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325 Chevy Small Block Engine - Bolt On A Cam And Heads And Add 120+HP

The GM Gen III 5.3L truck engines are inexpensive and make great power, especially when we show you how to get another 120 hp.

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With all the hype about the Gen III LS1 and 6.0L engines, a little 5.3L engine has appeared in well over a million GM trucks since 1998 that's been overlooked in the rush to make horsepower. This engine displaces a mere 325 ci, but what it lacks in displacement, it more than makes up for in horsepower efficiency. Over the years, we've heard about several low-dollar 5.3L truck engines that made excellent power with only a few minor changes, so we thought we'd try our own version and see what happened. We were pleasantly surprised when this basically stock engine made well over 430 hp with just a cam change. But there's much more to this story, so let's get to it.

The Truck 5.3L
The basic 5.3L Gen III engine began its production life in 1999. In its base form, it comes as either an iron-block LM7 5.3L or an LM4 aluminum blockversion appearing in GM light duty pickups, Suburbans, Yukons, and vans, which means there are literally thousands of these used engines now in boneyards. The original LM7 5.3 is basically an iron-block LS1 engine with a smaller 3.78-inch bore (the 5.7 is 3.89-inch) rated at between 285 and 295 hp and 325 to 335 lb-ft of torque in stock GM trim. These engines also share the 5.7L's 3.622-inch stroke, and some enterprising car crafters have built an iron-block 5.7 merely by boring the block to the 5.7 bore dimension and using a 5.7L rotating assembly (the cranks are different due to piston weight). The stock 5.3L comes with a decent 9.5:1 compression ratio right out of the box and uses essentially the same cylinder head as its larger LS1 cousin, but with a smaller combustion chamber.

GM also built a smaller number of LM4 5.3L engines that are aluminum- block duplicates of the LM7. Thisversion got an inkling of recognition as the original engine for the '04 SSR truck. Otherwise, it is exactly the same as the iron-block 5.3L engine and you can expect to pay more if you find one. Then, just to make things interesting, GM upgraded these engines to a Gen IV configuration in 2005, although they still shared much of the same Gen III architecture. The most plentiful Gen IV iron-block 5.3L is the LH5. There's also the LY5 aluminum-block variation. This engine is rated at 320 hp stock with 340 lb-ft of torque.

Identifying these engines is easy. Look first for the tall plastic intake manifold and then find the 5.3 cast into the block on a pad near the back. But be careful. Many light-duty trucks came with smaller 4.8L (293ci) engines. If the engine is still in the vehicle, look for the emissions decal under the hood. But even that isn't a guarantee. The beauty of the 5.3 is that there are so many of these engines out there, buying one with minimal mileage in good shape for an affordable price shouldn't be difficult. We found ours at a junkyard and landed the engine for $550 without the plastic truck intake manifold and the accessory drive. We also got the starter motor, water pump, coil packs, and flexplate.

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50 comments
Tony Lainhart
Tony Lainhart

Im still coming around to center bolt valve covers and serpentine belts...CarCraft is the only mag besides an occasional HotRod Ive stayed with since a kid in the 80s...I need a complete tutorial on the LS series-If you haven't already, Im sure your the mag to do it!

Michael Rapley
Michael Rapley

1955-87 SB Chevy, the New flathead's of this decade & Forever.

Steve Cardot
Steve Cardot

small block chevy's are great engines don't get me wrong but the LS engines are my all time favorite.

Derek van Valen
Derek van Valen

stock ls2 long block, cam,springs,retainers,pushrods, carb and set of headers. 470 to the tire in 94 degree shop. thats about 540 at the crank. was rated 395 stock in the tb ss it came from. glad i didnt have to buy heads lol.

John Smith
John Smith

Pound for pound the LS has has more potential than the Gen 1 as far as a production engine goes based on the heads alone, but I haven't seen a decline in interest for the Gen 1. Mostly because of the price to build difference.

Cam Beaton
Cam Beaton

The small block has gone the way of the flathead. RIP SBC.

Scott Alan Carpenter
Scott Alan Carpenter

Give Mast Motorsports a call at 936-560-2218 or check out www.MastMotorsports.com. They designed their own VVT cams 18 months before anyone else, they have over a dozen intake manifolds and many cylinder head designs which they designed and cast in-house, they engineered their own EFI system, etc. Thanks to Horace Mast's genius and an amazing team, they are THE ones to watch in the LS arena.

Zane Lund
Zane Lund

Beth Tubbs had to take a double take!!

Walt Nothnagel
Walt Nothnagel

I got more out of my 327 by shaveing the heads and decking the block with a cam swap

John Baechtel
John Baechtel

Gen 1 all the way for me. I appreciate LS motors, but don't see any particular advantage beyond all the media hype or if you just have to have an aluminum engine. The current piston powered land speed record is held by an iron block Gen 1 small block thumping about 2300 HP. Nothing really bad about the LS except poor crankcase breathing and that's why Dart makes an LS block configured like a Gen1 engine on the bottom end. Its generally more expensive to build an LS from scratch so why bother if the standard small block will do the job. Cylinder heads are no longer an issue in most cases. so it all depends on what you're building for and what your budget will support.

Josh Lindauer
Josh Lindauer

LS all the way! 6 bolt mains and just an all around better engine! I use to be into the gen 1 style blocks, but after the LS conversion in my ride I'm sold on the these LS setups!

David Leeman
David Leeman

I say fire it up and let those horses run wild

Rafael Torres
Rafael Torres

Ahh thanks. Thought it was an error. Still funny ..I guess he gained what he was looking for..to make me laugh lol..

Brian Reineking
Brian Reineking

Call 847-956-1244! Automotive Engine Specialties is the king of the LS world!

Elijah Rose
Elijah Rose

dont really care at this point. as long as it can growl and it can get me where i need to go

Arnold AutoNtow
Arnold AutoNtow

I sold all my old school sbc stuff to make room for more LS parts lol

Karl Loper
Karl Loper

It's not rocket science is what I say. Modern heads and cam should make 120hp on just about any V8 over OEM heads/cam. Look what AFRs do for an SBF, or Edelbrock Performer RPM on an SBC.

Ricardo Neves
Ricardo Neves

simply with port and polished bored heads and with a more agressive cam angle lobes in the camshaft.

Andy Martin
Andy Martin

Rafael, that's common vernacular when one is joking. It's not an error.

Chris Pirkey
Chris Pirkey

Late model Ls with a carb conversion kit...the original intake is on the back table

Timothy Hickman
Timothy Hickman

LS is the future, but there aint a damn thing wrong with a sbc

Jay Meilleur
Jay Meilleur

Probably gain 100hp just putting a cam in a LS motor.

Connor Doyle
Connor Doyle

It looks like he's got an invisible ratchet about to tighten something.

Rafael Torres
Rafael Torres

Lol what say you ? .... or what do you say? Lol..

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