Here’s the chart that comes with both the TSP and CRT distributors showing the various combinations of springs and bushings for making adjustments to the advance curve.  Those distributors typically are delivered with the silver bushing and medium silver springs which are suitable for most mild Y-Block builds.
  

Lorena, Texas (South of Waco)

Jeff’s (55blacktie) statement above is essentially correct.  Here’s more detail.

The mechanical advance curve as supplied with the TSP & CRT Y-Block distributors is very close as delivered.  Those two distributors already come with the lighter springs installed and a rate of mechanical advance suitable for most mild Y builds.  I have found that the amount of advance supplied by the vacuum advance chamber in the CRT/TSP distributors is excessive though and I will shorten that curve by adjusting the vacuum pot with an allen wrench inserted within the vacuum tube port of the pot.  All my adjustments are for 91-93 octane fuel as those fuels have a reduced amount of ethanol in them versus the 87 & 89 grades.  Carburetors in general are not happy with ethanol laden fuels and the premium grades in my part of the country only have 3-5% ethanol versus the 10% found in the lower grades.

The MSD distributors on the other hand come with a very conservative advance curve which they do for all their street type of distributors.  Those distributors come supplied with the already installed ‘heavy’ silver springs which makes the advance curve lazy but safe.  This is done to protect the unknowing out there that could inadvertently install a distributor with a long and/or quick advance curve in a highly modified engine that would create a propensity for detonation.

For the MSD distributors, the light blue and light silver springs with the supplied ‘blue’ bushing works well for most mild Y builds.  Where the camshaft and/or the compression ratio gets into some serious performance expectations, then the black bushing is used to shorten up the advance curve so that a higher initial ignition advance number can used while minimizing the total advance value.  There is not a ‘one size fits all’ scenario and hence, all the different springs and bushings that are supplied with the new distributors to tailor the advance curve for each individual application.

Lorena, Texas (South of Waco)

You can also try contacting Ted by email (eatonbalancing@yahoo.com)

Can Ted Eaton please confirm the details on this for me? Silver bushing and light silver springs if I understand correctly for advance curve. Where do I set the base timing to get 36 degrees total? On the vacuum advance screw it in all the way and back it out one full turn? Just want to make sure I got it right. 

Before you start changing the springs and bushing, you might want to try it right out of the box. At the very least, it will be a good starting point.

Thanks! That’s what I’m looking for.  

On 05-30-23, Ted replied to my email in which I asked the same question that you're asking. He said that the CRT/TSP distributors are similar in construction to the MSD., and they are happy with a similar advance-spring combination. He uses the light silver and blue springs, but I've yet to install mine. He also recommended screwing in the adjustable vacuum advance all the way in and then backing it out one full turn. For carbureted engines, he recommends a spark-plug gap no greater than .035.

I hope this helps. 

P.S. Looking at the charts that came with the CRT distributor, Ted said it looks like the silver bushing is comparable to the MSD blue bushing, which he uses. 

P.P.S. It might be helpful to also take a look at the installation instructions for the MSD Y-block distributor; compare their chart to the one included with the CRT distributor.

Looking for recommendation. Several options with it. Mummert head 312 with hot Isky cam. Peak horsepower at 6,200 rpm.