There you go. The combination of the late-closing intake valve and the accompanying loss of cylinder pressure, is your lazy start.
If you look at the opening rate of that cam, going from
[email protected], to .200@ .050, you can see that it is about 1* per .001 lift.
Therefore from .018, back to a cold lash of .010 is another 10*of duration. But, the rate of lash take-up, could be slower, so lets arbitrarily make it 22*. Thus your 200*@.050 cam becomes;
[email protected] + 30 + 22= 252* after lashing, which we're gonna call the advertised for purposes of determining the Ica. Yes, I'm guessing.
And so, the Ica is predicted to be...... 52 degrees, quite a bit better than the 60* I had earlier estimated. With this new information, the Wallace predicts;
at 8.4Scr/
800ft elevation;, 140psi and a V/P of 100
Thus, to get to 165psi would require the Scr to be increased to 9.5, which is predicted to raise the V/P to 117, which is a very significant increase of ~17%.
Disclaimer;
All my numbers are guesses. To be accurate, the Wallace needs your exact Ica , along with the exact and accurate cranking cylinder pressure.
Here's the deal; Your V/P is down some 17%, as I estimate. You can get that same 17% back, by increasing your rear gear by 17%, which would be 3.44s; rounds up or down.
This is what is so neat about using V/P numbers.
Now remember, once the Rpm gets to where the cam is waking up, the V/P numbers are no longer useful. This Is why I keep preaching V/P to guys with manual transmissions. When your engine is stuck well below the torque peak, as it often is, lack of V/P is gonna make you cry, while a preponderance is gonna make you smirk ear-to-ear.
Imagine a 360 with a V/P of 175, lol. (mine at one time). Lessee; 175/100= plus 75% that's like supercharging your 273..
Here's a tip, gleaned from my manual-trans testing;
get your second gear power delivery dialed in, and let the rest be what it will be. The math shows that you need at least 3.44s. Rounded to 3.55s, and with 25" tires that will put you at;
>5000 rpm=34mph, in First gear.
On the 1-2 shift, the Rs will fall to 62%=3100. But peak torque may not come around until 3500, or more.
That leaves you with a Second gear hole from 3100 to 3500, going from 34>38mph, with 3.55s. With 2.94s this gap is from 41>46mph, does that sound about right?
I have the same Commando trans, and the same 3.55s, and the same problem, and the way I overcame it was to spring the valves enough to rev to 7200, then buzz First gear up to 38mph, before shifting, which is 5600 in your case. Now it will drop into Second at 62% of 5600= about 3500.
There is only one other way to get around this, which is to get a transmission with a tighter 1-2 split, and then again, retuning second gear.
I know it sounds cliche, but "trust me"; I have tried every 23spline A833 ratio that Mopar ever commonly made, and every rear end ratio from 2.76 to 4.30 except 3.73s, and some beyond that as well; and I am confident in what I preach.
When it comes to splits, the Commando trans has the Second furthest apart 1-2 split, of 62%. It makes for a great holeshot with hi-way gears. But when first gear runs out, you better have a back-up plan. My Back-up is the GVod which handily splits that 62% into two halves of 78% and 79.67%. BadaBoom!
For you, either of the standard A833 transmissions would have the best 1-2 splits of around 72%, thus on the 1-2 shift the Rs would drop from 5000 to 3600, a powerband requirement of just 1400, versus the Commando 1-2 split of 1900rpm. The down side is that the T/A trans will need 1.77 x 3.91= 6.92, to closely match the Commando's
1.92 x 3.55= 6.82, to provide the same Second gear performance ................. and so, 3.91s just about kill any long-distance cruising. But yaknow, 3.55s were no hell either. To overcome this, about your only choice is an overdrive gear. For example, the .78 GVod would turn 3.91s to 3.04s
I'm not saying that you should rush out and get a different trans, a different rear gear, and a GVod. I'm using those items to preach gear ratios, to an engine with a sub-3500 torque problem.
Cheaper by far is to just increase the Dcr up closer to 8.0 to get at least some of that missing 17% V/P back.
Or even a different cam with an earlier closing intake valve. >Or the easiest of all, get the air intake out from under the hood. I can't tell you how much power my engine gained, when I cut the hole in my hood, and isolated the carb from the underhood hot air; but I can tell you that the 750Dp went from 68/76 jets to 72/80s .......... and she promptly ripped off a 93 mph in the Eighth, on a really crappy track.
One more thing worth mentioning;
As the cylinder pressure goes up, so will the Idle and Part Throttle vacuum. And so three things will come into being;
1) throttle response gets better,
2) the engine will need less Power-Timing
3) if you retune it, she will return you better fuel-economy.
4) it may be that, you can reduce the size of your carb to better the performance as a streeter, yet not compromise the power much if at all, in at least the first two gears.
Of all my testing, to have fun, two things emerged, ;
1) I needed a maximum load of not more than ~10 pounds per cubic inch. Thus my 3650 pound Barracuda(me in it), needed 367 cubes. At this load, the horsepower really didn't matter much. and
2) My favorite Second gear turned out to be in the range of 6.2>6.8, with 27" tires. Thus it now runs a 1.92 Second gear, with, usually, 3.55s.
So
Firstly; to fit the profile, your 273 at 2730 pounds of car weight, would need run 10pounds for per cube , with you in it. If yur not at 10/1 or less ....... you may never be happy. ...... but you might be, ...... with the right rear gears......
Second; to get into the 6.2>6.8 zone, yur combo is gonna needs 3.38 gears. Rounds up for a heavier car, to 3.55s.
Thirdly; In all my testing, whenever I swapped the cam out, I always reconfigured the Cylinder pressure to run about the same, and at the upper limit for 87E10. Which with Tight-Q Alloy-heads, turned out to be over 195psi. But I did not at first know that, I just kindof stumbled into it, while targeting 185..
My 367 , at 195 psi, and 3457 pounds, was outrageously overkill. I very soon reconfigured it, again, to run around 180psi.
Lest you think I must be rich, that is just not so. When I screwed that engine together, I planned ahead, by setting up the Targets so that these changes only required a minimum of machining, and all the gaskets were re-useable. Thus my only real costs were time. I took that engine out and down a minimum of Five times in five winters. It mightabin six.
But in all honesty, the 360, in it's current configuration, is just way bigger than it needs to be for my application. The torque at 195 psi is ridiculously high. The power to weight ratio of ~8.4/1 is similarly outrageous. I only built it thus, because it was so daymn cheap to screw together so effectively.
l mean, it fell together at first build at 10.7 Scr ! with off-the-shelf parts. I couldn't say no.
I know I'm rambling on now, but you gotta admit, you kindof egged me on, lol.
I sure hope you can find something useful in this post.
