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What's the story with double hump heads?

GsxrMike

GsxrMike

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I found these heads on craigslist and was wondering if they are any good. My buddy swears by double hump heads but I don't know squat about them. The heads I have now are 1.95/1.60 valves but thats about all I know. (they are centerbolt valve covers and the 2 intake bolts in the center are straighter up and down than the others) Would it be worth messing with. I know it would mean new intake, valve covers, etc.

http://kansascity.craigslist.org/pts/944247413.html

Thanks guys!
 
Don't mess with them, especially if you already have the centerbolt stuff.

Find a set of vortec heads from a 96+ 350 but watch for cracks in them. They're cheap and are some of the best heads that were ever put on a small block.
 
I bought my brand new vortec heads (casting 062 IIRC) for less than $500. Given, that was 5-6 years ago but used ones should be half that.

Many people will call any centerbolt heads "vortec", so watch out for that.

The brand new heads for $500 isn't a bad deal at all, Jegs sells them new for $290 each.

The 305 vortec heads are sucky, avoid them. Supposedly the 3/4 and 1 ton 350's got different exhaust valve seats and a different casting number that maybe doesn't flow quite as well but 062 is the general casting number you're looking for in vortec heads.
 
is 062 the last three digits of the #? If so I will stop by Bonner Springs tomorrow and look at those for the casting #. Where should I look for cracks?
 
[Edit] I guess I type slow, those two ^^ weren't there when I started.

Back in the day double humps heads(DHH) were a good performace mod. But now, you're better off spending your money on some Vortec's, or a set of aftermarket heads. Even after extensive porting/bigger valves, DHH won't flow as good as Vortec's for the money spent. True DHH don't have the ends tapped for accesories from the factory either.

Have a machine shop magnaflux the heads...that's the only way to find the cracks. Yes I have seen some cracked so bad you could see it, but most arent that bad. Should only cost around $30-$40.

$150 heads-Doesnt give much info, could be high millage, or something like that. Expect to rebuild these. (It's in bonner springs :haha:)

$500 heads-Says that they are new, but looks like they have had gaskets on them before. May be take offs of a crate motor. Price seems a little high. If they are indeed new, or have low miles, they could be a bolt on and go. With the correct intake ofcourse.

$1000 heads-Not to sure what he means by "BRZEZINSKI" maybe a local speed shop? If so then ask if they are completly rebuilt (for that price they better be ready to run). New springs, valve seals, studs (if they are ARP screw ins, then thats good), and possibly valves. I'd ask what he means by "UNDER COVER PORT WORK" too.
 
GsxrMike said:
is 062 the last three digits of the #? If so I will stop by Bonner Springs tomorrow and look at those for the casting #. Where should I look for cracks?
Click to expand...

Yeah, the casting number is much longer but 062 is the last 3 digits. Looks like 906 is the other casting number that I mentioned (with the hardened exhaust valve seats) and there are differing opinions on whether those are good or not.

As for cracks, you'll probably need to have the heads magnafluxed if you want to be 100% sure. Like most iron heads, cracking is always a possibility on used heads and eventually they spread. How long that takes can vary widely.

I don't know of any specific places that the heads crack but a google search will probably help you out, vortec heads are pretty popular ;)
 
38377k5 said:
I don't know of any specific places that the heads crack but a google search will probably help you out, vortec heads are pretty popular ;)
Click to expand...


Most of the ones I've seen have been in the exhaust valve area. Usually from the seat to the guide. Common sense says this would be the most likely area, temps are very high in that area. Also seen 2 crack between chambers...but that motor was very overheated. The drivers side cracked between 1-3, the pass side between 4-6.
 
38377k5 said:
Well, at that point they called it a 5L or 5000 but the 305 was certainly around during that era and had its own, smaller chamber and lower flow vortec heads.
Click to expand...

I have never seen a 305 head after 1995. I've rebuilt literally thousands of GM cylinder heads and every vortec head has been a 350. Without proof that a vortec 305 head doesn't exist i'm not going to argue the fact but i've never seen one and you would think with all the cylinder heads i rebuild i would have run across at least one pair if they did exist. There are plenty of 1987-1995 centerbolt valve cover 305 heads out there though. :dunno:
 
4X4HIGH said:
I have never seen a 305 head after 1995. I've rebuilt literally thousands of GM cylinder heads and every vortec head has been a 350. Without proof that a vortec 305 head doesn't exist i'm not going to argue the fact but i've never seen one and you would think with all the cylinder heads i rebuild i would have run across at least one pair if they did exist. There are plenty of 1987-1995 centerbolt valve cover 305 heads out there though. :dunno:
Click to expand...

