ChevyGuy87

In my basement right now I have a XE274 cam, the 981 springs recommended by Comp Cams, and some 1.6 Pro Magnum roller rockers. I did the math and figured out that I'll be running .522 lift with the rockers. The springs have a coil bind height of 1.150, so with an installed height of 1.70 I have .550 to play with. Is that going to be enough clearance with .522 lift? It sounds kinda tight to me.

If this combo will cause catastrophic valvetrain failure at 6000 rpms are there any other 1.25 diameter springs that will work?

Air_Adam

I've always heard (from our experienced members here) that you should have at least .060 "play room" with valve springs. Less than that and you are kinda pushing your luck a bit.

Why run a 1.25" spring though? Why not upgrade to a good hi-perf spring, like a 1.43" or 1.47" spring? Or a dual spring? You'd be much better off.

sofakingdom

iTrader: (1)

Comp only recommends the stock diameter spring for up to .500" of lift.

Apart from that, there's alot more to picking a spring, than just getting the least amount you can without bind. Springs are there to control valve motion; the XE cams generate ALOT of valve motion; they therefore require more spring per any given lift, than most other cams, as a result.

Look in Comp's catalog http://www.compcams.com/catalog/056_057.html and note that the very next cam in the series, which has less lift than the combo you are proposing, requires upgraded springs. I'd take that as a sign that the 981 isn't enough spring for what you're doing.

ChevyGuy87

Yeah, I was afraid of that. It's just getting frustrating to keep pouring money into these Vortec heads. I got them because they were cheap, but after I'm all done it'll be almost as much as some AFR's.

Looks like I'm going to have the spring pockets enlarged. Would the 986 spring be a good choice?

sofakingdom

iTrader: (1)

Yeah, that's kind of what you caould call, the biggest downside to Vortecs; they're just TRUCK heads, so to turn them into anything "performance"-like, every detail about them has to be touched. Guides, valves, springs, spring pockets, the list just goes on.

IMO the secret to using them and getting good bang for the buck, is to recognize their built-in limitations, and build a motor RIGHT UP TO the point that they allow in untouched form, WITHOUT going over. Otherwise, what's happening to you, happens. Bummer.

Anyway, yes the 986 should be fine. I've run that cam and 1.6 rockers and 986s before, with pretty good results. I've also used it with 987s, which cost the same and are one additional step further in controlling the valve; they're the same size and all that as the 986, just one more step up in their rate. Better valve train control = more RPMs before the motor "runs out".

Another way to go, which would give about the same spring action but not require machining the pockets, might be the 26918 "beehive" ones.

I think you'll like the cam, once you get over all the $$$ hurdles.

ChevyGuy87

I went and did some looking online, and discovered that the 986 and 987 valve springs have the same coil bind height as the springs I have now. So I did some more looking, and found a set of springs made by Lunati, part number 73943 http://store.summitracing.com/partde...9&autoview=sku

Here's a comparison between the 981's I have now and the Lunati's
. . . . . . . . . . . . . . . 981. . . . . . . . . . . Lunati
Diameter: . . . . . . .1.254 . . . . . . . . . 1.266
Spring rate: . . . . . 417 lbs/in . . . . . . 462 lbs/in
Coil bind height: .. 1.150 . . . . . . . . . 1.060

By looking at the specs, it seems to me that these springs may be just what I'm looking for. Stock diameter, stiff enough to control the valve action from the XE274, with clearance to spare. No more machine work and I can use the retainers I already have. Am I overlooking something, or did I just find a solution?

I realize I may be beating a dead horse, but I want to exhaust all options before taking another trip to the machine shop and buying new retainers and locks, as well as springs.

89gta383

iTrader: (5)

You didn't mention the installed height pressures and closed pressures on those springs, make sure they are comparable.

Stekman

Just because a spring has the same coil bind height doesn't mean anything. If you looked harder, you will notice that the 986's have a taller installed height to begin with.

ChevyGuy87

I just looked it up, the 981 has a 105 seat load and 295 open, the Lunati has a 110 seat load and 345 open. Is that going to be too strong, or will that just help out with controlling valve float?

F-BIRD'88

The Lunati springs will work fine if installed at 1.70" to 1.72"
Stock vortec retainers give a shorter installed height than the old typical stock SBC retainers.
The guide bosses will have to be shortened reguardless.

Crane sells a spring retainer combination kit that installs onto stock vortec heads without machining.

Use Crane #10309-1 spring and retianer kit for .575" lift with stock vortec heads.

contains crane #99845-16 spring
and #99914-16 retainer

have a higher installed height 1.75"

Outer Diameter Top 1.255
Inner Diameter Top 0.870
Damper NO
Seat Pressure @ Installed Height 124 lbs @ 1.750
Open Pressure and Height 374 lbs @ 1.150
Coil Bind 1.100
Average Spring Rate 409 lbs/in
Maximum Net Lift 0.640
Application GM vortec GM LT1

Special retainer with more space between the guide seal top and bottom of retainer without machining. good for .550" net lift. .575" total.

H-11 material

If you don;t like that route:
You can buy the machine tools to enlargen the seat diameter reduce the inner step seat diameter and shorten the valve guade boss height for less than $100 and do it all yourself in your garage at home.

Don;t worry, the extra work nessessary to get vortec heads ready for high perf springs and high lift clearance is well worth it.
Either find a shop that knows what they are doing to machine the heads ( this is routine stuff for a good shop cost should be resonable. Or buy the tooling and do it your self. its not hard to do. You can drill and pin the rocker studs for a few bucks.

ChevyGuy87

Thanks for the info.

I already took care of the valve guides and threw on some teflon seals, so that's not an issue any more. I'm just a little apprehensive about cutting the seats myself. That, coupled with the fact that the funds have run dry so there's no more money left for machine work, means no larger springs right now.

F-BIRD'88

do you already have the 981 springs? are you using stock "vortec" retainers? do you have any of the old style pre vortec retainers to use? (higher installed height)

I would set up the 981 springs at 1.72"
A old style retainer should give you 1.75" without the oil cap. and 1.72" with the oil deflector cap. (.030" thick"

vortec retainers will give you about 1.68" to 1.70"

there will be less clearance between the guide top and retainer bottom when using old style retainers on vortec heads than the new style vortec retainers.
so if you go this route check clearance again.

rob a set of old retainers off old heads.
if the inner damper on the 981 springs interfers with the inner spring seat diameter, remove the damper.

The comp catalog list the 981 springs with a 1.13" coil bind height not 1.15". Stick 'em in a vise and check for yourself thou.