MadBill wrote:o Were the springs, especially exhaust, still 'spot on' for load when you tore it down?
o Many rockers have more than advertised ratio; did you measure actual lift and retainer/seal clearance with checking springs and verify seal location on all valves? .
o Having only 6 seals crushed means something's different on the bad six. Less clearance, lower spring load, worse lifter pump-up, six valves that aren't hollow...
RW TECH wrote:I think your system isn't happy & that may be why the seals got hammered.
You've added ~8 grams of exhaust valve weight, ~4-5 grams of retainer & lock weight, 30 grams of spring weight, and a significant amount of rocker arm weight. It doesn't sound like you spend a lot of time at high RPM so I have to wonder how you arrived at your current valvetrain combination?
The following configuration has completed over 3,000 racing miles (see pic below) up to about 7500 RPM peak (long total run time per event). Actual limiting speed in that system (defined as .010" bounce at closing & not cleaning up 100 RPM higher) is about 8200 RPM.
-GM catalog hyd. roller cam (aka Stage 3 LS Cam)
- 1511ML springs, set up at 1.820"-ish
- Stock retainers & locks
- Stock rockers
*No "trunion kits"....completely 100% straight off the production line and zero failures in several engines like this & 2,000 or more racing miles. Trunion bearing failure was a 2007 era field concern that was fixed for later production. From a geometry standpoint the stock rocker arms will not cause problems if actual (net) lift is .650" or less. Above that you will have trouble. Otherwise, the stock guide material isn't extraordinary or great and earlier heads (2007-2008-ish) had machining issues that caused excessive guide wear. I assume you had the guides sleeved or changed somehow?
- Stock LS7 pushrods
*Actually delivered best stability with certain hydraulic roller cams & same ancillaries in comparison with a variety of same & larger OD & thickness 4340 1-piece pushrods.
- Stock valves (exhaust too).
*The exhaust valve problem on LS7 engines was fixed after 2008 and I never had any problems with the newer exhaust valves even with .800" lift solid rollers in a similar application to the link turning about 8,000 peak RPM. 100% of the 2013-newer COPO engines have the stock valves that include material & process changes after 2008.
I wouldn't necessarily climb all over the idea of adding more spring force because the combination really needs to be verified on a spin test rig but essentially you've added a ton of weight and you have about as much spring force as a decent beehive like the PSI 1511ML. BUT - with the disadvantages of additional spring/retainer/lock mass plus the dynamic stability disadvantage of straight wound springs (vs taper-wound like the beehive).
If it was mine to deal with I'd get the existing parts on a spin test rig (bet $100 you find the exhaust is pissed off), then compare to the proposed parts to make sure your system is correct/happy. What ends up being the best may surprise you.
mdrew wrote:RW - glad to see you respond. Always enjoy your insight. I've actually had the heads work twice now. This will be the third (new OEM heads with new MS 90 guides, mild port work retaining the swirl damn).
Long story short, after the heads were ported the first time, I had a cam spec'ed from the port work data, and it's what's in the engine now. I kept the OEM valves, had guide liners installed, and used stock rockers. After about 5K miles, I tore down the heads to find the guides wiped out again. Mostly top side wear. Sent the heads out again and had the guides replaced with new PM guides, and milled the rocker stands down for the Crowers. Kept the same springs as before. Went with the slightly heavier exh valve.
Decided to do something different over this winter, and found what I found, hammered seals. Good news, is that guide clearance looks perfect.
My personal experimentation with the OEM rockers on these heads, is the pad moves off center and starts side loading, right around .625" lift. Instead of fussing around with bolt on roller tipped rockers, I just decided to go with the Crower set up. Jesel was way too expensive for a street car.
I suppose I could always blow a bunch of money for spin rig testing, for a personal car.... but that's not happening. I'd love to, and completely understand the value, but for a one time deal??? I ain't made out of money.
Warp Speed wrote:Geoff2 wrote:Twenty degrees of extra exh duration [ compared to the intake ] will give you plenty of reversion issues....
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