Build suggestions for 340?

This work-up is for a manual trans streeter.
Keep your eyes on the cylinder pressures and V/P ratios
All calcs at 800ft elevation

>Here is a stock-cammed 318LA, Ica of 48*
Static compression ratio of 8:1.
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 7.10:1 .
Your dynamic cranking pressure is 135.60 PSI.
V/P (Volume to Pressure Index) is 113

> the 340@268cam mightta looked like, Ica of 64*
Static compression ratio of 10:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 7.98:1 .
Your dynamic cranking pressure is 158.75 PSI.
V/P (Volume to Pressure Index) is 126

>same 340@268cam,blue-printed to 10.5 Scr,Ica of 64*
Static compression ratio of 10.5:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 8.37:1 .
Your dynamic cranking pressure is 169.18 PSI.
V/P (Volume to Pressure Index) is 134
notice the changes in VP and pressure, from just a half a point of Scr
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from here down all are in a 340
with the 292/292/108 cam

> in a typical 1970-up stock 340; Ica of 70*
Static compression ratio of 10:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 7.60:1 .
Your dynamic cranking pressure is 148.68 PSI.
V/P (Volume to Pressure Index) is 111
The bottom end feels like a 318LA (see the 113VP above)
and the pressure is low, even at 10/1; lets pump it up

>blue-printed to 10.5, Ica of 70*
Static compression ratio of 10.5:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 7.96:1 .
Your dynamic cranking pressure is 158.21 PSI.
V/P (Volume to Pressure Index) is 118
still a low VP, and the pressure is close to the max for open-chamber iron heads; it's starting to feel like a 5.2M; Lets pump it up some more

>here it is at 165psi, Ica of 70*
Static compression ratio of 10.85:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 8.22:1 .
Your dynamic cranking pressure is 165.15 PSI.
V/P (Volume to Pressure Index) is 123
pressure maxed; feels like a 5.2M at low rpm

>cam advanced to 108*, for Ica of 66*,
and maintaining 165psi
Static compression ratio of 10.5:1.
Effective stroke is 2.52 inches.
Your dynamic compression ratio is 8.22:1 .
Your dynamic cranking pressure is 165.15 PSI.
V/P (Volume to Pressure Index) is 128
pressure maxed, she is feeling a lil stouter than a 5.2M..I'm not a fan of this much cam advance for this cam, in a street engine; it kills overlap, and annihilates any chance at fuel economy, because the extra degrees come straight out of the power stroke.

>Finally, let's slap some closed chamber alloy heads on it, with flat tops. Put the cam back to 102, and pump it up. This will make the combo come alive.
Static compression ratio of 11.7:1.
Effective stroke is 2.38 inches.
Your dynamic compression ratio is 8.68:1 .
Your dynamic cranking pressure is 177.54 PSI.
V/P (Volume to Pressure Index) is 130
compare this VP to the stocker at 126, or the blueprinted 134. Now you more or less have a stock-feeling 340 below 3000. This is more important for a manual-trans car like mine. And of course at WOT, it is ridiculously 292cam strong thru the power curve.
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now in my 367

> and of course, my engine is a 367 and in at 104,
the 292/108 looked like this
Static compression ratio of 11.3:1.
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 8.60:1 .
Your dynamic cranking pressure is 175.38 PSI.
V/P (Volume to Pressure Index) is 142
Which was NOT happy with 3.55s and a 2.66 low gear. I was very disappointed with the bottom end, and with the powerpeak up at 5400, this was at; 45mph in first, 63 in second, 86 in third. The biggest problem for me was the slowest speed I could drive w/o slipping the clutch, was about 5.8mph with typical Idle-timing. She really wanted one lower gear. I sold it to a racer and yanked it out.He was a happy guy.

>I replaced that cam with a higher lift, 270/276/110 cam,
dropped the Scr back, and got this;
Static compression ratio of 10.7:1.
Effective stroke is 2.88 inches.
Your dynamic compression ratio is 8.80:1 .
Your dynamic cranking pressure is 180.79 PSI.
V/P (Volume to Pressure Index) is 160 Whoa!!
Notice the VP, now ~15% larger, like swapping the 3.55s out for 4.10s. And this is the combo that got me 32 mpgs point to point, on a certain roadtrip........ with a double overdrive ......1.97 final drive, and 75= 1950rpm....... With a 3.09 low, and a lil idle-retard, the slowest no-slip speed was now 3.8 mph.
Badaboom! what a ripper!! Never looked back.
I no longer care about horsepower, swapping instead to torque, and TM (Torque Multiplication). Especially at low rpms, cuz over ~90% of the time, my engine is running under say 3400rpm. I mean with a VP of 160, it don't take a lotta throttle to getchit done.
>When this 270 cam dropped lobes I installed the next bigger cam from the same manufacturer, a 276/286/110 in at 106 for an Ica of 64*,lowered the decks a tad for a lil more squish, and got this;
Static compression ratio of 10.95:1.
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 8.75:1 .
Your dynamic cranking pressure is 179.44 PSI.
V/P (Volume to Pressure Index) is 154
whoops lost a lil VP, but gained a bit of useless power at high-rpm, which got me a 93mph in the Eighth, Badaboooom!, and it still spins the 295s to 60mph or more.


BTW; this Alloy-headed 367, in all three iterations, has never burned anything but 87E10, and has always run 32/34* Power-Timing, slightly delayed to all-in at 3200 to 3400. And, I run a 22* V-can, coming in as fast as possible. And when the tires are spinning, the tach runs up to just under the rev-limiter at 7200 and just stays there, until I lift. I asked my son to run it by me one time like that, but he, polite boy that he is, declined, so I only have his say-so as to how awesome it sounds, screaming thru the dual, three inch, full-length, cannons; your results may vary. lol

OP
I'm not suggesting you install a 292/292/108 cam in your open-chambered, iron-headed, 340. By the numbers above,you can see that below 3000rpm, your 340 will become lethargic due to lack of pressure and most especially VP. With a 4-speed and 3.23s, you cannot afford lethargic cuz your engine is married to the tires, with no hi-stall TC to help you. Your only option at that point is to slip the clutch to spool up the engine to where the power is. And of course, slipping the clutch only translates the excess power to heat...... or if the tires spin,then to smoke,lol.
I can pretty much guarantee you that a 292cam in a 10/1, open-chamber, iron-headed 340, with a clutch and 3.23s, is about the worst combo,that someone could throw together, in a streeter; second only to it being in a smaller engine,or with less rear gear; no laughing matter.