So that more or less wraps up the bottom end. Fairly standard stroker package, nothing out of the ordinary.

What about induction, and most importantly, what about the camshaft?

Well we are going to get to the camshaft last because while I am 95% certain that I have selected the specifications that are optimal for this engine, I am still having some discussions with an experienced engine builder to ensure I'm on the right track.

Let's back up a second and get practical. These engines are airflow challenged, that's why they make decent enough torque but are all done at 3000rpm. This asthmatic breathing is what makes passing so butt-puckering on a two lane road. The important question to ask first is "where is the restriction?". This is where a lot of those generalities we discussed earlier will get you in trouble. Let's say you read an article on motor trend where they took a 500hp small block chevy and swapped from exhaust manifolds to long tube headers and picked up 60hp. Does that mean adding long tube headers to your stock 360 will make 60hp? Absolutely not! In this fictional example they have an engine that is airflow limited by the manifold, and has intake/heads/cam that way outflow them, so adding the headers simply removed a block from anotherwise already strong breathing engine.

Unfortunately for us the airflow barriers on the magnum are many, and the solutions are...well, not great. This is so foundational to the build here that it forces us to make a decision early on about what sort of power numbers we are willing to accept. You see, horsepower doesn't increase linearly with dollars spent. There is low hanging fruit, and then there are diminishing returns. If you want to make 450hp naturally aspirated with one of these engines, you better be willing to spend some big money and accept significant driveability tradeoffs in a truck application (weight and towing matters). Meanwhile, a gen 3 hemi with a crank and mild cam will make that number with good driveability. Why? Because the eagle heads flow 330cfm from the factory, they also have adjustable length intake runners and VVT. Also, because of the deep gearing in modern transmissions, they can get away with having a softer bottom end (less low speed torque) and make up for it with gearing, something we can't do.

The first airflow restriction to discuss is the heads because they're the least problematic. Magnum heads are similar in capability to vortec chevy heads, which is to say they're decent for factory iron, but not spectacular. In stock form they flow 202cfm on the intake and 150cfm on the exhaust. However, because the stock camshaft only hits around .430" lift, you're really looking at slightly less than that.


Source: Steve Dulcich



According to AFR, a head that flows 200 cfm is capable of supporting 411hp if all other things are maximized. That means a camshaft larger than you'd want on a driver, unrestricted intake and exhaust, good tune, etc.



As you can see, with porting, we can get this magnum head into the 230cfm range which is probably around 450hp, again if totally optimized which we won't do. What this does however is let us be assured that the airflow restriction is not the head.

Now think about this for a minute. If I want to make 350-400hp and the stock head will support 450hp, then it isn't the restriction. What do I gain if I let the TV marketing propaganda motivate me to run out and drop $2400+ on a set of aluminum Edelbrock heads, because after all you know every performance build has to have aluminum heads! Mostly just the weight savings of a whole lot of dollars leaving your wallet. Yes, you could run a little more compression because aluminum removes heat from the chamber better, and they weigh a little less...but the performance per dollar here is awful! I'm not planning on spending more than $2400 on the entire engine build!







So stock heads with some home porting will serve us just fine for this application thank you very much.

 

Next comes the most critical restriction on a magnum, the intake manifold. This right here is going to be the defining feature of the engine that shapes all other decisions, and we will get into why.



The stock intake only flows around 180cfm. If we consider that the entire space between the throttle body and the intake valve is one continuous unit that must flow air, it stands to reason that the AFR specs above apply equally to the intake as they do the cylinder head. This means under optimal conditions the kegger is only going to support around 350-370hp. Performing the traditional "kegger mod" only nets a 10cfm gain. Typically it will present enough restriction that the power is far lower than 350.


However, there are a couple people who have gone further in their modification of these manifolds. One being Thomas Beyer. He fully ported one (all the way around the runners, hogged out until it had holes and then he tig welded them up) and made 357hp (converted to crank) and 418tq (converted to crank) with a fairly mild and streetable camshaft. This is 20 more than a slightly ported keg on the same engine. Swapping to long tubes he ended up with 376.



So we know the kegger is going to restrict us to around 350-370hp if we optimize everything else. If we were dead set on more horsepower than this, it would require dramatic tradeoffs due to the fact that it is the only long runner port EFI intake available for this engine. Let's explore the alternatives.

Option 1: Hughes Airgap
Option 2: Swap to LA heads (or mag heads modified for LA intake) run an LA intake
Option 3: Use a carbureted magnum intake.

Option 1 is the only thing that allows us to retain EFI. However, this intake now costs over $800 and is significantly worse down low because of the short runners. Dual planes may have longer runners than single planes, but they are far shorter than modern tuned runner efi manifolds like the kegger (which is why all the OEMs use them). Long runners sonic tune at lower RPMs, significantly improving low speed torque and throttle response, things we desperately want in a heavy truck. See dyno graph below, the air gap only starts to gain an advantage at 4000rpm and by 5000 the party is over anyway and it's time to shift. Keep in mind as well that dynos only show Wide Open Throttle performance, and give no information about how well a given engine will respond at part throttle, how it will be to live with day in and day out.

As for Options 2 and 3, for a daily driven car in the snow belt that will potentially get driven by a significant other or children down the road, swapping to a carb is just dumb. It also forces the use of much shorter intake runners because fuel cannot make a big sweeping curve through a long runner without falling out of atomization. Going backwards like this is a great way to pay a whole bunch of money for bad results that just so happen to make a higher peak HP number on a graph if you give it enough camshaft to take advantage of the better intake...which requires a converter...which ruins the driving experience. See how quickly this gets out of hand?


Just like the heads, the keg came along included in the original $100 purchase price of the core engine. So we will port our kegger and work everything else around that.

 

I noticed that you didn't mention the stock throttle body only flows 500 cfm. Opening that up will allow more air in( especially with a stroker kit). This is more than you plan on spending but would you put a 500 cfm carb on 400 ci motor? Not sure what your plans are for the throttle body but at least look into getting a larger one that will flow more air. Indy used to make(not sure if they still do) the Indy X heads available in both the magnum and LA patterns so you can run LA intakes. Have a LA intake welded with injectors ports and it's a lot cheaper than the intakes that are available for the magnum.
https://www.jegs.com/p/Mopar-Perform...82466/10002/-1

 

It's getting a ported 52mm because the intake was already opened up to match that size.

Also this: