What should I know about a GM 5.3 LM7

Found a deal on a 5.3L LM7 engine from a 2001 Suburban with 130K miles for $250. It’s complete minus the harness and starter. Now my LS knowledge is limited. I don’t know anything about if it comes with decent heads,rods, or what else can interchange. I wasn’t even shopping for an LS but didn’t want to pass it up. Guess my goal is to install it in my 85 C10 with the rebuilt 700R4 that’s already in the truck. Already read the trans should work but I need a crank spacer and maybe a different flex plate. What else should I know and look for on this year LS?

Score!

Check the flexplate as some of them already have a proper spacer, but the converter bolt holes will not match. Depending on your converter size, it may be possible to modify these, but there are swap flexplate kits out there for about $100 or so.

The Suburban radiator hoses will almost connect right up to the '85 radiator, at least in V8 trucks.

There are engine swap adapters out there to let you put SBC motor mounts on an LS1. I cut a set out of 4" wide, 1/4" thick steel strip myself.

Crank and rods are powdered steel and pretty beefy, I've seen them last a while at 750hp and they can go higher. Block is also cast and pretty stout (Can be bored to LS1 size to make it a 5.7L with ease), got a deep-skirt bottom end with 6-bolt main caps. Heads are cathedral-port just like an LS1 head but with a smaller chamber and valves. The camshaft is absolutely miniscule, if you're looking for power it's the best palce to start. Evne a stock LS1 or LS6 cam will perk it up a lot with a valvespring upgrade. Intake is also a chokepoint, long runners designed for torque and a small throttle body. Swap it for the LS1 or LS6 intake (Avoid the LS2 intake at all costs, it's a poor design) or the aftermarket equivalent and go up to the 90mm throttle body while you are at it.

There is a company called ICT. Web site is ICTbillet.com. They sell tons of LS swap pieces. You are going to want a set of their billet aluminum plates that mount to the LS engine block. There are 4 different mounting places for the small block chevy mounts to bolt up to and away you go. Plates are like $35 delivered, and are a work of art.

In reply to NickD:

I thought the truck intakes werent that bad? Lose 10hp but gain 10ftlbs over the ls1 style.

Personally if pop out a spark plug and look at the top of the piston, dish piston is 5.3, flat top is 4.8 because externally you cant tell the difference. 4.8 isnt bad but it might be a good barganing tool

Thanks, What about a harness and computer? What years and vehicles are the easiest to work with? Friend of mine has HP Tuners so he can remove VATs plus any other changes.

I almost want to say that some of the 4th-gen Camaro ECUs are to be avoided, because they have a hard rev limit that can't be tuned out. I seem to recall that when we were playing with them on a dyno, you could go in with HP Tuners and set whatever you wanted the rev limit at and reflash, but even if the rev limit red 10000rpm, it would still hit one at 7K. We were using HP Tuners on truck ECUs on an 8800rpm, 38psi, 1400hp 339ci destroker (Stock 4.8L crank and rods), so anyone that says an LS needs standalone has no clue

Most of the 99-later ECMs are 24x reluctor, but there are a LOT of varying factors that require careful selection. Some ECMs are drive-by-wire only (don't have the controller for IAC). Connectors changed a few times, so you have to match the harness to the ECM.

$250 is a steal and you should get it, but to be perfectly honest, don't fool around. Find out what it was from and get the harness and ECM from the same vehicle. Otherwise you'll go blind trying to find compatibility. Since its a truck engine, chances are its drive-by-wire, so don't forget to get the pedal and accelerator control logic box too. There are at least four different types of those as well as several different TBs.

Buy some books on LS tuning and swapping. They'll guide you through compatibility, but prepare for a bit of brain cramping. Best/Easiest way is to just get the whole package from the same truck as the engine.

Or get a $300 dual plane manifold and the $300 MSD timing control box and put the carb already in your truck on it.

Cam and a carb and you are well north of 400 HP Add headers and I think you are creeping up close to 450. It has been a while since I looked at those.

Considering you still have to run electronic ignition due to the lack of distributor, IMO, running a carb on an LS motor is utterly stupid.

rslifkin wrote: Considering you still have to run electronic ignition due to the lack of distributor, IMO, running a carb on an LS motor is utterly stupid.

Amen.

Bobzilla wrote:

rslifkin wrote: Considering you still have to run electronic ignition due to the lack of distributor, IMO, running a carb on an LS motor is utterly stupid.

Amen.

It is however a viable option to avoid the cost and headache of the wiring. I did it before on a 6.0L LQ9 and had great results. Of course, it does skip the wonderful tuning ability of the ECM, but I was able to do it cheaper than buying the wiring harness and computer to do the EFI.

In reply to curtis73:

A used harness and truck ecu is over $600?

chiodos wrote: In reply to curtis73: A used harness and truck ecu is over $600?

Easily close to that. Add $200 for pedal and accelerator box. Just the dash wiring harness for these trucks goes for $250 easy.

Quick search on car-part shows prices for engine harness (just the wiring) at around $350 and ECUs in the $200-250 range. Throttle boxes go for $75-150. Pedals go for $50-75

Check the camshaft. Certain model LS engines (those with the fancy lifters) will wipe out the lobes on the camshaft.

f6sk wrote: Check the camshaft. Certain model LS engines (those with the fancy lifters) will wipe out the lobes on the camshaft.

LM7 is non-AFM, so he is safe in that regard, although some early 5.3Ls did have soft cams.

oldopelguy wrote: Or get a $300 dual plane manifold and the $300 MSD timing control box and put the carb already in your truck on it.

no, bad opel guy.

the injection is so easy especially since you have a friend that can tune it for $100 in credits.

buy a used 01ish truck computer and harness, there are a dozen sites with instructions on how to make your harness stand alone, and switch a couple parameters in the computer. bowtie overdrives has a 700r4 tv cable kit for the newer engines.

If you are comparing the 5.3 to an LS1, it does seem a shame to carb it. But if you are comparing it to an old school sbc, it's an aluminum head 300+hp near drop in replacement that costs less than sbc heads would cost.

With a carb manifold and the MSD box it's a weekend swap for the sbc into almost anything. Sure it would be better efi and computer controlled, but even with the carb it's better than the stock sbc that was in the truck.

I'm actually kinda surprised that you don't see more 5.3s running TBI. While the injection on the truck motor is great, it's too tall for a lot of applications and you have to give the GM TBI credit for getting 85% of the benefits of fuel injection on 20% the complexity of the LSx efi system.

A junk harness for the engine side connectors and an MS2. Done!

It will need a few extras short harness, and Wideband O2 so you can tune it yourself.

NickD wrote: . . . We were using HP Tuners on truck ECUs on an 8800rpm, 38psi, 1400hp 339ci destroker (Stock 4.8L crank and rods), so anyone that says an LS needs standalone has no clue

my hero!!

How much better is a lq9?

Dude, you can ask {Dustin} Hoffman in case of any troubles with {canoes}

As for an {speedboats}, I can recommend [Peter Fonda] and [On Golden Pond]