Well, I certainly don't have the machine shop experience that you do Scott.

But I do remember coming across this when I decided on 062 heads for my 383:

The 305 vortec heads have smaller combustion chambers, smaller runners and smaller (1.84") intake valves. They are different and, like all 305 heads, will choke a larger motor.

12558059 is the casting number for most 305 vortec heads.
 
Why take the chance at buying old heads when they still need worked on?

Buy some new heads, World Products for example, and install them and be done with it.

There are several aftermarket companies that make some nice heads that flow and outperform any stock heads, modified or not.
 
I saw patriot performance(?) selling complete AL heads for $900/pr.

EQ cylinder heads sells "better" (thicker) Vortecs for reasonable as well AFAIK.

http://media.gmcanada.com/division/chevrolet/products/archive_prod_info/pguide/ckpickup/ckpeng2.htm
there's the Vortec 305.

I don't think I'd mess with used Vortecs...the cost to bring them back to "new" (new valves, springs, straightening, magnufluxing, etc., if you want to compare apples to apples) is pretty expensive, and if they are cracked, you are now out the cost of purchase, PLUS the magnuflux.
 
Alright guys thanks for the help. Now I guess I will start looking at all of my options. What kind of heads should I get. I don't know what cam I have. Is there a way to figure that out? I know it is a hydrolic roller cam. What size valves, intake runners, and chamber should I get? I don't mind going to 91 octane. (Thats the highest octane pump gas they sell out here) Aluminum or steel? New or used? Can I get something to match the intake I have now? Sorry for all the questions but I am still an infant when it comes to this kind of stuff. I do understand some stuff like smaller runners = higher velocity = better low end grunt.

EDIT: I found these but I think the valves are smaller than what I have now. I am lost!
http://kansascity.craigslist.org/pts/939421624.html
 
Vortecs are about your best bang for buck head out there. As cast they outperform (in every regard according to any dyno test ever done) anything GM made previous, at least as a production head.

Don't forget though, then you get into different valve covers if you aren't already center bolt, the new intake pattern, etc.

IMO the patriot performance heads I saw in the magazine looked pretty darn good. Head flow was good, but not so much it wouldn't make torque down low. Good chamber design. Complete.

With AL you can run *about* 10:1 on 87. It's easier with fuel injection, you'd be safe likely right around 9.5:1 on 87, if you matched the engine parts up right and had it tuned well. As cast Vortecs GM was running somewhere around 9.5:1, again that was injected, but it shouldn't be much less.

IMO 64CC heads are where it's at, as they are common and pistons are also common. Easy to figure compression when the heads and pistons are "made for each other". :)
 
Well I have center bolt heads and I belive but I am not for sure that I have a stock bottom end. I don't really know squat about my motor execpt that it runs good. Can I get a 10:1 or less with 64cc? What would it go to if I went for 60cc? I don't mind running 91 octane because I don't drive it much. Thanks for all of the help so far...
 
There are probably calculators out there to help you find compression, if you know your compression with 64CC on a given motor, changing CC should be an "easy" calculation.

If it runs good now I'd *really* consider leaving it alone, but it is of course, entirely up to you. :) My luck would be that the crank would break in half or something after swapping in the heads.

IMO going for highest compression is meaningless unless racing. More expensive, and the power gains, all else equal, are quite small. Again IMO, best to get the most performance out of 87 you can. Even if you go a bit too high for 87, you won't have to do anything but get mid-grade gas.

There is a TON more power to be had from the engine/exhaust components than there is just compression.
 
Here is a very user friendly compression calculator. http://kb-silvolite.com/calc.php?action=comp

The only way to find TRUE compression ratio though you'll need to know what the engine deck height is so unless you pull a head and measure you can only get "close". As a general rule though, most chevy engines are between .020"-.025" deck height from the factory. For those that don't know what deck height is it is the distance that the piston sits down in the bore from the deck surface of the block when the piston is at TDC.
 
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