Hello,
Maybe somebody can help me out. I have a 30-40 amp alternator on my chevelle with a msd6al box. She turns over and starts just fine when the car is cool, but when i drive it for about 15 minutes and shut it off it wont start up again. It cranked over for about 3 seconds and quit trying. when we jumped it- it fired off. Does anybody know if i need a larger amp alternator or a starter. The compression on this motor is 9:1 and it has headers. Thanks all

May not need a larger alternator or starter. If jumping starts the car right away, it sounds like a run down battery or poor battery/cable connections. Doesn't sound like solenoid heatsoak.
Another thing is some of the batteries being sold as replacements for the 72's are smaller than the ones used in more modern V6's. I've got one in my 72 that's large enough to fill the battery tray.
Once you get the car running, measure the output of the alternator for 13.5 volts to about 14.5 volts. The alternator/regulator may not be working well enough to keep the battery up.

This could be a calmity of problems, but "heat soak" along with the unknown condition of your batter, battery cables, grounds included, could be the problem. When you jump it, the improvement of higher available voltage at the starter makes it go. As John recommended, check the battery first, if okay...proceed to the next step of cables. Also read below....too much information ahead!

As heat builds on these wires, solenoids (coils and contacts) and starter motors the DC resistance of the wire increases limiting current to your starter...therefore limiting the amount of work it can sustain. Simply put..it quits turning.

To elimate heat soak once and for all you can do several things. One is make sure that all your connections/cables are in perfect shape and even upsizing the cables to number two ga. is an improvement. You can run heat shields for the solenoid/starter package which is a bandaid in my opinion esp when running headers.

The ultimate design change is to go to improved cables and put a mini starter in. These minis are not prone to heat soak like the bigger ones are and do not require the type of current/wattage that the old ones do either. They are lighter, clear the headers, require less current, easier on wiring and batteries, more cranking power, and sound cool as heck.

YOur alternator is not a factor here unless it can't keep your battery fit with all your accessories. Then....different story.

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Steve Jack - ConceptOne Pulleys and Brackets / Engineering & Marketing Technologies

[This message has been edited by HOTRODSRJ (edited 04-20-2002).]

[This message has been edited by HOTRODSRJ (edited 04-20-2002).]