The reason Mazda "ditched that design" is because you will get better results with the sequential turbo system working through a milder port timing setup than you will with trying to generate enough additional exhaust energy at lower rpms to spool up a larger single turbo. I'm skeptical as to how much of a power advantage HKS actually got from using a VVT setup with a turbo, versus if they were to fabricate a sequential turbo setup.

The turbo in the intake tract is a substantial obstacle to intake flow until it begins producing boost, so any increases in turbine size require major gains in exhaust energy to spool it up with the same speed. While playing with the port/cam timing might get you some gains, they still have to work against the turbo until it starts producing boost. Those gains will pale in comparison to properly sizing the turbo to the desired conditions. Changing the length of the intake runners or port/cam timing makes a far greater difference with NA applications because you don't have the turbo sitting in the middle of the intake tract.

A better solution (but still very blue sky, as are most of these discussions) would be VVT, but as in variable vane turbo. There was a thread a while back where someone mentioned this, and why they haven't been applied to performance cars yet. I stated then that the problem was those turbos originally were designed for diesel engines, which have far lower exhaust temps and slower turbine acceleration requirements, so you'd need metal alloys that could withstand the higher exhaust temps and quicker spool of a gasoline engine. Well, the new '07 Porsche Turbo apparently uses variable vane turbos now, and supposedly they are far superior to the previous versions, with virtually no lag, great midrange and screaming top-end. I guess they've found a metal alloy that will work. However, I heard that they are extremely expensive to fabricate and produce (naturally). And then there is all the peripheral components you'd need to control them.

 

Hey Kento,

Thanks for the explanation. It makes a lot of sense.

Also, I wasn't sure if you saw the thread about the VVTs that the '07 Porsche is using. Here it is: https://www.rx7club.com/single-turbo-rx-7s-23/vtg-turbos-new-911-a-526846/. Page one, then the last page or two are worthwhile. The pages in the middle I'd skip

~Ramy

 

here's the link to a lot of info on the renesis design (THANKS QUICKSILVER!!)

http://www.filefactory.com/?0fa456

 

Very cool info. Thanks for posting it.

Joe

 

It’s the thread about the custom tri-rotor-2JZ with a Vtec head.... No? lol j/k
but just remember folks retorque your muffler bearings or your hydraulic blinker fluid with over heat causing a major shut down of your flux capacitor... and we all know that takes 1.21 gigga watts of electricity to rejuvenate because that’s what makes time travel possible…..

LIMITED EDITION

 

A classic example of another college tuition flushed down the crapper.