|01-23-2013 10:00 PM|
Very informative read I found today. I wish I would've found this a couple months ago!
GM Performance :: View topic - LT4 Hotcam in L31 This pretty much clears up everything. 64nailhead- pm sent
|01-22-2013 09:05 PM|
|cobalt327||SBC Vortec heads have 11/32" valve stems. Some HD trucks use a 3/8" exhaust stem. LSx, etc. uses 8mm.|
|01-22-2013 08:49 PM|
I overlooked the fact that you were using FACTORY locks and retainers. Factory locks and retainers are designed for stock valves that have 8mm stems. If you use stock retainers and locks with aftermarket valves that have 11/32" stems, the locks will not fit correctly and will likely fail. That is the reason the stock valve locks and retainers sit higher on the aftermarket 11/32" valve stems. The ends of the locks were in contact with each other and did not provide the necessary clamping force on the valve stem. The ends of the locks should never be in contact with each other.
The combination of CCA-787 (7 degree) retainers and CCA-648 (7 degree) locks are designed for aftermarket SS valves with 11/32" valve stems and will fit properly.
I am using CCA-795 (10 degree) retainers, CCA-613 (10 degree) locks, CCA-26918 beehive valve springs, Scorpion 1.5 full roller rocker arms and Manley Race Master SS valves with .290" tips. That combination provides .035" to .040" clearance between the rocker roller tip alignment rails and the locks.
|01-22-2013 06:06 PM|
|flyingputz||I thought this thread was done, but guess what? I figured I'd buy some Comp hardened, machined #648 STANDARD locks, rather than reuse the FACTORY standard locks. Upon reassembly, these Comp locks actually give me 1.80" installed height, while giving me .025+ inch rocker rail to retainer/ lock clearance! The FACTORY vortec locks were giving me a 1.755" installed height! SO many variables in cylinder head rebuilding. Needless to say,after the unnecessary guide machining I now I have WELL over .620" retainer to seal clearance. Thought this info may be helpful to others.|
|01-17-2013 12:45 AM|
|01-16-2013 11:46 PM|
64nailhead or anyone else interested in Comp seat & guide cutters with 11/32" arbor? Used on just ONE set of vortecs. Worked like a charm! I'm finally back on track with this build. Cobalt, what determines whether or not distributor needs to be recurved? I've got GMPP (AC Delco) dist #93440806.
P.S. Just read your 'recurve' link.
Answered my question. Thanks!
|01-16-2013 05:54 PM|
If using a spring and retainer like the GM-recommended Crane p/n 10309-1 is a short cut, then so be it- but sometimes a cigar IS just a cigar. In any event it does address the clearance issues- w/o the need to machine anything- rather neatly IMHO. After verifying clearances all that leaves is selecting a pushrod that'll give you a good sweep (see links above). Don't forget to recurve the distributor.
There's little point in using lifts in excess of 0.500" on a production unported Vortec head. I don't know if you're planning to use a hydraulic roller or flat tappet, so I'll just say generally that a split pattern cam w/0.050" intake duration of about 222-228 degrees will get you to your goal w/room to spare. This is using long tube headers, an intake like the RPM, a carb no bigger than a 3310 Holley (750 cfm vacuum secondary; a Q-jet or 650/670 cfm carb will work as well) and the CR to match the cam, along w/good engine building practices.
If you want to see for yourself how different cams will "perform", try using Comp's Camquest program. Peak numbers are all well and good, but the average numbers often tell the REAL story...
|01-16-2013 05:14 PM|
|01-16-2013 05:11 PM|
I agree that the easy way is usually not the best way and also usually ends up with me reworking the original problem. I'm sure that you have been bitten by the 'take the easy way out' snake a time or two.
In terms of going more than .500" on a stock Vortec head, I always have to remind myself of what I'm after - 350 to 400 hp street machine. I'm not a drag racer, I'm more of tire burner. Presently, repeat presently, I believe the cheapest route to my HP desires are through a Vortec head. I have to admit that I would love to have a 500+ HP motor in a daily driver, but I am aware of the problems it creates. Personally I find more satisfaction in cheap HP. I know that alot of people on this forum aren't after what I'm after, but 'to each his own'.
Lastly, 'corollaries'? You made me use the dictionary!
cor·ol·lar·y (kôr-l r, k r-) n. pl. cor·ol·lar·ies. 1. A proposition that follows with little or no proof required from one already proven.
Thanks greatly for the advise
|01-16-2013 01:13 PM|
There are several situations going on each needs to be understood differently.
