Here's what the factory 3.9 looks like
240/112 cam, ICA of 48*
Static compression ratio of 9.2:1.
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 8.15:1 .
Your dynamic cranking pressure is 163.78 PSI.
V/P (Volume to Pressure Index) is 103...................................................
103
Notice that the pressure is right around the magic 165psi, about the maximum you can run on pump gas. Also notice the meager VP of 103, better than a slanty, but not by much.Remember, the big 225 is 3.2 liters (EDIT; 3.7 liters). and the 3.9 is just 238.8 cubes.
Here we have same 3.9, with 5psi boost
Static compression ratio of 9.2:1.
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 8.15:1 .
Your dynamic cranking pressure is 163.78 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of
5 PSI is 10.92 :1.
V/P (Volume to Pressure Index) is 103
Notice the effective compression ratio is quite high,at 10.92. You may not be able to keep this engine out of detonation at low rpm. You will have to delay the onset of boost to maybe 3000rpm, which with 2.45s, and a 2.74 low, will be about 35mph. With a 2.45 and 2.73s it would be about same,lol. And who wants to wait for that?not me!
Here is the 5.9Crate 300hp
250* cam,ICA of 51*(really small cam)
Static compression ratio of 9:1.(I guessed)
Effective stroke is 3.08 inches.
Your dynamic compression ratio is 7.88:1 .
Your dynamic cranking pressure is 156.77 PSI.
V/P (Volume to Pressure Index) is 146...................................................
146
Notice the VP of 146; this is 146/103=plus 42% more than the stock3.9 and will feel like it too, from idle to in the range of 2000 to 3000, when the torque is gonna blast that CMK into twist-the-chassis territory. At a Dcr of just 7.99/157psi this will probably run on 89 or less octane gas.
And just in case you ask; here's a stock 318LA non-Magnum
Static compression ratio of 8:1.(old LA)
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 7.10:1 .
Your dynamic cranking pressure is 136.77 PSI.
V/P (Volume to Pressure Index) is 114....................................................
114
Yes, this burns the worst gas you can imagine, and still manages a VP of 114
which is 114/103=plus 10.7% over the 3.9. And I think those old LAs were 180hp.
Ok one more, a 5.2Magnum
Static compression ratio of 9.2:1.(I guessed again)
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 8.15:1 .
Your dynamic cranking pressure is 163.78 PSI.
V/P (Volume to Pressure Index) is 136...................................................
136
I think these are rated 230 hp
Notice that the VP is up higher again to 136/103= plus 32% now over the stock3.9. And to 146/136= within 93% of the Crate5.9. Remember, this number diminishes with rpm, and is probably most noticeable below 2000rpm
Read about VP here;
V/P Index Calculation
So anyway; Happy HotRodding