Date: Wed, 02 Jul 1997 00:25:55 -0600 From: Will Wood Subject: Re: Singleport vs. Dualport (Sunday! Sunday!) All valve springs suffer from harmonics, as the spring is compressed the metallurgy wants to push back, this causes the spring to be a spring. Each spring for a given size load and compression and rate of compression will have a certain harmonic vibration associated with it. Typically, the larger the spring wire, the stronger the spring the higher rate of compression and more compression it will take before excessive harmonics come into play. When excessive harmonics come into play, the spring starts oscillating this oscillation results in a reduced amount of pressure the spring exerts. My boss used to work on software that was for ship engines, ya know massive springs with literally hundreds of pounds of valve spring pressure. The cams for these ship engines had to be designed very carefully, otherwise the harmonics involved for the spring would cause them to break. The same thing holds true for a car engine, for a given spring load, lift and rate of compression (cam ramp and RPM) will cause the harmonics and oscillation to come into play. When this happens, the valve doesn't fully get the seating pressure it needs since one force is expanding the spring and the oscillation is causing the spring to want to vibrate. This causes the valve to float or stay partially open. This happens with cams with fast ramps or high RPM. Stronger springs resist the oscillation factor and allow you to run more RPMs and or a faster ramped cam. The Ramp is the rate at which the valve goes from closed to open to closed and obviously has a direct effect on the valve spring. Why is this important in a bus? Heat. Heat reduces the effectiveness of the spring in such a way that the oscillation or floating factor happens and a lower RPM or with a comparably slower ramped cam that would be used in a bug. A bus does run hotter than a bug, no question about it. The engine has to produce more power for a given speed, weight and air and everything else comes into play. St. Berg has numerous articles about it, but all high RPM racers and every street bus I build now has at least high rev singles and in some cases duals. The 2110 I have in my 64 has dual high rev springs, the single high revs I originally installed wouldn't allow me to get up over 5500RPM easily, now I can rev to my hearts content. Valve float causes a lot of problems from broken valves and keepers to busted retainers and springs. This also contributes to early seat failure as well. The trick is balancing the needs of the engine and it's design with the amount of spring required. If you never will see over 5000RPM use single high rev springs. I say this because the stock springs in the busses have suffered from float at as low as 2500RPM. That's slower than freeway speed for most of them. Naysayers will tell you "heavier springs require more horsepower", which has some truth to it, but it is mostly bunk. When you eliminiate float, you provide better combustion, better valve life and your engine will work better and produce more power. Another naysaying is "Heavier springs cause the valves to break" again bunk. Think about it, your forcing the valve to follow the cam precisely, the cam is what closes the valve and it doesn't let the valve slam onto the seat! This promotes better wear on the cam and lifter surfaces as well since the lifter isn't flying away from the cam, they're maintaining good contact. As always, adjust your valves regularly. You also can use singles or duals with stock aluminum timing gears. Using straight cut gears does reduce horsepower demands and cam thrust bearing wear, but proper clearance checking of the thrust bearing will allow full life of the cam bearings using stock gears. Triple Springs are available from GBE, but do require straightcut gears. So, if you have a bus or use a non stock cam or want to run at higher RPM, you should change your springs. Single High Rev springs are about $35 bucks and can be installed in under 1/2 hour. You can rent the tool from a local rental place and DIY. High Rev duals require machining of the bosses in the heads and isn't for the average DIY. Will Wood 67 Standard Microbus 63 23 Window Deluxe 64 Crew Cab - Frankenstein 61 Single Cab - Annette (You guys figure it out) 61 Convertible 57 Oval Window Deluxe Sedan 56 Kombi 67 Westy (Parting out Smashed), 67 Deluxe rolled, 63 Kombi Taco-shelled 59 Panel Van 80 Rabbit X 2 93 Eurovan MV (Wifes) Hey, what the heck, I've got to keep the weeds down somehow!