We've found a solution to the discontinued Heavy Duty Valve Springs formerly offered by Rosten
The AHU uses a double valve spring design. Both springs are fairly light. The ALH on the other hand uses a single spring that is much stiffer. For a high performance ALH, we recommend using the stock ALH spring in conjunction with inner spring of the AHU.
This kit includes
qty 8 x lower spring seat
qty 8 - inner valve spring
The ALH Valve Outer springs are able to be reused for this endeavor but if you'd like to replace the outer springs at the same time they can be purchased HERE. 8 are needed for a full replacement
Per our tech:
"I have tried this & installed in a running motor (my compound turbo TT project). It works. I decided to go this route because I was concerned about valve float (which DOES occur on an over-revved, high-boost ALH). I have pistons here to show it too!"
Spring pre-load in pounds; valve closed/valve full lift (stock cam)
AHU stock springs w/ lower seat installed: 60/140
ALH stock spring: 70/130
ALH outer spring, AHU inner spring, lower seat installed: 88/170
With the double spring ALH setup there is another 3mm of lift possible over stock before coil bind, which means that a stage 2 or 3 Colt cam will work with this application.