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Old 08-13-2012, 06:37 PM
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Need help switching 5.0L to 5.7L

Ok, i know i'm about to catch a bunch of crap here but i'm broke and need advice on gettin this truck up and going. For starters i have a 1998 Chevy C1500 Vortec 5.0L 2wd with a locked up bottom end, she is siezed pretty got. Here is where the crap giving is going to start, i have a low miles, 80k or so, 1992 non vortec 5.7L just sitting in the shed that i got for free. So.... can i use the short block 5.7L
under the Vortec 5.0L upper end; heads, intake, wiring, so on so forth. i already know if i can that i'll probably have to flash the computer and/or change the injectors to 5.7L ones. iknow this isnt the best way of doing this, i know the 5.0 has small combustion chambers and small valves, this is a dirt cheap rust free pickup for me to drive back and forth to work so maybe i can make enough money to build a real motor for. can this work as a daily driver and does anyone have any advice to make it less painful? please dont give me too much crap, i just need a truck to drive, with hopefully the parts i already have.
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Old 08-13-2012, 06:41 PM
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forgot to mention, i know the 5.0L has a crank trigger and the older 5.7 doesn't, can those parts, front cover and all be switched? i'm asking before i yank everything out so hopefully i know where i'm going when i start this deal
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Old 08-13-2012, 07:35 PM
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Why not just rebuild the 305? You're already going to have it out, might as well put it on a stand and throw some new rings and bearings in there. The 305 heads on the 350 short block will make the compression pretty high. And by the time you get all the computer stuff figured out, you could have been done with the 305. Just my opinion on it.
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Old 08-13-2012, 10:48 PM
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The TBI engine runs a different timing cover, and balancer. The 5.0L heads will make a mess of the 5.7 considering a factory 5.7 tune won't do. It will need a custom tune for certain, and 5.7 injectors.
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Old 08-14-2012, 04:46 AM
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Or get an adjustable fuel pressure regulator and add more fuel pressure to increase the output from the injectors.

You need 14% more fuel (in theory) to run a 350 instead of a 305.

if the idle pressure is 30 psi then you would need 39 psi to get the injectors to spray 14% more fuel.

square root of (39/30) =1.14

Find out what the stock fuel pressure is then calculate how much more pressure to use.
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Old 08-14-2012, 10:29 AM
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Thanks for the info guys, I pretty much knew it wasn't going to work as easy as I hoped, only reason for the thought of trying was to use parts I already have and not spend a lot, I'll just pull the 305 this weekend and tear it down to see what it will take to fix it, thanks again
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Old 08-14-2012, 10:33 AM
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Just run the 5.7l short block, the 5.0l top end, the 5.0l cam, and bump up the fuel pressure. You'll only be out the cost of gaskets and perhaps an adjustable fpr. Your compression will be a little high but not terrible.
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Old 08-14-2012, 04:50 PM
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Quote:
Originally Posted by Rhaslettjr View Post
Ok, i know i'm about to catch a bunch of crap here but i'm broke and need advice on gettin this truck up and going. For starters i have a 1998 Chevy C1500 Vortec 5.0L 2wd with a locked up bottom end, she is siezed pretty got. Here is where the crap giving is going to start, i have a low miles, 80k or so, 1992 non vortec 5.7L just sitting in the shed that i got for free. So.... can i use the short block 5.7L
under the Vortec 5.0L upper end; heads, intake, wiring, so on so forth. i already know if i can that i'll probably have to flash the computer and/or change the injectors to 5.7L ones. iknow this isnt the best way of doing this, i know the 5.0 has small combustion chambers and small valves, this is a dirt cheap rust free pickup for me to drive back and forth to work so maybe i can make enough money to build a real motor for. can this work as a daily driver and does anyone have any advice to make it less painful? please dont give me too much crap, i just need a truck to drive, with hopefully the parts i already have.
What youíve got here is a change from the Vortec 305 with OBD II electronics to a 350 TBI Swirl Port of OBD I electronics, not impossible to do.

Both engines are the single rear seal type with a right side dipstick; the oil pans are the same only the timing cover and front damper are different. But the plastic Vortec timing cover will bolt to the 92 block so that gives you the mounting location for the crankshaft position sensor the Vortec computer needs to see.

The 305's damper is a multi-piece unit that is necessary to trigger the crank position sensor. The 305 unit will bolt in place of the one piece part on the 350's crank snout. Another problem solved.

The 305's Vortec required distributor will drop into the 350 block after the 305's top end is in place. Another one bites the dust.

The 1998 305 and 350 Vortecs use the same injector but a different cycle time program in the computer. You can either flash your computer or get a 350 junkyard computer; probably easier to get around the security system by having yours fixed to the 350 engine than trying to hack a foreign 350 computer into the vehicle ID.

The heads could be a problem, the 305 chamber is about 7-10 ccs smaller than the Vortec 64 cc chamber and they burn less well. I figure the 92 has the deep dish piston .068 inch and 4 valve reliefs which should add up to about 18 cc's in the piston. With a .020 thick gasket and the OEM .025 inch deck clearance this should give a compression ratio of about 9.6. The squish/quench will be less than desired so the engine may be ping prone but the detonation sensor on the electronic fuel injection will just roll the advance back till it doesn't ping, it in fact it does. You can always polish up the chambers and relieve the edges to gain a few more ccs in there. Youíre going to have to measure this stuff and do the math to be sure. Itíll probably need premium fuel.

All in all this should be pretty easy and except for gaskets and swapping some parts around should be easy and cheap.
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Old 08-14-2012, 07:23 PM
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Man that's awesome info there, that's exactly what I wanted to hear since when looking the truck over tonight I found a 4" crack in the right side of the block! So not to bother you anymore, but what would your suggestion be on getting my ECM flashed to run with this combination, anyone you know or trust to do what I need done?
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