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Old 09-29-2010, 04:20 AM
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vortec 305 heads on 350.

I have a 350 out of a 1980 chevy 3/4 ton truck that Im putting in my 79 Z29.
When I took the valve covers off I found I had miss matched heads
one is a 3888338 the other is a 3998993. this engine didnt feel to powerfull in that big truck backed by a 4 speed.

I have the chance to get a set of vortec 305 heads for $50, cast numbers 12552520. these heads are compleat and came off a 97' 1500. I under stand I will have to buy a vortec intake. And this should bump my compression a bit aswell (easly turn the engine over by hand on the flywheel)

will these heads bolt right onto my 1980 block? what will I have to change other then intake? and do you think they will perform better then what I already have?

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Old 09-29-2010, 05:10 AM
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They will bolt right onto the block. You will also need the self-guided rocker arms that came on the '97 heads, your current heads have pushrod guide slots in the head and non self-guided rocker arms, so you can't use those on the newer heads.

While the 305 Vortec's are not as good as the 350 Vortec's everyone loves, they are much better than the clunkers you currently have as far as airflow is concerned. Your current heads have 76cc chambers, the 520's have 58cc chambers, so they are going to raise your compression ratio about 1.6 points, from 8-1 to a little over 9.5-1, so it is going to require a cam change to something bigger than stock if it is to run on pump gas.

For the $50 price I say go for it if they don't need any rebuild work.

Going into the Z28, I am figuring you were planning on changing the cam to something a little more performance oriented than stock anyway?? There are some limitations as to how much lift the Vortec heads will take in stock form, but it is fairly easy to deal with.

Any idea what cam you want to use??
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Old 09-29-2010, 07:52 AM
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If you want to go the vortec route to more power you'd be best to hold out for some real vortec heads from a 350 L-31 casting number 062 or 906.

The 305 version are not the same. You'll spend more reworking them than just buying 350 vortec heads. Thats why they are for sale so cheap.

Ya get wehat you pay for.
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Old 09-29-2010, 11:46 AM
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Quote:
Originally Posted by 89silverado454
I have a 350 out of a 1980 chevy 3/4 ton truck that Im putting in my 79 Z29.
When I took the valve covers off I found I had miss matched heads
one is a 3888338 the other is a 3998993. this engine didnt feel to powerfull in that big truck backed by a 4 speed.

I have the chance to get a set of vortec 305 heads for $50, cast numbers 12552520. these heads are compleat and came off a 97' 1500. I under stand I will have to buy a vortec intake. And this should bump my compression a bit aswell (easly turn the engine over by hand on the flywheel)

will these heads bolt right onto my 1980 block? what will I have to change other then intake? and do you think they will perform better then what I already have?
Here is some info and photos for you:

L30 305 head info- POST #487.
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Old 09-30-2010, 06:37 PM
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How well does a 305 take 350 vortec heads?
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Old 09-30-2010, 08:59 PM
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Quote:
Originally Posted by spinn
How well does a 305 take 350 vortec heads?
Just fine, but it lowers the compression ratio if the 350 vortec heads are used stock, the 305 heads are usually 58cc and the 350 vortec are 64cc. Most who do this swap have the heads milled .020-.025" to remove 4cc's of volume, and install on the 305 with a steel shim gasket.

Either Car Craft, Chevy High Performance or Super Chevy magazine had an article about this in the past.
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