I have heard but not verified that the stock 5.9 cam was 250/264/110+19/37* overlap( 12* effective)/182/
[email protected]/.411-.430 lift.
But take note of the +19 advance. this makes the compression to be 116* with ab Ica of 64* and the power extraction to be 127*. Read it again; 64* . the intake valve is closing ridiculously late, killing cylinder pressure, and bottom end torque with it. Remember, I have not verified this. I got it off some other Mopar forums.
I can't say why the factory would do this but I can guess.
Firstly the 5.9 is advertised at 9.4 Scr, and perhaps they needed to give up some pressure.
Secondly the extraordinarily long extraction cycle may be their way of increasing the fuel mileage to some target they may have had in mind.
Thirdly they killed the overlap from a maximum possible of 37* to to just 12* Effective.
Why is this important?
because in the stock engine this marriage of 64*Ica and 9.4Scr predicts a cylinder pressure of just ;
Static compression ratio of 9.4:1.
Ica of 64* @800ft elevation
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.55:1 .
Your dynamic cranking pressure is 147.37 PSI. ............................. 147
V/P (Volume to Pressure Index) is 124 ....................................... 124VP
and a mediocre VP of just 124
now lets advance that cam to split overlap; and I get;
Static compression ratio of 9.4:1.
Ica of 51*,still 800ft
Effective stroke is 3.08 inches.
Your dynamic compression ratio is 8.23:1 .
Your dynamic cranking pressure is 165.42 PSI. ............................. 165
V/P (Volume to Pressure Index) is 154 ..................................... 154VP
Check it out! To read about VP click on the blue V/P in my sig.
This is an increase in cylinder pressure of 12.2% and more importantly, an increase in VP of 24.2%.
The compression duration is now 129* and extraction is more than adequate at 114*, and the overlap has grown to an Effective of 36*......... which means headers are now optional, and will make a power difference.
The downside to this is that the stock engine ran on 87 gas, but the new cylinder pressure may require 91 at WOT.
But make particular note of the over 24% increase in VP. This is like increasing your engine torque by a like amount, or could also be likened to adding a similar amount of rear gear. And..1.24x2.76=3.43s
You don't have to retard the cam timing to split overlap. Say you want to top out at 160psi pressure to run 89 gas ( I can't imagine why, but lets just say)
Here it is at
Static compression ratio of 9.4:1.
Ica of 55*,still 800ft
Effective stroke is 2.99 inches.
Your dynamic compression ratio is 8.02:1 .
Your dynamic cranking pressure is 159.81 PSI. ........................ 160
V/P (Volume to Pressure Index) is 144 .................................... 144
Notice the VP fell from 154 to 144. which is still waaaay better than 124. I like to say that 140 is where the fun starts.
This will liven up your bottom end like 3.17 rear gears would. So still winning!
Ok now, I hate to try and make you be the GuineaPig, but no one has yet spoken against this overly advanced factory install, soooooooo you might want to check it out. You know you need a chain-kit anyway right........ If this info I'm presenting is correct, and you end up correcting it, it will certainly plump up your torque throughout the rpm range, and especially at zero mph to ~3500rpm.......... which with 2.76s is about 35mph;BadaBoom: just try not to spin the tires ALL the time (154VP is incredibly potent off the line). It will not, however, make much significant power over the top. I mean it's still just a250* cam /182*@.050. But retiming the cam usually costs no more than a gasket and a couple of hours......... if you have or can borrow the tools.But in your case,an install change from 119* to 106* is 13* and you won't find an offset cam key for that...... So you are gonna need the cam/crank gears with pre-machined timing grooves, in addition to the offset keys... And not sure if that combo will even go 13*.
And most importantly; I don't know what this will do to your piston to valve clearance. I can say this; retarding a cam usually increases the valve to piston clearance, but you need to verify this; I will not buy you a new set of valves if they crash.
Is it worth it? On a budget,IMHO, absolutely yes. No contest, and I would go all the way to split overlap with the cam centerline in at 106*.
But if you can afford a new cam, then no; forget it. Just buy a cam with the same Ica and more duration in both intake and exhaust and then you get more power over the top, in addition to the stronger bottom end. This is kindof a unique situation. In the lightweight A, with a 360, you don't ,for street, actually need VP into the 150s ; on account of it will just end up in tiresmoke. 140VP would be lots. And that gets you an Ica of about 56*. So Any cam you might chose that can be installed at that 56* Ica will already have a strong bottom-end. So then you can concentrate on putting the power at whatever rpm that works out to. Just remember, with 2.76s It's kindof dumb to have a power peak at 75 mph in first gear, if the speed limit is 65.
Also with that overdrive trans, it's also kindof dumb to marry it to 2.76s with a hi-rpm cam. You are in a unique position with that .69 overdrive and loc-up TC, to do some pretty unusual things.
I would not bother with increasing the rocker-arm ratios.
To be continued.
