I put ZZP'* SR rockers ("first generation" ER'* I bought used--similar ratios) on my stock springs/retainers about 2 weeks ago, and my 1-2 WOT shift is set at 5650 (although it actually completes
at around 5900). Haven't broken a spring yet, but I definitely
will not go any higher on the shift with these
springs...besides this setup is only temporary until those new heads go on
I do believe the stock springs are giving me valve float at the high revs due to some things I see when analyzing my scans. Interestingly, I took the stock springs from those "other" heads and tested them on an Instron...they came out to an average 52 lbs at seat height...for a loss of over 25% spring strength over their intial rating--at only 30k miles. I wonder how much my 94k+ mile springs have lost?
Here'* an analysis I did of some spring/retainer options:
Ultimately, I'm going to go with the CompCams 105# springs. They have the desired high seat pressure, but lower spring rate than stockers (so potentially less wear). I already got some CompCams retainers, but I was strongly considering the Manley "thin" retainers from Intense, to even further reduce the potential for timing chain wear.
LS6 springs are cheap, and alot of people run them with the ER'*, but the horror stories I've read about what they can do to your timing chain put me off 'em quick.