IMO
Post 15, is on the money.
IMO
the 340 cam in the hi-compression 340 only worked as well as it did because of the package it was in, which included; a high compression ratio, log manifolds, a lightweight chassis, and limited rpm in a street application.
IMO
that 114LSA which may have worked well-enough in 1969, on the street; Today, that thinking is dead in the water, and there are many cams that can do a better job on the top; and if you match them up with high cylinder pressure, can carry the power right down to the bottom-end; which is always important for a street car with a manual trans.
IMO
Since 1970, I've had four 340 cars, all 4speed/3.55, all with that stinking cam in them. All of them laid down at about 85 mph. which is 5500rpm in Third gear. I had guys in 440 New Yorker family boats, and such, that I annihilated off the line, that by 75 were getting bigger in my mirror, and pulling on my bumper by 80, and had I not specified
"I only race to 85", they wouldda had me in the quarter, which none of my stockers could break 100mph; not even the nearly brand new one that I bought in fall of 1970.
BTW
My favorite of three cams I have run in my 367, was a Hughes HE2330AL This cam had it all, and if it had not lost lobes in 2004, I would still be running it. The duration specs were;
270intake/116comp./111power/276exhaust/110LSA/53*olap/Ica of 64
compared to the 340;
268intake/114comp./106power/276exhaust/114LSA/44*olap/Ica of 66
That doesn't look much different does it? Look again. 53* overlap compared to 44* AND more importantly, I run headers whereas the 340 ran logs. So you might as well say the 340 cam had NO EFFECTIVE overlap, because the exhaust was not tuned.
My 11/1, 367 ran 106mph with that Hughes cam, with a 4-speed/3.55s and hauling more than 300 pounds more than that 70 Dart I had, which ran 98 and change.
Oh and check out the difference in the Power strokes; 111 compared to 106. Even with my modest 53* overlap, and headers, my 367 annihilated fuel economy that a 340 car could only dream of. Even a stock lo-compression 318 couldn't touch it.
Ok but what makes that difference?
Well check out the relationship between LSA and overlap. First my Hughes, then the 340
110LSA to 53* overlap
114LSA to 44* overlap
4* change, to 9* change. IF the 340 cam had been on a 110, it would have measured
110LSA to 52* overlap, and then it would have been a reasonable cam.
As it happens, every 1* change in LSA, with no other changes, produces a 2* change in overlap. Overlap makes Power and has been called, "the Fifth Cycle".
IMO
overlaps in the range of 50>58 or so, make good street power, with good fuel economy. By the time you get to 68>78* yur more strip than street, and forget economy. Thus the window for a street/strip car is 58>68, which you can bias for economy on the low-end, to power on the upper end.
Having said all that,
IMO
cutting a 318 cam on a 106 LSA is not gonna amount to much, cuz the events are already too short at the factory 112*. So then, the LSA has to be matched to the rest of the events, to produce the desired results, OR,
to get the most out of whatever cam is chosen, the engine has to be built around it.
My current cam is advertised at 61*overlap, and it sux gas pretty bad. But nothing as bad as when I had the 292/292/108 cam that boasted 76* overlap. But the poor fuel economy is NOT all in the overlap.
IMO
If you compare the PowerStrokes, you can see exactly where the fuel economy went.
122>118 for the stock 318 cam; straight up, to +4 .
111>107 for my Hughes 2330, straight-up to +4
106>103 for my current Hughes 3037, straight up to +4
106>104 for the 340 cam, straight up, to +4
106>102 for the 292 cam, straight up to +4,
Heaven help you if you have to advance the 292 cam to in at 100*, to find cylinder pressure for bottom end, as, the power stroke drops to 98*, and you can see the gas gauge dropping every mile. If you gotta do that to get the pressure up, IMO, you got the wrong cam for the current engine configuration. I ditched that cam as soon as I figured that out, in it's first summer.
FYI
Opening the exhaust valve early, produces short Powerstrokes at cruise-rpm, which sends pressurized exhaust gasses out into the pipes, pressure which could have been used to push the car thru that 65mph wind. If you have log-manifolds like a factory 340, then some of those end gasses may end up in the intake at the end of the exhaust stroke. You'll see the evidence in the intake ports on teardown.
At high rpm, those short power strokes make Power for two reasons;
1) you got between two and three times as many of them in any given time period, and
2) the overlap cycle, with headers, is now working for you, instead of against.
Just my 2cents.
