340 max camshaft with exhaust manifolds

IMO
you are trying to marry race-engine design parameters into a street package, and just need to rethink it a little. Move your trapspeed from 108 mph to 65 mph, and then things will fall into place pretty quick.
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Ima thinking, on the street with an automatic, 4.30s and 26s will get your 340 singing to the tune of about 11.2 mph per 1000 rpm in Second gear; so 6000=67mph, or 7000=78mph; @10% slip in the TC.
How often are you gonna be in that zone?
Why cam your engine for a speed zone you will almost never be in, and thus sacrifice a really big chunk of low to midrange torque?
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Imo
what I want in a Saturday-night Warrior is power on demand, at the speeds I will normally be at.
Since first gear, on street tires and on the street, is practically a throw-away gear, there is no need for race gears, cuz; unless you throw sub 3.00 gears in it, it's still gonna light those 26" tires up. So really, First gear is just a means to get to Second gear. Cuz, second gear is where yur gonna spend most of your time.
And so, IMO, you need to consider what roadgear you want to be in. For instance with a TF trans the ratios are 2.45-1.45-1.00 and with 4.30s that gets you Roadgears of;
10.54-6.24-4.30.. But guess what, with 2.45 gears the numbers are
xxxxx-6.00-3.55-2.45; check out 6.24 versus 6.00, which are as good as identical. Say you want a lil better than 6.00 gear, say 8.00; like
8.00/2.45=3.23s. The new Roadgears are;
xxxxx-7.91-4.68-3.23 Compared to the 4.30s at
10.54-6.24-4.30
As you can see, the 3.23s give you a better gear at say 30 mph and a better gear at say 60 mph, than do the 4.30s; but, I admit, the 3.23s sacrifice the tire-frying 10.54 starter gear which to me is hugely excessive with an automatic, anyway.
Thus the Roadgears will dictate the cam.
Say you did go with 3.23s; with 26" tires this will get you 14.9mph per 1000 rpm@10% slip in Second gear; so 4000=59.5mph. A tad low I'd say, for your intended usage.
Say you wanted to top out around 60mph= 5800. Thus you would need 3.23 x 1.45=4.68, rounds down to 4.56s; and those will get you, 61mph @5800@10% slip.
allowing 300rpm overspeed, your cam could be running down the back of the power curve starting at 5500, and the powerpeak could be at 5300.
Sounds like a good number for a 340, so in the FTH world, that would be about a 230* @.050cam.
Now you are married to those 4.56s.... just to get the
Roadgear of 4.56 x 1.45=6.61.... which you could get
in FIRST gear with 2.76s, for 61mph =5870@10%slip
Now:
I'm just throwing the numbers around so you can see how one thing plays off another.
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For a 340; any starter-gear over about 8.5 with an automatic and a modest stall, is gonna satisfy First gear. 8.5/2.45=3.47 rounds to 3.55 gears. So 3.55s are gonna be your minimum targeted rear gear. 3.23s will also work, with just a lil more stall.
The smaller your rear gear is the sooner up the rpm band the car will hit 60 mph, and so the lower the power-peak can be....... which will pump up the midrange power. For a streeter that does not do 1.8second sixtyfoots no matter what the rear gear is, race-gears are not the answer.
IMO; The right gear in a Saturday-night Warrior is the one that gets me power on demand, at the speeds I will normally be at. And the right cam is the one with the most average power in that speed range.
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Now here's a secret; in terms of gear-ratios, the Four speed is a better street trans, in as much as it has a second gear ratio of 1.92, so getting that 6.61 Roadgear requires a rear gear of 6.61/1.92= 3.44s which is why my warrior has 3.55s in it. But, your 340, without a Convertor, now requires a lil more than 8.50 starter gear. and 2.66 x 3.55=9.44 may not cut it. The Commando gearset brings a 3.09 low gear to the party, which will get you
3.09 x 3.55= 10.97 which is on the money.
With 26s and 3.55s, Second gear will now get you 61@5400...... BadaBoom! Now you can use a cam that peaks around 4800 to 5000, which again, in the HFT world, is about 220*@.050
I know I didn't answer any of your questions; but; at these modest cam sizes (220 to 230 @.050, and sub .500 lifts) I see no good reason to eschew FTHs, unless your 340 has a really low Scr .
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My favorite all-time FTHcam in my 367 was a 223*@.050. Gobs of power beginning at under 3000rpm. With good heads, a free-flowing exhaust, plus headers, I regularly beat that lil cam to 7000rpm and beyond.

BTW;
on the street, no 340 will ever pull 955 cfm in street trim, normally-aspirated, with a .500 lift or less cam, and with 340 manifolds. 600cfm is likely to be adequate, 700 leaves room for growth. The cfm rating is relatively meaningless at street-rpms. In most cases you will only ever go to the rev-limiter once below 60mph, and that will be in First gear, with the tires on fire, so the engine will do that with a big 2bbl, never mind a 6-Pac. As soon as the auto-trans shifts into Second, the rpm will fall to 59%; so say from 5800 to 3420, and any 4bbl will be big enough there.
Happy HotRodding