Mike's Turbo Convertible Rx7 Project

The TII Differential (left) has a few advantages over the NA diff. Most importantly, it is stronger. Also, it has a limited slip. The differential is a 100% bolt-up affair. It requires the use of TII axles and the TII drive shaft. Note that the TII drive shaft will only work with a TII transmission.

I decided to use the NA intake system because adapting the TII intake to it is easy and affordable, and because takes air from in front of the radiator with out any modifications. I realize that other filters, like cone filters, probably flow better, but unless the cone filter is accompanied by a cold air box, such a system would pick up hot air from inside the engine compartment. Using the turbo to compress heated air is counterproductive and feeding the engine a warmer intake charge may lead to shorter engine life.

The exhaust is a complete system is from Racing Beat, but it still required some fabrication because it does not come with a catalytic converter. This car will be a street car, so it needs a cat.

I built a mid-pipe with a catalytic converter in it to replace Racing Beat's presilencer (far bottom right). This may have the effect of making the car a tad louder, but given the straight through design of Racing Beat's presilencer, the difference should not be great.

The mid pipe that I built uses custom fabricated flanges at either end which I built from 3/8" CRS (left). I created the flange's 3" hole by plunging a spotting mill around perimeter and then finished the hole with a rat tail file. I used a skill saw with a chop saw blade to create the flange's basic diamond shape. The rest of the mid-pipe (right) is 3" mild steel tubing, a universal catalytic converter, and an air injection pipe.


Home Contacts Links Tommy's Big Single 93 Rx7 Mike's Turbo Convertible Rx7 Parts List	Mike's S5 convertible is getting a Japanese-market S5 turbo motor from Tiger Japanese Auto Parts Ltd. The only performance modification beyond the stock turbo motor will be a stainless exhaust system from Racing Beat. Mike's performance goals for his car are quite reasonable, and should provide him a reliable and very serviceable car. Plus, the car will have the added pep that Mazda's convertible Rx7 has always needed.
	As mentioned previously, Mike's motor came from Tiger Japanese. In fact, Tiger supplied the engine with ancillary components, the ECU, the transmission, differential, axles, and an entire rear sub frame. The only part that they were not able to supply was a drive shaft. Their shipping was quick and, apart from a shifter that seemed a little stiff, the parts appeared to be undamaged when they arrived. More on this later.
	I generally prefer to pull the engine (left) and transmission as one unit. This makes the separation of the engine from the transmission much easier. It also makes re-installation much easier. The engine that Tiger shipped to us seemed to be in good shape, but to be sure I checked for metal in the oil pan by removing the pan, rust in the firing chamber by removing the spark plugs, and I checked for decent compression by turning the motor over by hand. Click the image on the right to view a video clip.
	Since the engine and transmission were out of the car, and because the condition of the j-spec clutch was unknown, a new clutch was installed. The clutch is an Exedy OE replacement part number 07067 manufactured by Daikin.
	The best way to wire such a swap is to retain the NA wiring harness and change only a couple of wires. The NA motor has no knock sensor. The knock sensor goes to pin # 2M on both the NA and TII computers (below). On the S5 NA harness this wire is a yellow wire with a black stripe. This yellow wire goes to a white solenoid connector which is not needed on the TII motor. I cut this connector off and connected the TII knock sensor connector to it (left). The connector that the NA motor uses for the 6 port induction solenoid needs to be cut off and the TII's Duty Solenoid connector added (right).

