Late Model Chevy Truck Heads (1998) on a 1981 305 block?

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Jeff

Not-quite-so-new-guy
Apr 29, 2017
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I saw a recent Car Fix Episode where they put heads off a 1998 Chevy truck on one of our 305 motors mine is in an 81 Monte. They put a cam in a performer intake manifold on and topped it with a Holley 600 CFM Carb and claim 300 Horse Power. Anyone have experience and success with such a modification? I am looking for more details. Thank you for your time. Jeff
 

Jeff

Not-quite-so-new-guy
Apr 29, 2017
5
6
3
I heard heads from a late model 305 in this case from a 1998 Chevy truck will fit on one of our blocks. And if you upgrade Cam, Intake and Carb you will flow enough to get 300 horse power. I would like to get 300 HP out of my 81 Monte on a budget. Anyone have details on this working or am I sadly mistaken. Thank you for your time. Jeff
 

1320John$$$

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Sep 18, 2019
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I did a similar swap on a 8.6 compression 305 ported 416 castings with 1.94 intake valve edelbrock performer intake small crane camshaft 216 @.050 600 Holley vac carb comp 1.52 magnum rockers 1 5/8 headers I did chassis dyno this car it made 229hp and 243tq ran very high 13s before the Auburn diff in the 7.5 rear broke
I think your vortec headed 305 would be closer to 300hp at the crankshaft
38A54417-325C-45E2-8BFB-A28EA2CE36FA.jpeg
 
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Streetbu

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Make sure they are Vortec heads off a 350 and not off a Vortec 305. Completely different heads. The 305 heads don't give nearly the performance gain.
 
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Streetbu

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350 heads will fit on your 305. Don't use the Vortec 305 heads, you won't notice much of a difference. Use the 350 heads. Casting numbers ending in 062 or 906 are the good ones
 
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Oct 14, 2008
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Make sure they are Vortec heads off a 350 and not off a Vortec 305. Completely different heads. The 305 heads don't give nearly the performance gain.
I am surprised they even bothered with different heads. I assume smaller valves and ports? I know the 5L Vortec were rated at 230 HP, got mid to high 20's mpg Imperial and only made a couple of years.
 
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Aren't the Vortec heads nearly as crack prone as the Dodge Magnum heads? Either buy new or get them pressure checked. Also what is the chamber size vs 305 stock heads?
 

MrSony

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Nov 15, 2014
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300hp budget 305 parts list:

1. 9.5:1 vortec head 350
2. See #1
 
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Doug Chahoy

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Nov 21, 2016
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The factory hp on the stock 350 was 260 from 96-99. That would be the better way to go. My 99 Tahoe REALLY came alive with a K&N filter charger short headers and a complete Magnaflow exhaust with their cats. I wouldn’t waste the time and money on a 305.
 

DRIVEN

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Apr 25, 2009
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No real need for two threads on the same subject. Yes, Vortec heads will "work" on an old 305. Whether you use Vortec 305 or Vortec 350 (they are quite different heads) either will be an improvement over the '81 305 heads.
However, as stated already, you're farther ahead to just find an L31 Vortec 350, both to reach your 300hp goal and also probably financially. Either way, you'll need a Vortec specific intake manifold.

We're all on a budget of some sort. My advice is not to spend any money on a 305. The ROI just isn't there. They were a compromise design that was intended primarilywfor fuel economy and lower emissions. The bore to stroke ratio is more conducive to building torque rather than horsepower.
 
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