Replacing V8 with Toyota MR2 2nd Generation Part 2

Note: This is the second article in a series of articles on V8 MR2 engine swaps.

In my introduction, I stopped when I decided to change from an Audi V8 engine to another engine for V8 MR2 swap. The reason I chose Audi first is that it’s very likely that it will fit without cutting the chassis of the car. Unfortunately, I didn’t know the axle clearance problem until I removed the oil cooler / filter from the side of the engine. After that, it became clear that the engine block itself was in the way. The oil pump and oil pump drive pulley were also in the way, so the block could not be cut and rewelded. I had to buy an engine to find these things. This is the nature of such swaps, and no one has ever done it. Do you know anyone who wants a 70K mile 1997 Audi ABZ 4.2L V8?

At that point, I realized that it might be easier to find a transverse V8 engine, cut the chassis and reweld it, even if it’s too long to fit. Welding some sheet metal is easier and much cheaper than trying to solve the problems you encounter with the Audi V8. This may be resolved, but only if you have a lot of very expensive custom machined parts. Still, I feel that axle clearance issues still cause problems, as I need to add a third CV joint to the right axle and need some large permanent angles. This is by no means a good idea for CV joints. The area of ​​the MR2 chassis that needed to be cut was thin sheet metal. Although they are structural, they are not heavy structures, so welding the sheet metal back into the cut area should not be too much of a problem. In addition, I have planned to strengthen those cutting areas. We’ll talk more about this later in this article.

We haven’t talked about the transaxle, another major component that needs to fit beyond the engine, so we need to backtrack a bit. During the initial investigation of this project, I decided to check what the Fiero people were doing. Manufactured by GM and Pontiac between 1984 and 1988, the Fiero is an affordable mid-engined car, with front-wheel drive vehicles simply transposed to the rear of the car, similar to the MR2 of all three generations. I was using it. The engine was sitting just in front of the drive axle, so when I moved the front-wheel drive train to the rear of the car, it became a mid-engine. Note that the definition of a mid-engined car is that the engine is in front of or above the rear axle, similar to the MR2.Please note that rear engine vehicles are equipped with an engine behind Rear axles like the Porsche 911 and the original VW Beetle. The Fiero guys have been doing V8 swaps to Fiero for many years since the early 1990s. The car is wider than the MR2mk2 (Mark 2), so it’s easy to match with the V8. I contacted one of the oldest companies that did the V8 Fierro conversion and found out that they were using the new GM 6-speed front-wheel drive transaxle. This transaxle was the strongest transaxle available to the average person. It had the highest torque rating.

Transmissions and transaxles are valued by factory torque. Transmissions and transaxles are not evaluated by horsepower, as horsepower does not kill the transmission. If the torque is too high, the transmission may stop. Thinking this way, when you turn a bolt with a wrench, torque is applied to the bolt. If you apply too much torque to a bolt that is already tightened, you can break your head. Transmissions are similar in that if the torque is too high, the gear teeth can break quickly from the gear.

The torque ratings listed are also based on the weight of the target vehicle. Torque rating means that the torque from the engine can be processed by the transmission or transaxle and still lasts for a long time (typically 100,000 miles). The heavier the car, the lower the torque capacity of the transmission. If you use the same transmission in a light car, the torque rating will be higher. Heavy vehicles generate more stress on the transmission components when the engine is producing maximum torque and when the vehicle is accelerating at maximum. This is always 1st gear. This is the increase in maximum torque given by the transmission to the engine while driving. The 1997 Audi V8 I tried to use was rated for torque up to 295 ft-pounds. North Star has a similar rating.

The new transaxle used by the Fiero men was a new GM unit with a torque rating of about 300 ft lbs in a 3500 lb car. The biggest surprise is that this transaxle can be purchased on eBay for a new $ 475 shipping !!! It was in 2007. Today, it’s available for about $ 375. There’s an inside story to this, but basically, GM decided to change it in 2007, which exceeded the 2006 version of this transmission.

This transaxle has the potential to absorb the torque of a healthy V8 engine. If the car is lighter than 3500 lbs (about 2700 lbs for Fiero, 2700-2950 lbs for mk2 MR2), the torque capacity of this transaxle will be higher than the application intended at the factory. The 6th gear is 1.75 inches shorter than the stock MR2 transaxle, leaving room for longer motors and adapter plates (if needed).

The icing on the cake, and what I didn’t know until six months after I bought the Audi V8, was that the Cadillac Northstar 4.6L V8 was bolted to this transaxle. We made a small bracket or welded additional aluminum to the sides of the block’s transmission bell housing flange. No adapter plate required!

Switching to North Star was able to solve the adapter plate problem, the starter position problem and, most importantly, the axle clearance. This is because North Star was first used in horizontal applications from 1992 or 1993 to 2002. It’s still used horizontally, but there’s a vertical version, and GM has moved the starter location. I checked the November 2007 memo and found that the North Star had a limit of 23.75 inches in length. This is the length of the engine from the bolt head of the crank pulley to the back of the bell housing flange. block. At the time, I might have mistakenly included the flex plate in the limit dimensions, but it’s not really part of the limit dimensions. It turns out that the 23.75 inch reading was incorrect.

