Sequential Turbo Question

[pwpanas]

Originally Posted by suprapoweredsoarer

I have a somewhat awkward question. As we all know the the Supras had the option of a turboed model. Of which was a sequential setup. Has anyone every created another type of Sequential setup. Here is my first idea. Two turbos (obviously) one small one large, two exhuast manifolds, two wastegates, and the two turbos. Plumb the "cold side" of the small turbo to the cold side input of the big turbo. The second exhuast manifold just feeds the big turbo, the bypassed gas from the first turbo would be fed into the a pipe that would koin exhuast gases from the other manifold prior to the second wastegate and also help spool the big turbo . Obviously after all pressurizing the air would be intercooled. What is your take on this idea. Inefficient?

Second idea, use one exhuast manifold two wastegates and two turbos. Set the wastegate on the small turbo to become open at a designated pressure. Allow the small turbo generate about 10-15psi. The dumped gas is then sent off to turbo number 2. Getting this done could be done via reentering the exhuast manifold or by plumbing a tube that is outside of the manifold but joins the gas flow prior to the second wastegate to feed the second turbo. Also mind you that the small turbo would always be spinning and pressurizing the big turbo. When the small turbo is being spooled the pressurized air would be routed to the inlet of the second turbo. Then the final air volume pressurized by the big turbo is intercooled.
Your take on this idea?

Third idea. By far the most complex. One manifold two wastegates two turbos and a two way valve on the small turbos "cold side outlet". The idea should allow for the least amount of lag an great power thorughout the powerband. Make the small turbo generate about 10-15psi. The valve on the outlet of small turbo would allow air to go directly to the intercooler up till the maximum set boost for that turbo 10-15psi. Then the valve would redirect the air to the big turbo for the remainder of the powerband in order to help spool the big turbo. The valve is used to not lose boost at low rpm due to resistance by the big turbo. Note that once the 10-15psi is met by the small turbo, not only would the output boost pressure spool the big turbo but the gases redirected by the wastegate would also help spool the big turbo. Not sure if the big turbo would need a fresh air supply on the inlet of the cold side when air is not being bypassed to it from the small turbo. If needed two pipes could be spliced onto the big turbo; one that would come from the small turbo the other being a fresh air supply.

with the thrid setup the lower rpm and low midrange woud look like Small turbo feeding 80-90% of boost and minimal boost coming from the big turbo
The high midrange and high rpm would look like 80-90% boost coming from big turbo being "prespooled" consistently with 10-15psi of air pressure and bypassed exhaust gases from the small turbo. The most obvious problem with this setup would be plumbing.

I need some opinions. Goals are this, a linear powerband, not a huge power jump at high rpm. Good low end power and hig low end torque and a peak horsepower over 700hp. Essentially I'm researching to find a minimal lag system that can generate a lot of power and offer good power at all rpm. The engine is the infamous
2JZ-GTE engine. What is your take on these ideas?

Feel free to criticise, as it can only enrich my knowledge of these complex systems. I see it this way. One big turbo, lots of lag huge power jump at high rpm, no good. Two small turbos working in parallel, consistent power low lag, lack high horspower potential. Sequential setup, could be the holy grail for little lag, power everywhere, and high horsepower capabilities.

Although I admit haven't dissected your ideas in great detail, I'd suggest a couple of initial considerations:
1) If you have a larger turbo and a smaller turbo both directly plumbed to the same charge-air system, the larger will overpower the smaller and start it spinning backwards. If this is allowed to happen repeatedly, it will drastically (negatively) impact the life of that turbo.
2) There is a very limited market for this type of kit. Single turbo kits for the 2jz-gte run upwards of $5K, and an HKS TT (parallel) kit is about $8K. With all of the r&d you'd have to do in order to perfect your idea (especially with the complex valving that'd be required), coupled with the rarity of this vehicle (relative to the Civic, for example), I'd guess you'd have to sell your kit for $15K or more to eventually recoup all of your r&d costs.

Fwiw, I do like your goals of "a linear powerband, not a huge power jump at high rpm. Good low end power and hig low end torque and a peak horsepower over 700hp...a minimal lag system that can generate a lot of power and offer good power at all rpm."

P.S. The oem Mkiv TT is already sequential. What you said "...Two small turbos working in parallel, consistent power low lag, lack high horspower potential" isn't correct. Two small turbos running in parallel lag almost identically to a single turbo twice the size.

Again, I think you have good ideas overall. Please let's continue this discussion: based on the two considerations I mentioned, which one of your three options do you think most warrants deeper exploration?