tylercamaro

iTrader: (1)

how does one select a valve spring? im fully aware of what it does but you go with too much seat pressure adn depending on cam and other variables you wip out the cam or lose engine performance with too little etc etc. how do you effectively choose whats proper? its something ive just always taken someones word for and ended up just using the cam manufacturers stuff most times. any good articles ive passed up? ive been researching and just cant grip a good understanding of it.

skinny z

Interested in a little reading?
Get David Vizard's book: How to Build Max Performance Chevy Small Blocks. 2009 (2nd edition)


or

https://books.google.ca/books/about/...d=kmTNubYf0p0C

It's full of great tech and there's a section that deals exclusively with valve springs.
You may find it informative. Be sure it's the 2009 edition .
Amazon may even let you take a preview of a couple of pages.

ploegi

Chat with the cam manufacturer, they will have recommended valve springs to match their cam.

redneckjoe

way above my knowledge. but the valvespring is amazing!

cardo0

Well Tyler there is enough science on vlv springs to write books on them. I know most owners just hope to bolt them on and go. For the novice beginner it's best just buy them matching vlv springs in a cam "kit". Next option would be contact the cam mfr.

Sorry but to fully answer your question I would be typing for hours and I'm no expert at all - hobbiest at best.

tylercamaro

iTrader: (1)

im probably in a similar boat, ive found cam manufacturers to be biased at best and usually veer away from them, i have a above par understanding of cam selection but as far as valve springs to match i havent even tried. i was hping to veer form the manufacturer advised such in the future as they dont fully know what your vehicles doing.

skinny z

Like I said, if you want some unbiased information, check out Vizard's book. And it's full of a lot of other great tech too.

ploegi

Cam manufacturers biased? As to what? Seems to me, they would be in the best position to tell what springs go best with your cam........ If nothing else, ask them what spring pressures they recommend, installed height, and all that jazz, then buy the brand you like.

sofakingdom

iTrader: (1)

The ABSOLUTE WORST thing that can happen, is coil bind. This amounts to trying to compress metal. In the universe I live in (maybe yours is different? maybe, but I doubt it) ANY operation wherein success is possible only if metal is compressed, has a low probability of success. Avoid this. Next worse is "valve float". Contrary to popular opinion this is NOT the tendency of the valve to keep opening as the cam reaches its peak; rather, it's the tendency of the valve to bounce when it hits the seat as it closes.

Seat pressure: you need enough to keep the valves seated at the instant they close (no bouncing) stock, maybe 90 lbs or so; an aggressive flat-tappet hydraulic, maybe 120 lbs; an even more aggressive roller-tappet hydraulic, maybe 135 lbs; solid rollers, well by the time you get there, you're measuring in laps or passes, so, basically, all you can stand without eroding the seats

Full-open pressure: you need enough to keep the lifter following the cam "over the nose". A flat-tappet hyd will want in the low-mid 300s; a solid flat will want a bit more; a hyd roller-tappet will want near 375 lbs.

Rate: how fast the spring tension increases as lift increases... correct value is determined by starting at the seat pressure, choosing an appropriate range for the pressure to be at when at full lift, finding the difference, and dividing by the valve lift. For typical street cams of all sorts, will want to be something in the mid 300s kind of range, but maybe more or less in some situations. Rate is lbs per inch, so if you want 120 lbs on the seat and 320 lbs full open, then you want 200 lbs of difference; if your cam lift is .500", then you want a spring that will add 200 lbs more pressure in .500" of lift, or about 400 lbs/in. A typical street spring is a bit less than that, around 350 - 375 lbs/in, which is OK. I would prefer a spring with a bit lower rate that I could set up to have "enough" over the nose, "enough" coil clearance to avoid bind, and then as long as it gives MORE THAN the "minimum" seat pressure, I'll just take it. I might for example choose a spring made of many turns of small wire with a relatively low rate, set it up for .100" of clearance from coil bind and 375 lbs over the nose, and just "accept" 150 lbs on the seat.

Coil bind: when the adjacent turns of wire of the spring touch when fully compressed (max valve lift). VERY VERY VERY VERY VERY VERY VERY VERY bad. Not only that, not good at all. You should keep the spring AT LEAST .050" away from this height and preferably farther; the more you drive it on the street, the more clearance you need. Once you get past .080" or so, you've maxed it out, and no further benefit is available. When the spring stacks up hard, BAD things happen, starting with parts breakage, and RAPIDLY getting worse from there. For example if a spring breaks it might allow the valve to drop into the cylinder, which will possibly put a hole in the piston or bend the rod, either of which is widely thought of as an adverse outcome which limits the engine's future performance. (to ZERO....)

