The dyno showed:
Horsepower 448 at 5,000 rpm
Torque 507 lb ft at 4,000 rpm

Timing was set to 35 degrees total. But that was also with an old, points-type distributor - not the distributor that's currently in it.

What was the a/f ratio on the dyno?
Did the carbs have the same jet plates in them?

Unfortunately, no a/f numbers - that function wasn't working that day (a catastrophic failure on a previous test had taken them out).

No on the jets, the carbs have been completely rebuilt and re-jetted since then. The test was run with a ProMax metering plate on the center carb. Since then, I've replaced it with a stock metering block so I can run vacuum advance.

I had a very similar build...same pistons ,heads and six pack. I used a Cometic .027 gasket and milled the heads .020. Has good quench and about 10.4 compression.... I can really put some timing into it. Made 522HP on the dyno. using a Mopar .528 mechanical cam

in my opinion realistic numbers. add a better cam and a couple of degrees timing and it's 475-480hp fairly easy. I don't think upping the jetting on a 6pak is a real advantage. .093" in the metering plates, #65 in the center, .052" for both PVCR and call it a day.

I was having a conversation with one of my customers who works on a lot of these cars in his area.
He was tuning a 440-6 in a Challenger that he had just put the motor together for, and got it running.
He uses a wide band gauge in the car to get them dialed in.
The carbs he was using had the OE calibration, the motor had iron heads set up for proper quench, and a cam that would put the DCR right about 8.0. This car runs ex manifolds.
With the OE jetting(OE metering plates), the motor was in the high-10’s/low-11’s a/f ratio at WOT.
He installed some Pro Max secondary metering plates with jets equivalent to the holes in the factory plates.
WOT a/f ratio was now in the hi-14’s/low-15’s.
It required going up about 5-6 sizes to get the a/f ratio into the mid/hi-12’s at WOT.

We have encountered the same thing on the dyno here when the OE secondary metering plates get swapped for the replaceable jet type.

One of the 440-6’s I had on the dyno, which had small headers, a Comp 280 cam, 346 heads...... ended up with 65 jets in the center carb(mid-13’s a/f ratio at part throttle cruise), and 86/86 jets in the end carbs(hi-12’s/lo-13’s a/f ratio at WOT).
This was a motor that was only making 500tq@3900/424hp@5200.

With regards to the feeling that the motor isn’t as impressive feeling as maybe the OP had hoped.......
Imo, 450hp, 3.23’s, low-ish stall speed, vs carbs, full weight car....... that’s a combo I wouldn’t expect to “feel” all that impressive.

The first 440-6 I had anything to do with made about the same HP, but less TQ by a fair amount than the OP’s build.
It went in a 70 Challenger RT/SE, 3.91’s, tight TA 10”(about 3400), small tube headers.
Owner brings the car down to the shop after getting it installed so I could take it for a little test drive.
First 6bbl I’ve ever driven........ and it’s the first “hot rod” type motor the owner has ever had.
He thinks it’s an animal......... I think it’s more like “eh”.
I told him it should go 12’s based on the dyno numbers, but it didn’t really “feel” fast to me at all.
They had some old slicks mounted on rims, brought the car to the track..... put the slicks on...... went 12.30’s@113.
Way quicker than it felt.

how do you calibrate a "butt dyno"?

You just keep adding power til it feels “right”

When I first put the 383 in my car....... and having not even run the car at all for 6 years...... I figured it would feel pretty decent(knowing that it’s really hard to go backwards, and the car ran 10.70’s on it’s last outing)....... and fully expected it to run solidly in the 11’s.

First pass on the 383........ maybe 1/2 way down the track I’m thinking to myself, “what the he11 is wrong with this thing? It’s a hound!!!”...... and expected to be handed a 12.80-ish....... or maybe even slower time slip.
It ran 11.82.
Next pass..... 11.62.

Butt dyno was waaaay off.

I just had to be satisfied knowing it was running like it should........ it never did feel fast.

guy up the street from me has a big inch Oldsmobile. at the time it was a low 11 second car. he took me a ride and hammered it. my butt didn't fell anything but I thought if I did this a lot my neck would need a chiropractor. if your used to slow cars it ain't hard to be impressed. if your used to fast cars then something just has to reach out and grab you. I went to the NMCA finals in indy last fall. mopar put on a gen 3 hemi shoot out with a 10.00 index. I watched a bunch of challengers run 9.90's and these cars were drove in. makes me fell like some old guy working on flathead fords. for old muscle cars the game is over.

