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Originally Posted by musclemustang8
as far as changing the springs, the springs i have are rated for the amount of lift and there is only 1lbs of pressure difference. the only difference between mine and the ones they suggest is mine is a single spring with a dampener and the ones they suggest is a dual spring. it there a major reason i cannot use the ones i have for turning 6500-6800rpms?
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I understand your previous point about being on a budget, still, you may want to consider asking Mark about a custom ground solid flat tappet camshaft, as the extra power benefit will be worth another 30-50 bucks.
I'd want to carefully check your springs before making any assertions as to their suitability for a particular purpose. If you know the spring part number, the installed (measured) height, your lobe lift and your rocker arm ratio, then it is possible to calculate everything needed. However, to put all of this into context, a "hydraulic spring" is basically one with lower seat pressure and open pressure than a "mechanical spring." High spring pressures used with hydraulic cams serve to collapse the plunger (internal valving) of the lifter and can cause all sorts of valve event timing oddities.
Higher spring pressures are necessary to control valve float at higher RPMs. This is especially true with large, heavy valves as are common with large valve Cleveland heads. Typical installed seat pressure of about 100# is common with a hydro cam, whereas 110+ is common with a mechanical flat tappet cam. For example, I have a basic, low-budget 351C with 4V CC heads and a mechanical flat tappet cam. I run 150# of seat pressure and use "cool face" lifters. A maximum of about 120-135# would be used with standard flat tappets for a streetable engine.
You need to ask yourself where your seat pressure is in order answer whether or not your "springs" are up to the task. It is not necessarily the material or the part number of the springs, but the installation details and the spring rate. Since you mentioned that the spring rate was the same for mechanical lifters, I'd be a bit suspicious without more details. Usually, springs recommended for mechanical cams have a higher rate than hydro springs, though not necessarily always the case.
One thing is for certain...you don't want to get too much or too little spring pressure throughout the entire valve operating range. Incorrect spring pressures cause all sorts of nasty problems. Too much = flat lobes, debris in the pan and really piss-poor performance. Too little = floating valves at higher RPMs, smacked pistons, broken camshaft dowel pins, sheered distributor gear teeth, bent valves and piss-poor performance.
If you don't know your spring condition, you're inviting a host of problems.
When you compare springs, especially comparing the dual versus single coil designs, you need to add the combined spring rates of the dual coil springs to get the combined spring rate. This can easily exceed a "standard" single coil spring, but, like nearly everything having to do with engines, not necessarily.
The thing that is of some interest is the harmonics involved with springs. Everytime we close the valves, we're basically hammering them against the seats. Some don't realize that the valves usually bounce off of the seats a few times before settling down kind of like dropping a BB on a glass table. Th force of gravity is like the force of the valve spring, though not quite. The hammering produces shock waves through the materials involved. These shock waves are picked up by the valve springs and can have a detrimental effect on their useful lives unless controlled.
The dampener aims to control harmonics. Dual valve springs also control harmonics kind of like the way a multi-chamber muffler controls exhaust noise.
My recommendation is to closely follow the spring recommendations of your camshaft maker. Different ramp designs will affect harmonics! Double check your spring rates using a spring tester and install them carefully to the desired installed height necessary to obtain the rate indicated by the manufacturer based on the actual measured rate for the given spring. Use proper cam break-in procedures and adequate moly lube during installation.
Another note on budgets, spring rates and cam break-in...just one wiped lobe will pay for the extra cost of a roller cam and related pieces if the flat tappet cam isn't carefully attended to...and with infinitely less frustration involved. You could sell a set of your heads to finance your roller cam. You'll make better power and be practically unconcerned with break-in...and, if you ever do occasionally street drive your engine, a roller will live so much better between stoplights than a flat.
:davis:
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