70 dart 470 ci drag car build.

PRH said

What I find fairly often, when running the timing locked out, is that when you’re hovering around whatever timing is giving the best results, is that slightly retarded will often make the peak TQ numbers better than the setting which yields the best HP number.

And then there’s the combos that are almost impervious to the timing unless you make a fairly big change.

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I have a very heavy spring tight unlocked curve and what you explained about the locked is pretty much what my engine is doing too. We had 24 in yesterday and it really struggled to get up to 6300 from about 6000, and I backed it down to 20 it ran hard through the pull, added 1 more degree of timing and it loved it all the way across the pull.
I was running 18 to get a good pull with the fairly restrictive dyno exhaust system.
It's about a 20 hp difference in peak but picked up everywhere besides 3000-3300 where it loses 5 ft lbs.