The Novak Guide to the

Chevrolet Small Block V6 Engine

The Chevrolet Small Block V6

The Chevrolet V6 fills an important niche as a Jeep conversion engine, being swapped into many Jeeps where engine bay space is at more of a premium.

By 1978, Chevrolet had 23 years of building its famous Small Block V8 under its belt. The energy and fuel crunch of the era dictated a lighter, leaner motor than the V8 and GM took on the engineering and production of this important new engine.


This new V6 would essentially be a V8 with cylinders #6 & #3 removed, similar to what Buick had successfully done with its V6 in the 1960's. This Chevy 90-degree V6 had the same rear block face & bolt pattern, as well as the same style of engine mounting bosses and accessory packages as its bigger brother. Because its crank was a shortened version of the V8 crank, this motor was an "odd-fire" design, firing its cylinders at uneven intervals. The motor was internally balanced and featured the standard two valves per cylinder.

The Release and Evolution

The V6 was released, featuring a 200 cubic inches displacement, sharing key internal dimensions with the original Chevy 262 V8. In 1980, displacement was increased to 229 CID using parts and dimensions based on the 305 V8. This V6 engine was largely found in Chevrolet cars (not trucks) during this era.

When installed into a Jeep and driven, the Chevy V6 is easily mistaken for a V8.

On one of our own installs into a CJ8 Scrambler, it would tear its 35" tires loose on clean asphalt, despite the particular Jeep's heavier build.

The V6's reasonably compact form and lighter weight make it perfect for many CJ's, Wranglers and even the heavier Jeep truck applications. However, it should be noted that the V6 in its injected forms it typically too tall for low-hood Jeeps, such as the pre-CJ3B Universals unless a small amount of body lift and a low intake is used. As a general rule, if the Jeep would allow for an F-head to fit, the 4.3L will fit nicely.

The Chevy V6 is not a good conversion candidate for the XJ / MJ platform.

In 1985, the V6 underwent its next upgrade to 262 CID; equivalent to 4.3L. To convert it to an even-fire design, it was necessary to balance the motor externally and the flywheel was no longer interchangeable with the previous V6's and most SBC V8's. However, because of its same 4.000" bore and 3.480" stroke as the ubiquitous 350 V8, this V6 was able to use the same pistons, same main and cam bearings, same valve components, etc. as the V8.

In 1986 the 4.3 received the one-piece rear main seal improvement that was implemented in the V8's. The V6 was the first to get the "Vortec" nomenclature that GM would eventually pin on all of its advanced truck engines to this day.

The Turbocharged LB4 / ZR9 V6 GM made a fun foray into the turbo world with the 4.3L V6 in 1991. Featuring multi-port injection, an intercooled turbo, hypereutectic pistons, special nodular iron main caps and other improvements, this motor was capable of 280 hp & 360 ft. lb. of torque. The engine was first offered in the GMC Syclone and then Typhoon models. However, this unique version was produced for only two years.

In 1987, after three years of suffering with the 60-degree 2.8L V6 in its otherwise successful mid-size truck platform, Chevrolet presented the 90-degree V6 motor as the throttle-body injected 4.3L. Though it had been a good engine prior to this time, this release was an immediate hit. The 4.3L then began to find its way into the full-size truck and van platforms, as well as the up-and-coming Astro / Safari vans. This great engine underwent constant improvements mechanically as well as electronically, as GM's engine management systems further refined in the early 1990's.

By 1992 the 4.3 was fitted with a balance shaft to reduce vibration. These engines are denoted by their VIN number having a "B" at the eighth digit, in lieu of a "Z". Of note here, "B" engines are rated at 200 HP where the "Z" engines were rated at 165 HP.

During the 1993 model year, multi-port fuel injection began to be introduced on the 4.3L V6 (VIN code "W"), with full implementation occurring by the 1994 model year. In 1996, the Chevy V6 was put forth as the new Vortec V6, a fully OBD-II compliant motor. It saw further acceptance and respect for its power and economy among buyers and performance enthusiasts. Minor refinements accumulated each year.

