Race Engine Build - Project Mini Stock

Next, the head moves over to the valve seat machine for a series of cuts. First, Yates opens up the valve guides so new bronze guide sleeves can be inserted. Then the valve seats are cut with a tool that does all three angles at once. Yates is careful to cut no more than necessary; keeping the cut shallow minimizes the depth of the combustion chamber. Finally, the interior of the bowl and the side of the combustion chamber next to the valve are cleaned to improve airflow.

Unlike many Late Model series, our Mod Four rules have no requirement for minimum combustion chamber size. This allows Johnson to pick the compression he feels the engine can support and deck the head until he gets it. The static compression goal for our engine is 12.3:1, which translates to petite 42cc combustion chambers. Yates has to take a total of 0.170-inch off the head on an angle to get there-on this head every 0.007 inch cut equals one cc removed from the combustion chamber.

Finally, it's time for head assembly. Yates triple-checks the stainless steel valves against the seats and then installs the camshaft. Johnson has his cams ground to his own specs. The CIA is more lenient with its secrets than Johnson about his cams, so don't even bother asking the specs. All we know is lift for both the intake and exhaust is 0.500-inch. Yates grinds the valve stems so they lift 0.500 inch with no lash, then sets the adjuster studs to 0.010 inch lash in the intake and 0.012 inch on the exhaust before locking everything down. We are using single valvesprings with a height of 1.625-1.650 inches and have 250 pounds of pressure compressed.

Johnson's Machine completed the package with a set of Race Engineering pulleys and belts that are about as light as they come. Ignition comes via a distributor and coil from Mel's Ignition. We are also using a racing-specific water pump from MPR Inc., which has a roller bearing and a backing plate over the impeller to prevent cavitation.

Johnson recommends we run this powerplant to a redline between 7,800-8,000 rpm, which is possible thanks to the single overhead camshaft design and solid lifters. There's no flexing pushrod and rocker arm monkey-motion (and weight and inertia) to help limit rpm with overhead camshaft valve actuation. We plan to feed this little zinger air and fuel with a Keith Dorton Series, Holley two-barrel carburetor (PN 80583-1). This 500cfm carb is based on Holley's 4412 model with some factory-installed tweaks to make it competitive right out of the box with a custom-tuned unit from a carburetor specialist. Now all we have to do is get in gear with the car and see how it all works together-easier said than done!

We mentioned previously that our Keith Dorton Signature Series Holley carburetor was based off the tried-and-true 4412 carb. So what's different? We asked Keith that question and he clicked off a list of upgrades like:

* The boosters are centered in the venturi for equalized and maximum airflow.
* Adjustable air bleeds have been installed in the metering block for precise fuel curve tuning.
* Stainless-steel throttle plates are held in place with buttonhead screws to improve airflow.
* 30cc accelerator pump replaces 50cc pump to improve response off the corners.
* Choke and other unnecessary hardware have been deleted for simplicity and smoother airflow.
* Fuel slosh/vent baffles have been put in metering blocks for better fuel control.