I need to know what the shaft diameter is on a TBI dist. I have a vortec longblock ready to go in my TBI equipped pickup and I need to get a different gear to go with the roller cam. I can get a bronze one from the local race shop in .490 and .500. Any ideas?
Thanks
Nick

 

I did this exact same thing. It's a .490 and there's nothing special about the gear. I wouldn't go with bronze unless you plan on changing it often. I'm using a new, OEM gear and have no problems. I asked around and I guess the custom cams (race stuff) require a bronze gear, but not the regular production cams.

 

The reason for the change is the vortec has a roller cam and I was always told they took a different gear.
Nick

 

I measured the shaft on one and it was .425

 

'LO5

Well, there are three different dizzy shaft diameters out there:

0.427 (small HEI hat) used on GM roller camed engines (both TPI and TBI)
0.490 (Full size HEI hat)
0.500 (Full size HEI hat) (aftermarket?)

If your Vortec is equipped with a roller cam (as it should be) you should use the GM-performance, part number 10456413, Diameter 0.491 in. distributor gear. This gear must be used on all crate engines with steel camshafts
It is also compatible with standard flat tappet camshafts. GM gear suppose to outlast bronze aftermarket gears.

This subject has a great deal of controversy and innuendo, so do a bit of research.

I have not found melonized gear for 0.427 diameter dizzy, end-up finding standard sized, with 7-pin HEI (0.490) on J-Yard and replacing original gear with 10456413.

//RF

 

Thanks for the replies. I remembered this afternoon that my gutted distributor that I use for engine priming used to be a tbi unit and it was indeed .425. Even better yet when I was throwing away the parts from the vortec injection(it was in a fire and all the plastic melted together) I decided to keep the original gear from the plastic vortec distributor. Sure enough, it fits so I should be set.
Nick