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Note: This is the second article in a series of articles on a V8 MR2 engine swap
In my introduction, I ended up at the point where I decided to switch from the Audi V8 engine, to another engine for my V8 MR2 byte. The reason I originally chose Audi was that it was a very good chance that it would fit without cutting the car's chassis. Unfortunately, the problem with the shaft distance could not be known until I removed the oil cooler / filter from the engine side. It became so clear that the engine block itself was in the way. The block could not be cut and re-welded, as the oil pump and the oil pump drive were also in the way. I had to buy the engine to find these things. This is the kind of swaps like this that no one has ever done before. Does anyone know who wants a 1997 Audi ABZ 4.2L V8 with 70K miles?
I realized at the time that it might be easier to find a transverse V8 engine, even if it is too long to fit, and continue and cut the chassis and weld it up again. Welding some plates is easier and much cheaper than trying to solve the problems created by using the Audi V8, which can be detachable, but only with very very expensive custom machined parts. Even then, I still feel that the shoulder spacing problem will still cause problems, as it would be required that a 3rd CV lead be added to the right shoulder and some large permanent angles would be required, which is never a good idea with CV leads. The areas of the MR2 chassis that needed cutting were thin sheet. They are structural, but they are not heavy structural, so the welding plate back in the cut areas should not be too much of a problem, plus I had a plan to reinforce the cut areas. More on this later in this article.
I need a backtrack a bit, because I haven't discussed the transaxle yet, which is another important component that needs to fit in addition to the engine. During the first survey of this project, I decided to check out what Fiero guys did. The Fiero, manufactured by GM and Pontiac from 1984 to 1988, was a cheaper car in the mid-engine, which also used a front wheel drive that was easily incorporated into the back of the car, just like all 3 generations of MR2. The engine was a little ahead of the drive shaft, so when the front wheel train was moved to the back of the car, it became the center engine. Note that the definition of an engine motor is one where the motor is forward or on top of the rear axle, just like MR2. Note that a rear engine car has the engine Behind the rear axle, like a Porsche 911 or the original VW Beetle. The Fiero guys have made V8 swaps in Fiero many years ago, since the early 1990s. The car is wider than MR2 mk2 (ground 2), so it is easier to fit a V8. I contacted one of the oldest companies that made V8 Fiero conversions and found out they were using a new GM 6-speed front wheel drive shaft. This transaxle was the strongest transaxle available to the average person. It had the highest torque.
Transmissions and gearboxes are marked with torque from the factory. Transmissions and transaxles are not rated by horsepower, because horsepower does not kill transmissions. Too much torque is what can kill a transmission. Keep this in mind, when turning a bolt with a wrench, apply torque to the bolt. Apply too much torque to an already tight bolt, and you can remove the head. Transmissions are equal to that too much torque can crush the gears directly by a gear.
The given torque is also based on the weight of the intended vehicle. Torque rating means how much torque from a motor can be the gearbox or gearbox handle, and still lasts long, usually 100,000 miles. The heavier the car, the lower the torque capacity. Use the same transmission in a lighter car, and the torque value will be higher. A heavier car generates more stress on the transmission components when the car maximizes when the engine generates maximum torque. This is always the first gear, since it is the maximum torque distribution given by the transmission to the engine while driving. The 1997 Audi V8 that I was trying to use was rated at 295 ft-lbs of torque at its maximum. Northstar has a similar rating.
The new transaxle that the Fiero guys used was a new GM unit rated for nearly 300 ft-lbs of torque in a 3500 lb car. The biggest surprise is that this transaxle could be purchased NEW on eBay for only $ 475 SHIPPED !!! It was in 2007. Today you can get it for about $ 375. There is a story behind this, but basically GM has exceeded the 2006 version of this transfer, as they decided to change it in 2007.
This transaxle can take the torque of a healthy V8 engine. If the car was lighter than 3500 lbs (Fieros is about 2700 lbs and mk2 MR2s is 2700 to 2950 lbs), the torque capacity of this gearbox would be higher than the factory-applied application. The 6 speed was also shorter than 1.75 inch MR2 transaxle bearings, allowing more space for a longer engine and adapter plate (if needed).
The icing on the cake and the part I didn't know until 6 months after buying the Audi V8 was that Cadillac Northstar 4.6L V8 bolted to this transaxle, except for a bolt that could easily accommodate a manufactured small bracket or weld additional aluminum to side of the transmission block housing flange on the block. No adapter plate needed!
By switching to Northstar, I was able to solve problems with the adapter plate, the starting problem and, above all, the shaft distance. This is because Northstar was originally used in transverse applications from 1992 or 1993 until 2002. It is still used across, but there is a longitudinal version and GM moved the start site. By checking my notes from November 2007, I found that I had written that Northstar was 23.75 inches long at the critical dimension - this is the length of the engine from the washer screw head to the back of the bell cover flange on the block. At that time, I can inadvertently include the flex plate in the critical dimension, but it really is not part of the critical dimension. It turns out that the 23.75 inch measurement was incorrect!
