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Old 09-18-2010, 12:33 PM
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Cam ??

Ok guys , I was talking to a summit guy he says that I could go with a Comp cam 224/224 470 lift with
my stock Vortec heads with out changing the springs , what do yall think??
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Old 09-18-2010, 12:59 PM
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Quote:
Originally Posted by old 94 gmc
Ok guys , I was talking to a summit guy he says that I could go with a Comp cam 224/224 470 lift with
my stock Vortec heads with out changing the springs , what do yall think??
If that's exactly what he said, I think he is full of it.
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Old 09-18-2010, 03:21 PM
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So you think that changeing the spring would be best ?
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Old 09-18-2010, 03:37 PM
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Yes, and here's why:

The original L31 cam had a lift of 0.414" int/0.428" exh. The new cam has not only more lift, but will require more seat pressure than the OEM spring will provide. This is because valve "bounce" (i.e. loss of control allowing the valve to bounce off the seat at closing) is as detrimental to performance and durability as "loft" or "float" (i.e. loss of contact of the lifter to the cam as the lifter goes over the nose of the cam), to a valvetrain, IMO.

An inexpensive set of "Z-28/LT-1" springs from the aftermarket can be used, or if your budget will stand it, Comp makes a nice beehive-type spring and retainer that would be good.
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Old 09-18-2010, 04:17 PM
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Quote:
Originally Posted by old 94 gmc
So you think that changeing the spring would be best ?
It's not just a spring problem. It's also a problem with the bottom of the stock retainer contacting the guide seal/guide at lifts exceeding stock.

When choosing springs and retainers for any camshaft other than stock, you have to consider a safety margin. Most cam grinders will suggest 1/16" to 1/8" (0.062" to 0.125") retainer to guide/guide seal clearance at full valve lift and will also recommend a minimum of 0.050" between the spring coils (0.010" minimum measured at the five places between the coils for a total of 0.050") to prevent coil bind at full valve lift. It has been published in several places and evidenced by the figures posted by Cobalt here in this thread that the max valve lift with a stock L31 camshaft is ~0.430".

I think what has happened is that some hot rodders have assembled the L31 heads with valves, keepers and locks without springs and found that the travel before the bottom of the retainer strikes the seal is maybe ~0.480"-0.500". Not taking a safety margin into consideration, they have concluded that you can run up to ~0.500" valve lift with the stock retainer/lock arrangement. This bogus information has, of course, been passed from one enthusiast to another until it has become gospel. Maybe it has even filtered into the ears of a cam grinder tech guy who believes it.

Others have concluded that they can include more lift AND A SAFETY MARGIN by grinding the bottom of the retainers for more clearance between the retainer and seal. This is called a "ghetto grind".

So, it's not just about changing springs, it's also about grinding the existing retainers or using aftermarket retainers that will allow enough clearance retainer to seal at the production installed height.

When mixing and matching retainers and locks, caution must be used to insure that the tip of the valve extends above the top surface of the retainer if you are going to retain use of the rail rockers. If you get your combination together and the sides of the rockers touch the retainers before the middle of the rockers contact the valve stem tip, you are going to be in trouble because the rocker will unload the locks. You have your choice of 3 different configurations of locks.... standard, plus 0.050" or minus 0.050" installed height that will place the retainer where you want it in relation to the valve stem tip. Changing installed height will also, of course, change the installed and operational spring pressure, so you have to work that out to insure that you have correct pressure and also correct retainer/seal clearance for the camshaft profile you're using.

The stock spring is retained laterally by the large O.D. of the guide, so you don't have enough room to run a decent spring in the first place in my opinion. The best fix is to cut the diameter of the guide and the spring seats to allow use of a decent spring. At the same time, I would cut the O.D. of the top of the guides for a PC seal (0.530") and trim the top of the guide to allow proper retainer to seal clearance at full valve lift (0.062"/0.125"). I would also cut the rocker stud pads and tap for screw-in studs and guide plates to get rid of those fosdick rail rockers and use conventional stamped steel rockers or a good aftermarket rocker with roller trunnion.

In closing, L31 heads do flow very well in relation to other production cast iron heads, but they are not without their bad points. If you are not equipped to do these alterations I have outlined and must pay retail to have them done, you may be better off choosing another cylinder head from an aftermarket manufacturer that is set up and ready to go.

Last edited by techinspector1; 09-18-2010 at 04:29 PM.
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Old 09-18-2010, 04:42 PM
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A recent thread on the subject- vortec heads 1.5 or 1.6 rocker

Be sure to check out the link at the bottom of my post in the link above.

Good luck.
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Old 09-18-2010, 04:43 PM
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Thanks guys , I'm new at this and need all the help I can get. Will a 1800/2000 stall converter. Help my stock 350 alittle ? I'm useing a 600 1405 eldelbrock carb on it now can I go with a bigger carb on it ?
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Old 09-18-2010, 04:46 PM
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Quote:
Originally Posted by cobalt327
A recent thread on the subject- vortec heads 1.5 or 1.6 rocker

Be sure to check out the link at the bottom of my post in the link above.

Good luck.
The 600 will probably be fine- as long as it's tuned for your combination. What intake, and what is the rest of the engine combination? Compression, heads, etc..

What vehicle- weight, use, gear ratio, trans type, etc..

The ignition timing curve could probably be improved on, as well. Have you done any work to the distributor yet?
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Old 09-18-2010, 05:17 PM
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Its a 90 350 stock engine in a 94 gmc reg cab truck with 062 Vortec stock heads and tranny is a 700r4 with 3.42 rear gears if I got the code right from the glove boxs (gu6), the tranny is stock to - want to go with a th350 but from what I heard
for a DD it best to go with the 700r. The distirbutor I bougth one of the summit ones. I just started to put this truck togther and from what I get from yall ,I need a lot to learn. Thanks for yalls help !!
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Old 09-18-2010, 06:40 PM
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The intake is a professional products one
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Old 09-18-2010, 07:14 PM
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That torque converter would be a help, but it will depend on the cam. And the cam depends on the use and compression ratio, gears, etc. It's all intertwined as a combination of parts that needs to be in sync w/each other. But if you were to use the cam you first mentioned, a looser TC will help.

I wouldn't get too large on the carb- either stay w/what you now have or go to a good vacuum secondary like a Holley Street Avenger or a 650 BG Speed Demon- that type thing.

Probably the best carb would be a Q-jet if you can find a good one.
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