The GM Generation III & IV Engine
It takes serious guts to replace the most famous engine of all time. Since 1955 GM had been building is Chevrolet Small Block V8 with accolades, respect and awards in the automotive press and racing and with commercial success with customers in marine, industrial and mainstream automotive markets. The Small Block was the most purchased, modified and swapped engine of all time.
The Gen III has now become the predominant swap engine into nearly all Jeep vehicles.
Research into what would become the Gen. III began in 1991. It took engineers two years to conclude that they could extend the life of the classic Small Block with several surrounding technologies (that were eventually rolled into LT and other Small Blocks), but they realized that they would soon hit a wall without an actual fundamental redesign of the flagship GM V8's.
Just like the Small Block used a then-innovative green sand casting method in its block founding process, the Gen. III uses an innovative lost-foam block founding process. The result is a very high resolution, strong and affordably manufactured block.
The introduction of the Gen. III motor in 1997 was actually understated, and it may have been this was so as to not lose the loyal adherents of the original Small Block. It was not until these motors got into the hands of enthusiasts that they began to realize the importance of what GM had done:
The crank featured larger main bearing journals. The connecting rods are made with an innovative new process with powdered metal, forged and then shot-peened. These rods are stronger and more balanced that previous methods would allow.
The intake on the LS1 and subsequent engines is made of a composite, reinforced nylon material. This allows for perfectly equal length and volume intake runners, smoother runner walls and better manufacturing economics over previous cast steel and aluminum styles. Our experience is that the low-profile intakes can swap for the high-profile intakes in the event that hood clearance is an issue (such as with the Jeep XJ Cherokee or other "low-hood" conversions) but that special computer tuning work is required.
In 2001, GM - for the first time since 1955 - changed the crank depth and its pilot bore diameter of the Gen. III. Pilot bushings differ for these motors and transmissions built from this time forward had a deeper bellhousing and different torque converter.
The 5.7L LS1 - the seminal engine for the Gen. III - and it's rear face, which is identical to the classic SBC of fifty years ago. This is just one of many things that makes GM so respected in the conversion world.
Though many technologies carried over from the LT engines, the Gen. III+ motors do not use reverse flow cooling. GM engineers decided that potential hot spots against the cylinder walls was a greater concern than detonation caused by high compression and hot heads.
The Gen. IV engines were introduced in 2004 are very similar to the Gen. III motors, but include a few new technologies; key ones include Active Fuel Management (also called Displacement On Demand) and Variable Valve Timing.
We've assembled a brief list of engines. Some are less preferable for Jeep conversions for obvious cost and horsepower insanity reasons. 4.8L, 5.3L and some 6.0L as sourced from truck/SUV platforms are the most popular and sensible conversions for most Jeeps.
|LS1||5.7L||97-||305-345||The groundbreaking Gen. III engine, released in C5 Corvette|
|LS2||6.0L||05-||400||400||2005- Vette & GTO|
|LS3||6.2L||08||430||424||436 HP with exhaust bypass option|
|LS4||5.3L||04-||303||323||One version available for transverse FWD Pontiac GXP|
|LS7||7.0L||06-07||505||470||Hand-built. LS7R version voted Engine of the Year by jury of race engineers|
|LM7||5.3L||99-07||285-295||325-335||G3. Possibly the most popular Jeep swap engine, currently|
|LM4||5.3L||04||295||335||G3. Aluminum block version|
|L33||5.3L||05-07||310||335||G3. HO aluminum block version|
|L59||5.3L||02-07||285-295||325-335||Flex-Fuel engine. Can be installed in a Jeep but more complex|
|LH6||5.3L||05-07||315-320||340||G4. Aluminum block|
|LY5||5.3L||07||315-320||340||G4. Iron block|
|LC9||5.3L||07||310||335||Flex-Fuel, aluminum block. Envoy models have front differential provisioned oil pan|
|LQ4||6.0L||02-07||300-325||360-370||Base level 6.0L with iron block|
|LQ9||6.0L||02-07||345||380||HO or VortecMAX version|
|LY6||6.0L||07||312-353||373-383||Aluminum block, variable valve timing,|
|L92||6.2L||07||380-403||415||Aluminum block, VVT,|
|LR4||4.8L||03-||270-285||285-290||G3. VVT. AFM|
|LY2||4.8L||07-||295||305||G4. No VVT or AFM|
An LS1 in a Jeep TJ Wrangler. Vortec and other Gen. III+ engine installations similar.
5.3L engines are usually only factory available with the flexplate that mates to the 4L60E transmission (a very popular transmission choice of our customers) and these motors were not available with a flywheel. However, 4.8L and 6.0L flywheels do interchange onto the 5.3L as the cranks are of a unified design and all Gen. III motors are internally balanced.
Flywheels and flexplates from Gen. I and Gen. II engines will not and must not be married to any Gen. III+ crank.
The Gen. III+ engines all use a block-mounted starter, in lieu of a bellhousing-mounted starter as done by other auto companies.
As stated earlier, the standard shift Chevrolet bellhousing designs from the previous 50 years will marry to the engine block of these new engines.
The Gen. III / IV engines are compatible with essentially every transmission, manual or automatic, as the Small Block V8. Some popular choices in Jeeps include:
|SM420 (*)||SM465 (*)||Ford T18 (**)||Ford NP435 (**)|
** Possible with modifications
|TH350||TH400||TH700R4 / Early 4L60-E||4L60-E (later)|
All Gen. III / IV engines are best paired or pulled with the same year of engine and PCM. PCM controlled engines getting a non-electronic automatic transmission should have their PCM programmed as if paired with a manual transmission. The 4L60E automatic is typically the best choice of automatic for nearly all Jeeps.
One is tempted to believe that the gasoline engine has reached its nirvana with the Gen. III+ engines as engineered and built by GM. When considered with the power, cost, package size, fuel efficiency and longevity, these world-class engines can compete with and beat - with flying colors in most cases - essentially any automotive power plant available. The fact that one of these engines can be installed into a Jeep with such success makes the decades-rich tradition of engine swapping more exciting than it has ever been.
This article is only a synopsis and a wealth of information on these engines exists from a multitude of sources. However, to remain germane to our topic, we've kept it brief.
We welcome any contributions or clarifications to this article. Contact us here.