I love your magazine, especially the engine buildups. After buying the Jan. 02 issue, a question popped into my head. You built a 406 small-block with heads that flow 300 cfm and an intake manifold that costs around $350 to make 515 hp. Now I remember a 355ci small-block that you featured called the Gladiator that was 51 ci smaller than the 406, used AFR 195 heads, flowed in the 260-cfm range with an intake that costs about $160, and made 524 hp. That sounds kinda weird to me. Was that 406 running on four cylinders? Both engines have roughly the same compression, camshaft, and carburetor. What do you guys think?
--John Kobik, via e-mail
One of the great things about a car magazine is how the readers constantly challenge us. John Kobiks letter asks a great question that we felt needed several pages in the magazine to answer completely.
Power is what everybody wants. If all you did was look at the peak horsepower numbers, it would appear that the Gladiator engine beats the much more expensive 406. This is especially true when you consider that the Gladiator is 51 cubic inches smaller. But this overlooks the torque created by the 406. So we decided to take an in-depth look at both of these engines and the power they produce.
The first thing we did was compare the power curves. Right away, its clear the 406 makes almost 50 lb-ft more torque at 3,500 rpm, which is the lowest common rpm point. Of course you would expect the larger motor to make more torque, but this is a ton of power.
As the rpm climbs, the power differential begins to favor the 355, and at its peak, the Gladiator makes 14 more horsepower.
Looking at the average numbers, the 406 makes more average torque, but the Gladiator makes more average horsepower. While 14 more horsepower sounds impressive, its average power that eventually moves the car down the track. So we plugged both power curves in the Racing Systems Analysis Quarter Pro computer simulation program. We simulated a 3,500-pound Chevelle with a TH350 automatic, a 3,000-stall converter, 3.73 gears, and a shift point of 7,000 rpm.
Heres where it gets interesting. The simulated quarter-mile passes for both engines in the same theoretical car were within 0.05 second of each other. The 355 Gladiator ran an 11.36/119.30-mph pass with a 60-foot time of 1.69 seconds. The 406 Muscle Mouse motor ran a slightly better 1.65-second 60-foot time and pulled off an 11.31/ 118.90-mph run. In both cases, we optimized traction with a big enough tire to eliminate tire spin. The 406 got to the finish line first, but the 355 motor had the stronger top-end charge. In reality, these two engines would run very similarly at the track despite the 406s apparent lack of horsepower.
This illustrates the significance of torque in the overall power curve and its importance in acceleration. In this simulation comparison, we left the converter exactly the same. However, had we subjected the 355 to a lower stall converter where that motor makes less torque, the 406 would have pulled the smaller motor with both a quicker e.t. and higher trap speed. This points out how important it is to tune your chassis and drivetrain combination to take advantage of the engines power curve. In this case, the Gladiator engine would really benefit from a four- or five-speed manual trans leaving at 3,500 rpm or higher.
We also looked more closely at the parts used in both these engines. Amazingly, these engines are far more similar than they are different. The Gladiator started life as a ZZ4 engine that Westechs owner John Baechtel converted to forged Federal-Mogul 10:1 compression pistons and rings for increased durability. He also added a set of out-of-the-box Air Flow Research 195cc aluminum heads. Then, over the course of years of beating on this small-block, the engine has witnessed dozens of camshaft, intake manifold, carb, and header swaps in search of more power.
In the test we included here, the Gladiator went into battle with a big-port Victor single-plane intake, an 850-cfm Speed Demon carb, and a set of 1¾-inch street headers pumping through a set of Flowmaster mufflers. Weve also included the complete cam specs on the Comp Cams solid-roller cam (see Cam Specs). As you can see from the chart, the Gladiator 355 enjoyed a slightly longer-duration cam. Combined with its smaller displacement, this is a big reason why the Gladiator made more power than the 406.
On the 406ci side, the Muscle Mouse motor enjoyed a much larger intake port with the 227cc Dart Pro 1 heads, which had also been treated to a full CNC porting. Compression with the 406 was slightly lower at 9.8:1, and the Comp Cams mechanical roller was also slightly shorter in duration and lift compared to the Gladiator grind. We used a similar large-port Dart single-plane intake, and the carb on the 406 was also a similarly sized Demon 825-cfm Race Demon fuel mixer. One difference was that we used a set of 17/8-inch headers on the 406 flowing through a pair of Borla stainless mufflers.
The power curve we published for the Gladiator was the culmination of dozens of dyno pulls on that engine, and it was one of the best power curves this engine ever generated. On the other hand, the numbers on the 406 represented the first test of this engine. Were not using that as an excuse, but we also now have a plan to improve the power curve.
For example, after studying the flowbench data, its clear that the Dart Pro 1 CNC heads demand a single-pattern camshaft where the exhaust duration and lift are the same as the intake. Combined with the outstanding 0.100-inch exhaust-flow numbers, a shorter-duration cam will help prevent the over-scavenging of the cylinder during the exhaust event. We think this hurt the 406s final power output.
Its clear that the 17/8-inch headers were too big for this combination. We also tested a set of 15/8-inch headers and at 2,800 rpm the smaller headers were worth an additional 43 lb-ft of torque. The downside of the smaller headers is a 20hp loss at horsepower peak.
If you look at these changes all together, were working mainly on the exhaust side of the engine. The smaller 1¾-inch headers will improve torque in the midrange, while the shorter-duration cam should help the peak by reducing the scavenging effect of the longer duration. Were not sure what all this will be worth, but were hoping for 10 to 15 horsepower along with an equal amount of torque.
All this illustrates the importance of matching components. We can conjecture and guess, but ultimately it comes down to trying several different combinations in search of more power, but even then it wont be even close to the ultimate power this motor can make. Thats what makes all this engine building and testing so much fun. Just when you begin to think you might have hit the power limit, somebody comes along with an idea and raises the power bar another notch.