Over the past year I have worked out lot of bugs on my SB stroker . The one last issue that has me puzzled is that after driving for 20 or 30 minutes the engine barely turns over. Here are the details:

Motor has less than 500 miles on a brand new build
Everything is new from the builder and ran on a dyno 458hp/497tq
Timing is as follows. 18 deg initial, 16 cent (recommended by prof builder.34 deg all in at 3100 rpm Distributor was sent out and put on dwell machine.
Cam is Comp Thumper Roller. Running temp with new aluminum downflow rad is around 175-180 deg. Engine idles around 950rpm with no issues. When I take the car out it runs great ( has a little surge) but overall runs ad responds great. However when I return to the garage and shut it off and attempt to reatart the starter ( a brand new Powermaster good to 13.5 comp ratio) mine is 9.5:1 , drags and barely turns the engine over. After waiting for 20 to 30 minutes it starts up without issue. Any suggestions as to a solution or remedy would be greatly appreciated.Could it be a timing issue? I might mention that one suggestion was to dial back the timing to 13 degrees initial and see how that works.

Headers close to starter? Heat soak? Once starter cools down, it works fine.

https://www.knowyourparts.com/technical-...-hot-heat-soak/

You don't mention what your ignition setup is but when the engine is hot and "barely turns over" unplug the coil (no spark is what you want), that will eliminate ignition as an issue if it still barely turns over.

If it turns over normal then it's an ignition related issue.

^^^ agreed, unplug & GROUND the coil wire & if no change you might put a 1&1/4" socket on the crank & see how much torque it takes to turn it & you might check the cranking voltage at the starter. Keep us updated. EDIT seperate the dist pickup zigzag connector to disable the ign (be sure to not let the metal (male) tip of the body half of the connector touch ground!)

Our `Cuda used to do this. Is your battery relocated to the rear?

The only thing that fixed our hard re-start in heat issue saw to install double 00 positive and negative battery cables. We cleaned up all the grounds as well by having them all end up on a copper ground strap that led to the negative battery terminal, no grounds on the body. When the battery is fully charged, she cranks right up even after driving around the race tracks in hot weather.

Sounds like the starter is getting too hot and quitting on you.

Our `Cuda used to do this. Is your battery relocated to the rear?

The only thing that fixed our hard re-start in heat issue saw to install double 00 positive and negative battery cables. We cleaned up all the grounds as well by having them all end up on a copper ground strap that led to the negative battery terminal, no grounds on the body. When the battery is fully charged, she cranks right up even after driving around the race tracks in hot weather.

"I agree check this"!

My 67 did the same thing added a ground from motor to frame she starts up right away!

mine did the same thing.it was the ground.i added another and it worked instantly.my headers are only 1/4 in. away from starter.its just a JY mini.

Make sure the relay is well grounded along with the starter.

My 408 liked a lot of initial advance and started great cold but then could barely spin if you needed to re start a hot motor.

I ended up putting a seperate switch (kill switch) on the ignition. What I would do is engage the starter and once it started spinning I’d turn on the spark. Worked great.

I also went through the remote battery needs a ground thing I hooked an old thick beat up arc welder cable from the batt ground in the trunk all the way up to the stud where the starter bolts to the bell.

Yup, this is the first place to start. I did an engine build and then by coincidence my voltage regulator went at the same time. Battery was getting a low charge and engine wouldn't restart hot.