5.0 vortec to 5.7 vortec engine swap

d57gmcbell · December 7, 2004

i have a 97 k1500 that came with a 305. spun a rod bearing at 90,000 miles. Rebuilt lower end, now at 150,000 it has a knock again. both times it started after changing the oil. i need more power so i found a 5.7 vortec short block. does anyone know if the 305 used the same casting heads as a 350? and would i need the computer reprogramed for the 5.7? any info would be great. thanks

bline · May 12, 2006

I'm looking to swap a 99 305 in a Silverado for a 03 350 from a fullsize van. My main concerns are if the fuel injection system is different and how much different the pcm is. Anyone done a similar swap?

snoman · May 31, 2006

I'm looking to swap a 99 305 in a Silverado for a 03 350 from a fullsize van. My main concerns are if the fuel injection system is different and how much different the pcm is. Anyone done a similar swap?

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No real problem with this swap as long as it is a 350 vortec replacing a 305 vortec. On the original poster, if you have a knock again you are not doing someting correct because the SB has a very sturdy bottom end and can easily go a couple 100K with proper maintainance. If you need more power you might look at regearing truck as it is likely too tall for the load and tire size.

silveradoHO · May 31, 2006

i have a 97 k1500 that came with a 305. spun a rod bearing at 90,000 miles. Rebuilt lower end, now at 150,000 it has a knock again. both times it started after changing the oil. i need more power so i found a 5.7 vortec short block. does anyone know if the 305 used the same casting heads as a 350? and would i need the computer reprogramed for the 5.7? any info would be great. thanks

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I don't think the 305 and 350 have the same heads. I havn't worked on many vortec engines, but I know the older 305's used alot smaller valve chambers. But, they could be ported to work, and the smaller valves helped the engine rev faster. The design of 305 heads also raises the compression if used on a 350.

silveradoHO · May 31, 2006

I'm looking to swap a 99 305 in a Silverado for a 03 350 from a fullsize van. My main concerns are if the fuel injection system is different and how much different the pcm is. Anyone done a similar swap?

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Correct me if I'm wrong, but didn't the 99 silverados come with either a 4.8 or 5.3.

snoman · May 31, 2006

I'm looking to swap a 99 305 in a Silverado for a 03 350 from a fullsize van. My main concerns are if the fuel injection system is different and how much different the pcm is. Anyone done a similar swap?

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Correct me if I'm wrong, but didn't the 99 silverados come with either a 4.8 or 5.3.

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Not if it is a OBS Silverado. (Silverado used to be a trimmpackage before they made it a truck model and I still think it is a stupid name for a truck modeland confussing given the above. )

snoman · May 31, 2006

i have a 97 k1500 that came with a 305. spun a rod bearing at 90,000 miles. Rebuilt lower end, now at 150,000 it has a knock again. both times it started after changing the oil. i need more power so i found a 5.7 vortec short block. does anyone know if the 305 used the same casting heads as a 350? and would i need the computer reprogramed for the 5.7? any info would be great. thanks

<{POST_SNAPBACK}>

I don't think the 305 and 350 have the same heads. I havn't worked on many vortec engines, but I know the older 305's used alot smaller valve chambers. But, they could be ported to work, and the smaller valves helped the engine rev faster. The design of 305 heads also raises the compression if used on a 350.

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Yes, the chamber and valves are smaller and it will raise CR ratio but it will improve low and mid RPM responce due to increased mixutre velocities.

silveradoHO · May 31, 2006

Yes, the chamber and valves are smaller and it will raise CR ratio but it will improve low and mid RPM responce due to increased mixutre velocities.

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The problem with this is he will probably need to use 93 octane gas. I've even heard of some people having to use octane boosters because this setup will produce about a 11:1 ratio. The best bet is probably to find a set of 350 vortec heads from a junk yard.

snoman · May 31, 2006

The problem with this is he will probably need to use 93 octane gas. I've even heard of some people having to use octane boosters because this setup will produce about a 11:1 ratio. The best bet is probably to find a set of 350 vortec heads from a junk yard.

Why is this a "problem"? Given today and future market prices and that 93 octane is only abot 4 to 6% more (and less percentage wise when gas hit 4 dollars a gallon) and that you will see improved power and better efficency too and better MPG that will more than offset extra fuel cost, this is not a bad thing. The effeicny MPG or a engine is directly related to CR ratio as all engine gas or diesel are heat engine (they convert the hot expanding gasses to work) and the higher the CR ratio, the more energy that is converted to work. Detriot has not raise CR like they could because on publics fixation with 87 octane fuel and EGR and spark control will not make 11 to 1 happen with 87. One reason a diesel gets better MPG is because of the higher CR so more work is extracted from fuel and the fuel has a slightly higher heat content too. No mistery here. . When detriot gets off their but and goes to DI on gas motors, it will allow better power and MPG and higher CR's too and it will greatly narrow the MPG gap between gas and diesel too.

silveradoHO · May 31, 2006

It won't be a problem unless it still knocks even with 93. It would suck to have to use octane boost in every tank of gas, which some that have done this swap say they had to do. That could add up quick. I just think d57 should know the affect that 305 heads have on a 350.

snoman · May 31, 2006

It won't be a problem unless it still knocks even with 93. It would suck to have to use octane boost in every tank of gas,

See I do not think like that as I do not even mess around with 87 in anything ecxcept a old JD farm tractor with 6.5 to 1 CR. Everything else is 89 or better and has been for many years. I remeber driving in late 60's and early 70's when there was 94 and 100 octane leaded fuel and no knock sensors and you could tell who was skimping on gas in their engine when the rattled away from light.

udlooz · July 24, 2006

You will also need to swap the PROM chip in the computer to keep the TBI and distributor firing properly for the 350. The 305 has a different pulse width and spark curve I believe.

mcreyaufmiller · July 25, 2006

From my research, if you are exchanging a 305 for a 350 of the same year and series, then there would be no computer mods needed. Mine is a 98 and I have been looking into this for some time now as I am thinking about the same exchange.

bline · September 20, 2008

Update: We did the swap (2 years ago), only thing we had to change out was the oil pressure sensor.

Kunfusion209 · June 13, 2011

Hey guys im new on this forum My name is Eziekel by the way. I just recently purchased a 1996 silverado truck with a 5.0 305 vortec and it had a bad motor so i replaced it with a 5.7 350 vortec motor and i left the 5.0 computer and after that i fired it up and im getting a misfire code and my truck is shaking bad in low rpms but after i drive it passed 2k rpms it seems to runs decent.. can somebody help me? thanks