GTA1990

iTrader: (1)

wot up crew

In process of the much mentioned L31R LT4 Hotcam build. Taking the LS6 spring and 787-16 comp cam retainer route with stock 1.5 rockers.

Question is I've gone with the stock keepers on this brand-new engine made by our Mexican friends. Now after reading some more between dates (leading an interesting double life here...) I'm slightly concerned the stock keepers may not provide the required clearance for the circa .49 lift of the Hotcam

I'm going to pick up a digital vernier calliper and see what actual clearance I have but in the meantime welcome thoughts really. Anyone gone with a similar setup or know a friend (or enemy on basis of keeping enemies closer) that has done so and the trials they faced?

skinny z

I've owned and modified a couple of sets of Vortecs but it's been a while so I'll go on memory.
The general consensus is that the stock Vortec setup can only accommodate in or around .450-.460" lift. My first iteration was with the heads as they came out of the box and used with an old spec cam that mirrored Comp's 268H grind. Something like 218 adv duration and (most certainly) .454" lift with the 1.5 ratio rockers, which falls in line with the lift statistic. That installation was trouble free until a missed shift put a valve into a piston. Nothing dramatic other than only seven cylinder remained functioning. The stock springs aren't anything to write home about.
That brought the next step which was Comps XR276HR (roller) cam with .502/.510" lift and then further extended via 1.6 ratio rockers. Using Comps 26918 spring, (which is a true beehive design with a very small retainer) allowed lifts approaching .550". The question here I suppose is how comparable is the LS6 spring to the 26918? My understanding is that they are basically interchangeable but I've been known to have misunderstandings before.
I will say that with the change to the bigger roller cam and higher ratio rockers I: modified the heads for screw-in studs and guide plates (eschewing the self guided rocker arms) and opened the pushrod holes to prevent any binding that might occur due to the added lift and use of guide plates. A side-note here is that if I were to do it again, I would still go with the screw-in studs but would seriously consider the self guiding rocker arms. I found the rocker to valve alignment got a little out of sorts probably due to the combination of factory machining tolerances and the mix of aftermarket parts.
At the very least this will bump your thread and perhaps someone (and there are many here) that have duplicated exactly your arrangement of parts.

GTA1990

iTrader: (1)

thank you sir, appreciate the hands on experience.

Being the hypochondriac I am, I've read online and scared myself into ordering the offset locks. But for posterity, I'll log my measurements and report back; so that years from now, some kid trying to get some horsepower on the cheap, can know whether to spring an extra $20 dollars after spending many thousands...

stuff should arrive in a few weeks

Orr89RocZ

iTrader: (20)

GTA1990

iTrader: (1)

okay so I picked up some 648-16 locks, which i then subsequently realised after fitting are not offset locks. I then went back and measured the seal the guide clearance. Silver lining is I've become a pro at threading nylon rope through the spark plug holes which I believe will come in use for my day job in investment banking...

So measurements below of intake and exhaust valves from two randomly selected cylinder. To rehearse, LS6 springs, 787-16 comp cam retainers and 648-16 locks.

intake 1 - 0.545
exhaust 1 - 0.583
intake 2- 0.543
exhaust 2 - 0.556

skinny z

Based on a .060" clearance requirement, you may have missed the mark by a few thou. Have you revisited your measurements?

Fast355

iTrader: (2)

Most cam manufacturers recommend 0.050" minimum. I have run a small block engine for 50K miles at 0.035" guide to seal clearance and it never missed a beat. I ran that engine at 1/4 turn lash on the hydraulic lifters.

skinny z

.060" is what I've got in my records as what to shoot for. If .050" works (and I'm not in disagreement), then the OP can has room to spare.
Once I set up my heads with .100" longer valves and the offset keepers, clearance was never an issue. I can't even say what the gap is in my current setup other than to say it's plenty and that's with .575" lift (or was). Now piston to valve clearance, with a 102 ICL, gets things pretty close.

Fast355

iTrader: (2)

I run .100" longer valves and double springs in my Assault heads with plenty of clearance at .580". My intake centerline is 106 but my duration is only 215/224 so I have plenty of PTV clearance.

GTA1990

iTrader: (1)

yep I thought the recommended clearance was 0.05". Glad to read about 1/4 turn lash. I thought that clearance could probably be limited by bolting the rocker down too much and so stands to reason that being a little lighter on the last would help prevent that.

I also suspect my measurements are ever so slightly conservative and will get a few extra thou with the pressure of the springs?

Note I didn't hammer the valve seals down to fully seat and there is, I think, around 0.1" clearance on average extra to be had from doing that

I'd also add the 648 locks are more fragile than the stock locks. I had one break in two on me when trying to remove. Granted I'm not the most delicate in my method but still, these were new locks that had no miles on them between fitting and removing a few weeks later...

Fast355

iTrader: (2)

I changed the seals and fully seated them on every set I have worked with. Has not created an oil burner for me yet.