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Rocker-Arm Tech Talk: Intake Valve Speed

Early Hemi Rockers
When Titan began designing rocker-arm systems for the early-Hemi heads manufactured by Chrysler in the 1950s and copied by Toyota in the 1960s, we made several different types of test units. After making various design changes, we realized that it didn't make a lot of difference what we did with the exhaust, as far as increasing horsepower; the gains all came from the intake rocker — and it's all in the geometry.

You can make rocker arms move fast at either end of the lift, or in the middle. The middle is where almost all rocker arms are designed to be moving the quickest. That makes sense, but it doesn't make the most power. Maximum power is made by making the intake rocker move very quickly at, say, .100- to .150-inch up the cam lobe. Fast movement occurs when the valve stem is 90 degrees to the rocker fulcrum (measured through the shaft center) and the fulcrum is 90 degrees to the pushrod (center of ball). In a Hemi, it's impossible to get the pushrod end perfect, due to the variables involved (e.g., base circle; lifter-button height; deck height; etc.).

When the typical racing rocker arm is designed, the engineer will base it on whatever camshaft racers are using at the time. For example, on an early Chrysler, you've got some old fuel cam that might have a .410-inch-lift lobe, which is pretty common. Most manufacturers would take that halfway up the lobe; in other words, subtract the lash and go halfway up the lobe, at which point they'd go 90 degrees over to the fulcrum from the end of the valve.

Running Titan rockers is like running a longer valve, because the pivot is the center of the axle on the roller, instead of the actual end of the valve. We decided to make it real fast at low lift, because we found that a lot more horsepower resulted from getting the valves to move quickly at low lift. It's basically like putting a longer lobe on the cam, only better, because you don't have to run a longer lobe, and the air flows sooner.

Our favorite example involves a nostalgia Top Fuel team. These guys already had a set of custom steel rockers on which the pivots had been changed around, and they wouldn't try ours. Finally, though, they broke some rocker arms, and didn't have any way to fix them before they went back East to race. Only then did they finally put our rocker arms on there — and went 13 mph faster than they had ever gone before, on the very first pass! Then they beat that pass by another three or four mph. After that, the red Titan rockers were on that car. There's definitely a lot more horsepower freed up in a fuel motor by this fast-moving, low-lift technology.

The ratios on our early-Chrysler and 8.3L Arias/Fontana rockers are just a hair over stock on the exhaust side and as high as 1.7:1 on the intake, with a real strong spring and a long push rod. On the intakes, if you run the .250-inch-longer adjuster that we make, you're effectively shortening the pushrod by .200- to .250-inch, so the ratio drops back to about 1.50: to 1:53:1. That's a plus because you can adjust the ratio of the rocker arm by changing the length of the pushrods on the intake. It doesn't change the exhaust much, because all of the angles are a lot straighter, since the rockers are really long. On the early Hemis, the books all say the stock ratio is 1.5:1; when we were checking them, they actually ranged from about 1.40: to about 1.44:1. So our intakes can be about three-tenths of a point above the stock ratios.

Titan's rocker-arm systems make a big difference in various ways. Our billet-aluminum rockers are much stiffer, so there's less deflection, and they accept more ratio. In the Toyota 1.6-liter engines, the stock ratios are 1.33: to 1.35:1. Our rockers take it to just over 1.5:1, with a strong spring. That's worth 10 to 12 horsepower over conventional, high-rate rockers in a little Toyota Hemi. Our Chrysler rockers free up 20 to 30 horsepower in even a mild 354/392 iron Hemi.

Our Toyota rockers employ conventional mounting; the Chrysler and Arias/Fontana models are all-needle-bearing on the fulcrum. We install a full-complement, 3/4-inch-wide needle bearing in each end of the rocker arm, so it's real large and super strong, with a huge load-carrying capacity. We also came up with an oil hole that oils the Chrysler and Arias/Fontana rocker like a connecting rod: It just drip-oils. On the early Hemis, especially with a wet-sump system, the pushrods seem to get lubricated real well with the oil that's thrown up off the lifters. We also drip-oil the intake-pushrod cups in the Chrysler and Arias/Fontana rockers.

Numerous other evolutionary design changes have been made as Titan engineers identified better ways to build these parts. In addition to the standard V8 rocker systems illustrated on this site — direct, bolt-on replacements for the rocker assemblies of Chrysler-style and 8.3L Arias/Fontana cylinder heads — Titan offers custom rocker-arm systems for use with the billet heads now gaining popularity with nostalgia racers and serious street rodders. For more information about the custom systems we manufacture for special Hemi applications, please call or e-mail.

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