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Old 10-04-2007, 10:58 AM
Twistedwrench's Avatar
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Vortec heads 12558059 305 5.0

I have seen a few members ask questions about the 12558059 vortec heads from the 305. I have a set here and thought I would put up some pics to show the differences in them.
Like its been said they are different in ways. They still have the raised runners and no center bolts. The intake ports have a strange raised portion in the bowl area. They do not have the heart shaped chamber; here are pics of a set that I just got ready to run. I know they are not the head of choice but I wanted to experiment with them and try them out.


http://i207.photobucket.com/albums/b...s/DSCN4664.jpg


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Old 10-04-2007, 01:24 PM
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305 heads.

You've answered your own concern with mention of the "raised portion in the intake bowl"- the so-called ramport or swirlport head. It and the sharp "hook" just inside the the intake manifold mounting surface limit the RPM potenential to about 4500 RPM. Those two obstacles in the intake port induce swirl into the chamber. Have'nt heard of anyone porting/grinding the ramp out or even if it's possible. Not a performance head and probably not much potential there either; RV cam, those heads, small carb, and dual exhaust ; stick it in a truck like I did with mine. Oh, and they're NOT Vortecs like a lot of people seem to think they are; Vortecs have the heart shaped chamber and 8 bolts to bolt the intake down (aftermarket excluded).
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Old 10-04-2007, 02:14 PM
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To be honest you won't get anything out of those heads there design is really out-dated and do not allow for a clean flame pattern. You will lose more than you will gain especially if they came off of a 305, that thing is a smogger to heart they just choke your engine. Those corners create pockets of air/ fuel that is ignited WAY after the the rest of the flame pattern. You also see that large niget of metal which your plugs go in? The flame has to travel all the way around that. This is what your looking for.

http://www.tristatecylinderhead.com/...n%20Vortec.JPG

notice the heart shaped chamber and how deeply set the plug is to allow maximum flame travel?
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Old 10-04-2007, 02:27 PM
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Quote:
Originally Posted by junior stocker
You've answered your own concern with mention of the "raised portion in the intake bowl"- the so-called ramport or swirlport head. It and the sharp "hook" just inside the the intake manifold mounting surface limit the RPM potenential to about 4500 RPM. Those two obstacles in the intake port induce swirl into the chamber. Have'nt heard of anyone porting/grinding the ramp out or even if it's possible. Not a performance head and probably not much potential there either; RV cam, those heads, small carb, and dual exhaust ; stick it in a truck like I did with mine. Oh, and they're NOT Vortecs like a lot of people seem to think they are; Vortecs have the heart shaped chamber and 8 bolts to bolt the intake down (aftermarket excluded).
years ago my boss had me playing around with those on the flow bench,if you try and remove that ramp it will kill the flow,trying to smooth them is not worth the time or the money.
start with a better head.
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Old 10-04-2007, 02:47 PM
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Wooo good god, easy up here fellas. I am NOT trying to prove anything or say they are even possible to gain any performance with. I am merely throwing these on just for the kick to see what the seat of the pants performance is like. I have a beater that we try different things out on from time to time in our shop. I have true vortecs, I know what they are I know what they do and I like I said I am not comparing them. I simply placed them on here because I saw others that asked questions about them.
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Old 10-04-2007, 04:37 PM
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my bad
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Old 10-04-2007, 04:54 PM
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Quote:
Originally Posted by Urbanfarmer
my bad

Lol, no, no bad at all, just felt like I was being slammed on their performance when I was merely showing to others what they look like. I have seen the question raised about these heads before. They may not be the quote true vortecs but they are a vortec head removed from a 99 K1500 Vortec engine. I replaced the 305 vortec with a 350 vortec last weekend. A very easy swap to do. Change the egr sensor and the knock sensor and itís a direct bolt in. all other components are the same. Injectors, intake, TB, and so on. An instant performance increase and runs like a champ. Very sorry if I came off sounded rude, just felt I was taken wrong with my intentions. They may just fall flat for what I am doing but I am the type of guy that likes to experiment with things like this.
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Old 10-04-2007, 06:49 PM
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ramport heads

My original thought on these heads was to use them on a small CID engine;1.84 intake valve, 58cc chambers, and the port size, even with the ramp, should be adequate for a built up 283. At least better than Power Packs, have hardened seats, and don't bring top dollar. Mine were free and only had 14,000 miles on them. Wound up putting them on a dished piston 350 with an RV cam for the truck but have'nt finished it yet due to spinal surgery. Post your results, and don't feel "attacked"; I don't think that was anyones intent.
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Old 10-24-2007, 07:53 PM
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Thanks for the info and pics. I've been wondering for years if they were designed like the L31 350 heads, but I never found out for sure until now.
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Old 10-28-2007, 03:16 PM
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Uh Oh... I think these are the heads I picked and had installed on my 283. I never saw the heads before I ordered them, just knew that they were on the 5.0 Vortec truck engines. Looks like a GM swindel to me

I was looking for the heart shaped chamber and smaller valves and combustion chamber cc volume.

Wasn't there any true heart shape Vortec cylinder head ever made with the small 1.84 intake and 58cc (or thereabouts) combustion chamber?
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Old 10-29-2007, 03:54 AM
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Thanks for the pictures of those heads, they will have cleared up a common misconception (at least for me) that the 305 Vortec heads are just a downsized fast-burning L-31 head, which unfortunately for me, they obviously are NOT.

How thick is the casting on those heads? How much could one mill them down to increase CR? I have these heads and need to reduce the combustion chamber about 5cc's. I've read that about 0.006 milling reduces volume by 1cc. Thus I would need to remove about 0.030 material. Is this a safe amount for these heads?
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Old 10-29-2007, 02:40 PM
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i wonder if their any better than the usual 305 junk aka 416, 601, 801, ect? they work very well on the 305 "vortec" engines in the full size z71 trucks. plenty of torque for a little 305. i couldn't tell we had a boat behind us "most" of the time.
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Old 10-29-2007, 03:05 PM
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They actually flow less than some 305 heads, plus they have big chambers which would require big domes in a 305 to keep you above 7:1
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Old 10-29-2007, 05:25 PM
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Quote:
Originally Posted by curtis73
They actually flow less than some 305 heads, plus they have big chambers which would require big domes in a 305 to keep you above 7:1
do you have the flow numbers? i've never seen them.

how does the z-71 trucks run so good with the 305 if the heads suck that bad?
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Old 10-30-2007, 01:00 PM
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This is an interesting thread. You would think that a 305 Vortec head would be just a "little brother" to the 350 vortec head, but I guess not? Is there any casting of a 305 Vortec head that fits this bill?

From the little I know about marine engines, the pre-vortec 305's were rated at 190 HP with a 2 BBL carb. The Vortec 305's with a 2BBL carb are rated at 220 hp. So, there has to be some improvement between the two heads, right?? That's a 15% increase in HP rating.
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