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Fiat 124 SC "Gruppe 5" race engine preparation

Posted: March 28th, 2019, 4:14 pm
by OSM Team
Hi everybody

We building the 1969 Fiat 124 Sport Coupe "Gruppe 5" race car to the FIA Historic European Championship.
The gruppe 5 rules system is very freedom, permissive but we must keep the engine block, because just this fit to the homologation.
The Fiat 124AC engine blokk is very rare and some engine parts dimension is very unique, and this facts make my work is hard.

Fiat 124AC engine size is 1438 ccm ( 71.5 stroke x 80 bore ).
The rules is permit we modifing the size, but we must stay under 1599 ccm but the stroke and the bore is free !
We dont know what is the best and maybe cost-efficient way about enlarge the ccm size.
We will using the race piston and steel connecting rod but the crankshaft is not clear.

My questions.

1. Whats is the maximum bore in the 124AC engine block with special, unique cylinder head gasket ?

2. Which factory crankshaft fit to the 124AC block ? The connecting rod bearing diameter size is free, because we use unique connecting rod. The flyweel dimension and bolts is free because we use steel flywheel.

I searched on the internet, but not find performance crankshafts to the 124AC block, just to the bigger, newer engines !
But I found the performance crankshaft with the ideal stroke to the Fiat SOHC engines ( 128, X1/9, Punto ) and i try to checking the crankshaft dimension but i just found the bearing sizes.
The SOHC crankshaft bearing sizes is okay to my 124AC block, but the other dimensions is not clear.

My questions.

3. Maybe some SOHC crankshaft fit to my 124AC block with little modification ?

4. Someone know, where buying the steel crankshaft to my 124AC block?

Other engine information : performance camshaft, 2 x IDF44 carburator, electric ignition, 4-1 rust free exhaust mainfold, bigger oil pump.

Thank you the answers.

Re: Fiat 124 SC "Gruppe 5" race engine preparation

Posted: March 28th, 2019, 7:12 pm
by Guy Croft
the 124 AC crank, can you publish a high quality (not monster gigabyte) photo or two please?

I am interested in the crank webs only, I need closeup - from this I can tell you if it is a forged steel item or cast...

Either way I shall comment and you should listen to my comments carefully please.

I have never had one at my works, only 1608 units, sorry..


Re: Fiat 124 SC "Gruppe 5" race engine preparation

Posted: April 9th, 2019, 12:10 pm
by OSM Team

Thank you for your fast answer.
I will a best quality pictures but my engine preparator partner is on holiday and i cannot access my engine parts.
If he back, i upload the pictures.

Re: Fiat 124 SC "Gruppe 5" race engine preparation

Posted: April 24th, 2019, 7:49 pm
by Guy Croft


Re: Fiat 124 SC "Gruppe 5" race engine preparation

Posted: August 8th, 2019, 12:54 pm
by OSM Team
Mr croft.

After a long time, i can make the pictures.
I made some pictures of my factory crankshaft, and the engine block with 81mm bore.

Best regards

László Skripeczky