1987-1991 Mazda RX7 Turbo II 

BNR Supercars specializes in perfecting a flawed design of the 87-88 Turbo II turbocharger.  Although the rotating assemblies are the same for all the 87-91 turbochargers, there is a big difference in the turbine housings on each of the turbochargers.  The 87-88 (series 4) differs from the 89-91 (Series 5) in just a few ways.  The biggest difference is the turbine housing (exhaust housing).  The S4 turbine housing has a very inefficient internal wastegate design.  This is why most every S4 car owner changes over to a series 5 turbo and manifold.  The manifold design for the internal wastegate on the S5 was improved for better boost control, thus helping eliminate boost spike.

The internal wastegate port on a stock S4 turbocharger is a puny 12 mm in diameter.  Comparing the S4 to the S5, there is no comparison.  The dual wastegate port on the S5 has 2 holes that are both considerably larger than the S4, therefore making it the elite housing to have with a hybrid upgrade.  But now things have changed.  BNR has designed a custom internal wastegate set up for the S4 that will out perform the S5 wastegate any day of the week.  We take your puny 11mm port and make it anywhere from 34-35mm in diameter!  How's that for a wastegate port job! 

S4 (87-88) ported wastegate

S5 Ported wastegate and turbine housing entrance

87-91 BNR Stock Remanufactured turbocharger

The stock reman comes with a fully balanced and blueprinted rotating assembly, new journal bearings, piston rings, thrust collar, thrust bearing and carbon seal. A stock remanufactured turbo comes with a 1 year warranty from BNR Supercars. 

• fully rebuilt with new piston ring, carbon seal, thrust collar, thrust bearing, journal bearings, and O ring
• balanced to .5 gram/in2
• 1 year warranty
• tapered inlet modification

Price:  $375 with rebuildable core

87-91 BNR Stage 1

The BNR stage 1 hybrid is stock appearing on the outside, but when you look closer, a larger/more efficient compressor wheel has been fitted in the stock compressor housing for more air volume over stock.  The wastegate is also reworked to 34-35mm to handle boost control.  The rotating assembly is balanced and blue printed and the turbine wheel is clipped to decrease backpressure, this also tends to reduce boost creep. The bearings and piston rings are replaced and the 270 degree thrust bearing is also modified for additional oil flow going to the rotating assembly. When you want everything to "look" stock, but not perform like stock, this is the turbo for you.  You can see anywhere from 300- 320 RWHP from the stage 1 depending on your set up and boost level.  Spool up should stay reasonably around where it spools with the stock turbo.  Power band is very linear and comes online very quick, also it hits way harder on the top half of the RPM band.  The stage 1 comes with a 1 year warranty.  This turbocharger upgrade is bolt up and no fabrication is required.

• fully rebuilt
• T04b V trim compressor wheel with stock compressor housing machined to fit
• Clipped turbine wheel
• fully balanced rotating assembly (.5 gram/in2)
• adjustable wastegate actuator preset to 7-8 psi
• 100% bolt up no fabrication required
• 1 year warranty

87-88 Price:  $675 with rebuildable core

89-91 Price: $575 with rebuildable core

87-91 BNR Stage 2

The BNR Stage 2 hybrid is an improvement over the stage 1 in a few ways.  The most visible improvement is the TO4B compressor housing and backing plate.  What this does to improve the efficiency of the turbo is to gain overall volume of air with the larger compressor housing.  You can see improvements as much as 10-15% when you go to a larger compressor housing.  Another benefit to the stage 2 turbo is it has the 360 degree thrust kit.  What the 360 bearing does is provides a constant supply of oil to the rotating assembly to ensure that the rotating assembly is in constant contact with oil when pressurized.    The factory 270 degree thrust bearing has a 90 degree relief which does not have a constant contact with oil and acts as a oil drain for the thrust bearing.  A 270 degree thrust bearing is not fatal to a turbo, but when you start running an abundant about of boost, friction will start to work against the two metal pieces.. Also with the 360 thrust comes a dynamic seal instead of carbon seal.  What this does is decreases friction on the rotating assembly therefore improving response. 

The 87-88 BNR Stage 2 comes with a 360 thrust kit, T04B package, all new bearings and piston rings, clipped turbine wheel, balanced/ blue printed rotating assembly, 34mm wastegate port, and a 1 year warranty. The S5 stage 2 also comes with a ported wastegate and all of the above options..

We have customers that have been very pleased with the performance of the BNR Stage 2.  One of which made 332 RWHP at 14 psi, and the other running an ET of 12.3 at 114 mph in total street trim.  The turbo responds like the BNR Stage 1, but has the extra edge of reliability at higher boost levels and also the extra volume of air with the larger compressor housing.  This turbocharger upgrade is bolt up and no fabrication is required.

• fully rebuilt
• balanced to .5 gram/in2
• T04B upgrade package with 3" inlet and 2" outlet
• T04B H3 compressor wheel
• 360 degree thrust bearing assembly
• clipped turbine wheel
• ported wastegate
• adjustable wastegate actuator
• turbocharger clearanced for easy install

87-91 BNR Stage 3

The BNR stage 3 looks almost identical to the stage 2, but the only differences are a larger compressor wheel, turbine wheel that has more of a clip to reduce back pressure and the wastegate is 34-35mm in diameter.  We have had a customer trap 118 mph on the stage 3 which indicates he is making around 360 RWHP in a full weight Turbo II.  This turbo is good for up to 15-16 psi of boost.  This turbocharger comes with the T04B package, 60-1 compressor wheel, 360 thrust bearing for higher boost applications and the turbine housing and wastegate is ported to reduce backpressure.  This turbocharger upgrade is bolt up and no fabrication is required. Twin scroll system is optional to the customer.

• Billet seal plate
• 60-1 compressor wheel
• more aggressive turbine wheel clip

 

87-88 BNR Stage 2 and 3 price:  $800

89-91 BNR Stage 2 and 3 price:  $700

87-91 BNR Stage 4

The BNR Stage 4 is the world record holder for ANY S4 or S5 turbocharger upgrades for most power ever recorded on a dyno!  It made 402.7 SAE RWHP and kept that power all the way through the power band.  The boost went from 18 down to 15 psi and the car generated that HP at 15 psi.  So why go to another manifold when you can throw down a tremendous amount of power with a sleeper of a turbo!  The turbo upgrade consists of a P trim turbine wheel, 60-1 compressor wheel, 35mm wastegate port, and the trick is in the porting of the turbine housing.  A 360 thrust bearing is standard on the stage 4.  The turbocharger is common, but we specialize on getting out what you put in!  The turbine housing is opened up tremendously therefore decreasing backpressure.  Not only did we make 400+RWHP, we did it using a factory style internal wastegate!   This turbocharger upgrade is bolt up and no fabrication is required.

• all new CHRA (center housing rotating assembly)
• fully balanced
• 360 degree thrust bearing
• billet seal plate
• T04B package
• 60-1 comrpessor wheel/P trim turbine wheel
• CNC machined turbine and compressor housings
• ported wastegate
• adjustable wastegate actuator
• comes with 1 year warranty