Got questions?
We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re talking valve spring pressure and how it affects valvetrain performance.
C.K.• Somerville, OH
Q: I have a 1967 Ford Bronco. Being the serious gearhead that I am, I want as much power as I can get out of the 302 that’s in it. So far, I’ve added an Edelbrock Performer carb and intake, headers, roller rockers, and a Summit Racing .471-inch lift cam kit. I have a set of Crane “universal fit” dual valve springs–should I install them, too? I’m on a tight budget; is there anything else you could recommend that won’t break the bank?
A: Using universal valve springs is like wearing a pair of universal shoes–not ideal! If you use valve springs with too much pressure, you will wear the lobes off the camshaft. If the springs are not strong enough, your valves will float at higher rpms. The camshaft you’ve installed requires valve springs with an installed height of 1.703 inches, a seat pressure of 95 pounds, and an open pressure of 260 pounds at 1.200-inch height. Try a set of Crane Cams 99833-16 springs.
It sounds like you’ve addressed the incoming air and fuel and have the outgoing exhaust handled. As far as additional upgrades, the next step would be to ensure that the air/fuel charge is properly combusted in the cylinders. For this, we recommend adding an ignition system, such as an MSD 6A ignition, to your truck. Also, your engine would probably benefit from having the distributor advance curve adjusted.
Hi. I’ve plotted the cam profile and calculated the resultant acceleration and hence inertial load of the valve. There is a huge very short duration acceleration lasting less than 0.5 ms at 6000 rpm at the initial ramp. Is it expected that the valve spring matches the resultant inertial load at this point? I should say that at all other points on the profile the valve spring force does exceed the inertial load of the valve and is 180 lbs at the peak. I guess I’m trying to get the design criteria with governs the required valve spring load. Thankyou in advance of your comment.