I'm getting ready to throw on some L31 Vortec heads (P/N 12558060)and Scoggin-Dickey says that the max lift is .450". I can't believe it's that low and the cam I want has more lift than that. Does anybody know if this value is correct? Otherwise I guess I'll end up changing the springs.

Any help is appreciated

Jason

 

i'd believe them before i would anyone on here. can you buy the heads bare and add your own parts? might be cheaper to go that route.

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ICON Motorsports

1st & 3rd

 

89,

They must have put some fairly tame valve springs on the heads. Almost any stock 1¼" SBC spring will take .450" lifts without failure.

I'll have to agree with Ed (big surprise, huh?) The bare castings are P/N 12529093, $260.00. The complete Vortec (P/N 12558060, $210.00) head has smaller 1.94/1.50" valves and pressed rocker studs. For the cost of removing the studs and installing you own, you might as well buy the complete heads, strip them, install 2.02/1.60" valves and decent springs and studs. You can get a nice set of 2.02/1.60" Manely Race-Flo stainless valves for $205.00, and GMPP screwed rocker studs for $18.60. The LT4 Valve Spring Kit 12495494 (16 PCs of 12551483 ) $35.95, retainers are 12495492 (16 PCs of 10212808) $15.54, and retainer key kit (keepers) P/N 12495503 $6.83 For less than $300.00 in parts, you can have some big-valve, screwed stud Vortec heads that should easily 0.540" valve lifts, and out-flow standard Vortecs. Typical machining costs for valve enlargement runs around $200-250, so add that in as well.

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Later,
Vader
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"I'm gonna talk about some freaky sheet now..."
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KaleCo Auto Parts

[This message has been edited by Vader (edited January 28, 2001).]

 

The cause of the low lift rating isn't the springs alone. The valve guide is relatively tall on those heads. So the lift limit is when the bottom of the center part of the retainer hits the top of the valve guide. Needless to say, this is as destructive to the rest of the valve train as coil bind.

That makes those heads yet another little bit less attractive for a serious performance application: you have to add having the guides milled down to the list of must-have mods. Keep in mind, as they come out of the box, they are a replacement truck head, not a race-prepped performance piece. Flow numbers aside, they are nowhere near ready for any kind of all-out high power application.

The springs that come with them are also just regular stock type springs, not really good for lift much past .450" either. So while you're getting the guides milled down and screw-in studs and guide plates and larger valves installed, you might as well get your machine shop to cut out the spring pockets to 1.45" while they're there. I would strongly recommend against using the GMPP spring above .500"; many problems have been reported on this BBS and elsewhere by people who have trusted what is IMHO an overly optimistic rating. Considering that GM has never sold a high-perfomance valve spring before (even their own racing teams have always used aftermarket ones) I think they will prbably get burned enough times by warranty claims that they will scale that claim back to being the same as every other 1.25" valve spring on the planet.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Thanks for the info fellas, for the price I'll spend on the Vortec, I guess I'll just go ahead and mess with the L98 Vette heads then.

Thanks again,

Jason

 

my cam has done fine on the stock heads (with stock rocker arms and .480 lift)....engine has seen over 6000 on accident of course, but just the same. Hot rod built an engine with my exact same cam and said that was the biggest bumpstick they would give those heads. Just some food for thought

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91 RS W/carbed 350, Vortec heads, performer rpm, Comp cams Xtreme energy 226/230 duration and .477/.480 lift. BFG Drag radials. 3.42 posi,Corvette servoed 700r4, ****ty stock converter. Edelbrock TES, 3inch cat, flowmaster with single 2.5 inch exit.
13.24@104

 

Jason,

It always helps to know what you're working with. If you're starting with L98 heads, you can save the cash you would have spent on the Vortec castings and do almost all the same machine work on your aluminums. These respond well to port work, and can end up flowing almost as well as the Vortecs.

Remember however, that if these are indeed aluminum L98 heads they have steel inserts in the valve seats, and can therefore NOT be resized to 2.02" valves without machining through the inserts. The maximum face size is 2.00", and that's a bit of a stretch. Your flows might be a little restricted by the valve bowl diameters and smaller valves, and you would have to make that up with more lift (i.e., better cam and springs). Iron castings in this design can easily be machined for 2.02" or 2.05" valves if you want to reharden the seats.

For a similar out of pocket cost, you might consider the World S/R Torquers with larger valves. A pair of these can set you back as little as $650.00 per PAIR, ready to bolt on. 2.02/1.60" valves, screwed studs, hardened seats, springs rated to 0.500" lifts, ready to roll. The World Sportsman IIs aren't bad for the price, either. Since you would be spending about $500.00 to machine and provide parts for your original heads, the difference might be worth the extra cash.

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Later,
Vader
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"Make Me Bad..."
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KaleCo Auto Parts

 

The L31 heads come off of the 305 and the L30's come off of the 350??? Is this correct?

I have purchased, but not received a set off of a 305 vortec engine.

Someone wrote that they have not had trouble with a 480 lift cam, but I was wondering if that was on L31's of L30's.....
Thanks.

 

L31 is the 350. L30 is the 305. I would wager a guess that they have the same springs...just a guess though.

-Mark W.
'88 SC Camaro w/ 305 TBI

 

Also don't forget that you can affect that clearance, and therefore the "max lift" rating, by changing the retainers. That might be an easy way to gain some lift, or a short path to disaster.

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"So many Mustangs, so little time..."
ICON Motorsports

 

A lil FYI: The bowls on the vette heads are already too big for the 1.94 valve, I would think that the 2.02 would easily be blended in.
And if you are running these heads on a 305 forget about changing the valve sizes.