On the springs I got, it says installed height of 1.780" which is about .080 higher than a stock L98 i think. uncompressed, the new springs are a tad bit taller. Is this cause for concern? Do i have to mill the spring seat down to get the installed height to 1.780 or can I just leave it as is and have it be ~1.700?

 

do you need the extra .080 for clearance, during max lift??

nick

 

I'm getting the valve guides milled this week to accomodate an lt4 hot cam so retainer-to-seal clearance won't be a problem. my concern is just the installed height of the spring but i dont see why it should be a problem.

 

oops, double post

 

The machine shop that I used to work on my heads, told me that if I had gotten the oversized valve springs that comp wanted me to use. That the machine would have cut down the valve guides at the same time. Have you asked your machine shop their opinion? After I told mine about my spring troubles, they said they would just handle it and they did. For a very good price.

Nick

 

When a spring is measured, they measure the pressure at a given height. So let's say that the spring pressure is #200 @ 1.780", aka seat pressure.

If you vary that meaurement at the spring while the valve is seated, you will also vary the seat pressure. If you decrease the height, then you effectively raise the pressure a certain amount. So i.e., if you lower the seat height by .080", you may increase the spring pressure as much a 10-15# (just round #s off the top of my head).

This may be very critical, depending on what cam you are using. It could cause the lobes to wear considerably faster than normal. And it will also effect how much pressure the spring is putting at max. lift which can also determine lobe wear, valve bounce, RPM operation, and yes, even retainer-to-guide clearance. And it may even wear the valve seats faster than desired.

There are a number of ways to accomplish the proper seat height, so let the machine shop figure out the best route for you. That's why you pay them the $$$!!!

But USE THE PROPER HEIGHT!!!

AJ

 

I'm using a hydraulic roller setup so that should reduce the wear on the lobes.

 

U-Train,

AJ is correct about the seat pressure. And you are correct that with a roller, wear is a little less of an issue, but still has some bearing. You really need to check the spring ratings at various heights to see how you'll be loading the valve train with your lifts. Also pay close attention to the coil bind height, realizing that you would have 0.080" less to work with if you install at stock height.

As long as the guides are being machined, it would be very easy to have them take another 0.100" off the spring seats, then shim to your desired install height. Shims are a very good idea in aluminuim heads to prevent seat wear anyway, and don't hurt anything on iron heads. If you are changing valves or retainers, that will affect the installed height as well.

The beauty in this is that you can then install whatever springs you desire with no additional machining, just shims or spring cups.

 

Here are the springs I got.

At 1.7" I figure the seat pressure is about 155#, subtract .492 for lift of the cam and there's still about .050-.060 til coil bind. So if I use the standard seat height, I should have ~355# at max lift. I think I've read that roller cams want 350# at max lift so would this work at standard seat height?

 

not sure what you have or what you've done, but basically match the springs to the cam. run the spring makers installed height, trash the factory rotators and go with aftermarket retainers.

 

anyone else have opinions?

 

the guy at the machine shop said 5# over the max recommended at full lift won't hurt anything so i'm leaving the seats alone and just taking .050 off my valve guides to clear the retainers.