7vette6

I finally got around to setting my timing and changing the springs in the distributor. I know step one is checking the dwell angle. But since I have HEI system do I need to check my dwell angle or is it preset and unchangeable?

jnb5101

i've installed two hei's. never gave the dwell a thought! you do have to adjust the vacuum can, though.

7vette6

Oh really? could you please give me some info on this?? what did you do to your vacuum cannister and why?
I just thought my current vacuum advance would work fine with increasing the timing and switching to manifold vacuum

69427

The dwell angle automatically changes with RPM and battery voltage. It does this to keep the coil charged up at high RPMs, and preventing burning up the coil at low RPMs. It also compensates for the battery/alternator voltage being too high or too low.

The module does all the work. Nothing you need to do.

jnb5101

go to msdignition.com. they have installation info on their street fire hei distributor that has a chart showing the engine vacuum, degrees of advance and the number of turns the advance screw needs to establish that number of degrees. there may be other sites that have the same info. just google it.

7T1vette

That is for an MSD electronic ignition system...not a GM H.E.I. system. The only 'adjustment' on the HEI system is to reposition the distributor.

7vette6

yes. Now im pretty sure I have the ar-10 vac can. which has a 3-5 start "hg and 9* distributor advance. My main question is if this can is o.k. to use, or if I need to buy a new one.

7T1vette

The type of vacuum advace can you have is (or should be) dependent on the amount of vacuum your engine produces at idle. Lars has a good write-up on this issue. You should send him an e-mail and request a copy of that paper.

V8FastCars@msn.com