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Old 06-04-2001, 04:01 PM   #1
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How much lift can stock valve springs handle?

OK, Im gona go with a new cam,but now
I heard I will have to get new spring too.
I just got the heads rebuilt 2 months ago
wish I would have known this at the time.
I need to know how much lift can stock springs take,the cam I have in mind is comp
cams#08-432-8 Lift is 510/520. How much will
the springs I need cost?I only have about
$350 to spend and the cam is $239+ the gaskets + new timing chain, can I
make this happen..Thanks for any help..

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Old 06-04-2001, 04:06 PM   #2
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Forget stock springs at that lift, You will just be asking for problems.

Comp's matching springs for that cam Won't be more than 60 bucks, You should be in under your limit w/o a problem.

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Old 06-04-2001, 04:51 PM   #3
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Stock springs will defintely not take THAT much lift. They're good for about .490 from what I know. Get the springs they recommend. You shouldn't have to do any additional work to the heads like enlarge the spring pockets or anything.

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92 Z28 5.7
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Old 06-04-2001, 06:23 PM   #4
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keep in mind pressed in studs are only good to approx. .490 lift if you plan on taking it to any RPM at all
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Old 06-04-2001, 06:24 PM   #5
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DO NOT ATTEMPT to use your stock springs with that cam!!! I doubt the engine will last 5 minutes before something breaks. Either a stud will pull out, or a spring will break and drop a valve, or something. It won't be pretty no matter what gives out first.

The springs that Comp will recommend for that XR282HR will be their 986. They will not fit the stock spring pocket in your heads. To use them you have to get the spring seat enlarged from the stock 1.25" to 1.45". Ask them about their new conical springs; those might work, while still fitting the small pockets. In either case you'll need the matching 1.45" retainers.

There are few places in a motor where cheaping out is riskier than the valve springs. Especially with a big roller cam like that with super-fast valve action and steep ramps. If you ever see the insides of a motor that dropped a valve due to a broken valve spring at racing speeds, you will never again even think about putting a big cam in a motor with marginal springs. Let's just say that fragments of valves are incompressible. Broken pistons, broken heads, bent rods, etc. are common results.

I have that cam in my 400; used to have a 282 solid; the 282S lobes like like eggs with little points, the XR282HR lobes look almost square. It's alot more cam than the numbers make it look like, typical of rollers. It's a whole bunch of cam, even in a 400. I love it. I have Comp's 1.6 roller rockers on top of it, and 986s; I should probably consider moving up to their next level of spring, the 987, which is their largest 1.45" spring.

IMHO you really don't have enough compression, or heads, for that much cam. You might want to reconsider, and get one with about 10 to 12 less duration. Their XR270HR would be a much better match for the rest of your motor. I suspect it would go faster with that one than it would with the 282. It would still require a spring upgrade.

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Old 06-04-2001, 10:22 PM   #6
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Ernie,

I've always used the 0.480" limit as a rule, and then only with NEW stock-sized springs. Notice I didn't say stock springs, but stock-sized. Stock springs don't have anywhere near enough seat pressure to control the valve train with that kind of ramp. For the cost of another pair of head gaskets, you might as well do the machining now and not take chances. Make sure your studs are screw-ins as well. If not, you can install them yourself for about $15.00.

Listen to RB - he knows his she-ot! He wouldn't steer you wrong - O.K., maybe if you were a Ford driver, but not otherwise...

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Old 06-04-2001, 10:36 PM   #7
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Hey Vader & RB,

Do me a favor and help the guy in the TBI section. He is putting a LT1 cam in a 305 TBI. Maybe you can elaberate a little more than myself on what he is doing. I tried, but I can only tell what I know, not what you guys know.

His post is "Will a cam swap make me want to kill myself?"

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Old 06-05-2001, 08:35 AM   #8
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The heads also require machining. Take the guides down. Ive found with the ZZ4 cam (.510 on the exhaust) the reatainer just hits (well more than just) the valve guides. Springs def have to be changed...
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Old 06-05-2001, 05:28 PM   #9
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Thanks for all your help guy's
I feel like I know what im getting
into a lot better now..
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Old 06-05-2001, 05:28 PM
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