LONGITUDINAL V8 FIERO ENGINE SWAP
Using GM TH325/TH425 automatic transaxle
Mounting a big V8 longitudinally in the back of a Fiero seems to spark a lot of interest. Possibly because it's the same orientation as so many high end exotic cars. I'll admit that's partly why I chose to do it in my Countach replica. I'll try to describe the swap in as much detail as possible. Please confirm any info on this site before trying to use it, as it is possible that I have made mistakes or left something out. The type of engine can vary, most common are the Chevy small block V8, Buick-Olds-Pontiac V8 (BOP) and the Buick V6. I chose a 5.7 liter small block Chevy V8 because they are fairly cheap, powerful and performance parts are readily available. There are three different transmissions that can be used. The TH425 (three speed) was was used in the Buick Riviera, Olds Toronado, and Cadillac Eldorado from '66-'78, the TH325 (three speed) used from '79-'81, and he TH325-4L (four speed) used from '82-'84. I used a TH325-4L four speed auto from an '82 Eldorado. The engine can be mounted with the pulleys facing the front of the car, or they can face the rear of the car. If the engine pulleys face the rear, the installation will be referred to as 'reverse rotation'. I chose to face the pulleys forward because I didn't know any other way at the time. This seems to be the more popular way to do it.
Engine/Trans Adapter.
Both the TH425 and TH325/-4L have the B-O-P bolt pattern. If you are using a B-O-P engine, that's fine, but for anything else, you'll need an adapter. You can buy a BOP-Chevy adapter for about $55 (TCI part# 230000), or make one from 5/16" steel plate as I did. pic#1 A standard GM automatic flexplate is used. The oil filter will need to be relocated due to clearance problems with the trans. I used a standard oil filter relocation kit (Summit part# SUM-G4985) and added two 45deg fittings for extra clearance. The oil pan will need to be modified to allow clearance for the right axle to pass under. It's basically the same mod needed for a S-10 4x4 V8 conversion, for which oil pans are available. I used the stock oil pan and moved the bottom up to where the internal baffle was. The axle that goes under the engine needs to be supported. It has a bearing at the end with a support bracket. I modified the bracket so it would bolt to the unused side mount holes on the engine block.
Cradle Mods
I started by removing the rear cross member from the side rails. I set the engine/trans combination on the floor and positioned it so that the axles were directly in line with the lower ball joints on the cradle. I positioned the engine side to side so that the right and left axle shafts would be the same length. I then made sure the cradle was sitting flat on the floor and the engine was level, and began making a new extended rear cross member. I used rectangular tubing to construct a new rear cross member that extends out around the rear of the trans. To support the trans I fabricated two mounts using steel plate and universal round bushings. pic#1 pic#2 On the front I started by making a U shaped bracket that bolts to the front of the engine block with four bolts. I welded a piece of angle iron to the rear of the front cross member to meet the engine bracket, again using urethane bushings. The tie rod mounts that were removed and discarded as part of the rear cross member needed to be relocated. There is no way to make them fit where they were, so here's the trick. The spindles, calipers, tie rods, etc. will be swapped left to right. This puts the tie rods in front of the axle centerline. A new cross member needs to be fabricated to mount the inner joints to. They should be spaced the same distance apart as they were originally, and at the same height to prevent additional bump steer. An alternative would be to use an '88 cradle and suspension.
Axles
For axles I used two left side Fiero automatic axles. I had two flanges machined to fit the trans hubs with a hole in the center for the Fiero joint. The Fiero joints were pressed into the flanges and welded. I've since discovered that The stock applications for the trans use a joint very similar to the one I had fabricated. I probably could have saved some time and money by mixing stock GM parts to end up the same thing.pic#1 pic#2
Body/Chassis Mods
This setup as described will fit within the stock Fiero body panels with the exception of the rear hood. Depending on the type of induction system and engine you choose, it may even fit under the hood. My 86 TPI required hood modification, even with the Countach body. There is absolutely no chance of retaining the trunk. Whatever space isn't occupied by the trans, will be filled with exhaust pipes. Due to the large increase in rear weight, the springs need to be upgraded. I chose to use a coil-over conversion from Held Motorsports (formerly Ryane Motorsports) with 350lb springs. The coil-overs allow ride height adjustment, and just about any spring rate you want. pic#1 pic#2 pic#3
Exhaust
My exhaust system is entirely custom made. I made the headers using a Heddman weld-up kit (part# 65600). I also had them coated with aluminum and wrapped them with Thermo-Tec header wrap. The Muffler is a Dynomax OE fit for a Buick Grand National. It is a cross flow design with dual inlets and outlets. Everything is connected with 2.25" mandrel-bent aluminized pipe, and tipped with Monza dual chrome outlets.
The Reverse Rotation Option
After I had already started my conversion, I found out that it can be done differently to better distribute the weight. By rotating the entire engine/trans 180 deg so that the pulleys are at the back of the car, you can get a lot more of the weight in front of the rear axle. The differential housing then needs to be rotated 180 deg to an upside-down position to make the axles turn the opposite direction. This also places the pinion shaft below the axle centerline, effectively lowering the engine. I have never done a swap this way, so I can only speculate what changes must be made. First off, the tie rods can probably stay where they are. Also, the trunk may be able to be retained, or at least more of it. I would expect that the oil pan modification would be more extensive. If I were to do another longitudinal swap, I would definitely do a reverse rotation due to the weight distribution advantages.
Here are some pictures:
Coolant filler before I switched to the TPI intake pic#1
The chassis, even more hacked in preparation for the Lambo body pic#1 and with TPI pic#2 pic#3
A Buick turbo V6 with 325-4L in a Countach replica pic#1 engine conversion done by Fiero Concepts
Pictures of Hugh Lemma's Fiero with a 350 and TH 425 pic#1 pic#2
Take the same basic idea and apply it to a VW Beetle, and you have Crazy Joe's 500ci Caddywagon!
Wayne Wright's '79 Fiat X19 with a reversed TH-325 and Chevy V6! Read his story!
