you got that right
my 360 is on a 112 but it's a mopar master not a chevy so the timing's shorter\
problem with low compression is the wide lobe centers close the intake even later mine has a true 9:1 with Iron heads and a towing application
you do not build compression till the intake is completely closed
one reason the factory hyd cams suck is the very long closing ramps (for anti noise reasons mostly during long warranty)
I think I get what you are saying;
I once put a 340 cam and X-heads on a smogger-teen, and that teen needed 4.10s and a hi-stall,just to get off the line. It did however have pretty good passing power at 65 mph in second gear with 3.23s.
Whereas one particular 340short combo I assembled as a teenager, with early teen heads and cam, was an absolute blast to drive, 2bbl and all.
A lotta effective compression, brings an A-game to a streeter, which for the most part is a oneandahalf to two gear deal, and spends most of it's life just cruizing around.
IIRC that 340 cam in my 1970 Swinger340 4gear/3.55s was a 268/276/114 cam with 44* overlap. As I remember it that cam was rated at .008 tappet lift. And that engine was rated at 10.5 Scr altho I never had it apart to actually measure it. I thought that car was pretty quick back in the day, going 98 in the quarter. It was 3330 with me in it.
My second-iteration 367 had a 270/276/110/53* overlap Hughes cam also rated at .008 which I installed in my 10.9Scr Eddie headed 3650pound beast me also in it, and that combo went 106 on it's maiden run. Also a 4-gear/3.55s.
The first engine maths out to a W/P of 13.5 so at 3330 that is 247 hp
The second is a W/P of 10.8 so should be 338hp@3650pounds
That's 91 hp
Where'd it come from? Well that's anybody's guess, but the second combo had headers and 28 more cubes so that's gotta be worth an easy 45hp. Leaving say 46 in the Eddies and cam, cuz it sure won't be in the approximate 1 point of static compression ratio.
I have no idea what the Eddies may bring to the table, but let's look at those cams;
Mopar says that 268 cam is a 228/235/114/44 overlap cam@.429/.444@1.5 arms
And Hughes says their 270 is 223/230/110/53overlap cam*@.538/.549 @1.6 arms
So the Mopar appears to be one size bigger @.050, but several sizes smaller in lift. Lets call the power specs a wash. But what about the Effective Crs? Well without degreeing those cams and trying to pinpoint a closed and not leaking intake spec, It would be impossible to say. But we could have fun guessing.......
What if the actual intake duration on that Mopar cam @.001lift was 300* and the Scr was 9.9 in the 340. Then the pressure would be predicted to be 133psi@ sealevel, and
What if the Hughes gets to .001 at 290* and is installed at 10.9Scr, then the pressure is predicted to be 170psi@sealevel
Wait what? Go do the math yourself.
Wallace Racing: Dynamic Compression Ratio Calculator
Then you back up the bus and factor in what the headers are doing with the 53* overlap on the 360 versus the logs and 44* Mopar overlap, and you gotta wonder why my car only went 106, right? LOL.
Anyhow it's always fun to speculate, but I just gotta throw this out there;
Wide LSAs give up overlap, and cranking cylinder pressure.
The pressure you can usually get back,or work around, but the loss of overlap, if you're running headers, is for me, a deal breaker. I think it was Smokey Yunich who called overlap, the Fifth Cycle.
Also; wide LSAs with long period cams throw away fuel economy, by leaving a lotta energy still in the exhaust. This may look cool when it blasts dirt up, 2 or 3feet behind your car, but you pay for that coolness every time you fill the tank. This becomes even more pronounced with long, slow-to-close-after-advertised-spec, ramps.
Take for instance that Mopar 268/276/114 cam that
might be (I'm guessing)300/308/114 at valves finally sealed. But let's just say you had a cam, some cam, some other cam, whatever-cam, like that, then the actual on the seat and sealed specs could be;
intake opens at 40BTDC closes at 80ABDC for 300*
exhaust opens 92ATDC, closes 36ATDC for 308*
Compression is thus just 100*, and
Power is 88* , and
Overlap is 76*
Cruising speed with 3.55s might be 2800 and the vacuum peaks at about 2000, perhaps a little less... meaning reversion is no longer an issue at cruise rpm. So by itself, reversion is not affecting fuel economy,much.
So why are 340s known to be gas-guzzlers? Well look at that 88* of power extraction; the piston is not even half way down when pop, the exhaust begins to open,and that hi-pressure,still burning, not-yet-spent charge goes right out into the exhaust, never giving all it could to the crank.
And maybe, just maybe, some of that hi-pressure exhaust as it moves thru the log manifold, finds it's way into another low-pressure cylinder, screwing it up .
Additionally,if you have headers, then they do their magic, and yank a portion of every fresh charge right thru the chamber and into the exhaust, with that 76* of overlap.
I'm not pointing the finger at the 340 cam specifically, just using it as an example; all long-period-slow-ramp cams are gonna have this characteristic, to one degree or another. But, you say, the Mopar 268 is not a long-period cam. Well, no, looking at the .050 spec it's not. And looking at the advertised spec it's kindof middle of the road for a streeter. But when you look at the seat to seat closed and not-leaking, just how big is it really?IDK, I haven't measured one; but I bet there are several other companies that can get you a quite-a-bit shorter seat to seat/not leaking, still at 268/276/*** or,more importantly, cut you a 228/235 with really short seat-to-seat/not leaking.
So in my opinion, as for myself, I would be willing to replace my cam quite often,and install a cam with the fastest ramps possible, before sacrificing pressure and overlap to a quiet, long-lasting slow-ramp cam. In year2000 when I installed that cam, that's what I thought I was getting with the HE 2430AL Hughes cam. Silly me. It did however teach me a lot about cams. If there is another cam in my future, it's gonna be custom for sure.
