How To Swap Buick V6 3.8 to SBC 350

dougfather

dougfather

Master Mechanic
Jul 11, 2006
288
16
Altoona PA
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)


Disclaimer:
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.

Suspension:
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.

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 transmission (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.

Electrical:
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.


LEGEND:

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


Fuel Line:
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.

Cooling:
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.

Revs
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.
 
dougfather

dougfather

Master Mechanic
Jul 11, 2006
288
16
Altoona PA
FAQ
All questions have been deleted and added here.
************************************************************
Q: Were can i find i good set of motor mounts? I have a chevy 350. Also,
where would is a good place to find the block mounts (steels not the clamshells) be? The junkyards around me do not have any older cars in them.

A: Check our sponsors, local auto parts stores, or a junkyard. Whichever mounts you need, make sure to order it for a Chevy powered G-Body (83-87 Pontiac or 78-87 Chevy, with a 305 gas V8 ). As for the inserts, Energy Suspension makes the polyurethane inserts. Any Chevy powered G-body will have what you need.

************************************************************
Q: this thread is great! just wondering what differences there are with the 350 sbo mounts? thanks!

A: Way different, not even close.

************************************************************
Q: So if i have a/c on a 3.8 engine will it all bolt up or do i need to convert everything to the sbc a/c system?

A: None of the 3.8 V6 a/c parts will bolt up, you'll need all the appropriate SBC bracketry. (answer by Blake442)
A: just the bracket dont need a diffrent compressor or lines (answer by Johnny MV1).
A: Doug's Comment - you may need different AC lines since the compressor is in a different location.


************************************************************
Q: Found this article most informative. It answered a lot of questions I had. however exhaust was not mentioned. Do I look for headers specific to the body style, 78 Lemans Safari in my case, or will any G body system of the correct year work??

A: Any G-body SBC header will work, though some brands fit better than others. I got mine from DynoMax and am very pleased with the fit and quality. As far as the rest of the exhaust, a standard G-body kit won't fit the wagon, as there are differences with the tailpipes necessary to clear the fuel tank. (answer by Blake 442)
************************************************************
 
CALI-WAGON_09

CALI-WAGON_09

Apprentice
Feb 2, 2009
66
0
Los Angeles,CA
transmission mount & cross member question

i have a 79 malibu wagon i am at the last stages of a engine swap from a buick 3.8/t200 trans to a chevy small block 350/t350 trans i want to know can i use the same cross member and mount or what do i have to do because my original mount is offset to the side of the trans andmy cross member is not lining up its off about a quarter of an inch any help is appreciated
 
jrm81bu

jrm81bu

Comic Book Super Hero
Jul 9, 2008
3,010
48
Antwerp, OH
Assuming you put the new small block mounts in the correct holes, you should be able to use the stock crossmember and mount.
 
CALI-WAGON_09

CALI-WAGON_09

Apprentice
Feb 2, 2009
66
0
Los Angeles,CA
I PLACED THE MOTOR MOUNTS IN THE SAME LOCATIONS THAT YOU DID IN YOUR PIC ITS ALMOST LINED UP SO I THINK IM GOING TO TRY AND SHIFT THE TRANS OVER A LITTLE BIT WITH THE ENGINE CONNECTED TO THE CHERRY PICKER(RELIEVE SOME ENGINE WEIGHT) I HOPE IT WORKS THANKS FOR THE ADVISE!!!! ALSO DO YOU HAVE ANY PICTURES OF THE WIRING CONNECTIONS ON THE ENGINE
 
E

eighty3gresr

Not-quite-so-new-guy
Jun 11, 2009
6
0
the transmission isn't offset just the cross-member. You should get a new transmission mount because it has a bracket that offsets the mount to the side.
 
chromemoly4130

chromemoly4130

Not-quite-so-new-guy
Aug 4, 2009
37
6
┌∩┐(○_○)┌∩┐
Here is a picture of the Moroso 62630 solid frame pad for 1974-81 Camaro/Firebird mounted on a 86 Monte Carlo ss


as you have stated
dougfather said:
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.(only one bottom hole is used).
and if this is true,comparing the pictures

I would say that they will work on the Regal as well....... now for the solid motor mount,you will need to get the Moroso 42515 thats for these frame pads. sorry for the pic. size but I thought I would pass this info along.
4130 :twisted:
 
dougfather

dougfather

Master Mechanic
Jul 11, 2006
288
16
Altoona PA
just deleted a few posts and combined them in the FAQ above.
 
pjpj1979

pjpj1979

Apprentice
Sep 16, 2009
72
0
Houston, Tx
Quick question...If I'm going from a 2004r to 700r how much shorter on my drive shaft to I need go? Just an estimate.
thanks!
 
81CRUISERbrougham

81CRUISERbrougham

Not-quite-so-new-guy
Jun 10, 2010
42
0
Duluth,MN
i was thinking doing a sbc with th350 over the winter while im not driving my wagon. it had a 260 th200m now a 3.8 th350.. when installing the mounts will new holes need to be drilled for the mounts and from what i gathered if i use th350 chevy it will work on the oldsth350 crossmember? how much of the olds wiring will work on the sbc. just FYI ive never put in a chevy motor in anything. i had a 78-79 ford pick up and bronco addiction before my newfound Gwagon lots of 400m and 429's.
 
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