	The A/C compressor on the TII motor did not have the correct hose connectors on it, so the convertible's original compressor was used. The J-Spec P/S & A/C bracket (left) did not have the correct A/C compressor mounting holes for the original A/C compressor, so it had to be swapped out for the US-Spec Version as well.
	The plastic pipe that runs from the turbo to the rubber elbow on the intercooler was damaged when it arrived, so I made a replacement from steel (left). The steel piece is painted with a zinc rich primer and high temp engine paint. The completed pipe has the necessary 5/8" nipple for the bypass air control (BAC) valve and a Greddy style blow off valve (BOV). To keep the BOV from being too noisy, it recirculates air back into the intake pipe (barely visible at right) that runs from the mass air flow sensor to the turbo inlet.
	The original lines on Mike's car looked OK, but you can never be too careful with oil cooler lines. These stainless lines were less than $30 from Lopers in Mesa AZ and they should provide many years of trouble free service. To install the stainless lines, I cut the high pressure hose ends off of the hard lines and banjo fittings. This revealed steel tubing with a barbed end. The stainless hoses are clamped on with ordinary worm drive hose clamps. Worm drive clamps are not as pretty as anodized an fittings, but they work just as well for this application, and they are far less expensive.
	The TII Differential (left) has a few advantages over the NA diff. Most importantly, it is stronger. Also, it has a limited slip. The differential is a 100% bolt-up affair. It requires the use of TII axles and the TII drive shaft. Note that the TII drive shaft will only work with a TII transmission. I decided to use the NA intake system because adapting the TII intake to it is easy and affordable, and because takes air from in front of the radiator with out any modifications. I realize that other filters, like cone filters, probably flow better, but unless the cone filter is accompanied by a cold air box, such a system would pick up hot air from inside the engine compartment. Using the turbo to compress heated air is counterproductive and feeding the engine a warmer intake charge may lead to shorter engine life.
	The exhaust is a complete system is from Racing Beat, but it still required some fabrication because it does not come with a catalytic converter. This car will be a street car, so it needs a cat. I built a mid-pipe with a catalytic converter in it to replace Racing Beat's presilencer (far bottom right). This may have the effect of making the car a tad louder, but given the straight through design of Racing Beat's presilencer, the difference should not be great. The mid pipe that I built uses custom fabricated flanges at either end which I built from 3/8" CRS (left). I created the flange's 3" hole by plunging a spotting mill around perimeter and then finished the hole with a rat tail file. I used a skill saw with a chop saw blade to create the flange's basic diamond shape. The rest of the mid-pipe (right) is 3" mild steel tubing, a universal catalytic converter, and an air injection pipe.
	The big day finally came. All of the fluids were topped off, the battery was connected, the key was turned and... the car would only run on one rotor. After making sure that the motor had spark, which it did, and checking the harness for wiring issues, I finally swapped in the old NA N373 convertible computer, and the car fired immediately. Click the image on the left to view a video clip of the car firing up for the first time. Assuming that this J-spec N374 ECU was just a bad computer, I returned it to the supplier in exchange for an other unit of the same description. Unfortunately, that ECU did not work either. I tried two more N374 computers of the same description with the same results. From what I can tell, none of them would send a signal to the primary injector on the rear rotor. I finally installed a US-spec N370 ECU, and the car ran beautifully. I have read many forum posts claiming that the N374 Japanese S5 turbo computer will run a US spec car. I have also read about several people's experiences with J-spec computers that will not fire the rear injector. My experience is that the J-spec computer is not compatible with a US spec harness.
With the car now running, I took it for a short and gentle drive down the block to assess the situation. Unfortunately, the shifter was much too stiff. So, the car went back up on the stands, the exhaust came out, and the tranny got pulled and disassembled. I removed the shift box from the TII transmission and replaced it with a unit from an NA tranny. Now the transmission works fine. When I took delivery of the engine/trans/subframe/etc, one end of the rear sub frame (which came complete with the differential, suspension, axles, brakes, etc.) was resting on the transmission's shift box. This probably caused the shift box to bend during shipping and thus caused the shifter to be too stiff.
Finally, the car had a motor that ran properly, a transmission that shifted smoothly. All it needed was an open stretch of road for a little deep breathing. Between the recently installed turbo motor and the Racing Beat exhaust, this thing positively inhaled the road! The car's owner now plans to put a couple thousand miles on the car before painting it, and having a new top installed. He jokingly says the car is fast enough now that he's afraid he might wreck it, so he wants to hold off on the paint just in case. Thanks to: Anthony (Flooder on AzRx7.com) for selling me his TII hood an a very reasonable price. Avelino Sanchez of San Antonio Texas for selling me a US-spec N370 S5 turbo computer and wiring harness at a very reasonable price. The owner, Mike Casto, for patiently waiting for his car to be completed. Tiger Japanese Auto Parts Ltd for having a very good return policy.