throttle body bore size?

Way too cold here to go out and measure.
It uses a K&N RU-800 Filter which mounts on 62mm flanges.
So, a ~58mm Bore would be a reasonable guess.

Thanks for the guess.  I'll be interested to know the actual size if anyone lives in a warmer climate :-) 

I thought I'd find it listed somewhere, but I haven't been able to.  58mm sounds way too big, but EFI can get away with larger bores compared to carbs since the computer handles the fuel flow. 

Rusty

Carbs need a restriction to work EFI can go big, less restriction more efficient. There are websites the make EFI throttle bodies and systems that you may need.

I have converted Carb engines to EFI all the hardware I needed was found at Jenvey.... (TB levers, horns. fuel rail etc) then I just needed an ECU...I am sure there are others...

there are calcs for TBI basically working out required air flow from cubic capacity and assuming 110% volumetric efficiency then choosing a velocity etc...plenty of EFI info out there.

https://store.jenvey.co.uk/

That Jenvey place is like a candy store :-)  

If I were going direct to EFI, I wouldn't worry about getting too big, as long as it's not insane.  For a car, a huge TB would screw up driveability, but we don't have that problem.  I already have everything I need to go straight to EFI other than modifying manifolds.  I've been refreshing my limited welding skills the last few days. 

The reason for the question is that I'm thinking of doing something even more unconventional.  The thought is to use the Rotec TBI 40 with a custom manifold like Edge and SDS.  Once that's running, I'd add fuel injectors and all the rest of the EFI stuff to the existing setup.  The idea would be to avoid duplicating the EFI components for redundancy, but to use the TBI as the backup fuel source.  It would be fairly easy to switch between the high and low pressure fuel pumps, which should be all you'd have to do to switch systems in flight. I don't want to stink up the 912iS section with this silliness, so this was just to explain why I was asking what the stock size is.  

Cheers,

Rusty