3800 V6

General Information
Engine Swap Pictures
David Cole's 3800/5-speed swap
Tom Corey's 3800/AOD-auto swap
Fieroman's 3800 Registry and Info Page [off-site link]

General Information

Just a side note here, all 3.8 FWD engines arn't the same. The basics maybe, but a lot of the ancillary stuff varies with each vehicle that it comes from, so when Dave or I talk of a line being in a certain place, it may be completely different on another 3.8. Lets just put in this caveat, "Your engine may vary".

From: Tin Man

"What year/model 3.8 will be the easiest/best to use?"
  1. don't buy a 3.8 - any year. Only 3800's
  2. I don't know the years but the intake should appear to be made of gray painted aluminum or black plastic. It should have an appearance that shows the intake runners. I will look something like the fingers of two hands interlocked. If the intake looks like a "log" running parallel with the cam shaft and has 6 short straight runners down to the heads, it is an older engine and you should keep looking until you find a newer one. I THINK that 90/91 was the first year for the best choices. If the engine is a supercharged, almost any year will be ok.
  3. make sure that the engine has a distributorless ignition system. Some engines have a distributor which will be up against the Fiero fire wall once installed making timing adjustments an interesting exercise.

My engine is a 94. I know 93 is not appreciably different. 95+ are a series II engines and I have no experience with these but I would NOT turn one down due to the increased HP.

From: David Cole

David Cole's 3800/5-speed swap

This is a summary of the 3800 conversion done by David with the help and brain support of:

Bret, local BMW 2002 fan, rig master and welder
Clinton (88 GT 3800 SC), Huston, Texas
Chris, of West Side Machine, Marina Del Ray, California
ARP Racing Fasteners
CV Products, High Point, NC (ARP distributor)
Royal Pontiac, Raleigh NC
Loop Road Auto Parts, Garner, NC
Advance Auto, Garner, NC
NC Steel, Garner, NC
Bobs Muffler, Garner, NC
Car Parts Depot, Inc, North Manchester, IN
Packard Electric (now Delphi something)
Car: Red on grey 85 2M4
Trans/subframe/drive axles: 87 GT w/ 5spd Getrag
Engine: 94 Bonneville 3800 orginally with T60E computer controlled transmission normally aspirated, Sequential Fuel Injection, SFI (read: computer fires each injector individually)
Clutch: fresh NAPA clutch for stock V6 Fiero
Other: Koni shocks, Yokohama UV+4 on after market 15 in wheels for everyday, Yokohama A008 RSII on GT wheels for track driving, shortened shift lever, GT steering wheel and instrument package w/ volt and oil pressure pod, passenger side glove box, tacky but functional Holley side scoop.

Engine and trans bolt directly w/o mod. Custom flywheel has to be made to bolt to *8* bolt crank pattern of 3800. I had the Fiero V6 f/w modified to accomplish this. I believe the 96 F-body (Camaro/Firebird), which uses the 3800 Series II, has a flywheel which may work stock or at least require less modication. This was the hardest part of the mod. I had to find (get this) 5/16-18 bolts for the crank. Thats right - SAE bolts on an otherwise Metric car. They had to be very strong with a thin head for clutch disk clearance. I settled on some 190 ksi cam bolts from ARP. Seems to be fine so far. Starter ring gear and teeth are the same.

I used the shift and select cables from the Getrag. The 4 cylinder slave clutch cylinder was used as the 4 cylinder SS braided hydraulic line would not clear the transmission casing with a stock V6 slave. The 4 cylinder slave was spaced back almost to the end of the mount studs to maintain the same preload on the slave internal spring thereby keeping the same slight load on the throughout bearing.

I used the two stock transaxle mount locations with new mounts. I created 2 new engine mount locations, both use stock Fiero engine mounts. One sits just forward of the engine block between the block and the square cross brace on the sub frame. The other is mounted to a plate bolted between the rear toe link nuts. The mount sits up next to the passenger toe link nut. An adapter bracket runs from the rear side engine block, over the passenger side drive shaft (with clearance for worst case deflection) and to the mount location between the link nuts.

One important note: I do not have a dog bone. I am relying on the arm than runs over the drive shaft for torque control. I have had a few people express concern over this. I understand, but I can point to 5 k miles of success including approximately 200 miles of hard shifting and driving at the Rockingham NC NASCAR Speedway road course (Weekend driver schools are great!!!!!) plus the day at Waterford Hills during FOCOA 95.

Time will tell.

The new mounts were designed to set the engine about 1/2 lower on the passenger side to assist in clearance of the deck lid torsion bars. The alternator needs to be lowered another 1/2 inch also. This is accomplished via a 1 in shackle at the rear of two mount bolts. The other bolt forms a pivot. This allows the center of the altenator to be about 1/2 in lower.

