Mechanical rollers (left) are slightly lighter than hydraulic-roller lifters (right) and offer better performance in high-rpm applications. High dynamic loads on the hydraulic piston in the lifter will actually force it down, losing lift and duration. One thing that can help prevent this piston movement in hydraulic lifters of any kind is to use a thicker oil (like 20w50) along with a higher oil pressure.
Small-Block Power
SSG Brian Norman, Afghanistan, via e-mail: I have a 383, cast crank, two-bolt-main motor. It has Dart 220cc heads, a Victor Jr. intake, small base circle 0.525-inch lift, and 294-duration hydraulic-roller conversion with a 10.5:1 compression ratio. It also has forged pistons, good rings, and standard rods. The carb is a 750 double-pumper. I want to put nitrous on this motor but am not sure the cast crank will be safe. This motor pushed a Vega with a 9-inch Ford rearend with 3.55s to an 11.50 e.t. The drivetrain was a Turbo 400 with a manual valvebody and a 3,500-stall converter. My "new" Vega is mini-tubbed with 31x12.5x15s and a four-link setup. I want to build one of the following motors: 406, 415, or 420, internally balanced with all forged internals and a four-bolt-main block. The Dart heads, Victor Jr. intake, and hydraulic-roller conversion cam mentioned above will all be installed. What kind of numbers can I expect with one of these motors versus my current 383? Would the 406 or 420 be effective? What gears would you recommend for this combo? I know I'm asking a lot of questions, but I'm deployed to Afghanistan with very little access to knowledgeable individuals
Jeff Smith: Wow, Brian-lots of questions. First, let's look at your current combination. You mentioned the 383 has a set of Dart 220cc race-series heads. These are excellent heads and one of the highest-flowing 23-degree heads that Dart sells using 2.08/1.60-inch valves. These heads will move some serious air. What seems odd with your list of parts is the 294-duration (I'm assuming that's advertised duration) hydraulic-roller camshaft. All the other components tend to support a higher peak torque point, which means the 383 will achieve peak horsepower around 6,500 rpm. You didn't mention who ground the cam, but to hazard a guess, we plugged your combination into Comp Cams CamQuest6 cam-selection software and it came up with its XR294 hydraulic-roller cam that the simulation estimated would make 530 hp at 6,500 and peak torque at 5,000. This was basing the flow numbers on the 215 Dart head because we didn't have any flow numbers on the Dart 220. While this probably would work, our question is, why use a hydraulic roller? The problem will be that the lifter is heavier than a mechanical roller. Combined with your higher engine speed, this will require more valvespring pressure to keep all the monkey motion happy at 6,500. Unfortunately, the higher spring pressure often will overcome and push the hydraulic piston down into the lifter at these higher engine speeds, causing a loss of power. The smarter move is to go with a mechanical-roller cam that allows you to run a little more spring pressure with no loss of power.
To make things fair, we found a Comp Cams mechanical-roller cam with similar specs of 242/248 degrees at 0.050-inch tappet lift but with better lift at 0.570/0.576. Remember, you have to subtract the 0.018-inch lash from these lift numbers to get the true valve lift. With this solid-roller cam, the Comp Cams simulation predicted it would make 555 hp at 6,000 rpm with 541 lb-ft of torque at 5,000 rpm. Note that the roller-cam simulation is worth 25 hp but also at a 500-rpm-lower engine speed. Plus, you have the option with the mechanical-roller cam to experiment with the lash a little bit by either tightening the lash to increase the duration or loosening to decrease duration (roughly 1 degree per 0.001 inch of lash change). If this was my engine, I'd sell the hydraulic-roller cam-and-lifter package and invest in a mechanical roller
As for your question about a larger-displacement engine, all those parts would work equally well on a larger-displacement engine. If you are going to build a strong-rpm engine, then you'll want to invest in a good steel crank. If that's part of the agenda, then consider building the largest-displacement engine you can with more stroke. Let's say you decide to buy a Lunati 4340 steel crank. The price is roughly the same for a 3.75-, 3.875-, or 4.00-inch crank, so you might as well build the biggest displacement you can because it's worth more power. If you're using a stock 400 block, then I'd go with 3.875-inch stroke with 4.155-inch bore, and you'll end up with a 420ci small-block. If you are going to spend the extra cash on an aftermarket block, then either a Dart Little M or a World Products iron block will accommodate a 4.00-inch stroke, which with the same 4.155-inch bore will bump up the displacement to 434 inches. In the case of 420 ci or more inches, I'd go with a bigger cam because you'll have increased the displacement by almost 10 percent or 40 cubic inches. Now you could increase the cam duration up to 250 to perhaps 260 degrees at 0.050 and take advantage of the additional lift to get it up around 0.600 inches. This displacement will add a minimum of 30 hp and probably even more torque. This puts a 420 at roughly 580 hp or so, which is very possible.
As for gear ratios, we'd need to know a little more information, such as the transmission ratios and (assuming it's an automatic) the stall speed of the converter. But the basic concept is to determine the overall height of the tire, which will help dictate the trap speed. Assuming around 550 real-wheel horsepower in a 3,200-pound car, that's roughly 130-mph trap speed. With a 29-inch-tall tire and a 3.91 gear, that puts you at roughly 6,250 rpm at 130 mph, depending upon converter slippage and how well the car runs in the first 60 feet.
This is the equivalent of low 10s if the car hooks well. That's a good ride if you can put it all together. Good luck, Brian.
More Info
Comp Cams; Memphis, TN; 800/999-0853; compcams.com
Dart Machinery; Troy, MI; 248/362-1188; dartheads.com
Lunati; Olive Branch, MS; 901/365-0950; lunaticamshafts.com
World Products; Ronkonkoma, NY, 631/981-1918; worldcastings.com