Cylinder Head Flow
The bores were prepped by Outlaw Racing Engines (Upland, CA), with final honing shown here. With any build, internal clearances are critical. Andy Mitchell and the crew at Outlaw cut no corners in assuring our engine was dead-on. | 
Additional measurements at the bottom end include the crank endplay, main and rod bearing clearances, and rod side clearance. We quickly discovered that Outlaw Racing checks all clearances meticulously. | 
Make sure the rods and pistons are assembled properly, and the ring gaps are staggered to specs. On start-up, Outlaw likes the top ring gap at the intake valve, where the chamber runs coolest. The second ring gap should be placed opposite of the top ring. The pistons should slide into the bores smoothly without hanging-up on a ring. An extra set of hands can help guide the rod to the journals. |
With Hunkins helping to man the wrenches, the bottom end of the engine went together with no unforeseen problems. This is where thorough preparation and quality components pay off. We liked the digital Snap-on torque wrench, which alerts the user with audible and vibration cues. |  | 
All the work proved to be worth it on dyno day, with 635 lb-ft of torque and 626 hp. Hunkins had to cough up a $20 wager when Mitchell's power prediction proved to be virtually dead-on, exceeding the numbers Hunkins had expected. |
We found some interesting tidbits when we dug into testing the flow of our new RHS cylinder heads. Only a few issues back (see "The Ironman," July 2007), we used a set of Summit iron cylinder heads, and were more than impressed with the numbers recorded when the machine shop sent them out for testing. What surprised us was that testing the RHS cylinder heads at Westech on its FlowCom-equipped SuperFlow bench showed nearly the same flow. However, we've preached the importance of not taking numbers from two different benches when making comparisons, and were curious enough to re-test the iron heads on the same bench to get a valid comparison. It seems the Westech flowbench is definitely less generous than the bench used to originally test the Summit heads. Testing back-to-back on the same bench gave us a valid set of numbers for the comparison.
| RHS 320CC ALUMINUM HEADS |
| VALVE | INTAKE | INTAKE | EXHAUST |
| LIFT | cfm(poor) | cfm(good) | cfm |
| .050 | 37 | 38.6 | 29.3 |
| .100 | 72.2 | 73.6 | 60.5 |
| .200 | 131 | 129 | 114 |
| .300 | 191 | 186 | 156 |
| .400 | 248 | 238 | 193 |
| .500 | 296 | 286 | 224 |
| .600 | 320 | 330 | 252 |
| .700 | 328 | 356 | 276 |
Have a steady hand when checking the P/V clearance
Checking P/V Clearance
One check that should not be neglected is the piston-to-valve clearance. Coming up short here can be disastrous, though our assembly was well within Outlaw's safe specifications. The proper procedure is to place a few dabs of clay on the piston valve reliefs, then coat them lightly with oil. Install the cylinder head temporarily on the block, install the valvetrain on that cylinder (using light "checker" springs), then rotate the engine over by hand. The valves will leave witness marks in the clay, which can then be carefully bisected, and the clearance measured. The p/v clearance measured .178 inch with the Thumpr cam, which is more than enough. You should look for a bare minimum of .100 inch, with .120 being preferable as a minimum.
| SUMMIT/DART IRON HEADS |
| VALVE | INTAKE | INTAKE | EXHAUST |
| LIFT | cfm(poor) | cfm(good) | cfm |
| .050 | 35.5 | 32.4 | 31.5 |
| .100 | 72 | 69 | 66 |
| .200 | 144 | 143 | 103 |
| .300 | 196 | 197 | 152 |
| .400 | 247 | 249 | 188 |
| .500 | 286 | 292 | 217 |
| .600 | 307 | 320 | 240 |
| .700 | 307 | 326 | 256 |
The Howitzer Vs. The Ironman
What's The Diff?Sharp eyes will notice there's a lot of commonality between The Howitzer and The Ironman, a 468-inch big-block we put together in the July issue. Both engines are one and the same. Sort of. When we put the iron-headed 468 on the dyno and made 579 hp, we decided to go back for a little more power and a little less weight before dropping it into the Chevelle. The primary differences: Swapping the iron Summit 308cc heads for the RHS 320cc aluminum heads, boosting the displacement from 468 inches (basically a stock .060-over 454) to 496 inches using a longer 4.25-inch stroke, and-surprise-stepping back from the brink in the cam department, forsaking a radical-for-the-street .647-inch lift solid roller cam for a street-friendly .570-lift hydraulic roller (COMP's new Big Mutha Thumpr). Another smaller change was a slight increase in carb size from an annular booster 825 Mighty Demon to a downleg booster 850.
The Ironman 468 made 579 hp at 6,200 rpm and 545 lb-ft of twist at 4,200 rpm, and had a build-it-yourself price of $6,633.09. We were initially concerned that the stroked 496 might blow the budget with a more expensive set of aluminum heads, but the calculator only registers another $890.28 over the Ironman's price, and produced 47 more hp and another 90 lb-ft of torque (coming in 400 rpm earlier). We like that trade-especially with the weight savings-and we're glad we made it. Andy Mitchell of Outlaw Racing says he can build The Howitzer for you just like this for about $1,500 over the do-it-yourself price we're listing, and interested parties should call him at 909-931-4612.