- The first is the distance between the valve's head and the lock groove on the stem. This can be independent of the total length of the stem as measured from the head to stem tip. So this is a value you need to know as it doesn't have to change just because the valve is longer. But it could so you cannot make an assumption; you've got to have the measurement. Many valves are sold at .1 sometimes .25 inch longer than stock. These usually but not always are intended for aftermarket and OEM over the counter performance heads that raise the port which also raises the spring pocket. These valves often raise the lock groove a like amount to the stem length increase so as to retain the production part installed spring length. They might retain the production distance between the lock groove and the stem tip.
- The second is the distance between the lock groove and the stem tip. This is independent of the valve length but may be married with a longer valve.
There are problems encountered when trying to avoid shortening the guide height on Vortec heads by using a longer stem and shimming the spring:
- A thick shim needs to be placed under the spring and a separate spring locating pad will have to be included in the stack up.
- Longer stem lengths are more unstable they bend especially with increased spring pressures.
- The rocker studs usually prove to be too short because the longer valve forces raising the rocker. You will have to obtain longer studs. At this point longer studs become unstable with high spring pressures you may well find that you must use a 3/8ths stud and maybe even girdles to keep even a street engine from having problems busting studs.
- You will have to also use a longer push rod to keep the geometry of the rocker at the valve stem tip correct. This probably can't be ascertained until after engine assembly so all the dimensions can be accounted for in the tip sweep.
So as you can see a lot of elements come into this when you try to get around grinding down the guides.
Over many decades I developed a deep understanding Murphy's Laws of engineering and mechanics and added a few corollaries of my own, one of which is:
- The easy way out of a problem always leads back in and at greater expense.
Frankly, I'm rather of the opinion that if you're planning .5 inch lift or more the production L31 Vortec is not the head to be using. There are many aftermarket heads that just don't require so much messing around with for about the same price.
|01-16-2013 06:14 AM|
The Manley valves with .290" tips will work with aluminum self aligning rocker arms. You will have about .035" - .040" clearance between the rocker rails and valve locks. We used Comp Cams 795 retainers Comp Cams 613 locks. That is 10* equipment. The 10* locks are wider than 7* locks which gives additional clearance between the retainer I.D. and the rocker alignment rails.
The push rod length and rocker arms stud height are different issues. You will need to determine the correct push rod length after the camshaft is installed. There are several different 3/8"-24 rocker arm studs that have a different effective heights in order to get the correct adjustment length for the poly-locks. We used ARP 134-7104 rocker studs which is the most common suds used for full roller rocker arms and poly-locks. .
The push rods we used were Comp Cams High Tech #7940 (7.200" ) but the length must be determined for your heads using your lifters and camshaft.
|01-16-2013 02:31 AM|
|cobalt327||FWIW there's a relatively inexpensive tool that'll allow the retainer and lock installed height to be checked/verified. It's Howards p/n 92010. Use your own calipers.|
|01-16-2013 02:20 AM|
• Vortec heads
• Valve train points to check
• Valve train geometry
|01-16-2013 01:48 AM|
The problem that's been encountered here is the exception, not the rule. flyingputz had a problem because he used locks that added 0.050" to the installed spring height because the springs he used had a little too much seat pressure without the added height. The added installed height the locks provided also reduced the clearance between the locks/retainer and rocker arm.
Ideally, the 26918 springs (130 lb @ 1.8" installed height) would be used w/+0.100" valves. Another way around this would have been to use guideplates and ditch the self aligning rockers or use guideplates w/the rockers he has now, after removing the alignment 'rails' from his rockers (shown below). Then the +0.050" locks would clear.
If the rockers were the type that used the thin "washers" on either side of the roller for aligning on the valve tip, this might not have been an option. I thought this was what he had after it was mentioned by someone but it turns out they're the cast-in rails that could be removed. After seeing his rockers and thinking it over, that's what I would do, along w/using the +0.050" locks. It would be time consuming, but using care it can be done. I'd use a dremel and run several turns of mashing tape over the rollers to help protect them. Obviously this would require guide plates, different studs and the boss cut down, but I believe that would be the least expensive way to go about it, other than to just go ahead and run a little extra spring pressure.
|01-16-2013 12:04 AM|
Through all of this thread, and it is a thread and a half, I've gathered that inorder to eliminate the clearance issues between the rocker and locks and rocker and retainer for a stock Vortec head with .500 to .525 lift the solution is valves with .290" stem height above the the lock - is that correct? And this should eliminate the need to machine the guides for retainer clearance and spring pressure will be relatively easily adjusted with shims, correct? And from there I will have to get the correct stud and push rod lengths.
From what you guys have posted, this will work with several different brands of self aligning roller rockers and ratios.
I ask, as I am planning on a Vortec head install with a set of 062's that I already have.
FYI - I don't want to hijack the thread, but this will help me from finding myself in flyingputz's situation (and you guys from answering the same questions again in 4-5 months).
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