How much power can I make from a 5.3l LS with these limitations?

Joined
Aug 4, 2022
Messages
31
Hi all. I'm looking to replace the dead 350 in my old 87 Silverado. Needs new piston rings. I want to use a 5.3L LS engine from a newer truck, but I figured why not add a little spice to it first. However, there are some limitations I want to abide by. They are:

1. Can't harm the factory fuel mileage very much.

2. Can't harm engine longevity. I want the engine to last 200k miles or whatever the 5.3L is typically known for.

3. Can't harm the factory road manners. I want the factory idle, so no rough cam. No obnoxious racket or bad smells.

Even given those restrictions, I believe there is still room for improvement on the 5.3L LS engine. We just have to get into the details. For example, I don't want a loud exhaust, but that can be mitigated by using flowmaster hushpower mufflers. And I can't use a big cam, but there is room for a slightly larger cam that won't affect the idle any.

But what else? What all can I do to improve power, while not spraying much more fuel? Should I do a medium overbore on the cylinders? Polish the cylinder heads, but no porting?

What are all the specifics of such a build? Thank you
 
Last edited:
I’d do a mild cam, something like the Texas Speed Low Lift truck cam, which they claim added 45.1hp and 21.5lb ft of torque to an otherwise stock 5.3. Their stage 2 truck cams add more but start getting into a lopey idle. If you want more, then I’d go with ported and polished cylinder heads, catted long tube headers, and an upgraded intake manifold.
 
I don't want to be rude but you're talking in circles. Engines are nothing but air pumps and the more air you pump the more power you get. If you don't want to improve air flow with porting and polishing the heads or changing the lift and duration of the camshaft AND putting a high flow header system and extractor on the engine and you don't want to increase fuel flow which would definitely be dictated by the greater air flow then what specifically do you want to change? There is no free lunch.
 
I'm no LS engine expert, but there are tons of things you can do and a large aftermarket to support you. First question is what's your budget? Personally if it were me, I'd do the swap and leave it stock to get it running without issues. Wait a year or so and then go from there once you figure out what you like and don't like about the LS motor.
 
Hi all. I'm looking to replace the dead 350 in my old 87 Silverado. Needs new piston rings. I want to use a 5.3L LS engine from a newer truck, but I figured why not add a little spice to it first. However, there are some limitations I want to abide by. They are:

1. Can't harm the factory fuel mileage very much.

2. Can't harm engine longevity. I want the engine to last 200k miles or whatever the 5.3L is typically known for.

3. Can't harm the factory road manners. I want the factory idle, so no rough cam. No obnoxious racket or bad smells.

Even given those restrictions, I believe there is still room for improvement on the 5.3L LS engine. We just have to get into the details. For example, I don't want a loud exhaust, but that can be mitigated by using flowmaster hushpower mufflers. And I can't use a big cam, but there is room for a slightly larger cam that won't affect the idle any.

But what else? What all can I do to improve power, while not spraying much more fuel? Should I do a medium overbore on the cylinders? Polish the cylinder heads, but no porting?

What are all the specifics of such a build? Thank you
The factory has done all this for you.the engine Is designed already to get as much power as you can for the fuel mileage. Anything you do from here will will have a negative you don't want. Sure you can make more power, but that requires more fuel and or more noise.
 
Pour some seafoam in the tank and let her rip.

Anything you do to get more umph from an engine will result in lower gas mileage. Even of the cruzing mileaage is the same the lead foot at the stop lights will nullify that effect. otherwise why have the extra torque and HP of you won't be goosing it every now and then.
 
supercharger...

or...

increase compression and run premium fuel - should increase mileage as well as power output

port/polish heads

long tubes with cats - will increase sound slightly, or at least change the quality but be pretty stock it if you keep the rest of the exhaust stock

new intake manifold - will require tuning

remove torque management (tune)

slightly overbore for more displacement - refresh the engine with a bore, grind, hone, etc. slightly larger pistons (great chance in increase compression ratio)

The last 6 things should have little effect on MPG, net some power, and meet your goals. Really with any small block chevy, the sky is the limit, only reigned in by your budget. If I were installing a used truck 5.3L in my ride while trying to stay as mild as possible, I would do all 6...and maybe a cam ;-)
 
Hi all. I'm looking to replace the dead 350 in my old 87 Silverado. Needs new piston rings. I want to use a 5.3L LS engine from a newer truck, but I figured why not add a little spice to it first. However, there are some limitations I want to abide by. They are:

1. Can't harm the factory fuel mileage very much.

2. Can't harm engine longevity. I want the engine to last 200k miles or whatever the 5.3L is typically known for.

3. Can't harm the factory road manners. I want the factory idle, so no rough cam. No obnoxious racket or bad smells.

Even given those restrictions, I believe there is still room for improvement on the 5.3L LS engine. We just have to get into the details. For example, I don't want a loud exhaust, but that can be mitigated by using flowmaster hushpower mufflers. And I can't use a big cam, but there is room for a slightly larger cam that won't affect the idle any.

But what else? What all can I do to improve power, while not spraying much more fuel? Should I do a medium overbore on the cylinders? Polish the cylinder heads, but no porting?

What are all the specifics of such a build? Thank you
You can bore the cylinders on an LM7 5.3 to LS1/LS6 spec, use an LS6 cam and intake.

Or, you can get a LQ9 6.0 and build a 408 stroker
 
I would imagine there will be too much work and money into engine computer, harness and electronics fiddling.
I suggest to reman the 350 at your local, trusted machine shop. Maybe Put a 208 retrofit roller in there. Maybe quality long tube headers with a Y and single exhaust. Enjoy the big torque hit where you want it.
 
Here's what I'd buy

EFI

Carbed
 
Last edited:
I have never done an LS swap but I seriously doubt it is a drop in and plug and play operation. I can see fuel system, ECM, engine mount, cooling system, transmission fitment, and a host of other mods that may be needed just to make it work. I would do a lot of research first before I worried about how to make it produce more power.
 
What 5.3 are you starting with? Depends really on what motor you're starting with to gauge some good recommendations.

Are you going for a 99-early 2000s LM7, mid 2000s, LM7 or L59 (Gen III w/Gen IV rods), Gen IV 5.3?

Gen IV 5.3 you will need to DOD delete.

Are you going EFI or putting a carb on it?
 
Are you planning on running 5.3 ECM, wiring, controls, fuel delivery, etc.? A carburetor & aftermarket intake would likely hurt MPG, and require a standalone controller for the transmission-I think I would build a 350 instead, run a mild marine cam, open up the exhaust & maybe clean up the heads, intake, & exhaust. There's a LOT of things different on an LS, and a 350 TBI can get decent highway MPGs, I had a 200K+ mile C1500 Suburban that got 17 highway consistently.
 
The LS engine will respond to the same improvements as your current 350. Free flowing exhaust, an improved camshaft, and tuning go a long way on both engines. The biggest downsides I see are the cost and complexity of the engine swap, and the higher torque curve of the LS.
 
I threw out an absurd suggestion for the exhaust manifolds. Me? I would rebuild the 350 and get some Vortex heads or something good.
 
I'm all for LS swapping anything, but unless you want a project and enjoy working out electrical bugs and doing some fabrication, your best bet would be a new 350, or better yet a 383, and hot rod it a little. A better cam, some better inexpensive iron heads, rollerized everything, better intake, etc.
 
Back
Top