To illustrate what the stock motor had to offer, we installed a stock 400M cam (from Elgin
When it comes to cam timing, it's relatively easy to add power by increasing duration. The downside is that the extra top-end power comes with a loss of torque lower in the rev range. The difference between selecting an off-the-shelf cam and having a shop like Cam Research custom-grind a cam for your specific application is a ton of extra power. You know you've done something right when you install wilder cam timing and have the power increase throughout the entire rev range.
Were this a 400-inch Windsor motor, we might be tempted to choose a dish piston, but the 400M two-barrel heads featured large (as much as 79cc) combustion chambers. These large chambers required a flat-top piston to produce a reasonable compression ratio (near 9.0:1).
All of the later two-barrel (and four-barrel) heads have a reputation for increasing the likelihood of detonation. The open chamber heads (including those on the 400M) were designed to lower the compression ratio, but the lack of a proper quench area actually makes them more sensitive to detonation. Thus, the static compression ratio should be kept lower when running factory open-chamber heads compared to the more desirable closed-chamber or quench heads
A factory-style timing-chain assembly was then installed over the stock cam and retaining
We cured this situation with the installation of aluminum Cleveland heads from Pro Comp. The Pro Comp heads feature all of the positive aspects of the Cleveland family, poly-angle valve configuration, including the large 2.19/1.71 stainless steel valve combination.
You may be wondering why we chose a set of aluminum heads for our low-buck build, but the Pro Comp aluminum heads can be had for about the cost of a set of used factory four-barrel heads. For roughly a little more than the price of of Windsor heads, Cleveland (and 351/400 Midland) owners can enjoy the benefits of a set of bolt-on aluminum heads. Not just aluminum heads, but performance heads that are head and shoulders above either of the factory two-barrel or four-barrel heads. It would take a serious set of ported four-barrel heads to equal the flow potential of the Pro Comp Cleveland heads, and you'd still be stuck with heavy cast-iron heads with relatively huge (and potentially lazy) port volumes. Airflow is one thing, but it is always better when a given flow rate comes through a smaller orifice.
To put this into perspective, the intake-port volume on a set of CNC-ported Pro Comp Cleveland heads is less than a set of stock, as-cast four-barrel Cleveland heads. These smaller ports flow as much as 50 to 60 cfm more airflow than a stock four-barrel port. In addition to the reduction in weight and improvements in airflow, the Pro Comp heads also came with a 2.19/1.71 stainless steel valves. Complete heads come with your choice of valvesprings for the intended cam (flat-tappet or roller), chrome-moly retainers and 10-degree locks. The heads also come with studs and guide plates to properly orient the pushrods.
Impressive right out of the box, our Pro Comp Cleveland heads were given a once over by Bryce Mulvey of Dr. J's. Bryce worked his magic on the heads by applying not only a precision valve job, but further improving the flow potential. As received, the unfinished Pro Comp Heads flowed 325 cfm on the intake and 228 cfm on the exhaust. After Bryce completed the porting and valve job, the flow numbers jumped to 348 cfm on the intake and 252 cfm on the exhaust (all measurements taken at 0.800 lift at 28 inches). What the additional airflow does is allow you to reach a given power level with milder cam timing. Thus you have a powerful engine combination without the usual idle quality and drivability issues associated with wilder cam timing.
Fel Pro supplied all the necessary gaskets for our application including the head and inta
For our baseline tests, we ran the 400M first with the stock iron two-barrel heads. The bo
This gives you an idea of the difference in port size between the two-barrel and four-barr