Ok guys, I have a set of L98 aluminum heads with stock springs. I have a ZZ4 cam which I will be using with a combo of 1.5 rockers on the exhaust and 1.6 rockers on the intake. With that setup, it gets about .510 lift on both intake and exhaust. I bought the heads used, so I have no idea how many miles are
on them, so it would probably be a good idea to change them anyway.

So now comes my question. I am considering using the LT4 springs, since they should be good for the lift I intend to run and the price can't be beat.

First off, will these springs work on the L98 heads? If not, what springs would you recomend running.

Second, If the LT4 springs will work, does the head need any kind of machine work to accept these springs?

TIA

 

The specs may say they will work, but if they actually do, they are the only 1.25" springs on the planet that will. GM has never (big word, "never") made performance springs before; they have always used aftermarket ones in their own racing programs. I personally think those springs are no different from anybody else's top quality 1.25" springs, and as such, are not reliable at more than .500" lift.

If you're having machine work done, especially if it involves modificaion such as screw-in studs which are also IMHO mandatory for lifts above .500", you should have the spring pockets enlarged at the same time. It's not very expensive, should be well under $50. Then you can run any spring you want without having to worry about breaking springs and ingesting valves.

Have you ever seen what happens to an engine when a spring breaks at speed? Let's just say that valve fragments are incompressible, and pistons are much softer. Better springs are very cheap insurance. Even with the machine work, the increase in the total price of your buildup will be essentially unnoticeable, and you eliminate the risk of having your entire motor turn to shrapnel.

I also would not downgrade the exhaust rockers. That side needs more flow than the intake. If you are doing this just to fit within some lift limit, stop!! You need to get the right springs and do it right.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Thats just plain wrong. Check these out:

Summit part # KMO-K-750

These are a stock diameter H-11 tool steel wire made for racing classes that limit valvespring size to stock. They are a little more pricey than a common 'silicon' spring but really hold up very well.

Specs:

130# @ 1.700" 380# @ 1.150 with bind height @ 1.030"


This means that with the stock spring height they will bind at .670" of lift. I got these springs but installed them higher at 1.750 to lower seat pressure a little. This allows coil bind @ .720" If I want to upgrade my ratio or cam these springs WILL handle the task quite nice. My retainers are still the limiting point. They may be overkill but H-11 is the best material.

 

Read the specs a little more carefully...

What they say is that those springs require 380 lbs of pressure to deflect to .550", whereas no normal flat-tappet cam will survive at over 300 lbs for any length of time. Pressed-in studs will pull out at about that pressure. For comparison's sake check the open pressure of a decent racing spring such as those from Comp or Crane or Lunati (people who have to warranty them and cams together) and you will see exactly what I am talking about. Look at a Comp 981 and a 986 specifically. Those cheap K-Motion springs are a time bomb IMHO at any lift above .475". Now if you choose to run them at lifts over .500", that's your business; but don't be too surprised if terrible things happen.

130 lbs of seat pressure is fairly normal for a performance-type application. It shouldn't be necessary to leave the shims out like that.

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"So many Mustangs, so little time..."
ICON Motorsports

 

I'm not running flat tappets. Hydraulic roller with .525 on the exhaust. TPIS recommended lowering the seat pressure. They said 90# on the seat and 320# on the nose is all that would be required. The lower pressure you can get by with the better everything lasts. He wasn't referiing to a flat tappet cam. The ZZ4 is a hyd roller and that pressure is just fine.
I'll trust my springs no prob. I have screw in studs.

[This message has been edited by JoelOl75 (edited February 23, 2001).]

 

First off, do the L98 aluminum heads come with pressed in studs or screw in, and how can I tell? I wasn't planning any head work, but if it is a good idea to have it done with this cam I'm using, I most certainly will.

Second, Joel with those springs you are talking about, did your heads need machine work or were they a direct fit?

TIA

 

David,

I understand your willingness to make the change as economical as possible, but don't get lured into false economy. The L98 aluminum heads should get spring seat machining if you are going to use an improved cam profile, regardless of the spring diameter. The increased pressure and acceleration rates of the valves will cause the stationary end of the springs to wear into the pockets in the heads, effectively changing the installed hieght and seat pressure. The trick is to machine enough depth to allow the use of steel spring cups in the heads to prevent the inevitable wear.

And since you are machining the depth a bit, you might as well open the diameters to accept the largest springs you might ever want to use. The spring cups will keep the stationary ends of the springs concentric with the valve stem, and the larger springs can use larger diameter cups. Also, if the rocker studs aren't screwed and you may want to use push rod guide plates in the future, you need to condsider the depth required by both of these items and machine accordingly. If you do it once, all remaining changes can be done with the heads on the engine. If you take the most ecomonical way out, you may be doing it again sooner than you planned.

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Later,
Vader
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"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0

 

I went with cast iron so the only prob was retainer to guide interference. If you have to pull the heads to get this done he's right.... May as well get them machined for larger springs.