1) Well, that's too bad we can't know which purple, but there's enough information in this last post to know that your combo suffers from the triple failure of not enough compression, not enough stall, and not enough gear; ALL THREE.
Pretty much any "upgrade cam" to a 318, in an 8/1 stock bottom end, with uncut big-port heads will be soft on the bottom. Actually even the stock teener cam is already soft with the factory 2bbl heads,lol.
2) One thing comes to mind; you said a 340 Purple cam. The common factory 340 cam was a 268/276/114 .429 lift cam. You might already have a similar cam. The equivalent Purple 340 cam is P4452761 with specs of 268/272/110, and .450/.455 lift. But,you can't easily prove that.But you can easily check the cranking compression.
I highly recommend a compression test to see just how bad it is.
To make the 318 come alive, it will need cranking compression up near 165psi combined with a LeakDown no more than 4%. Your hot 318; hates 110,120,130,strongly dislikes 140,150 and probably 155 too.
3) IMO the 268Purple is about as big a cam as a street-318/automatic should go.
And this 268Purple WILL work(sortof) with the 2500TC, but it still won't like the 3.23s very much off the line, and not at all at the track cuz it's still a two-gear run. You need to use all three gears to ET well.
And wonder of wonders, this 268*cam wants a compression ratio of just 9.8, which is a total chamber volume of 74.4 cc. Since there may be 11cc in the deck clearance; with a thin gasket of 4.5cc, the heads will now need to be 58.5cc. While I suppose you could cut your J heads down to this, there are other ideas
4) Your current chamber size with factory uncut parts is probably around 92cc. To make the 268 cam happy, this needs to get down to 77.4; so you can see the problem, I think. I'd be surprised if the current combo could muster an 8.0Scr.And that coupled with a 60* ICA spells around 125 psi, and that would make the teener take off just a little stronger than a slanty, if it was married to a clutch.
The 2500TC will get it thru that dead-zone a little better, but then the 3.23gears keep the rpm too low for too long, and it just becomes a huge disappointment; I know exactly what you're going thru, having gone thru this many decades ago. The power didn't really come on until she was into the 4000s, and the valves floated at about 5500, and shutting down that early, while she's just waking up, makes for a disappointing run, to say the least. But it did have dynomite passing power, I'll give it that.
5) To get the total chamber volume down, I see three options:
Option 1; is small-chamber heads,on a zero deck block. The stock teener has pistons waaay below the decks, sometimes in the range of .050 to .060. This is about 11 to 12 cc. We have to get rid of that. But hang on; in conjunction with machining the decks .050 or more, you would also have to machine your J heads way down and when you bolt this all together, you will find out that the intake will now also have to be machined. And so that's a lot of set-ups and a lot of machining costs. AND having it all fit and not have leaks when you're done, is sortof a crapshoot.
6) Option 2; is pop-up pistons, with the current open chamber heads, and no machining.. The KB-399s are a good solution, and they will allow you to get the squish up into the effective zone, possibly allowing you to run one grade lower gas. And all the factory parts go together pretty good without any machining.The bonus of that is that if you blow it up, you don't have a ton of money in the machining which you can never get back.
7) Option 3;Some guys have put a small-main 3.58 stroke crank into the 318. This pops the stock pistons up, 1/2 the stroke difference higher, which is .133 inch.This could bring the stock pistons up out of the holes maybe as little as .076, depending on the year of the 318.I haven't done this, and I think the top ring might be a little close to the top, so you'd have to measure and be ready to spring for new pistons,again. You could make this work with open-chamber heads and the right head gasket. And the bonus outta this deal is, you get 345 cubes,(an extra 23 cubes over your current 322).
8) So there are three possible solutions if keeping the 318. Oh and to ET well,you'll still need some gears. But you won't absolutely need them for the street.
But you should know,that IMO the best solution is a taller piston,and that if you decide to install pistons, it will cost about the same whether you do it, to either your 318 or to a 360, and altho the 360 will have a fair bit stronger bottom end strictly due to the cube difference, you may still have to change the TC and for sure the gears, to take advantage of the new combo, at the track.
9) You can bandaid the teener as it is now,with something like 3.91s and a 3500TC and it will be waaay more fun to drive, but it won't change the trap speed much cuz you haven't changed the absolute power at all. Your average power will be up some with the 3.91s; but they are really not the right answer for the quarter. The engine will still not be in the power-zone going thru the traps with 3.91s, and it still is waaay late getting onto the power, the ET won't change much either. So the bandaids would just make it funner to drive.
10) Cheer up;I'll bet that with the 3.23s you were still in second gear running thru the traps.The math says around 5600.Which with a 268* cam isn't that far off the mark, but running the strip in just 2 gears, I'd have to say that 94mph is pretty good with that combo.
11) Parting shots
A) But if you put all your top end and cam into/onto a zero-deck 365, And assuming the heads aren't junk,she might go 106 easy enough..... and at 3330#, that is 320hp, and that could be 12.5 with SSsuspension, maybe just sneaking into the 12s with street suspension. You want faster/quicker? It gets expensive in a hurry! Get you some hi-flow heads and upsize the cam AND bringing the compression along with it, and you'll be in the mid twelves. Make it hook, and into the 11s you go.
B) But I just gotta say one thing; A 360 powered car that goes 12.9 with street suspension is plenty fun on the street. The cam is still small enough that the 360 can break Swinger-sized tires loose, with 3.55s, even in second gear, almost any time after 3500 rpm. Which, if you have a 3500TC......DOH....... is just about any time at all.
But you, set-up to run the Quarter, will be running at least 4.30s, so..........you're gonna have to spend more money; spinning ain't winning..
C) I stopped setting up for the Quarter, years ago;the gearing is just all wrong for a streeter. And I'm getting too old to be swapping chunks all the time. So I set up for doing the 1/8, and let the qtr be what it will be. I'm happy just knowing from the Eighth numbers, what the Qtr might be.(online calculators). A 106 qtr is about 85 in the Eighth. So perhaps set your car up to go 85 at about 300 or so rpm past peak power, in second gear and call it done. This will be about 3.23s for your assumed-to-be-268 Cam. This will get you about 5400; just a little low perhaps, but you already got 'em...... 3.55s would be 5900, and..... 3.73s are 6200.
And 3.23s are a good cruiser gear. And they're a perfect gear for going hammer down into first at 32 mph.That's an instant 3400, so who cares what the stall is, we got TM. Yeah the starter gear is a little soft at 7.91,but give that combo a workout while your tuning for the new compression ratio. Maybe you'll kick the 3.23s to the curb..... but maybe not; especially if you go 360,then leave them for a while.
Happy HotRodding!