race rods.
X19 1500 crank, cast, GC race rods.
A 005.jpg (438.09 KiB) Viewed 14354 times
A casting has a thin bead (yellow box) where the mould boxes join during pouring.
A casting has a thin bead (yellow box) where the mould boxes join during pouring.
cast crank.jpg (54.56 KiB) Viewed 14337 times
A forging or stamping has a thick band (red box) formed by the two havlves of the die coming quite close together but not actually touching. Of course a forging starts out from an oversize casting, which is then stamped in a press.
A forging or stamping has a thick band (red box) formed by the two havlves of the die coming quite close together but not actually touching. Of course a forging starts out from an oversize casting, which is then stamped in a press.
forged crank.jpg (93.34 KiB) Viewed 14336 times
X15 1500 vs Tempra 1600 full spec flowtests std OE valves.GIF
X15 1500 vs Tempra 1600 full spec flowtests std OE valves.GIF (27.86 KiB) Viewed 14320 times
bugar

Re: Fiat SOHC Turbo Race - Crank / Block options

Post by bugar »

In past have limit nombers of forged 55,5 crank but they wos hot in OE engines Abarth sale separate like special parts .
Guy Croft
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Re: Fiat SOHC Turbo Race - Crank / Block options

Post by Guy Croft »

Bugar, that is true of many engines, ie: race cranks are available in the aftermarket.

It is not relevant here.

GC
Acki

Re: Fiat SOHC Turbo Race - Crank / Block options

Post by Acki »

Hello Guy,

Look at this crankshaft, it's a 63.9mm crankshaft! Looks like a 67.4mm. Small design of the counterbalances.
Image

It shall be forging die produced (maybe liquid forged?! and because of this the small thin bead?!)
I think it's the same like on the serie 1 uno turbo without cat rods and the later rods.

They have a divisional level but when you work on the material you detect that the material is tougher.
I know this from the rods. The crankshaft's I don't had in my hands.
Maybe you can tell us/me something about it.

Did you ever seen a broken Fiat SOHC crankshaft? I didn't see or hear ever about one.
I think the "small design of the counterbalances"-crankshaft (I think it's better than I call the crnakshaft forged, maybe they aren't forged...) is better for us because of the weight.

But why you find different types of the same crankshaft?!
Why the don't used everytime the same small design?! I think this crankshaft was cheaper than the stronger crankshafts in the uno turbo 1301 or X1/9 1.5?!

Your arguments are good, I will speak with people which told me that this should be a forged crankshaft...

Regards, Martin
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