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Old 04-02-2013, 09:27 AM
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Vortec 5.0 downsize to 4.3

Hey i have a 305 with busted crankshaft and would like to swap it out for a smaller mor economical V6. Will the engine mounts n electrical, tach, speedomiter oil pressure.. work or how much extra work is it?

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Old 04-02-2013, 11:56 AM
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it is NOT more economical to run a 4.3l v6 vortec.
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Old 04-02-2013, 01:37 PM
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A 4.8 LS is
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Old 04-03-2013, 10:13 AM
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In a fullsize GM truck, the L35 4.3 would only be more fuel effecient on the highway MAYBE.
200hp/260 lb/ft torque for the L35 4.3
230hp/285 lb/ft torque for the L30 305

I know that both use the single cat, y pipe arrangement with 3 precat O2 sensors and 1 aftercat O2 sensor.

The PCM's are the same, just need to be reflashed with the proper V6 calibration.
Be sure to use a V6 TC or the truck will be more of a dog. The V6 uses teh DBLF higher stall TC than the V8's.

You would need a V6 fan shroud. Trans will work, driveshaft is the same.
The V8 harness will work if you swap out the big connector that plugs into the fuel distribution block on top of the intake manifold. MAF is the same,
Throttle body is different between V8 and V6.

But honestly, I would find another 305. The 4.8 is a good idea, but off idle torque is lacking, but they pull great after 4000rpm.

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Old 04-03-2013, 11:06 AM
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The 5.0L isn't really that bad on gas for a truck. I had one in a 3/4 ton ex-cab/sb with a 4l60e and 3.73s through a 14bolt sf. Still got 15 mpg in city and cracked 20 on the freeway. Just yanked it with 250,000k on it (still running) to go in my 1984 Caprice. I have 5.7L vortec with an F-body LT1 cam that's going in it's place. Find another 5.0L or step up to the 5.7L. The best gas mileage improvement you'll see with these trucks is good control of your right foot.
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