Advance curve for CRT distributor

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)

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slumlord444	Posted Last Year
Supercharged Group: Forum Members Last Active: 3 Months Ago Posts: 1.2K, Visits: 137.2K	Looking for recommendation. Several options with it. Mummert head 312 with hot Isky cam. Peak horsepower at 6,200 rpm.
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Ted	Posted Last Year
Co-Administrator Group: Administrators Last Active: Yesterday Posts: 7.4K, Visits: 205.0K	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)
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Advance curve for CRT distributor

Advance curve for CRT distributor

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