The 1-2 split of the 3.09-1.92 combo, with my hi-pressure 367 works great.
The Dcr/pressure/V-P in my current combo is about 8.8/180/156
It has been to 9.3/195/169 with a smaller cam.
IMO
with a 340/3.23/2.66 street-combo, pressure is gonna be your best friend. I would gladly sacrifice power at 5500 to get over 3000 ftlbs into the axles at zero mph.
Here's how you work backwards;
From empirical testing. I know that 3000 ftlbs into the axles is about where I wanna be to bust a pair of 295/50-15s loose and roast them. Skinnier tires with no traction-aide, will bust loose with less. Therefore; 3000ftlbs is my target.
3000/(3.23 x 2.66) =349 ftlbs at the crank. If you want crisp take off at WOT, yur gonna have to rev up your engine until you find that amount of torque. Maybe your 340 will make it at 3000; but maybe not until 3500, it depends on the combo of parts you use and specifically on how much pressure it builds. Heaven help her if she can't get there until 4000.
FYI; My 367 makes that almost right of idle.
But say you swap out that sick 2.66 low for a 3.09; Now the numbers are 3000/(3.23 x 3.09)= 300 ftlbs. any 340 should be able to make that at under 3000 rpm at WOT.
But say you don't want have to go to WOT, all the time just to bust them loose. so say you want to be able to do that at part throttle, say at 240 ftlbs, then
3000/(3.09 x 240)= a 4.04 rear gear
But say you want to keep both the 2.66 and those 3.23s. Then
3000/(3.23 x 2.66 )= 349 ftlbs, but you want those to show up at 2200. Well your 340 is gonna need a lotta pressure to do it.
With an auto trans, you could depend on the TC to help the engine, but you don't got no TC so your engine has to do it all-motor style.
So then, how do you build a 340 to make 349 ftlbs at 2200?
IDK but I can guess;
1) it's gonna need a lotta pressure
2) Pressure is your friend
3) It all starts with, you guessed it; a high-pressure design
Ok so what is a high pressure design?
Well you can make pressure a few ways;
1) with cubic inches
2) with a High Scr design
3) with an Early closing intake
$) with forced induction.
However, you have to stay within the limits of the fuel to resist detonation.
Let's say you had a smog era 318 at a true Scr of 8.0, and the stock 240/248/112cam in it, which,installed at 4* advanced it is in at 108. The Ica becomes 48*, and so, the Wallace predicts
at 800 ft elevation; 7.1Dcr/136psi/113 V/P
Lets install that same cam into a 340 still at 8.0 Scr. The Wallace predicts 7.1/136/121 V/P, an increase of 7%, which is the exact difference in cubes from the 318, measured in percentage; therefore a 440 could be expected to produce;
440/318x 113=156V/P and that is exactly what the Wallace spits out, still at 8.0 Scr and 800ft elevation.
Now a V/P of 156 is pretty nice.
So that is how Scr plays out
Lets go back to the 318 and start playing with the Ica
First the stocker at Ica = 48* ; the Wallace predicted 7.1Dcr/136psi/113 V/P
Lets go to Ica of 58, which is just tickling performance. The numbers fall to;
6.7 Dcr/125 psi/ 97 V/P and so the bottom has fallen into the basement.
Lets add 5 more degrees to get an Ica of 63, which is a typical performance cam. The numbers fall again to
6.47/119/89 V/P which is tickling on slanty terrible-tory. So that's what the Ica does with no other changes, it kills the bottom end.
To get the V/P back up to 119, of the stocker, with that final Ica of 63*, the Scr would have to be jumped up, to 10.0 .... to have the sub 3500 rpm performance to be about the same as ... stock. And where do you think a 318 street car spends the vast majority of time? Yeah I'll bet under 3500. So don't put a big cam in a stock 8.0 Scr 318. Not ever.
So now we get to the 340..
