V8Astro Captain

iTrader: (1)

I have my engine out right now so I want to get a larger cam. I like the specs on the LT4 hot cam but I need to know if my 981 Comp valve springs will handle them. These springs came on the Dart Iron Eagles I bought.

I found all the info for the springs on Comps website but it doesn't really tell me much. I have 1.6 ratio rockers so the lift will be .525".

here is the link to the spring info
http://www.compcams.com/catalog/302.html

...link for the heads
http://www.dartheads.com/sbiron180.htm

Will the 981's do the job?

thanks...

Z_Ghost

Comp recommended the 986 springs for the cam I got and the lift on it is 495. I also remember the cam one step under the one I got (488 lift) said to use the 981, so I would say no the 981 springs will not work, why not just call Comp and ask them.

RB83L69

I'd suspect that Comp will tell you that those springs won't work. They're 1.25" outer diameter, stock size. Nobody that sells both cams and springs, and warranties them, will sell you a cam with more than .500" lift and 1.25" springs, except maybe GM. K-Motion will sell you the same springs and tell you they're good to .550", but they won't warranty anything when the cam lobes wipe out, studs pull, springs break, rockers eat themselves for lunch, push rods bend, etc. etc. that always happens. The GM springs are the same way: people have all kinds of trouble with that kit, resulting from the inadequate springs and the inferior rockers, and believing that "GM wouldn't sell me somethin that doesn't work, would they?" when they just stick that stuff into an otherwise stock motor with pull-out studs etc.

They'll tell you that you need part # 986 like the other post said. They'll fit right on your heads. You'll need the retainers that go with them too. Don't try to cheap out on that, it will surely come back to bite you in the butt, which would be a shame because that combo ought to run pretty good. Nobody likes reliability problems.

V8Astro Captain

iTrader: (1)

I see. So it's not so much a matter of coil bind and seat pressure, but how much strain is on the coil of a small diameter spring.

So in your experience, how much valve lift is safe for a 1.25" spring in a daily driver?...with a cam like mine.

Even if I keep the cam I have now I will have .481" on the exahust with 1.6 rockers.

RB83L69

You're right, there's more to it than just coil bind. Alot depends on the cam profile and the RPMs, as much as just raw lift numbers...

Think about what a spring is doing. It's bending back and forth many times a second. For a quick illustration of what that does, go bend a coat hanger back and forth a few times until it breaks; then immediately just as soon as it breaks, pinch the end between your fingers.

When you get through cursing me for how bad you will have just burned yourself, think about those springs. If you imagine yerbasic stock spring made of few turns of thick wire, each "unit length" of the spring has to bend farther than a spring of otherwise equal properties made of more turns of thinner wire. The spring will actaully heat up in operation, just like tha tcoat hanger did; and as we all know, heating and then slowly cooling steel anneals (softens) it.

The on top of that, the faster you bend the metal, the more heat builds up in it. So a spring that might be adequate on some lazy cam like a 151 might let the valves float at 4000 RPM on something like an aggressive roller even if the peak lift is the same. The HOT cam isn't as aggressive as some, but it's a whole lot steeper than your typical stock cam like the one you have now.

Personally, there are 2 places in an engine I never take risks if I can help it: rod bolts, and valve springs. The cost of good ones is so little compared to the cost and hassle from the destruction they can create when they fail, it's not worth taking the risk. Others may feel differently, and it's your motor, so you ultimately have to make the decision and live with the consequences; but FWIW, that's my advice. If you're even near the edge, step up to the next level of spring, it will never hurt. You're proposing to go beyond the edge. And to make it easier for you in your specific situation, your machine work is already done for you by Dart, so that's an expense you won't have. All you have to do is install the parts.

V8Astro Captain

iTrader: (1)

Thanks for the explaination.

At school we have a bunch of trash motors that are used for demonstration. A couple that we took apart had broken valve springs, which dumped the valve into the cylinder and the piston got beat to ****...not pretty.

Looks like I'm gonna stick with the cam I have.