This is a "How To" Post to swap the following engine in a G-Body:
From: Buick V6 - 3.8L (231) and 4.1L (252)
To: Small Block Chevy V8 (305, 350, 400, and others)
Parts and "How To" are listed in each section. I consider this a continous working and living post. This is by no means a final revision and other topics related to engine swaps will be added. While topics as rear end ratios and transmission are somewhat related, specific details of those topics are beyond the scope of this post and deserve their own unique topic.
Feel free to reply or send a private message in regards to the specific engine swap mentioned. There is more that needs added and if you have specific knowledge, feel free to share.
The Front Coil Springs need replaced with ones used in any V8 G-Body. This assumes you won't be taking out any weight (such as A/C- Heat removal, installation of fiberglass/aluminum body panels, etc) Ones from a Monte Carlo SS are a little stiffer than other V8 G-Bodies.
While you're at it:
If you still have the original suspension bushings, ball joints, tie rods, etc, now is a great time to replace all this stuff. Since you already need to change the front springs AND with the engine out, it is much easier to do this work. Also makes it easier to change out the motor mounts.
You will need the proper G-Body Specific Chevy V6/V8 Mounts. When properly installed for a V8, one of the motor mount holes will hang off the frame. Only 3 of the 4 holes on the motor mount are used.
Passenger side engine cradle, viewed from front, with and without the mount installed. Motor mount holes are marked. The top holes on the mount are spaced 2-5/16" centers and the bottom hole are 1-3/4" centers (only one bottom hole is used).
While you're at it:
If you bought motor mounts form a junkyard and have the old rubber bushings, drill open the old mounts and replace with new Energy Suspension (or your favorite equivalent) polyurethane inserts. Chances are the 20+ year old rubber is well worn. Instructions are included with the new bushings
Transmission and Cross-Member:
Most V6 cars got a THM200C (3 speed). These make a great door stop or practice for learning to rebuild a tranny (like I did). It most likely won't withstand any power from a V8. Besides, it has the wrong bolt pattern. You will need a specific SBC bolt pattern OR a dual bolt pattern transmission
. A THM350 (3 spd) with Chevy Bolt Pattern
will work with the THM200C cross-member.
If using the THM200-4R (4-Speed overdrive), you will need the specific cross-member. Any G-Body built before 1984 will need a mounting point for the TH200-4R cross-member added to the frame by welding in a piece of steel. It will not bolt in otherwise.
Along with rear differential, the transmission you chose depends on budget and goals and therefore further discussion goes beyond the scope of an engine swap.
ALL G-bodies have a wire harness that mounts to a bulkhead on the driver's side, right under the wiper motor. This does NOT include the ECM wire harness on 81 and later gas powered G-bodies. The harness has 2 pieces. The left half (viewed from the front of the car) is for the engine. The right half (which can be pried out, carefully) is for lighting and horns. The picture below shows the ENGINE harness with the lighting/horn harness removed. The black plastic wire loom is removed for clarity.
PURPLE - Starter Solenoid (has a ring terminal at the end)
PINK - Distributor (most likely a slip on terminal)
RED (2) - Starter at the battery terminal. Have larger ring terminals with fuse link. Has a splice for the HVAC system.
GREEN - Temperature sending unit
BROWN - Alternator sending unit
The following three work together in one circuit and depends on weather you have guages or idiot lights
LT BLUE - Choke heater
LT BROWN - Oil Pressure Light
BROWN/WHITE Oil Pressure Light
You will need to swap the fuel line so that it routes to the passenger side. Given the car's age, now would be the time to run new fuel line from the tank to the engine. If keeping the emissions controls, you will need at least 2 lines, one for the fuel and the other for the charcoal canister. If using a fuel pump with a return OR if you decide on fuel injection, a third line will be needed for a return.
You will also need the radiator, fan shroud, fan, hoses for a V8 G-body. The radiator for a V6 will not be sufficient.
Also the proper water pump is needed for the Chevy V8. Be sure to use the proper water pump for the belt drive system you decide to use (serpentine or v-belts). The 2 work in opposite directions.
REV A - 09/11/2007 - First Release
REV A1 - 09/12/2007 - Text font and color changes
REV B - 9/14/2007 - Combined Transmission and Cross-member. Added notes about pre-84 frame for TH2004R. Added Fuel Line and Cooling sections.
Giving Credit where due:
85 Cutlass Brougham - info on pre-84 frame for transmission cross-member and fuel lines.