A Brief History Lesson: Built With a Purpose

The keyword for building a car is more mpg and it carries more weight now than ever. Over the past 30 years cars have lost their edge in the quest to be more fuel efficient. I don't blame them, make and market what is in demand. Car enthusiasts only make up a small part of the market and everyone else wants more mpg. The 90's was one of the last decades where Japanese car manufacturers collectively said screw it. Lets make a car for the sake of making a car and they delivered it in something as simple and as 1+1 = MORE POWER. This was the decade that made way to the Supra, R32 and R33 GTR, 300zx, 3000gt, RX-7 and they all have one thing in common. Can you guess? TWIN, MOTHER, F******, TURBOS.

The advent of turbo charging has greatly impacted the car world when naturally aspirated V8 motors predominantly ruled America. “There is no replacement for displacement” held more true at that time period. All the while in 1962 the American manufacturer by the name of General Motors decided to place a turbo in an Oldsmobile Cutlass along with something akin to what we call now as methanol injection. The potential was astronomical and they knew it at the time but unfortunately the knowledge and efficiency to do so was quite lacking. It wouldn’t be till decades later that turbocharging would reveal its latent ability.

​Fast forward to the 90's when the Notorious B.I.G. And Tupac were still kickin it technology and materials advanced and a large single turbo had a major weakness, lag. The time it takes that compressor wheel to deliver the full volumetric efficiency took longer than expected and resulted in significant amounts of turbo lag in high horsepower applications. To fix that someone said lets bring up the past, say what. By using two in either sequential or parallel conjunction you reduce the need for a single large. That exact methodology was applied for these specific 90’s cars. ​

Sequential

Excuse the H4 boxer motor but this graphic depicts a simple sequential setup. If you take a closer look at the blue bypass valve in the left diagram you can see that it is blocking flow to the intercooler. All the while the primary turbo is spooling. Upon reaching a specified point in engine speed/output the bypass valve is then sequentially opened to allow flow from the secondary turbo for boost.

Here’s how it works, in a FD3S RX7 the sequential twins operate at different Rpms. The smaller of the two turbos begins feeding boost until 4500 rpm then cuts off. While the larger secondary is on standby, after a specific rpm mark it fully transitions. By effectively incorporating two varied sized compressors you eliminate turbo lag. KEISUKE AND KYOKO INITIAL D FLASH BACK. Cue in eurobeat: "No one sleeps in Tokyo.

Parallel

Comparatively in a parallel setup the fundamentals are the same but each turbo is paired to different cylinder groups depicted below. All the while both turbos are actively  providing pressure in conjunction with one another. There is no staging or waiting till a specific engine speed for one turbo to kick in. Simply put one is not on standby as they are always active together. Ex. lets say target boost pressure is set to 1 bar (14.5 psi)  the work load is divided so each turbo supplies exactly .5 bar (7.25 psi)

In a R32 GTR the RB26 runs a parallel setup by banking three cylinders to each turbo. In this case primarily both turbos are the same size. By dividing the work load you can have two smaller turbos instead of one large one to also eliminate lag.  

300zx Twin turbo

Supra Single turbo

Looking at both dynographs  between a 300zx twin and a Supra single you can see that the 300zx has a more steady incline of RPM vs HP. The Supra has a more bell shaped curve with a drastic inclined curve in power. Although both graphs have a different peak HP resulting in the Supra having a higher HP the 300zx climbs to a higher power output in a shorter amount of RPM. In the real world the 300zx would essentially pull away from the Supra in the beginning of a drag race and the supra would have to play catch up. Depending on the distance of the race if the two cars were pitted against each other, theoretically the supra would eventually catch up