318, made changes, no gain?

Nice Glass said
Riddle me this Batman...

I have a '65 Barracuda with a mild 318.
- 9.0:1 Flatheads
- Mopar Perf 484 cam
- 360 heads
- Thorley Headers
- 3.23 gears

I ran 14.30's-14.40's fairly consistent last year with this set-up. Changed gears to 3.91 and went from 22" to 26" tires for the 1st race this year, really no change. (Pulled a 14.09 but weather was awesome, adj. altitude was 578 ft.)

Changed out the tranny (was running the original in it yet) it's from a '68, still a 904 but with a taller 1st gear, Griner manual valve body (works awesome and sharp) and a 4000 stall converter. I ran anywhere from a 14.60 to a 14.90?!? (Adj. Alt was between 1800 & 2300 ft)

Question here is, is it just too much converter for the motor.
Is there a way to build this a little more consistent, I seem to get wild numbers out of it sometime. What should I be looking for that can throw a really slow number in there or why it will progressively fall off during the day.

What can I change here to get a nice mid-13, solid Sportman class car?

I'm not looking for crazy fast here, just the best, least expensive way of fixing the problems and putting me into the class I want to run.

Thanks!
KC

first why did you go from a 22'' tire to a 26" tall the taller tire will take some of the gear away with the smaller tire that might make the 3:91 run like its in the low 4:00.s give or take a little there is a way to work out how much it well change the big thing is you'd idealy want your tach reading about 300 rpm under make for hp rating not over the cam max hp at what what ever they say it is ( if the cam makes say 300hp at 6000 rpm you should cross the finish line at about 5700/5900 so you motor is still making max hp not droping hp
also you know going to the 369 heads on the 318 you will drop the compression the combustion chambers on the 360 heads are bigger so a loss in compression