i am running headers yes. I never had this problem with the 350, i did a 400 swap (also with the same headers). Put a new starter on, heat shield, new positive battery cable and checked my connections to make sure they were clean. Checked ground cable for good connection and it still struggles to start when i drive it for 30 plus minuets. The whole starter engages and turns over, but it does it super slow and wont start sometimes. have to let it sit for 20 minuets or so. any help would be great.

 

Sounds like a tired starter-

 

But the starter is brand new....

 

Could it be the headers are still getting the starter hot with the heat shield?

When it is cold, or first start of the day, does it lag at all? It could be that you need to shim it too~ does the starter make a LOUD almost whining noise/grind during a hot restart?

 

cant be the headers i dont think, like i said before i had a 350 in there with the same exact headers and it never once gave me this problem, and i didnt even have a heat shield on my 350. it will start no problem when the engine is completely cooled down. and no it doesnt lag and no it doenst need to be shimmed. it doenst grind or make any weird noises (hot or cold starting).

 

Have you load tested your battery?

 

I've had issues with my starter for years.

How much space is there between your starter solenoid and the exhaust?