Clearance was ground on the stock engine mount flange welded to the subframe. About 1/2 in deep curve was removed for stock 3800 oil filter location clearance.

The 3 ignition coils and their control base were relocated from a bracket near the forward corner of the engine to the stock battery location about 8 inches away. This displaced the battery to the front of the car. It now s its on the custom shaped board placed in/on the inverted spare tire. 1/0 welding cable links the battery terminals back to the engine. It is grounded near the spare and on the engine block. A new battery was purchased w/ H2 vent nipples to which I attached vinyl tubing to carry the hydrogen out of the front trunk. I did not want any surprizes one day while turning on the vent fan.

The A/C compressor and power steering pump were removed. The flat idler pulley was replaced by the grooved idler from a 3800 SC engine. This allows the belt to be run with the grooves on the pulley (instead of the flat back). Removal of the compressor and pump, coupled with the lower altenator, allows the use of a standard 51 in 6 groove belt (designation: 510K6). The spring tensioner is maintained.

Fuel is delivered via the standard 85 4 cylinder metal lines. A GT fuel pumps is required as the SFI needs 40+ psi like the Fiero V6 MPFI. The 4 cyl TBI used about 15 psi. Therefore, all rubber fuel lines must be upgraded to Fuel Injection rated hose (100 psi working pressure). I removed the crimped rubber hose at the end of each fuel line leaving the metal fuel line terminating near the strut mount. To this I double hose clamped Fuel Injection rated fuel line (3/8 in on inlet side, 5/16 in on re turn side). The inlet side runs to the stock 3800 fuel filter and is then double clamped. More hose is attached after the fuel filter connecting it to a section of hard plastic fuel line from the Bonneville. This allows the use of the Bonneville quick disconnect feature between the fuel line and the fuel rail. Return line is similar in construction.

Stock 85 fuel vapor recovery method was used. A Fiero V6 air cleaner was installed the output of which is the same OD as the 3800 intake. A piece of flexible intake hose connects them. The PCV valve is an intregal part of the 3800 intake manifold and requires no hookup or modification.

Stock coolant return hose on passenger side was used. Driver side was modified to include a reworked 4 cylinder thermostat housing and cap. This allowed for a high point in the system for coolant addition. The radiator is upgraded to a four core unit having the same hose attachment points. This was custom made but is not thicker overall than stock. Stock fan is used. All coolant carring hoses were replaced with new including the heater hoses. Longer heater hoses at the engine are required to attach to the under car pipes.

The exhaust system uses the stock 3800 header which wraps around the heads. It exits in the single stock position across from the rear center cylinder. A short pipe is attached here and curves down feeding an upside down Y. Each end of the Y is redirected to feed a baby cat (also called pre-cat, they are about 4 in OD and 7 in long.). These are mounted between the sub frame and the trunk. Each cats exhaust is turned and heads straight out the back of the car. You can see about 1/2 of each cats body from the back of the car. The heat shield on the trunk is removed and Mylar faced insulation has been added under the trunk carpet to compensate.

Ninety plus percent of the stock computer related wires are maintained without modification or extension.. To connect the engine and computer (PCM), the Bonneville uses a two piece multipin connector that clamps thru a hole in the fire wall. This is maintained. The hole through the Fiero fire wall is enlarged to accept the larger connector. The PCM is mounted behind the driver seat. All dash instruments and lights are connected except for the Service engine soon which I left off. I am sure this conversion leaves the computer a bit confused and sets some codes, but from what I have read none of the codes I expect are set affect the fuel curve, etc so I chose to ignore them. The 94 PCM does not have the capability to blink codes via a grounding of a terminal like the Fiero units do.

Tachometer feeds off the 3 coil control base, Speedometer feeds directly off the transaxle sender in parallel to the PCM input. 3800 oil pressure sender is used to feed the oil gage. The transaxle gear select switch inputs (a 4 bit binary) are jumpered to be in drive continuously.

Pass Key theft deterant must be by-passed. I had the ignition key and could therefore measure the resistance of the pellet. A 10 turn pot was matched to this and soldered to the inputs of the stock Pass Key module which will feed a 50 hz ok signal to the PCM. A more eligant solution of a 50 hz wave generator is suggested but mine works.

I get 31 mpg highway, 23 around town. HC was 4 out of 250 ppm max (was 220 with the 2.5l) and CO reads 0. This car is mean and green.

I will expand on some of these sections if requested. Let me know which ones you want.