By the end of its production life, the LU3 4.3L V6 featured an impressive 195 HP and 260 ft. lbs. of torque and a broadly usable RPM range. Roller rockers, powder metal rods, composite intake manifold and a robust engine management computer turned the 4.3 into a rowdy good engine, one that is especially well suited for swaps into many Jeeps.

merriam_v6_install_readyA 4.3 TBI about to be installed into an early CJ by customer T. Merriam. Behind it is the SM420 transmission and the Dana 18 transfer case.

It should be noted that the Vortec V6 did not receive the massive redesign the Small Block did in 1999 (based on the 1997 LS1). It continued to feature cast iron block and heads and the same key features of the classic V6 and V8 motors that typically fall under the Generation I heading.

In 2001, GM - for the first time since 1955 - changed the crank depth and its pilot bore diameter of the V6. Pilot bushings differ for these motors and transmissions built from this time forward had a deeper bellhousing and different torque converter.

GM was tenaciousness in sticking with the V6. In this case (much like the famous 700R4 automatic transmission) they opted to debug and perfect the wheel they had instead of inventing a new one.

Flywheels and Bellhousings

The 4.3L Chevy V6 is among the strongest of production V6’s ever produced, especially in its later versions. It was first produced in 1978 and that design stemmed from the 1955 Chevy Small Block V8. It holds a unique place at GM and the automotive industry in that it has been able to break through into this modern era, complying so well with emissions and efficiency standards among engines that were fundamentally more advanced from their inception.

The 4.3 V6 is typically found with a 168 tooth flywheel (11" clutch disc) behind it instead of the 153 tooth (10.5" clutch disc). This is done for clutch engagement, but more so for the weight and resulting torque provided. Therefore, the V6 requires the "big clutch" bellhousing which affords greater clearance. As the V6 has the same crank flange as the V8's, caution should be taken when swapping flywheels around from the V8 to the V6. We're told (this is hearsay, folks) that the 153 tooth flywheel from the 305 V8 will bolt up and be properly balanced. Further interchange information is found here.

Transmission Compatibility

The Chevy V6 is compatible with essentially every transmission, manual or automatic, as the Small Block V8. Some popular choices in Jeeps include:

Manuals, non-native upgrades

The SM-420 transmission The SM-465 transmission The T-18 transmission The NP-435 transmission
SM420 (*) SM465 (*) Ford T18 (**) Ford NP435 (**)
* Preferred
** Possible with modifications

Manuals, Jeep native

The Jeep T90 Transmission The Jeep T150 Transmission The Jeep T176 Transmission The Jeep AX15 Transmission Jeep NV3550 Transmission
T90 T150 T176 AX15 NV3550
* Preferred
** Possible with modifications

Automatics, non-native upgrades

The TH-350 Transmission The TH-400 Transmission The 700R-4 Transmission The 4L60-E Transmission
TH350 TH400 TH700R4 / Early 4L60-E 4L60-E (later)
Electronic transmissions are typically 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.


Hydroboost 4.3's vs. Vacuum boost 4.3's

Many GM vans featuring the 4.3L have hydraulic boost brake systems. The S-10 Blazers and other models, do not. Like the Jeep, they operate on vacuum boost. The 4.3L engine used in both the vans and trucks have an upper composite intake manifold with a molded tower for a vacuum line. On the vans this is plugged with a removable cap and o-ring. To pull brake boost vacuum from the van engine, you simply order the vacuum port for the Blazer and screw it into the existing tower, replacing the cap.

- Thanks to customer J. Wilson.

The mechanical history of the Chevrolet V6 motor is richer than this synopsis, and we do recommend more research and reading for the enthusiast. However, as there are some important mechanical details that are pertinent to Chevy Small Block swaps in Jeeps, we have created some valuable interchange information.


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