Disappointing ET's with 408 - UPDATE

My 2 cents...

Don't waste your money on a header upgrade unless you go to a full length 1 3/4 or 1 7/8" tube header. They hang down and suck for driving on the street. Stay with the hang down hookers you got for the moment. Dougs and tti fit better, but you won't see any significant performance increase with either set up. Especially for the money they charge---BTDT You say you have 2" pipes exiting the mufflers... can that, as it's a restriction point. 2.5" all the way out the back is what you need or turn them down right after the muffler.

Work on the fuel system to insure adequate delivery. 3/8 minimum from sender forward. A 750 proform just isn't big enough to feed that beast.

Get the distributor timing/advance curve figured out. Simple as a spring change, but a pain on some mopar distributors.

Get it so it will hook. Work on leaving at different RPM's to see what the car currently likes. I had a car that ran 9.40's and it hated to leave loaded on the convertor. Load it against the verter and it would act all funny, left lazy. Leave at 1500, stab it, and it would stand on the bumper w/ 1.30 60'. Your car should run very low 12's pretty easy, IMHO. It should run 11's if you can get it to leave hard. If you could get it to 60' in the 1.4-1.5 range, that will pull roughly 1 second off the big end.

That engine should make close to, or exceed, 500hp when dialed in. I have a 360 with mild ede's ported, juice roller, slightly less duration, more lift, that we expect to make right at 500hp.

Best advice I ever got and live by to this day... Over-chassis and under-motor. Get the chassis sorted out and the car will ET regardless of engine. Lots of guys just throw more power at a car that doesn't work. Yeah they eventually go faster, but, with a working chassis, it's much easier. It's fun to watch a 450-500hp car that works take out a 700+ hp car with a bad chassis. Happens a bunch.

If possible, CHANGE ONE THING AT A TIME using a scientific approach. That way you know if THAT change was positive, negative or same. If you change more than one thing at a time, you have no idea which change was beneficial.

It's a work in progress... make it fun, a learning experience and keep a log book of changes. That way you know where you've been.

I did a quick deal using camquest and it came up with 484hp at 6000rpm and 494tq at 4500 using some rough guesses of what you have XR286HR and ede's with 250-260 flow. It improved to 499hp using a 950hp carb