Why not use the Stock Fiero one? - the V6 flywheel has 6 crank bolt holes, 3800's need 8. You can't use the stock Fiero flywheel without extensive mod.

option 1: modify a F-body Flywheel: The F-body flywheel (p.n.#24503285) is 1.110 inch thick. This needs to turned down to .840 inch to match the V6 Getrag flywheel thickness. Once done, this will work for a normally aspirated Series II 3800 (1995+). The supercharged started using the Series II set up in 1996. Previous 3800 SC engines had a slightly different imbalance in the flywheel compared to the normally aspirated engines (SC specific rods/pistions required this). First generation 3800's (1987?-1994) require a diffent amount of imbalance than the Series II. Options? - rebalance the flywheel to match the flexplate removed from the engine or see the print mentioned in option 3. Cost: new GM flywheel approximately $250 plus machining. Aftermarket sources will eventually appear for this flywheel.

Option 2: Modify a stock V6 flywheel. Due to lack of information on the 3800 imbalance this is the 1st method I chose. I would not do it again. You need to fill the 6 crank mount holes then have the solid plate drilled to match the 8 crank holes on the 3800. (They are NOT evenly spaced - 1 is off by 3 degrees to act as a key. This time through, the machinest used the flexplate to determine the hole locations. What a hack job.) Then neutrally balance the rigged-wheel; then balance it to match the flexplate. This probably works ok. During recent dissassembly of my engine, I determined why this method did not work well (my engine had noticeable shake). The guy balancing the system was off by 60 degrees on the placement of the imbalance!! Try moving a weight on your tire by 60 degrees and see if it still rides fine - NOT. The reason it was wrong? The fella must have bolted the flywheel and flex plate faces together before match balancing the system. He created a mirror image of the flexplate - not a copy. Cost $300 (I paid TOO much). It can be done right.

Option 3: make a new flywheel (installation currently in progress) Cost wise, this is not that much more. $350-400. Prints can be found on the web page below. I will be using a bolted on imbalance weight to create the balance required. This setup will be installed in less than 1 month and I'll post results then. This print can be used as is for properly modifying the crank bolt pattern on a filled and drilled stock V6 flywheel. The print will be updated with backspacing details after I know more.

Option 4: Use part of the above options, leave the flywheel neutrally balanced and have the engine balanced so that it does not require external balancing. More $, better at high RPM. As with all high performance: How much $? answer: How fast do you want to go?

Option 5: By the ACE kit. They use Option 4, but their own design. Seems to work fine in the installations I have seen. I do not like their engine mount method but it seems to work for the few people I have talked to. I don't know how hard they drive their cars. I don't see how they properly support the front of the engine. I think they only use the forward tranny mount.

From: David Cole

Tom Corey's 3800/AOD-auto swap

First of all I assume you don't have an 88 Fiero. If you do, the solution is different. I recommend you use the motor mounts and axles from a Pontiac Transport Van (or Olds Silhouette Van) They have the exact same track (width - axle end to axle end as the Fiero. Use the inside joints from the engine/transaxle you purchased and the outside joints from an 88 Fiero 5 speed. This will match up the splines. If you use these mounts and axles your installation will put the engine nearly centered in the engine compartment and you will not have to trim the deck lid.

The cradle on the 88 is smaller and I don't think the mounts I told you about will work properly. On my 88 GT I used the 95 Bonneville side mount, a stock fiero front mount and a MOPAR small truck mount at the rear of the transaxle with a dogbone under the right side. (The torque from the 3800 kept bending the rear GM transaxle mount I started with. And the axles on the 88 are from different sources than I told you earlier.

You can use Supertrapps & mini cats for the exhaust system. However, I really don't like the hornet sound they have and wanted a near stock, but throaty sound. So I went to a $1500 system that includes a Flowmaster muffler for an 82-92 Camaro (single inlet dual outlet) and the stock tips. You can always cut away part of the trunk and prett much fabricate any exhaust system you might like. However, I tried to maintain a completely stock exterior look (blows those Mustangs minds!) It's still a bit noisy.

I have found the stock radiator to be just fine, but have added a 160 degree thermostat and removed the underside of the deck lid grills for air circulation.

One other thing-- it works real well if you relocate the fuel pump and A/C relays form the engine compartment to under the center console with the pass key and ECM. Fieroman probably has more info on the passkey and speedometer circuitry required. If you can't find it on the net, I can mail it to you.

As for the Supercharger ECM wiring, it is only slightly different, because of the one wire I can remember in the harness for the supercharger control. Maybe Stuart or one of the other guys can help you more on that issue. CAUTION be sure to SOLDER all the wiring harness connections. Fieroman (on the list) is more knowledgeable than I about the wiring. For the Supercharged version you will need to install the stock Bonneville fuel pump. It requires simple modification to install. I recommend you move the battery to the front for better weight distribution. And finally I do not recommend a high stall torque converter. While it is great for stoplight racing, it is a bitch for driving curving roads because you have very little engine braking.

From: Tom Corey

For more 3800 information, visit Fieroman's 3800 Registry and Information Page. [off-site link]

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