Slow cranking (not only when hot)
 

The last few times I've had the GTO out I've noticed that it cranked VERY slowly when starting, whether cold or hot (actually needed a boost the other day to get it fired back up). Motor is a RAIII 400 w/ RAIV cam and just over 4K miles since restoration (everything is new/rebuilt). Cables are 4GA, all grounds are in place and check out with <1ohm resistence back to the battery. Battery is a Optima Redtop 800CCA, 1000CA and I assume was new when restored in 2008.

Battery voltages seem ok when running (~13.35V) and at rest (~12.7V). When cranking however, the voltage dips down to ~9.6V, which I believe may be too low? I plan to have a load test done on it, but I am leaning towards a battery issue (which offers a good excuse to get a maintenance-free R59 and spring-ring cables)

When we tested batteries, anytime it went under 10.0V when cranking or under load, we would call it a bad battery. Make sure it is fully charged before testing.

Sounds like the starter is drawing a bunch when hot or the timing is too far advanced.:)

Thanks for the replies guys. I brought a clamp-on home from work to check current draw and also need to check the timing, but haven't had a chance. Will also get that load test done before I make a final call on it.

Just an update - the battery checked out through two load tests fine with well over 900CCA @ ~13V. Timing was a touch too far advanced @ 15' BTDC so I dialed it back to 12' BTDC, however this didn't help with the starting issue.

I finally had a chance to get the car jacked up and have a look underneath this morning. The starter connections were a touch loose, however the main issue was the ignition wire was close to the block and the insulation had worn/burnt off causing a partial short. Tightening the connection rotated the connection away from the block, (which is how I noticed) and resolved the problem.

Thanks again for the suggestions guys :)