1968 NOM BB. Not a TI, or HEI distributor. Currently with a black plastic advance limiter bushing I'm getting 30 degrees total mechanical advance. Would like to get only 20, starting at 18 and ending at 38.
1. Can I buy a bushing to do this and where?
2. If not, can I fabricate one and out of what?
3. If no to 1 and 2, I guess I'll have to reduce the slot. If I'm getting 30 and want 20 is that a 1/3 slot reduction?

Still shaking out the engine but it seems to like a lot of advance, but I'm at 2200 ft elevation and its cold outside. The engine is now at 14 initial with 44 total all in at 2800. I am concerned the 44 at lower elevation and warmer temps will be too much. thanks.

 

I've had to change the advance cam in my distributor to get the advance limit where I needed it. Some folks weld the slot smaller to do the same.
Changing the bushing will not give you the range you want/need IMO.

 

assuming you have the original GM Delco distributor try the bushing in this kit

http://www.summitracing.com/parts/mr...make/chevrolet

 

Been there, done that.
There is only 1 bushing in this kit and it's no larger in diameter than the black plastic OEM one (may even be a hair smaller).
This isn't going to get you where you want to be.

 

Being a BB your gonna want a lot more timing then a SB , if it is not pinging and pulls strong you may have no worries , and that your at 14 initial gives you room to back her down.

 

That's a common problem.

The stock distributors often have a very long advance slot, and it's not possible to get a "good" advance curve even when using the advance stop bushings on the pin. With modern fuels and camshafts, it is desireable to run about 16-18 degrees initial with 36 total. Big blocks will often produce best power with total timing up to 38 - 41. This is often not possible using the stock setup. Your have 2 options:

Fabricate a custom advance stop bushing from brass round stock with a larger diameter than the stock rubber one and the Mr Gasket 928G brass bushing - I have made myself a huge assortment of these for when I rebuild distributors. The slot is wide enough that you can go about .030" larger on diameter and still fit in the advance stop slot. But you're limited to a bushing no larger than the width of the slot - this is often inadequate.

So, if this doesn't do it, you have to weld the stop slot. Complete instructions on doing this are in my timing paper, including the calculation on how much to weld. E-mail me if you need a copy of the paper.

Your 14 initial is not enough, and your 44 total is too much: Even at 5000 ft elevation, I've never seen a BB on the dyno make power beyond 41 degrees. Back your total off to about 38 - 40, and then shorten your curve to allow about 18 initial (about a 20 - 22 degree advance curve). Use the calculation in my article to achieve this.

Lars
V8FastCars@msn.com

 

look at my thread:

http://forums.corvetteforum.com/c3-t...al-timing.html

and yes its possible to make a bushing that is wider than the slot. Looks like an egg.
But it should sit strong on the pin, so that it cant move.

 

Since I don't have the equipment or talent for welding, I swapped the advance cams instead. Using a '718' stamped cam, I was able to limit my mechanical down to 8 degrees distributor (16 degrees crank) with the stock bushing. I run 18-20 degrees initial.
For reference, a '728' stamped cam got me 11 degrees distributor (22 degrees crank) with the same bushing.
Just a thought..