Slow crank when hot

[Ravage]

I had an Autocraft Silver series 625 CCA battery in my car that served me well for years, until it got old and tired and I replaced it with the exact same model. The car started like a champ when cold, but after I stopped for anything like fuel or any other short stop it would crank very slow and it damn near couldn't start the car, leaving me sweating. I took the battery back to Autozone and they even heated it up and tested it but it was fine. They tested the ignition system. The next thing I was worried about was heat-soak on the starter, but the test said the starter and alternator was fine, BUT the test cancelled itself due to voltage loss. And with the ignition off it was reading a 3 amp drain that the guy said was pretty significant. So what should I focus on at this point? Of course it started pretty well during the test, slow to start then picked up and kicked over well and I did cruise it around for 20 minutes to get to full temp.

The only other thing to change besides the batter was I had the heads rebuilt. There was some serious exhaust valve leakage and it has more noticeable bottom end. Even if that is making more resistance, the original manufacturer recommended battery amps was 325.

[70chall440]

Did you have the heads shaved when they were rebuilt? If so, that would up the compression a little. That said, it sounds to me like you have some pretty decent electrical power loss. You need to check your cables (both ends) and make sure they are clean and tight. I would recommend adding a dedicated heavy ground from the engine to the chassis as well. Is this a small block or big block? Are you using a factory style starter or one of the new mini starters?

[Ravage]

The heads were shaved a bit. Standard starter on a 318. All the connection points seem good. Adding a ground strap is probably my next best try.

Did you have the heads shaved when they were rebuilt? If so, that would up the compression a little. That said, it sounds to me like you have some pretty decent electrical power loss. You need to check your cables (both ends) and make sure they are clean and tight. I would recommend adding a dedicated heavy ground from the engine to the chassis as well. Is this a small block or big block? Are you using a factory style starter or one of the new mini starters?

[70chall440]

My focus would be on the connections, I would also ditch that factory starter for a mini (higher torque, less weight). If the connections are clean and tight, it comes down to the battery and/or the starter. 325 CCA isnt a whole lot; you might try a jump box or jump the car from another car just to see what effect that has.

[jhaag]

Assuming battery, starter, wiring/cables etc. are all in good condition, I would check ignition timing as well. Slow crank on a hot motor could be too much initial advance.  You have increased the efficiency of the motor by rebuilding your heads so it may need a different tune than before. I would also suspect starter heat soak as a potential problem.

[70chall440]

He brings up an excellent point, I was basing my suggestions on the assumption that this was a current problem; as in it just started doing this.