Help determining 340 cam
thank you that is soo much more than i thought'd get i appreciate it
My computer stalled, I wasn't finished lol.
Part 2
How much P/V do you need?
Well that kindof depends on how LOW a stall you want to run. If yur running a 3000, then you don't care. But if a 2200 then the more the better.
By my experience, with a manual trans, over 160 is really nice.
Personally, having experienced over 160, I wouldn't run under 140 ever again, but I have a manual trans so there are many many times , maybe most of the time, that my engine is in that 1800 to 3000 zone. In fact, with the generous P/V, I usually shift at 2800, which drops into Second at 1740, yes my 367 is a bit of a tractor.
How do you change your P/V ?
In a given engine, there are only two ways; changing the Scr (Static Compression Ratio), or changing the ICA (the Intake-valve closing angle).
Going back to your 10/1 340 still at 800 ft, lets install a cam about two sizes smaller that has an Ica of 57* ( from 64* previously). And the pressure rises to 169, with P/V rising to 142, very nice.
Next, lets put the 340 Cam back in it, but increase the Scr to 10.5, And the numbers come to 169psi and 134 P/V; almost as nice.
Except you cannot normally run these pressures with iron heads on pump gas.
Now, lets say you switched to a cam with a more narrow LSA than the 114* of the 340 cam. Lets say a 108, how can we fudge the numbers into a pressure that we can run, with as much P/V as possible?
I'm glad you asked.
here is the factory cam showing all the events
268/116 comp/104 extraction/276ex/44* overlap/ 114Lsa/64* Ica. Next
268/120 comp/112 extraction/276ex/56* overlap/ 108Lsa/60* Ica. same cam except Lsa tightened up
So, the Ica has changed to 60 from 64 and still at 10/1 and 800ft elevation;
pressure jumps to 165psi@P/V of 135 here yago. This is about the max pressure you can run on pump gas. and even this will require a tight Quench design. But the P/V is creeping up to the magic 140 that I kindof like to see.
Now about the numbers;
the extra 4 degrees of compression, is where the pressure increase comes from.
the extra 8* of extraction, is gonna take the 340 out of the realm of gas-hog, and into the realm of having the potential of making reasonable hiway fuel economy.
Intake and exhaust are the same.
The overlap jumps from 44 to 56 which, with headers has the potential to add a big old hump in the power curve, the downside being a more narrow powerband. Do you care? No Because the increase in pressure will make up for it, as will; at under 3000, the 9 points of additional P/V, now 135 up from 126 .. This will allow you to run less stall.
So what is the downside to the 108? besides the slightly more narrow powerband; there are two;
1) the jump in overlap is gonna require a higher cruise rpm to slam the door on reversion, which negatively affects fuel economy. But with 3.23s this is NOT an issue; and unless you get an overdrive, it will NEVER be an issue.
2) the TorqueFlite has ratios of 2.45-1.45-1.00, with splits of .59/.69
That 1-2 split of .59 means that whatever you rev the engine to, on the 1-2 shift, the Rs will fall to that percentage. This 268 cam might have a powerpeak at around 5200, and a shift rpm of 5500. So, shifting at 5500, the Rs will drop to 3250, which is a powerband requirement of 2250rpm; pretty enormous. Well; that 108LSA cam is not gonna cover that, so on the shift, the engine will definitely fall off the cam, meaning, at 3250 in Second gear; she needs all the help that you can give it.......... and we did! We pumped the pressure to 165, tightened the Q to .040 or less, and if it's still too far off the pipe, just rev it to 6000, and come in at 3540; easy-peasy.
Disclaimer;
I'm NOT saying you should run a 268/276/108 cam!!
This is just a study to show you what can be done with the Ica and Scr to maximize your combo.
The 340 has enough cubes that it does Not necessarily have to be at optimum, in a streeter, to still be a lotta fun.
Finally, with alloy heads you CAN pump the pressure up to 185psi and STILL run 87E10/
Jus saying. And that will get you a boatload of flexibility in cam choices. I once ran my combo up to over 190psi@176VP, which was insanely fun. I ran that with a double overdrive, and geared for 65=1600; dressed like that, my 367 pulled over 30 mpgs, on one certain daytrip. That's what a VP of 176 will do. Those alloy heads paid for themselves in just a few years as installed on my DD.
BTW;
the 8/1, 318LA makes about 136psi@113P/V @ the same 800ft, just for comparison.
