Your facrory cam choices are
1) The 273 2bbl cam; 240/248/112 ,this is same as the 318cam
2) the 360 2bbl cam; 252/260/112
3) the 340........cam; 268/276/114
Read about VP here; V/P Index Calculation
For the following exercises,all cams are in at split overlap,
1) Just for kicks, here is the 273 with the factory cam, ICA of 50*
Static compression ratio of 8.0:1.
Your dynamic compression ratio is 7.04:1 .
Your dynamic cranking pressure is 135.24 PSI.
V/P (Volume to Pressure Index) is 96 .....................................factory... 96 ..
1B) same 273,A/A, with more compression
Static compression ratio of 9.2:1.
Your dynamic compression ratio is 8.07:1 .
Your dynamic cranking pressure is 161.70 PSI.
V/P (Volume to Pressure Index) is 115 ............................................... 115 ..
This is about as good as a 273 2bbl cam gets
This level of VP should be your target, This should be reasonably peppy........
even tho..........,Oh well;Put a 4bbl on this and a free-flowing exhaust, headers optional, and it will be super-fun with 3.91s.
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2) Here is the 2bbl 360 cam, in at ICA of 56*
Static compression ratio of 8.0:1.
Your dynamic compression ratio is 6.79:1 .
Your dynamic cranking pressure is 128.93 PSI.
V/P (Volume to Pressure Index) is 88.................................................... 88 ..
This is pretty doughy
2B) That 360 cam wants more Scr.
Static compression ratio of 9.5:1.
Your dynamic compression ratio is 8.03:1 .
Your dynamic cranking pressure is 160.66 PSI.
V/P (Volume to Pressure Index) is 109 ................................................ 109
This is as good as this combo gets
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3) At same Scr of 8.0 the 340cam,in at ICA of 66* looks like
Static compression ratio of 8.0:1.
Your dynamic compression ratio is 6.32:1 .
Your dynamic cranking pressure is 117.18 PSI.
V/P (Volume to Pressure Index) is 73..................................................... 73 ..
What can be said about 73 except that this is as weak,or weaker,than a factory slanty
3B) that 340 cam wants more compression
Static compression ratio of 9.5:1.
Your dynamic compression ratio is 7.46:1 .
Your dynamic cranking pressure is 145.95 PSI.
V/P (Volume to Pressure Index) is 91 ........still super doughey city.............91 ..
So, as you can see, the 340 cam would want a new TC, cuz 91 is like slanty territory. Or it would need more compression to bring up the low-rpm torque.
3C) the 340 cam with most compression
Static compression ratio of 10.25:1.
Your dynamic compression ratio is 8.03:1 .
Your dynamic cranking pressure is 160.66 PSI.
V/P (Volume to Pressure Index) is 101.................................................. 101 ..
This is as good as this combo gets,and will now feel about like a stock 273 from stall to maybe 3000 rpm,or about 23 mph.
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I wouldn't put that 340stick in there; but if you do, and with,long-tubes,I would put it in at 112. This is split overlap, and it gets you 2 extra degrees of extraction, to help with fuel economy, cuz that cam sucks gas pretty bad, as I imagine do most 114* cams of that size or bigger.
One problem I see in that 273 is that trying to build compression for any other than the stock cam, is gonna suck, so the bottom end will likely be doughy. Personally, I think the 340 cam is not right for Mrs.Red. You already have the 3.91s, so you don't need a lot of engine to motorvate the fish after that. So I'm kindof liking 2B cuz with 3.91s you can afford to give some VP up, and the 2bbl 360 cam does pretty good at the top, so long as you control the valve gear, and don't get into lifter pump-up.
So I think I would put the high compression pistons in there, and work the formula backwards after I see the actual Scr available. Yeah, that's probably the way I'd do it, except I might use a solid lifter cam.
But I also think the best idea I heard was the one about just detuning the engine you have in there already. And that was memike in post #3