That's the exact message Mopar is sending:
"Sell all that old garbage...we don't sell hardly any parts for them anyway, and go drop 60 grand on our
latest awesome new plastic computerized thing."

It's really not over, it's just put into perspective and now there are more choices (as long as you have a giant pile of money to spend or are willing to go into debt).
The only limit being interest of people, and available funds of whoever works on this stuff in the future.

Does a person want a fun and relatively quick old hobby vehicle with character, authentic old musclecar vibe including a few of the primitive aspects,
or does a person want a touch screen, air conditioned, much more comfortable computerized thing that looks and feels like every other
modern vehicle and admittedly runs faster in many cases?

The old Buick GS Stage 1 didn't become obsolete when Grand Nationals started showing what they can do...."9 second driven to the track" is quite common with those....
The old GS was already obsolete well before that, and the cars still have a pretty strong following. There must be a reason why.

The car hobby is wrapped up with emotions...It's not just about the ET, it's about how you got there and how the thing makes you feel.

I drove the GTX to the strip recently, raced/tested and drove back home... and the number of people who just came up to talk, was pretty amazing.
My youngest boy asked "Where do you know all these people from?". I had to explain that's just normal, but moreso when you've got something
that isn't quite a cookie cutter...

I love the modern vehicles! I drive a 5.7 hemi equipped vehicle every day, and was involved with early Drag Pak sales and development.
But Heritage still counts for something. Even though Fiat has chosen to only trot it out when they can make a profit from it (can't blame them)
it runs a little bit deeper than they know.

I guess it's all a matter of perspective. i'll be 71 in a couple of months. lived the '60's muscle car/drag racing thing. like about anything old, except grouchy old women. my friend with the olds had another engine built over the winter. 540 cubes, 670hp/670tq (bunch of $$$$ of an old guy like me). wants to run mid tens and beat up on the mustangs. I imagine those challengers I saw would run mid tens with the air on. I still ride my old dinosaurs and still get all the looks and conversations, but it's mostly people who lived the era. only thing certain is change.

It truly is a matter of perspective, I have to agree.

Myself I will always love old school the best. But that's just me. One thing about the new cars that are very fast is they all have power adders which makes a huge difference. Super and turbocharging will just about double an engines power. And not everyone can afford to spend 60k on a car. I know for 60k I can build an old car to be a lot faster then the new ones. Heck I think I have a total of about 12k in my 63 but I do all my own work also. And I agree with you Rich that its not all about et but much of it is to some people. Myself I try to look at any car for how it runs for what the combo is. You know a mild N/A 383 Roadrunner that runs 12's with 3.55 gears can impress you sometimes more then a 572 eng in a car running 10's or a turbocharged car running 10's. To me its all about getting your combo to run good for what it is. It is awesome that they are building such fast cars and that in todays world they can warranty a supercharged or turbocharged car since they make them to work so well today. Ron

Did you try disconnecting the vac can on the distributor before you rolled the timing back ?

What is the distributor you are currently running?

Me ?, I'd change the head gaskets as I believe that quench/squish works based on my limited experience... but you first need to figure out what's going on and right now it's pointing to the distributor setup.

Love this thread. I have a similar engine I built for a car I sold 4 yrs ago. Zero deck, Edlebrock heads, KB hyper pistons, etc.
Re the DCR - I found this to be very interesting: http://victorylibrary.com/mopar/cam-tech-c.htm

Not trying to be a butthead, but there is absolutely ZERO reason to use a Mr Six Pack cam in ANYTHING unless you are trying to pass Pure Stock tear down tech…the clown won’t even give specs for it and there are literally TONS of better cams out there…I don’t understand why anyone would buy one?? 🙄🤦‍♂️ He’s NOT a camshaft guru…he’s just taken ONE combination and tried a few different grinds that all have the same lift and found one that works good for that combo…by running his magic cam 😂 all anyone is doing is limiting how good their motor will run…🤦‍♂️