For now I'll be using the comp cams 282s camshaft. Eventually I'll be getting one of harolds 280/284F10 cams for my 406. I have wide spring pockets and don't want to use the comp cams 981 springs beacuse of too much clearance and I don't want to use cups/locators. Plus, the seat pressure seams too low to me. Instead I want to install the isky 6005 springs. Here are the specs.

Comp Cams 981:
422 lbs/in
105 lbs @ 1.70"
316 lbs @ 1.20"
Single Springs

Isky 6005:
275 lbs/in
135 lbs @ 1.75"
271 lbs @ 1.25"
Dual Springs

How are these springs for an engine that will rarely see 5K on the street and 6K at the track (if I ever go)? How is the open pressure of these springs?

Thanks

Good spring for a small block if your installed height is 1.750.
Don't run out & but them until you know your installed height though.
You need to check that you don't have a taller installed height with those heads & the 2.05 valve.

Hey Mike, perhaps a dumb question but, given the smaller size and ligher weight of the exhaust valve could less spring pressure be used on them than on the intakes?

Originally posted by Pat Kelley:
Hey Mike, perhaps a dumb question but, given the smaller size and ligher weight of the exhaust valve could less spring pressure be used on them than on the intakes? =
Pat,,,,,,,shame on you ;) The only dumb questions are the one's we don't ask :(
Ya know, when we quit askin I guess that means we must already know everything huh????
Sad day in my humble opinion :rolleyes:

But to digress to the question,,,yes it is possible to run lighter springs with lighter parts (or have the capability of higher RPM) but I think it would be more trouble than it would be worth from intake to exhaust given the difference.
I guess technically a lot of cams have less open pressure on one side or the other already depending on rocker ratio & cam lift.
And of course, if you get into a blown engine then you have to worry about more spring on the intake to get it closed,,,let's see, 20 lbs of boost on a 2.3" valve,,4.15 sq inches, 83lbs,, but I guess that's another thread :eek:

An old boss of mine once said, "A day you don't learn anything is a day wasted." At least this day wasn't wasted smile.gif . In my pursuit of a deeper understanding of the theory of these engines, I sometimes ask questions like this. From your answer, it looks that the practical results are minimal. As you mention, this may already be the situation, in my case it is, at least as far as open pressure. The cam I'm using has less exhaust cam lift (by a few thousandths) and I'm using lower rocker ratios (1.6 INT, 1.5 EXH). Of course, the seat pressure remains the same for both, and I'm guessing that is where the lighter exh valve might get by with less spring. Thinking out loud here, it probably wouldn't make any difference, though since the float limit would be determined by the heavier intake valve. So no gain.

I ran that cam for many years in a 400. However, I used 1.45" springs, since it has a lift of .485" or some such.... right on the ragged edge for the 981s. You're about the thickness of a business card away from exceeding the 981s' capabilities with that cam and 1.5 ratio rockers. If you run 1.52 ratio or 1.6, you're even closer, or over the cliff.

I'd strongly recommend using Comp 986 or 987 instead of the 1.25" stuff. That way you have some safety margin.

Wolfplace: Good to hear... and yes, my silly a$$ bought standard sized valves. I checked my installed height already, and it's 1.70". So I got the matching +.060 retainers and a mini shim pack. I'll have to check rocker to retainer clearance (crane full roller rockers), but I should be fine.

RB66SS396: Yeah, I'm not even going to use the 981s at all. They have an outside diameter of 1.254" and my pockets are 1.550". Cups/locators would through off my installed height (see above) and I would have to use +.060" retainers and +.050" locks. Then I might have some clearance issues. The Isky springs are dual (good for an added safety bonus :D ), and have an outside diameter of 1.430" so cups aren't needed. And yes, 1.6:1 ratio rockers would put my bind clearance at .044" (with the suggested .022" lash).

Anyone wanna buy a set of comp cams 981 springs w/ matching retainers? :D