MSD timing vs Vac readings questions

[Rat Patrol]

This question is in part a response to Rockinrobin's question.

Heres the results of my vac Gauge testing -

Scenario 1 - My motor draws 16" of vacuum (makes 6.84 PSIa man pressure) at 850 rpm - idle - so my timing is 16 static plus 12 MAP = 28

Scenario 2 - It draws 20" (makes 4.88 PSIa) at cruise at 2500 rpm so thats 24deg RPM + 12 deg MAP = 36 total

Scenario 3 - It draws 10" (makes 9.5 PSIa) during part throttle acceleration on primaries between 2000 and 6000 rpm. This means with my current MAP settings...it's still adding around 5 degrees on top of RPM timing under light acceleration.

Two questions:

I am wondering if I should change the MAP so that it relies solely on RPM timing under light acceleration conditions (refer scenario 3)?

Should I also add more MAP timing at idle (refer scenario 1)?

 

[Rat Patrol]

Two questions:

I am wondering if I should change the MAP so that it relies solely on RPM timing under light acceleration conditions (refer scenario 3)?

Should I also add more MAP timing at idle (refer scenario 1)?

I managed to get the answers to these two questions for those that are interested....

1 - Having some MAP timing added under light acceleration conditions simulates exactly how a vac advance works in a distributor - That is...its not an "On/Off" condition...so some MAP timing under light acceleration is appropriate...as long as there is not so much to make the engine ping.

2 - I'll look at adding a little more timing between 20" and 15" of vac (or the PSIa equivalent) as the motor can handle more timing at cruise and idle.

A test on this forum - http://www.300cforums.com/forums/1s...ake-exhaust-mods/18005-stock-timing-srt8.html

- indicates that timing went as high as 48 degrees at cruise under light load.