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Old 12-19-2011, 10:09 PM
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sbc 350

building sbc 350 with cam 460/488 i need to know what head work needs to be done

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Old 12-19-2011, 10:31 PM
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Really depends on the head.. maybe just cut the spring pocket and the top of the guides to fit the spring and clearace for the lift.. .. if even that.. if you are asking about porting.. not much... if any..
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Old 12-19-2011, 10:47 PM
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vortec heads

its a set of used vortec heads off a 98 suburban thx for the info
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Old 12-19-2011, 11:31 PM
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Do yourself a favor and get them checked for cracks.. very bad about that.. That head has a very tall guide..you will probably need to cut the top of the guide for lift clearance.. .comp cams has a number 941 spring that we use in Dirt Stock cars.. you will have to remove the dampner to clear the boss at the base of the Valve guide.. Honestly if you could spare the money.. a set of the aftermarket Vortec style heads made by Most head manufactures would be your best bet..
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Old 12-20-2011, 07:02 PM
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Quote:
Originally Posted by dtwan2000
building sbc 350 with cam 460/488 i need to know what head work needs to be done
As little as doing a "ghetto grind" on the stock retainers (google it) or using +0.050" locks and replacing the stock springs w/"Z-28/LT-1" springs w/the damper removed, to machining the guide boss shorter and cutting it for aftermarket seals, along w/different valve springs and retainers. Springs (and retainers if needed) are available from cheap to expensive, depending on whether they're beehive (requires new retainers) or what. If you do a search here you'll see dozens of threads on this.

More info on Vortec heads and mods to them, etc. is HERE.
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Old 12-21-2011, 12:32 PM
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Everytime I think about the L31 heads, I get a little less excited about them from a total cost standpoint. The only thing they have going for them from a hotrodder's standpoint is that they flow well.
1. Thin wall casting, prone to cracking.
2. Pressed-in rocker studs, prone to pulling out with stronger springs. I seem to remember that the stock springs are about 260 lbs over the nose of the cam. Either need to be pinned or the heads need to be milled, drilled and tapped for screw-in studs. Pushrod holes will need some work too. Guide plates will eliminate the rail rockers.
3. Stock guides are too fat. You can't install outer springs with a damper spring without cutting them to a smaller O.D.
4. Stock guides are too tall. You can't run any more than about 0.420" valve lift with them if you use the stock retainers and valves due to retainer/seal interference.

The only way I would use these heads unaltered would be on a mild street motor. I'd keep everything stock on the heads, including new, stock springs, new seals, rail rockers and use a cam with no more than 0.420" valve lift. Some heads will suffer from the seals not being pressed all the way down on the guide, so use a socket and small hammer to seat all of them down snugly.

Here's an example of a combination that might work....
Cheapo to build, cheap gas 350 street motor....
These pistons...
http://www.summitracing.com/parts/UEM-KB142-030/
This cam and lifter kit...
http://www.summitracing.com/parts/HRS-CL112011-11/
L31 heads from a boneyard, casting # 12558062 or 10239906. Magnflux 'em for cracks. Fit new STOCK springs and seals. Make certain seals are fully seated on the guide boss by tapping them with a socket and small hammer. The stock springs will work well with the mild cam and will not pull the rocker studs out of the heads. Doesn't matter whether the heads have hard inserts in the exhaust or induction hardened seats, either way will work. Same casting, both styles flow the same. Maybe freshen up the valve job and otherwise leave 'em alone. Use the rail rockers that came on the heads stock.
Align-hone the main bearing bores in the block and cut the block decks for 9.015" block deck height, referenced off the main bearing bore so that you know the block deck height is equal on all four corners. This will insure that the heads sit level and flat on the deck and that the intake manifold will sit square to the heads with no gaps to cause an internal or external vacuum leak. Use GM head gasket #10105117. Static compression ratio will be 9.1:1 and squish will be 0.042". Use Edelbrock #7116 Performer RPM intake manifold. 600/650 carb is all you'll need.

Makes 365 hp @ 5000 rpm's with a double torque peak of 420 ft/lbs @3500 and 4000. Should make this power on crummy cat-pea pump gas without detonation and make a real nice daily driver motor.
Cam begins making power at 1200, so it's your call whether or not you need a looser converter. If I did anything at all with this combo, it would be a mild 2000 stall unit just so I didn't have to contend with the car creeping at stoplights and also to get up into the 1500 rpm low range of the intake manifold when the light turns green.
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Old 12-21-2011, 02:11 PM
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This ain't a pissing contest- the following are my opinions.

Pushrod holes are basically a non issue, the holes are ~7/16" round, or in other words, as big around as an older head's slots (that used the pushrod slots as a guide) are long. The only way there'd be any need to modify the holes would possibly be if 1.6:1 ratio rockers were used.

I believe the Vortec heads are a heck of a deal for a guy on a budget and has no expectations of making more than about 450 HP (400 HP is almost a complete no-brainer w/them). For an engine cammed and sprung for the area of 5000-5500 RPM, the heads are fine. They're no more prone to pulling studs than any other SBC head in my experience.

If any of the other free/cheap mods to gain more lift clearance aren't acceptable for whatever reason, the tool to cut the guide bosses down costs $50.00. If the studs were such a worry- pin them, a set of pins w/a drill costs <$15.00. Or much better the pressed studs can be pulled and the boss tapped for non shouldered screw in studs (set of these studs are <$35.00, plus a tap if one isn't on hand already. Use care or farm it out if needed). Then reuse the rail rockers like the heads came with.

But other than assuring retainer to boss clearance, much of this isn't needed unless using valve springs w/a lot more pressure or a lot more RPM is being turned than what the 'average' street cam will need to make peak power. I wouldn't recommend stock springs because (even if the open pressure was sufficient) they lack sufficient seat pressure to keep the valves from bouncing- especially true of fast ramped cams.

I cannot comment on the heads cracking any easier than any other late casting SBC head. I DO know a lot of heads that have been overheated bad enough to crack them are found. Judging the crack-resistance of heads coming off of core engines isn't the best indication. Using heads from a running engine or an engine that suffered a bottom end failure will be fine in all likehood.

Are these heads the end-all do-all of all SBC heads? Of course not. Aftermarket heads are capable of flowing better and have heavier castings. And if someone takes a set of Vortecs in to the machine shop and simply says "give them the works!", an aftermarket head will likely make more sense from a cost standpoint.

But for the guy who knows how to fend for himself and who does his homework (right head for the right application), they are a bargain IMO. The fact remains that they are the best production SBC head- when flow and combustion chamber design is considered- than any previous SBC Gen I (and argueably Gen II) head. They can be easily found, cheap to buy and easily made to work w/more than stock lift.

Last edited by cobalt327; 12-21-2011 at 02:34 PM. Reason: Typo.
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