Before putting any load or revving the engine, it should first go through a break-in period. First, triple check to make sure everything is correct (throttle linkage, plug wires to the correct cylinders, and so on) so that the engine fires up immediately. Don't let it idle long, because at idle rpms the oil pump isn't providing enough pressure. Check the timing and then allow the engine to run approximately 45 minutes between 2,000 and 2,500 rpm to allow everything to break in. Make sure to keep an eye on the oil pressure, water temps, and listen for any strange sounds.

After break-in, go back over the engine. Look for oil leaks, water leaks, or anything else that can be amiss. Here, Ken Troutman resets the valve lash. It will probably change a couple thousandths of an inch as the cam lobes and lifters mate in together. This is also a good time to check the O-berg filter for chunks of shrapnel that can give you a clue to potential problems before they become big problems. Now, you're finally ready to start making dyno pulls.

On the first couple of pulls we were down on power from where engine builder Ken Troutman thought we should be. He thought our cam might be a bit too large for the application (the duration is 248/252 at 0.050 lift with 0.310 lobe lift), so he gave us a set of aluminum Comp 1.5:1 ratio rockers to switch out for the 1.6 rockers on the exhaust. Dyno pulls after making this change showed that we picked up 5 horsepower at the peak and extended the curve after peak power. Previously, the horsepower curve fell off of a cliff after the engine made its peak number. The smaller rockers proved that the engine can probably do with less cam. Later, we may try swapping out the intakes for 1.5 rockers as well. Another option if the shop you are using to dyno your engine doesn't have extra rockers to loan you is to increase the valve lash (this only works if you are using solid lifters) which will make the engine think the camshaft is smaller.

After making the rocker change we were still down on power, especially in the upper rpm range. After sniffing around a bit, Troutman said he suspected the plugs we were using were too hot and causing pre-ignition. Swapping out to a set with a colder heat range (the plugs are designed to pull more heat away from the tip) picked up 9 horsepower and greatly extended the upper rpm range. This is a perfect example of how important spending some time on the dyno with a professional tuner can be.

Engine builder Ken Troutman of KT Engine Development mans the controls while he puts our Limited Late Model engine through its paces.

Limited Late Model engine dyno graph.

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