Max lift: what it sounds like... the ABSOLUTE MAX that the spring is supposed to experience between full open and full closed. Usually given a somewhat "optimistic" "rating" on the part of the mfr. Not to be trusted except as a rough guide, and then, something to stay WELL AWAY from.

Installed height: the height of the spring "at rest". Determined by valve length, spring pocket configuration, retainer shape, etc. The spring you choose should have the SEAT PRESSURE as described above, AT this height. I.e. if you have an aggressive flat-tappet hydraulic (let's say, a Comp XE268, as a typical-ish example) which will want a seat pressure near 120 lbs, you will want to choose a spring that can provide that much seat pressure at a height you can actually install it at, which might be 1.750" for a small-block Chevy V8, and won't exceed (or really even, approach very closely) the max open pressure or the min coil clearance.

OD: the heads usually have a pocket cut into them. The spring MUST fit into that, and MOST NOT be able to move around more than a few .001"s in there. (maybe .010" or so) For heads (usually aftermarket) that have a pocket bigger than the springs you want to use, you can get a discrete "spring seat" that fits closely to the guide and matches the spring OD. Stock, SBC spring pockets are 1.250", and guides are .675" or so, varying widely according to how drunk the machine operator at the factory was that day, whether they're Vortec heads (in which case they're MUCH larger than that), and so on. A reputable machine shop will cut them to .530" or .500" to fit Teflon seals onto them. Spring "seats" or "locators" often need to fit fairly precisely to this, so pay close attention when ordering machine work and parts.

ID: the spring MUST fit over the guide. This should be somewhat obvious. It should also clear whatever seals you want to use.

If you want to have some real fun, go get yourself a suspension coil spring and play with it. A junkyard one (you can find em laying around all over the yard) will work fine. A couple of things you'll find instructive include just throwing it at the ground, and hitting it REAL hard with a BIG sledge hammer. (be ready to DUCK and RUN) A valve spring acts EXACTLY the same. The action of the cam is pretty much the same as a hammer blow hard enough to FULLY compress it. Valve springs live in an EXTREMELY high stress environment and does all manner of things that aren't obvious to the casual observer. One of the main reasons for avoiding "coil bind" is that the spring VIBRATES and RESONATES: it goes "boioioioioioioionnnnnnggg" when the rocker arm hits it. If the coils hit, parts WILL break, because then even though it hasn't "stacked up", it's STILL acting like trying to compress metal, except that THE SPRING is trying to compress everything around it. (rockers, push rods, studs, lifters, cam lobes, etc.) If the coils touch, some one of those other parts WILL break, unless the spring breaks first. Either way, SOMETHING is gonna break.

There's different other things, like beehive springs (smaller at the top than the bottom), retainers, weight of all the parts, shims, seats, keepers including offset ones, and so forth. Those are not matters for somebody at the level of asking the question you asked, so I'll leave those aside unless you find yourself in the situation of needing to know.

I'm not a real big fan of trying to cheeeeeeeeep out on valve springs. I'd rather err a bit on the "too much" side than AT ALL toward the "not enough". There are FEW parts inside an engine that seem so simple yet can have such profound effects. I would cheeeeeeeep out on main bearings before I'd do the same on valve springs, if that puts the risk/reward balance into perspective adequately.

AlkyIROC

My camshaft was a custom grind. There was no spring recommended but they did give what seat and full open pressure should be. You then look for a spring that will give those specifications.

I set up the springs in my BBC heads. Valve lift is over 0.800". I use triple springs. Closed pressure is around 280 pounds and full open is around 750 pounds. My install height is enough so that I don't get coil bind and get the pressures I was after. I did a lot of tricks setting up my springs including isolators, shims, 10* locks etc. Just because one spring gets a 0.010" shim to get the required install height doesn't mean they all get the same thickness shim. My intake valves even have lash caps but that was more for a geometry issue.

Like Sofa listed, there are a lot of factors with valve springs. Worst thing you can do is a more aggressive cam swap but keep the worn out stock springs. Use springs with similar specs as to what the cam grinder recommends. Many will give you a Comp Cams spring number to use unless they have their own line of valve springs.