The solenoid isn't the problem. If it cranks too slowly, it does crank so you know the solenoid is turning on and engaging the flywheel. It's the motor that is warping and causing it to drag when it gets hot.
There are some other things to consider. First of all, headers don't get any hotter than the original exhaust pipe unless you're burning something other than gasoline. If the headers are a lot closer to the starter, you might consider installing a heat shield to deflect cooler air over the starter. Chrysler used that starting in the late '70s and never had a problem with starters.
Second, a lot of GMs used non-ported vacuum to their distributors for the vacuum advance. That vacuum started to show up as soon as you started cranking the engine. The clue was to get the engine started originally, you often had to back off the timing a little, then set it to specs once it was running. Hot engines that had a little residual fuel in the cylinders were especially hard to start when warm. If your vacuum hose goes to the intake manifold or to a port on the carburetor that's under the throttle plate, move it to a port that's above the throttle plate.
Third, if your engine is higher compression, say 10.5:1 or more, consider using a Chrysler starter. They were gear reduction and drew about 150 amps to crank a big 440 c.I. Where the GM and Ford starters drew over 200 amps for a little low compression 350 c.I. I don't know how they were modified, but many of the local stock car drivers in my area who raced GM products used Chrysler starters until they came out with their own high-torque units.
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Wednesday, March 14th, 2012 AT 2:05 PM