That's a bogus test, cuz the TC was not fully stalled, on account of the car was already moving. However, it proves the TC is probably a stocker. And the 340s were rated at 2350 +/-100; so you're in the ballpark of stock.
The chirp into second kind tells me one of three things; 1) the rpm was not high enough to continue the spin, or 2) the car has exceptional traction, or 3)
the low rpm power is already soft...... cuz with 3.91s it should be spinning both tires pretty much all the way through second, or at least 55/60 mph. 55 is about 4200rpm and so a little past peak torque, so yeah a healthy340 should do that easy.
Since yours does not, it speaks to the 152.5 average psi being correct. And so mandates the LD test.
Here's the deal, working the formula backwards to get 152 psi, the Wallace calculator says that your compression ratio is about 9.8, and her VP comes in at a soggy 117. The factory cam is a 268/276/114 with an ICA of 66*, in at 112.
The next bigger cam,one with just a little attitude, could be a 274/282/110
in at 108 the LSA is 65*, and now the VP climbs to a little less soggy number of 120
meaning......................... the power to about 3000/3500 will be about zero difference. The power difference won't be significant until late in the 3000s and peaks at about 5400. So lets say you begin to feel something at 3600, that would be 28mph in first, and 5400 will be 42 mph. and the shift will come about 6000/47 mph. Then the Rs will fall to 3551, and you start all over, in a part of the curve, where she is likely making less power than the current cam.So now in second, she struggles to about 4000/53mph, and then begins to take off again. By 60 she is getting on the pipe at 4500, and 65 will be around 4900. The powerpeak of 5400 is not reached until 71mph
So, this cam is working, and making more power than the current cam, from 28mpg to about 45mph, and again from 53 to 71. This is calculated using your 153psi.
Rub #1;
your 340 should have had 165psi@128VP with the current cam. If it would have 165psi, it would likely smoke that 274 at 153psi, especially below 3600/3500 . It would make about the same absolute power as the 274, but it would have a broader powerband , more suited to an automatic, and so it would make more average power. And the hotter VP number indicates a slightly stronger bottom end, about plus 7% And of course with just 44* of overlap, it will burn less gas than the 58* of the 274* cam, at lower rpms. On the hiway they'd be about the same with both pulling 65=3200@zero-slip.
Rub #2;
the rumpidy-rump is caused by overlap period, and the factory cam has 44* of it, so you know what that sounds like. The 292/108 in my 360 had 76, and it was quite noticeable.The 58* of this theoretical 274 cam is right up the middle..... but my current cam has 61* and at 700idle I can hardly hear it. Even when I drag it down with the clutch,it is just noticeable, soooo
I don't think you will be happy with the above cam.
That means you will be wanting a cam with more than 58* of overlap, and that is when things rapidly take a dump. Your engine does not have enough cylinder pressure for that,with the current TC, unless the LSA is really tightened up or if you go to a solid lifter cam with earlier closing intakes.
And that is why I keep coming back to the LD test, to prove you still have an engine. It may be that the LD proves your 340 is healthy, and that maybe the compression tester reads low, and then all is well. But it could also be that the cylinder pressure is leaking every which way, proving the compression tester is right, along with the 1-2 chirp.
Theoretically a 10.5 340 should have 165psi or more. If you gauge is right at 152, then you have 152/165=92% of what it should be. That is an 8% loss. That is at least as much power loss as the next bigger cam will get you; at least.IMO, you really need to look into it, even just to be sure.