Back in November 2007 I did not use a straightener on Northstar, which I looked at in the wreck yard, just a tape measure. In addition, at the time, I assumed that an adapter plate would be needed for Northstar to mate with the GM 6 speed (which was wrong I later discovered and discussed above). If you have ever measured a motor for length, you would know that getting an accurate measurement can be tricky because the engine has a lot of width and parts to measure. In December 2008 (a year later) I went back to the wreck and measured Northstar again. This time, I was much more careful. I found that it was actually 23.0 inches long, but remember, no adapter plate was needed (which would add about ½ inch to the entire unit). This gives another spin on the problem.
OK, so if this is a bit confusing, or difficult to form, I will simplify this. The bearing MR2 turbo engine is Toyota / Yamaha 3S-GTE, and the bearing shaft is Toyota E153. 3S-GTE is 20 inches at the critical dimension. The E153 is 16 inches long. The total length of this train is 36 inches. However, there is a snap in the left side of the car that matches the E153 case perfectly, which gives a little extra approval. It will not match the GM 6 speed. Bearing MR2 drive train has approximately ums inch release at the crank disc, and the same at the transaxle end.
Now Northstar is 23 inches, and the 6 speed is 14.25 inches, a total of 37.25 inches or 1.25 inches more than the MR2 stock drive. This would not fit, since the MR2 chassis section at the transmission end does not match the 6 speed. Cutting of the chassis is required, but not so much cutting.
The previous attempts to make a V8 MR2 byte in Gen2 attempted to use a Toyota 1UZ-FE V8 which is 26 inches long and E153 which is 16 inches, a total of 42 inches. This is 4 inches more than stock! 4 inches may not sound as much, but it is a lot when you mount a driving train. To make matters worse, an adapter plate is needed to feed 1UZ to the E153 gear. Then add another ½ inch.
This approach required complete removal of the MR2 subframes, which are only 2 or 3 inches wide in those areas on either side of the car. This would weaken the car quite a bit. Also, the right impactor would probably hit the back of the 1UZ V8, so it would have to be cut a lot. I think the guys who did the previous trials thought this out after they cut their MR2s, and they gave up.
In December 2008 I went ahead and bought a low mileage Cadillac Northstar. Fortunately, 1994-1999 was the same, and I found out that they were the easiest to add a standalone engine management solution to. The latter 2000 and up versions are much more difficult. The 1993 version is also the same, except that the intake pipe was cast from metal (aluminum or magnesium), instead of plastic as the 1994-1999 versions.
I was able to mate Northstar to my 6-speed that I had purchased in December 2007, a year earlier. Finally! I made some progress! Then I did a test pass in my 1991 MR2, and made the cuts to the chassis, so now the Northstar and the 6 speed fit in the car. I have just recently installed an alternator for Northstar and found a way to fit it very tightly against the block, giving the engine additional space around it in the car. I am currently building the engine and gears. When clear, I can send my shoulders to shorten and splines.
Getting back to the cut of the chassis as I promised at the beginning of this article: The chassis areas I had to cut are part of a stamped sheet "pseudo" subframe. It is not really a subframe as its stamped sheet that is spot welded in the body, but they are in the form of traditional frame rails (ie rectangular cross section). I twisted these "frame rails" on either side of the car to clear the Northstar washer and the case of the GM 6 speed. The metal is thin metal plate. I will weld these areas with new sheets to cover the holes, and I will probably add additional sheet doubles over these cut surfaces, which overlap the weld joints. This will ensure that the repairs become stronger than the original. This is the standard method in the aerospace industry when facing a similar issue.
In addition to the doubles, I will create a new rear wheel suspension cross section from the beginning, because the original cross member interferes with the GM 6 speed bag and the new shoulder pads. This new cross member will have extended sections that the original did not have, which will extend the cut portions of the subframes, further enhancing the strength. I didn't have to cut the right shock tower, but it's not entirely safe yet. I had to remove some metal attached to the outside of the shock tower. It didn't add much to the structure, so I felt it was OK to do this.
The end result of these modifications will probably increase the weight of the car, and I will weigh the new parts to get an idea of how much weight it will be, but I appreciate that it will be less than 20 kg more than stock. V8 should easily handle an extra 20 kg car!
Please keep up-to-date for the next in this series of articles.
Update: It turns out that the custom cross member is not needed! I found a way to use layer MR2 cross member (with minor minority changes). This is good, and it is a great time / money saver. The MR2 cross member is extremely important because the rear suspension and rear locking bars are attached to it, so you try to duplicate it exactly, and with sufficient strength is extremely difficult and time consuming. Now that I found a way to reuse the original cross member, I have saved tremendous time and money.