Project Toyota MR-2 Turbo Part IX: Back From the Grave

In our January 2000 issue of Turbo we gave the readers a recap of Project MR-2 over the past year-from the first day it was purchased to the day we blew up the stock 3S-GTE engine. We are trying to figure out whether the project has been filled with more joy than pains.

Although we blew up the factory powerplant we do not want to send out the wrong message. Our goal from day one has been to push the Toyota to the limits so you don't have to find out on your own. By doing so, parts are going to break and unfortunately for us the factory cast pistons let go. The cause was a lean air/fuel mixture causing the pistons to superheat and melt. After careful research we were able to discover that 3S-GTE engines always melt the number two cylinder before any other. Due to a poor factory intake design more pressurized air is fed into the number two cylinder. Although the MR-2 was running a safe air/fuel mixture at the downpipe (which is an average of all four cylinders) the number two cylinder was probably running a couple of points leaner on the air/fuel ratio causing the meltdown. Unless you plan on building an entire intake or purchase a stand-alone engine management system that is capable of squirting more fuel in that particular cylinder there is no way to remedy this problem. The only suggestion we have is running a slightly richer air/fuel to compensate for the number two cylinder's extra air flow.

Since we did not want to remove the block from the vehicle and have it sent out to machine shop to be bored we had the machine shop sent to our driveway. After the removing the head and pistons from the block we called upon Casey Moir of Casey's Portable Boring. Casey measures the diameter of each individual piston and bores each cylinder according to the size of each piston. When the piston melted in the cylinder it scored the wall of the block. Trying to make the best of things we decided to go with 1 mm overbore units from Arias. The Arias pistons are made from forged 4032 (high silicon) aluminum alloy. Our pistons are flat top 9.0:1 compression units with extra large valve relief areas. Forged pistons are capable of withstanding higher temperatures and more extreme conditions when compared to the factory cast units. Aftermarket forged pistons are highly recommended if you plan to do a lot of hard driving or racing. Prior to installing the pistons in the block we had the ring end gap set at .016-inch for the top chrome ring and .018-inch for the ductile second ring. The pistons were installed with the factory rods and bearings. We examined the rod bearing that came off the number two rod and found it to be in excellent condition so we reused the bearings.

To ensure a perfect seal between the head and the block we sent the head to JG Engine Dynamics for resurfacing. Since we did not want to add anymore compression to our engine the head was resurfaced only until it was perfectly flat. Having heard of problems with the factory composite gasket we decided to go with a TRD head gasket. The TRD gasket is made from steel and is less likely to deteriorate over time which is somewhat common with composite gaskets. The best part is that the TRD gasket is only a few bucks more than the factory. The head is sandwiched to the block with ARP headstuds. One of the misconceptions many enthusiasts have when installing head studs is that they torque the studs into the block. Never torque the studs into the block always hand tighten them. In doing this, the ARP nuts will apply more pressure o the top of the head rather than threads in the block. Torquing the studs into the block can cause the block to distort possibly resulting in a bad sealing surface. However use a ruler to make sure all the studs are the correct depth into the block. Always use the lubricants recommended by the manufacturer when installing the studs. The downside of installing a stud kit on the 3S-GTE engine is that you can't install the head onto the block with the intake attached to it. Although we have an ExtrudeHone-processed intake we decided to go with the factory one for now so we can find out if the intake makes power at a later date. To remedy our maxed out injector problem we installed Blitz 540cc injectors into the factory rail. The injectors are 100cc larger than the original units and should be good to manage an extra 70 to 80 horsepower.