Mopar 318 5.2l rebuild/upgrade

Here are some preliminary numbers, all cams installed at split overlap
1) First the factory 5.2,
Static compression ratio of 9.2:1.
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 8.07:1 .
Your dynamic cranking pressure is 161.70 PSI.
V/P (Volume to Pressure Index) is 133 .
Notice the cylinder pressure is already at the max for pumpgas, and the VP index is pretty good. You're not gonna improve much on this for your application

2) Next the factory 5.9
Static compression ratio of 9.2:1.
Effective stroke is 3.02 inches.
Your dynamic compression ratio is 7.80:1 .
Your dynamic cranking pressure is 154.70 PSI.
V/P (Volume to Pressure Index) is 139.
Again pressure is pushing the limit, and VP is getting up there.

3) Next; the 5.9 with a 5.2 cam
Static compression ratio of 9:1.
Effective stroke is 3.13 inches.
Your dynamic compression ratio is 7.93:1 .
Your dynamic cranking pressure is 158.06 PSI.
V/P (Volume to Pressure Index) is 148
Notice I dropped the Scr, again still pushing the limit, and the VP is now a nice big fat number.

4) Next,stroker
the 5.2 with a 4" arm, and the 5.9Magnum cam
Static compression ratio of 9.4:1.
Effective stroke is 3.35 inches.
Your dynamic compression ratio is 8.04:1 .
Your dynamic cranking pressure is 160.92 PSI.
V/P (Volume to Pressure Index) is 158 ..
I had to up the compression a tad. Notice the VP has climbed to 158/133=plus 18.8%. This is a huge boost in low-rpm performance compared to the 5.2. This is a similar boost to swapping the rear gears from 3.92 to 4.66
Read about VP here..... V/P Index Calculation

5) Here's another;
the 5.9 with a 5.2 cam and with aluminum heads.
Static compression ratio of 10.6:1.
Effective stroke is 2.97 inches.
Your dynamic compression ratio is 8.96:1 .
Your dynamic cranking pressure is 185.09 PSI.
V/P (Volume to Pressure Index) is 166
Check out that VP! this is now 166/133 plus 24.8%!!
Say goodbye to the 3.92s and hello to 3.23s. Now you could be cruising at 65=1530 with still guessing 100 inch tires. That would make a huge boost in mpgs.But I know what you're thinking; how about those heads on my 5.2.Right?
Okay here it is
6) Static compression ratio of 10.6:1.
Effective stroke is 2.74 inches.
Your dynamic compression ratio is 8.93:1 .
Your dynamic cranking pressure is 184.29 PSI.
V/P (Volume to Pressure Index) is 146 ..
At a VP of 146, this is now very similar to the 5.9 with the 5.2 cam. But notice I pumped the Scr up to get 185ish psi. In my engine this pressure is happy with 87E10. So to run these aluminum heads, in your combo, the reason is soz you can pump up the pressure, and not for power, cuz with the 5.2 cam, the absolute power will not be that much better. More power will come from the increased pressure .


The thing about the stroker is that it makes so much power beginning at such a low rpm, that you will be able to run the beast with the throttle valves barely open. And that is where the fuel economy will come from.
But with a stroker and a 5.9cam, you could take some rear gear out of it, and run at a slower rpm down the hiway, and that will theoretically increase your economy even more.
This is usually a slippery slope tho with a smaller engine, as sooner or later,the engine starts to make so little power, that the throttle valves end up quite far open, and economy takes a dive. Theoretically it should be hard for the stroker to get into that, unless you go crazy about reducing the Rs.
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But I gotta tell you, if you are getting a confirmed mileage in the 17 to 19 zone, it's hard to imagine any other combo improving enough to warrant spending this much cash on it....unless you are traveling huge amounts of miles per year.
Here is a quick calculation
Suppose you were able to increase your fuel economy to 22mpgs, from 18., and
suppose you traveled 12000 all-hiway miles per year. At 18mpg, this would require 667 gallons, and at 22, just 545, for a savings of 122 gallons.
What's that come to in dollars? Well at 3.15 per gallon this is a savings of 384.30
If you spend $ 3843.00 on engine upgrades that guarantee the 4mpg better economy........it will take 10 years to break even, assuming no change in the cost of the fuel. But if your economy only goes up 2mpg.. then it will take 20 years to break even.
In either case, it is doubtful that you would still be driving it in 5 years, so you would NEVER break even.