Swapping a V8 Into a Toyota MR2 – Build Your Own Supercar
Please note: This is the first in a series of articles on this subject.
For many years, I have dreamed of owning a mid-engine exotic supercar. Unfortunately, they remained out of my reach financially. I decided that the only way I was going to get one was to build it myself. I have always been fascinated by mid-engine sports cars due to their superior handling, braking, and traction over a front engine sports car –even those front engine cars with a rear transaxle, that have a supposedly optimum 50/50 weight distribution. I like to call them the “dumbbell cars” because their weight distribution is just like a dumbbell–heavy at the ends, and light in the middle. This is decidedly suboptimal for acceleration, handling and braking.
Compare this to a mid-engine cars, where if you were to make a dumbell resemble the mid-engine car, the weights would be slid to the center. Now, if you want to make the dumbell, or the mid-engine car rotate about its vertical axis (called “yaw” in aircraft terminology), it will do so much easier and more quickly. This is because the tire traction does not have to overcome the inertia that a front engine/rear transaxle car would have over each end of the car. The result is that the car will be able to change directions faster, and with less tire wear. The peak G-forces will be much higher in a mid-engine car as well, meaning its faster around the corners. Rear wheel traction during acceleration is superior, since more weight is on the rear wheels. Strangely, there are a lot of “side-effect” advantages to mid-engine cars that the automotive press fail to mention.
1) Exhaust piping is usually very short in a mid-engine car (compared to a front engine car), so the engine has to overcome less “pumping losses” or the resistance to the exhaust travelling out the tail pipe. This means more power. The exhaust system will also be lighter since there is less of it. Dumbell cars have no advantage here.
2) The rear brakes do a LOT more of the stopping vs. a front engine car. When you hit the brakes, weight transfers to the front wheels. This means that the rear wheels become unloaded. On front engine cars, the front brakes do about 80% of the stopping. This is why disk brakes in the rear took a long time to catch on. They simply are not needed in the rear. A mid engine car has a LOT more of the weight (usually around 55 to 60%) on the rear wheels. When you hit the brakes, weight transfers to the front, so under braking, you might get 50%-60% on the front. Dumbell cars get some of the help that mid-engine car gets, but not nearly as much, because the engine is still in the front and is still far heavier than the trans at the back.
3) the mid-engine car has no driveshaft (unless its an AWD car, like the R8, or the Veyron), so there is a weight savings here.
Unfortunately, most mid engine cars are very expensive. Ferrari, Lamborghini, McLaren, Zonda, Koenigsegg, Bugatti, and so on. Some of these cars are above a million dollars! Mid-engine cars do tend to be more difficult to work on as well. Changing sparks plugs on the exotics is a major operation. The McLaren F1 requires engine removal to change the plugs!
In the realm of affordable mid-engine sports cars, there are Pontiac Fieros and there are Toyota MR2s. In each case, the cars came with 4 cylinder motors. The Fieros also got V6s, but those V6’s were very underpowered, with a whopping 140hp. In 1990, Toyota redesigned the MR2 and upgraded the power as well. Base models got 130hp and the high-end Turbo was 200hp, which at the time, was quite a bit for a car that weighed 2700 lbs.
The new body was very good looking, much like the Ferrari 348 at the time. The build quality was also superior as it was, after all, a Toyota. I decided to purchase a 1993 Toyota MR2 turbo in 2005 with the intention of doing a Toyota V6 swap, which up to that point, had been done by many people. At about that same time, I found that there were some attempts to install a V8 engine into the earlier MR2 (Generation 1, 1984-1989 body style, or mark 1). There were also attempts to install a Toyota/Lexus V8 engine into a MR2 mark 2. The attempts at doing the V8 into the MR2 mark 2 were not completed, and the project owners gave up. The reasons were not clear, but it appeared to be due to the fact that the Toyota V8 was simply too long to fit in the car transversely, even after cutting the car severely in an attempt to make it fit.
As a Mechanical Engineer who happens to be a mid-engine sports car nut, I became intrigued with the possibility of putting a V8 into my MR2 mark 2. With a strong V8 engine, the MR2 would be transformed into a supercar, with supercar performance. The Fiero guys have enjoyed swapping V8s into their cars for many years. Fieros have an advantage over MR2s in that their engine compartment is wider allowing for a larger and longer engine, like a V8. Fieros and MR2s all have transversely mounted engines. Another advantage the Fiero guys have had is that the stock Getrag transaxle bolts up to a Cadillac 4.9 L OHV V8 from the late 1980’s/early 1990’s. The later Cadillac Northstar also bolts up without an expensive custom machined adaptor plate.
In late 2007, another V8 in a MR2 mark 1 (1st generation) was completed by a guy in Europe. The car was crazy fast, and would do cookies at the drop of a hat. What fun! So, I took another hard look at the prior attempts to install a V8 into the MR2 mark 2. What I realized was that they were attempting to “keep it in the family” and use a Toyota or Lexus V8. There wasn’t really any valid engineering reason to use this power plant. It did not bolt up to any of the MR2 transaxles, and it was too long. The Toyota V8 used,(engine code 1UZ-FE) is about 26 inches long from the crank pulley to the rear face of the engine, or bell housing interface. This is the critical dimension. Compare this to the stock MR2 engines like the 2.0L 3S-GTE turbo motor which has a critical dimension of 20 inches. This dimension is critical because it fits between the unibody pseudo-frame rails of the MR2 chassis.
I decided to take a different approach. I started searching the internet for a V8 engine that would fit the MR2 chassis, preferably with no cutting, or possibly with only a small amount of cutting of the MR2 unibody. My requirements were that it be a V8 with at least 300 horsepower, that it is available, that it would cost somewhere under $5,000, and that it would be short enough and narrow enough to fit the MR2. I succeeded in finding one. Audi has an interesting habit of making very short V8’s. They do this because they want to use their Quattro drive train, but at the same time, not compromise handling too much. Audi seems to prefer longitudinal engine and transmission arrangements over transverse. The Quattro drive train involves a driven front axle, which they had to locate behind the engine. If the engine is too long, it puts too much weight in front of that axle, so they compensate by making a shorter engine. This has the added benefit of allowing Audi to install this engine in smaller cars that were originally intended to have a 4 cylinder power plant. For my purposes, I found that the 1991 through early 2000 Audi V8 engines are approximately 20.6 inches long at the critical dimension, and about 29 inches wide, not including the headers, or other easily removed items.
I purchased a 1997 Audi 4.2L V8 (engine code ABZ) and a transaxle, and started working on my project. Unfortunately, after much trial and error, I finally decided that the Audi V8 was not suitable for this engine swap. The problem laid in the fact that the engine was always designed to be longitudinal. In my case, with a transverse layout, the right size axle had to run along side of the engine, and Audi did not design the engine with that in mind, so there are large portions of the block in the way of that axle. The starter, oil filter/cooler and engine mount are also in the way on that side, however, I did solve those problems. The nail in the coffin of the Audi was the adaptor plate. I determined that the adaptor plate required some of the mounting bolts to be located inside of the bell housing of the 6 speed transaxle I was using, so it was impossible to tighten them. At that point, I decided to change my approach and use a different engine.
Please stay tuned for the next in this series of articles.
Source by Chris Bulen