In November 2007, I did not use the North Star straightedge I saw in the wrecking yard, only the tape measure. Also at the time, Northstar thought he needed an adapter plate to match the speed of the GM 6 (which I found out later and was wrong as explained above). If you have measured the length of an engine, you know that it can be difficult to make an accurate measurement because the engine has many widths and parts in the measurement method. In December 2008 (a year later), I returned to Wreckers and remeasured the North Star. I was more careful this time. It turned out to be actually 23.0 inches long, but I didn’t need an adapter plate (which would add about 1/2 inch to the entire assembly). This puts another spin on the problem.

OK, if this is a bit confusing or hard to imagine, I’ll make it easy here. The genuine MR2 turbo motor is Toyota / Yamaha 3S-GTE, and the genuine transaxle is Toyota E153. The 3S-GTE has a limit size of 20 inches. The length of the E153 is 16 inches. The total length of this drivetrain is 36 inches. However, there is a notch on the left side of the car that exactly matches the E153 case, giving you some room. It doesn’t match the speed of the GM6. The genuine MR2 drivetrain has a clearance of about 3/4 inch on the crank pulley and the same clearance on the transaxle end.

Today, the North Star is 23 inches and the 6-speed is 14.25 inches, a total of 37.25 or 1.25 inches more than the MR2 stock drivetrain. This is not applicable because the notch on the transmission side MR2 chassis does not match the 6th gear. I need to disconnect the chassis, but I don’t disconnect much.

Previous attempts to perform V8 MR2 swaps on Gen2 attempted to use a total of 42 inches with a 26-inch long Toyota 1UZ-FE V8 and a 16-inch E153. This is 4 inches more than in stock! The 4-inch may not sound very good, but it’s quite a lot when installing a drivetrain. To make matters worse, we need an adapter plate to connect the 1UZ to the E153 transaxle. Therefore, add an additional ½ inch.

This approach required the MR2 subframe to be completely removed. The MR2 subframe is only a few inches wide in the area on each side of the car. This will weaken the car considerably. Also, the shock tower on the right will probably hit the rear head of the 1UZ V8, so it will have to be cut a lot. I think those who made previous attempts understood this and gave up after turning off MR2.

In December 2008, I went ahead and bought a fuel-efficient Cadillac North Star. Fortunately, everything was the same from 1994 to 1999, and we found it easiest to add a standalone engine management solution. Versions after 2000 are much more difficult. The same is true for the 1993 version, except that the intake manifold was cast from metal (aluminum or magnesium) rather than plastic like the 1994-1999 version.

I was able to match the North Star with the 6-speed that I bought a year ago in December 2007. At the end! A little progress! After that, I made a test fit on the 1991 MR2 and made a cut on the chassis, so the North Star and 6 speed fit the car. I recently found a way to attach the alternator to the North Star and fit it more tightly into the block, giving the engine extra space around the car. I’m currently building a motor and transaxle mount. Once that is done, the axles can be pumped out, shortened and resplined.

Let’s return to the chassis disconnection promised at the beginning of this article. The area of ​​the chassis that had to be cut is part of the “pseudo” subframe of the engraved sheet metal. It’s not really a subframe, like a punched sheet metal spot welded to the body, but it has the shape of a traditional frame rail (that is, a rectangular cross section). We made cuts in these “frame rails” on either side of the car to clear the North Star crank pulley and GM6 speed case. The metal is a thin gauge sheet metal. Reweld these areas with new sheet metal to cover the holes and possibly place additional sheet metal doublers over the weld joints in these cut areas. This makes the repair more powerful than the original repair. This is the standard approach in the aviation industry when faced with similar issues.

In addition to the doubler, the original cross member interferes with the GM 6 speed case and the position of the new axle, so create a new rear suspension cross member from scratch. This new crossmember has an extension section not found in the original crossmember, straddling the notch area of ​​the subframe for even greater strength. It wasn’t necessary to turn off the correct shock tower, but it’s still not entirely clear. I had to remove the metal on the outside of the shock tower. Structurally, it hasn’t been added much, so I felt it was okay.

The end result of these changes will probably add weight to the car and weigh the new parts to figure out how much weight will be added, but estimate that it will be less than 20 pounds more than in stock. The V8 should be able to easily handle an extra 20 pound car.

Stay tuned for the next article in this series.

Update: It turns out that you don’t need a custom cross member! I found a way to use a genuine MR2 cross member (with minor changes to seme). This is great and can save you a lot of time and money. The MR2 cross member is very important because it has a rear suspension and rear toe control rod attached, and it is very difficult and time consuming to replicate accurately and with sufficient strength. I found a way to reuse the original cross member, which saved me a lot of time and money.