Alternator/Fan belt size for 77 Carrera 3.0 engine

[jwakil]

I need to order the fan belt for my car which has a 1977 carrera 3.0 engine, 11 blade fan, stock pulleys I believe. I'm seeing sizes for different years ranging from 10x725 to 10x710 to 9.5x710. I don't know if mine would be same as for the turbo car or normal 2.7 engine or what. Anyone know the correct size?

[James Brown]

Well you have a mix of parts there with the 3.0L and a 11 blade fan. so order all the sizes and go with the one that fits best, send the rest back and note the size on the fan housing for future reference.

[jwakil]

Well, I noticed the one that is on the car now is 10x725. This has worked fine so far but it's starting to show some loose threads. There is a spare in the trunk that is 9.5x710. I'm wondering if both of these are equivalent since a thinner belt would need to be shorter to fit with the same number of shims. I will see how the 9.5x710 fits, if that works, I won't need to order another.

[Flat6pac]

725x9.5 was used on the first 2 years of the SC and on the 77 911S I believe to compensate for the 5 blade fan and the smaller fan of the SC.
Use with the 12 hole fan center and pulley half.
Bruce

[Flat6pac]

And all the 9.5 new belts are now 10mm
Bruce

[jwakil]

turns out the 9.5x710 is definitely not interchangeable with the 10x725, much shorter and wouldn't even allow me to screw on the outside pulley half. So 10x725 is the way to go.

[johndglynn]

I tried 10s on my car: absolute waste of time. Spent some time tracking down the right size skinny belts and delighted I did! Twice the price but fitted properly first time.

[johndglynn]

PS: the 11-blade fan is right for a C3 depending on the year.