305 to 5.3

Hey all, I’m replacing the old 305 in my 86 c10 with a gen 4 5.3 (LY5). I’m keeping the 700r4 and topping the new motor with the edelbrock LS1 performer intake so I can run a carburetor. My question is what parts do I need to retain from the old 305? (power steering pump, a/c compressor, fan shroud, etc). The 305 is 100% complete so I can keep anything I need to make the swap easy. Any help is appreciated!

its not going to be any cheaper to do that than it would be to just run a stock computer and standalone harness. You will have to run an MSD box or similar to fire the coil packs using the crank sensor, since the LS motors don't have any provision for a distributor. The edelbrock intake manifold and ignition box are going to cost you more than just getting it running with all the stock LS stuff and you will be losing all of the advantages of the LS swap by going to a carb anyways.

Honestly, I'd suggest just getting a junk yard 5.3 with all the accessories still attached. Rigging an LS to accept v belt accessories is probably going to be more trouble than it's worth. This would also give you an opportunity to have an AC compressor that accepts r134a refrigerant to begin with. As for the transmission, you need to setup your throttle linkage to allow a TV cable to be used, or you can shop carefully and find a 5.3 with a 4l60e still attached to it. It'll do everything a 700r4 can do and more.

Like the poster before me said, you'd be better off leaving the LS in its factory fuel injected form for both ease of set up, and power potential. If you're dead set a carburetor and use a 700r4, make sure you adjust your TV cable perfectly, or you will cook your 700r4. If use a 4l60, you must get a stand-alone shift module, since the ecm wouldn't be a part of the equation anymore.

Or stick with traditional small block and swap a L-31 Vortec engine into it with the carb.
Just needs an electric fuel pump set up on it.

Catbox said:

Or stick with traditional small block and swap a L-31 Vortec engine into it with the carb.
Just needs an electric fuel pump set up on it.

Click to expand...

This method works great, because unlike the LS, it essentially bolts in with no substanial modificatios. The Vortec small blocks are over-looked gems thanks to the LS swap craze.

Hey guys, thanks for the response. I already have the 5.3, and I’m doing the carb swap for a multitude of my own reasons. I didn’t get a computer or 4L60 with the engine so it seems like running a carb is the most simple solution. Plus i’m familiar with carburetors and I like the look so those are some of my reasons. I have most of the accessories from the 5.3, I just didn’t know if I needed to keep anything.

Possible PS hoses from the old setup, otherwise all accessories should be from the new 5.3.
Possibly keep your fan shroud, depending on how you do it.
x4 on the TV adjustment, you can cook the 700-R4 pretty easy. Don't know what you have for existing carb, but you might be able to drop it on, carb, bracket, throttle cable and all.
Adding a trans cooler is a good idea while you're at it, since you will be putting a decent bit more power down.
Again, depending, keep your gauge senders and buy the conversion adapters to keep your dash working.

Adapter plates that are 1" setback or slider type can keep your transmission/driveshaft in the same place, but will not allow you to use the modern AC compressor. If you go that route, keep your stock compressor and lines, you may be able to get a set of brackets that will put the old compressor in the right spot. I'd consider using Tejas mounts which move the engine forward ~3" but keep the AC compressor from the new truck, at the expense of needing a new driveshaft that is a good idea anyway. Fan clearance would need to be checked, and you might have to do electric fans.

Catbox said:

Or stick with traditional small block and swap a L-31 Vortec engine into it with the carb.
Just needs an electric fuel pump set up on it.

Click to expand...

Or swap in an l31 with the transmission, computer,injection the whole ball of wax. No vortec wet manifold problems and total modern drivability. And it all bolts right in on factory pieces.

ShielatheC10 said:

Hey guys, thanks for the response. I already have the 5.3, and I’m doing the carb swap for a multitude of my own reasons. I didn’t get a computer or 4L60 with the engine so it seems like running a carb is the most simple solution. Plus i’m familiar with carburetors and I like the look so those are some of my reasons. I have most of the accessories from the 5.3, I just didn’t know if I needed to keep anything.

Click to expand...

Honestly, a 5.3 with a carb swap and keeping a 700R4 is quite possibly the absolute worst combination of parts you could possibly have. You are keeping the least reliable and labor intensive parts of the drivetrain and losing the simplicity and drivability that comes from modern fuel injection.

You are still going to have to run a computer and a bunch of wiring to run the ignition, since you can't run an LS with a distributor. The simplest solution is an MSD 6014 system which will add $500 to the swap.
https://www.speedwaymotors.com/MSD-...qgL8PtLAh5JHrGa9Fcupo9htnNuVjs2xoCKVcQAvD_BwE

Then you need a special intake manifold, which is another ~$500... or get a combo like this that has both.
https://www.speedwaymotors.com/Edel...-LS1-Manifold-Timing-Control-Module,6763.html

Then you need a good carb.. because the factory quadrajet is either going to need a LOT of work to go from the setup for your anemic 305 to being able to support a 400hp 5.3 or you are going to need to get a new 750cfm or better carb. So figure another ~$500-700.


or... you go back to the junkyard and get yourself a 4l80 that doesn't smell burnt up for $200-400, get an 0411 ECU for about $40, and order an LS swap harness from any of the reputable manufacturers for about $500. Then you get a factory reliable modern drivetrain that is practically indestructible and only needs about 3 wires tied into your truck. You are 2wd, so you don't really have any major issues to deal with in a trans swap. A 200k mile 4l80 will last longer behind an LS than a freshly rebuilt stock 700R4 and will put up with WAY more abuse.

^Hit the nail on the head. I swapped my 305 to a 5.3 nearly 3 years ago now. As said, you'll be money ahead and the truck will be far more enjoyable sticking with factory LS injection and a 4L60 or 80e behind it.

But, to answer your question, there's nothing on the 305 you need to safe except the power steering hoses. They'll screw into the back of the LS power steering pump.

Hunter79764 said:

Possible PS hoses from the old setup, otherwise all accessories should be from the new 5.3.
Possibly keep your fan shroud, depending on how you do it.
x4 on the TV adjustment, you can cook the 700-R4 pretty easy. Don't know what you have for existing carb, but you might be able to drop it on, carb, bracket, throttle cable and all.
Adding a trans cooler is a good idea while you're at it, since you will be putting a decent bit more power down.
Again, depending, keep your gauge senders and buy the conversion adapters to keep your dash working.

Adapter plates that are 1" setback or slider type can keep your transmission/driveshaft in the same place, but will not allow you to use the modern AC compressor. If you go that route, keep your stock compressor and lines, you may be able to get a set of brackets that will put the old compressor in the right spot. I'd consider using Tejas mounts which move the engine forward ~3" but keep the AC compressor from the new truck, at the expense of needing a new driveshaft that is a good idea anyway. Fan clearance would need to be checked, and you might have to do electric fans.

Click to expand...

I believe you'll want to keep the hose fitting on the back of the power steering pump. If I remember correctly it bolts right into the LS power steering pump. This way you can use stock hoses with the new pump.

Thanks guys, I’ve reconsidered my plan and I think I’m dropping the carb swap idea all together.