Technical 850 Spider Power and Wheel Question

[PeachsGarage]

Greetings from a 1974 Fiat 500 owner!

I'm planning to significantly increase the power of my 500, close to 100 HP and 100 lb-ft of torque, and I'm looking at using an 850 spider rear hub/axle assembly.

I have two questions:

• Does anyone know if running this much power/torque through a stock 850 Spider drivetrain (axles/hubs) would last without issues?
• Does anyone know if a Fiat 500/126 (12") wheel would fit on these rear hubs?

Thanks!

-Bobby

 

[timmycm850]

Hi Bobby.

The 850 gearbox is used in the ot1300/124 where the SS version is rated at 99hp.

The regular 850 rear drums are used for the 850 saloon and 900t rear brakes both of which run 12 inch wheels. You would be wise with 100hp to be seeking the brake shoe material you can get and go for discs on the front. You would be encouraged to go for 13 inch wheels and rear discs ideally but I'm guessing this reduces your tyre choices within the wheel arches.

Tim

 

[PeachsGarage]

Thank Tim!

This all sounds great! 100hp is an over estimate on my end, and looking at the stock gearing on the 850 spider (1st and final), vs what I'm doing, it's not that big of a difference. Good to know the drivetrain is sufficiently designed to handle more power!

Definitely planning on upgrading the brakes (front discs are pretty common) but good to know the 12s work on the drums without issues. I may upgrade to 13s in the future, but it would require new arches that I don't feel like adding at the moment.

Thanks for the help!

 

[timmycm850]

What engine are you looking to mate with the 850 gearbox

 

[PeachsGarage]

What engine are you looking to mate with the 850 gearbox

I'm actually going with a motorcycle engine using an Elite differential, so I'm mainly concerned with the axle, outboard CV, and hub strength.

 

[timmycm850]

The rubber outer joint is normally the weakpoint but some cv joints can be found to fit on the splined axle shaft

 

[PeachsGarage]

The rubber outer joint is normally the weakpoint but some cv joints can be found to fit on the splined axle shaft

Copy that, thanks!