Say this one is already at 8.73Scr, and has a stock 340 cam in it with an Ica of 64*. The Wallace kicks out;
Still at 800ft,
a Dcr of 6.99/pressure of 133psi/ and V/P of 105; which is back in the basement; under no circumstances would I build one of those. Ok but say you really wanna use that stinker of a pressure robbing cam, and yur still looking for 349 ftlbs at 2200rpm. I'm gonna say; that will never happen with the Scr still be low enough to run pumpgas, But, let's work the calculator anyhow. At 10.0 Scr the Dcr is topping out at 7.99, the pressure is topping out at 159psi, and the V/P is up to a whopping 126/lol. This is less than a stock 5.2 Magnum, so that is as much as you can expect with that cam and best pumpgas. Will it spin the tires? yes I think so, but a Doubt it will make 349 ftlbs at 2200, so yur gonna have to rev it up to get the numbers.
So in that iron-headed combo, the bottom-end is still seriously soft; and keeping it a 340, and naturally aspirated, typically, you only have one other choice, which is to slam the intake closed sooner.
But IMO, it's not gonna work at the modest 8.73 Scr
Lets try 58 degrees , and max the pressure again to 160psi.
The best the Wallace will do is at 9.6 Scr, and I get a Dcr of 8.0/159 psi/132V/P, which IIRC is about what a 5.9 Magnum musters, so you know, ho-hum; and 5.9s do spin skinny factory tires.
Will it make 349@2200? Yes I think so.
The downside is that the 58* Ica, makes for a low power-peak , which is a kindofa waste on good heads. You might as well put small valve stock iron heads back on her.
So what's the solution?
Well, I know that my closed chamber alloy heads do NOT detonate on 87E10, at up to 195cylinder pressure, even running a constant coolant temp of 205*F, which allows me to, with an Scr variable from by gasket changes from 11 to 11.3, run just about any Ica from a low of 54* to a high of around 72 degrees; which is a heluva thing.
Therefore, I have no trouble recommending alloy heads and high pressure.
This should make the required 349 ftlbs with ease, even at 2200; even with the 3.23s and the 2.66 box. So the money you save NOT BUYING gears and/or an overdrive, you can stick towards alloy heads. And who knows the hi-pressure combo may run even less gear than 3.23s.
Mine, a 367, has pulled 2.76s for a short time .... allbeit with the 3.09 low, lol. That's a starter gear of 3.09 x 2.76= 8.44 which compares to your 2.66 box x 3.23s = 8.59, hunh! IDK if I ever smoked the tires with that combo. It wasn't in there for long. I was testing for something else.
BTW
If you are stuck at 8.73 Scr because of budget constraints, then there is notta chance I would spend the coin on alloy heads, because the cost to satisfaction ratio is just not there no matter what cam you put into that engine.
The smallest cam I would consider is one that can be installed at say 53* Ica, at 800 ft elevation, this works out to a
Dcr of 7.56/pressure of 148psi/and a hu-hum V/P of 138. But the cam I would choose would be a Tight LSA design of say 106*, to get some decent overlap back, to extend the operating rpm at the top, cuz that's gonna be a pretty small cam.
Here's my cam guess; 262/268/106 in at 102, will get you an Ica of 53*, and overlap of also 53*; yeah that should work. Yes it is pretty small, but still being about 3 sizes bigger on the intake than a stock 360 2bblcam, which IIRC was 252/256/112.
A V/P of 138 is about as low as I would suffer.
altitude loss looks like (pressure and V/P)
at 800 the numbers are ........... 148/138 V/P
By 1800 the numbers are ......... 142/133 V/P
By 2800, she be down to;.......... 137/128 V/P
by 3800, the wheezer is down to 132/123 V/P
So looking like dropping about 5 and 5 per 1000 feet.
If the client is not running headers, the overlap is not helpful, so you can run a 110 cam but you will quickly lose pressure/VP again. With that same 262 cam now running a 110 Lsa and in at 106, the Ica becomes 57*; and the Wallace spits out,
142psi/119VP ....... so you know, I wouldn't do that; I'd install headers and pick up the power over the nose.
Happy Hotrodding
