I'm installing LT4 springs in my 86L and just wondering if any one that's done this mod has the specs handy...height, int/exh..coil bind etc. Thanks.

 

Single spring with 1.32" O.D. and 1.22" solid height. The pressure at installed height IS 101# @ 1.78" with 332# the average rate of pounds per inch.

 

Height is set at 1.78" when they're used on the LTx heads so that's what I'd shoot for. When they're used with the Hotcam and 1.6 rockers they're just about maxed out at .525" lift. In other words, they're close to their safety limit for bind. If your lift is that or less than that you should be fine. Does that answer everything?

 

I think so thanks, I'm using 1.6 rockers and LT4 springs, caps. shims. sounds like all I have to do is shoot for 1.78 height and .60 for spring bind and I should be good. Oh and cam is staying stock

 

You're good as gold then.

 

Here's a cut and paste of a post I put in another thread. Food for thought
You can't use any of the 128 head spring assembly parts with the LT4 spring. You will need the LT4 base+cap and new locks for piece of mind.
The exhaust rotators add height to the spring assembly so the head is machined to lower the exhaust valve spring seats. This causes a little grief when using the LT4 springs as you can't stack enough shims between the seat and spring to make up the difference of rotator.
The first year I used these springs, I put the shims under the seat. This works but I really never felt 100% comfortable with this because the shims do not fit snug to the valve guide and there is a chance that the shims could do a little walking around.
When I rebuilt my 128 heads 2 years later, I came up with a better mouse trap, I mean plan.
I took a tapered stone and enlarged the ID of LT4 base to slide over the L98 base. In between the 2 bases, I added my shims to get the correct installed height. There is now plenty of room to get all the shims in that you need to make up the exhaust rotator height. I did the same for the intakes, which only required one shim between bases.
Here are a few pics

 

I called GMPP to order springs, caps, shims, and base. they told me they didn't show a base, where else can I find the base any ideas, should I go to my local dealer..yuk. Thanks

 

Dan, I never was sure of the specifics of adding LT4 springs to earlier heads were but I knew folks had done it. Maybe you ought to add this info to Andy's sticky thread.

 

I believe they call the base a shim. I will check #'s after work.

 

I'm in the process of gathering parts for this spring replacement and have a question.

I started down the LT4 path because the springs were so much less expensive and the alternative seem to be recommended here (about $40 for the set instead of $8 a piece-relying on memory here). Then I learned that I needed all the other items (caps, keepers, shims) and it isn't so cheap anymore.

So why is this a better alternative than just replacing springs or using something like the $75 Competition Cams' High Energy Valve Springs listed by one of our sponsors?

 

If you did go comp cams or similar, you would also need more parts unless you plan on keeping the exhaust valve rotator, as it is the cap also. I went with LT4 kit because it does away with the mass of weight on top of the spring and leaves breathing room for more lift.

 

The part# for the LT4 spring 'shim' (or base) is 10212809
LT4 Spring is #12551483 (each) or #12495494 for a set of 16 (cheapest option by a long way is to buy the set!)
LT4 retainers are 12495492 (set of 16)
Crane sell longer and shorter (by 0.050") installed height keepers that help a lot when trying to set up the installed height and avoids having to use shim stacks sometimes. Summit sells em.
Hope this is helpful.