What's the max timing for a hp 500 efi? I know that it's over 3500 rpm but how much advance should you have? The manual says to set it at idle but that doesn't work for me I want to set it at full advance and then check it at idle. Thanks for any help.

set it for 34-35° but its may not match what the table says or the scan tool.if you want it right,have it retuned.

When you set base timing at 8 degrees with timing tool the timing at 5000 rpms and up at 100 map is 35.9, you will not easily get motor to 5000+ at a 100 map to set timing unless you are on a dyno. The curve is kinda lame from 3800 to 4800 at 100 map but on dyno with a 502 w iron heads and 500efi cam best peak hp was at 36 degrees at 100 on 89 octane, lost hp at 38, even on 93 octane.
IF you jack up base timing to gain more overall timing keep in mind you are adding that amount everwhere, ie IF 70 or 80 map timing is 39 or 40 degrees and you jack base 4 that table becomes 43 or 44

Set it 8* base and let the ECM do the rest. If you want it tweaked so you can gain maybe 10hp, send the ECM to Whipple.