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 LT4 springs come stock on ZZ4 heads, which are the same as L98 heads, so I think they're a direct fit.

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West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
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I bought the valve springs for my stock L98 iron heads from TPIS for my LT4 Hot Cam. The springs are the ones that TPIS suggests using with the ZZ9 cam, and since the ZZ9 and LT4 Hot Cams are very similar I used those springs, they work great so far!

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End

Current Mods: LT4 Hot Cam, Comp Cams 1.52:1 Roller Rocker Arms, Edelbrock TES 1 5/8" Headers, Hooker 3" Aerochamber Cat-Back System, Performance Resource Chip, Accel Ignition Coil, Cap, Rotor, 8.8mm Wires, K&N Filters, JET TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET (w/o LT4 cam): 14.32 @ 97.7mph
(corrected for elevation)

7.5" 10 Bolt with 3.42s soon to come!

 

That's good to hear. So basically these are a direct swap, and no machine work is necessary?

 

Well, I also posted this topic over in the Tech section as well, and I am getting conflicting information. Is the 1.25" spring to small to handle lifts over .500? If I went with a bigger spring size, will that require machining the head?

Also, It was recomended not to run the 1.5's on the exhaust side. I have a 305 and with 1.6's it bring the lift to around .544, is that too much for a 305


Also

TIA

 

This spring selection business is very critical and can be confusing.

Let's look at the easy part first: More lift many won't hurt anything provided:

1. Your springs can handle it without being worked beyond their design limits or coil bind.

2. You have adequate piston to valve clearance. Most companies recommend a conservative .080 on the intake and .100 on the exhaust. I've even seen some recent numbers of .100 on both. You can run those clearances tighter, but you give up over-rev protection when you do. How much you end up giving up depends on how far you fudge the numbers.

3. You are not running big 2.02 or larger valves on cylinder bores smaller than 4.00", inwhich case the valve could hit the cylinder wall, which may happen even at lower lifts.

4. Your pushrods and rockers are up to the loads the higher lift will impose. To get high lift while keeping duration short calls for the valve to be accelerated at very fast rates requiring stronger pushrods and rockers to prevent deflection.

5. Your intake tract can only flow a specific amount of air. Lifting the valve well beyond the point of max flow has been shown to actually reduce flow with some heads. Flow bench tests have shown a drop in flow at .550 from what was flowed at .500 Of course a 305 only needs so much flow anyway, unless you plan to rev it into the five figure range. So the law of diminishing returns kicks in and lifting the valve another .020/.030 probably will show no power gain.


Now the hard part:

CompCams sells a spring that will work with the cam you've chosen and not require the spring seats to be cut. I believe they are call conical springs. They are intended for guys who do not want to have to cut their spring seats for larger diameter spring. They do call for new retainers and (I believe) locks though. Call their toll-free Tech number to make sure they will work with your profile.

1.25 springs are marginal at the lifts you are contemplating. Remember, the harder you work the spring, the shorter it's life. There is a recent article on back to back tests in one of the mags on what happens when springs that are too weak are run with a healthy cam. How about 143 HP at 6300.

You're best move would be to get the exact springs recommended by the cam maker since they are designed to work with that profile. CompCams, for example, HIGHLY RECOMMENDS, that ALL the valve train components be changed when swapping in one of their Xtreme Energy cams.

Cams with aggressive lobes - fast acceleration ramps - call for a better than stock spring because the cam works the spring so hard. Stock springs are designed for stock lobe profiles and weren't intended to be used with aftermarket cams which almost always have more aggressive lobes.

The amount of aggravation you'll end up causing yourself down the road will FAR OUTWEIGHT the expense of putting in the correct springs now.

Remember the old "Pay Me Now Or Pay Me Later" commercial?

In dealing with the valve train, you really don't want to take any chances. A mistake in that area can cost you your engine.

Hope this helps.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9