Build suggestions for 340?
Either there is something off in my input, or this is an outstanding cam. Please correct me if I've entered something incorrectly...
-Jim
Yeah; you inputed the wrong numbers. the first timer often does that.
if you look at the very top of the calculator it says;
Dynamic Compression Ratio Calculator
(Use seat to seat or advertised specs for Intake spec for best results)
You inputed the .050 numbers, and the calculator is not set up for that.
The .050 numbers are a throw-back to the earlier years when there was no consistent way to compare cams. You could take five 268 cams each from a different grinder, and have five different running engines, yet all were the same rated 268. Somebody got smart and said, we gotta level the playing field; so after that day,the cams had to be rated at .050. This still does not mean that every grinders
[email protected] cam is gonna perform the same in your engine! it just narrows the choices a whole bunch.
Anyway; the Wallace is all about being able to compare LOW RPM performance, and the .050 numbers have nothing to do with low-rpm. So you cannot use them. And you cannot even use them to fudge the calculator by adding an arbitrary number, like is done with some other calculators.
So
You have to use the advertised numbers. Which, in the case of the
271H10 are 271/279/110+4.
And you have to generate all the missing numbers from those, and it can be done.
Ok,so;, I'll work it out for you, then show you how to do it. The numbers are;
271/279/110+4/55overlap/119 comp/106 power/ Ica of 61*
There is your magic Ica of 61*; but
Notice the PowerExtraction is only106*. That's just ducky at WOT and 5000 plus rpm. But the rest of the time it is gonna cost you fuel usage.
Furthermore, the checking tappet lift is .006 inch, so the cam measures bigger than it would when compared to the same cam when the checking tappet lift is .008, like Hughes and Mopars are measured. No big deal, but you just cannot compare it to those other cams.
Furthermore, that 61* on this .006 rated cam
IS NOT
gonna be 61* when remeasured at .008 tappet rise; even tho it is the exact same cam! This is how guys get screwed.
Ok so here is how you can generate all the numbers from just the four given numbers, in blue above.
Overlap first;
Take the average of the given durations and subtract double the LSA; easy-peasy. So
(271+279/2) - (2 x 110) =275-220 =
55*overlap
Next we have to figure out where the intake installed centerline is. the spec is +4 so; so
110 less 4=
106 Icl easy peasy.
Next; We need to figure out how much of the overlap to give to the intake stroke and how much to the exhaust stroke. One would think, we could just divide it in half, and sometimes you can; but usually the vendor wants to give a lil extra to the intake, to get a lil extra compression degrees. In this case; take half the intake duration and subtract the installed centerline, and so
271/2 -106=
~30*.. leaving 25* for the exhaust.
Next; now we can figure out how many degrees are allocated to the compression stroke; Here's how; The four stroke cycle is two revolutions, right? On the first revolution the engine does intake and compression and on the second it does compression and exhaust. There is a short period of time where both valves are open, one is closing and the other is opening; and they call that overlap,cuz,well the cycles are overlapping, go figure,lol.
Ok so for the first two strokes, we have in this case 360degrees plus the 30*of overlap, that we earlier allocated to the intake stroke, and from that we subtract just the intake duration. That which is left is the compression duration. So that looks like
(360+30) -271=
119 compression.
Finally, we need to calculate the ICA. The theoretical compression stroke is 180*, but in our case it is physically, just 119, so we subtract the smaller from the larger and out pops the Ica, like so
180-119=
61*= Ica
Of all these numbers, the only one that the Wallace wants is that 61* Ica
done