Single Sequential Twin Turbo (SSTT)

[Lextreme II]

What do you think gang? Single pipe power a T3/4. Once it hit a preset boost like 8 psi or so, the actuator will open up and feed exhaust energy to the second T3/4turbo to take it all the way up to what ever your final boost is.

There are few exhaust bypass out there we can use. Most of the exhaust bypass uses actuator and control my vacuum. However, this bypass also can be accomplish by a large wastegate. Once the wastegate open, the second turbo kicks in. This is almost like the Surpa's Sequential...

Beside the twin T3/4. I guess you can also do T3 for the first stage and T60 for stage two too. Whatever combination you like. For example power band would be Low to Mid, Low to High, Mid to high and so on....

Benefit, low end boost and high end power.

 

[Pagong]

How do you plan on making it fit?

 

[Lextreme II]

It wont be that hard.... Use an actuator to control the opening and closing of the secondary turbo exhuast flow.... Its like a Y pipe with a gate and opening and closing is control by the actuator. Which is control by vacuum/boost.

 

[turboandrew]

IMO, a sequential turbo system is quite tricky. Bringing a second turbo online is not easy. I would look very hard at the sequential system on the Supra and RX7. FWIW both of those use a matched pair of turbos.

 

[edz]

There's also been a lot of articles written in Zoom Magazine about the problems, lack of smoothness in transitions, they actually tested an RX7 by replacing the system with a single turbo and it was much smoother, more responsive and powerful. Sounds like a lot of hrad work for not a lot or negative gain?

 

[Pagong]

I think you should try another Twin setup, but instead of having them down low like you had them before, put them up high..one on the old battery location and the other on the old airbox!

 

[Lextreme II]

It can be done... R u interested?

 

[LEXUSV8NZ]

I read an article (similar to that in Zoom that Edz mentioned) and they compared a stock sequential setup, to a well thought out ballbearing single turbo
The single had better response, smoother and made more power
Not to mention was cheaper and simpler to setup
But then again dont let me stop you, I just think you could save some time and money (which could be used to purchase a better turbo e.g. garret as opposed to purchasing 2 lesser turbos and all the neccesary extras)

Logan

 

[Lextreme II]

I think the combination of turbos and setting of the actuator play a very important roll. If the combination is worked out and the order of the turbos then it should able to do its job.

 

[LEXUSV8NZ]

But in many cases it is simpler and more effective to use a single turbo system (or in this case single per bank/twin turbo)
If you do this what sort of power level will you be aiming for?

Logan

 

[turboandrew]

I'd rather do a supercharger / turbocharger setup. Have the turbocharger blow through the supercharger. Supercharger will give you instant boost and the turbo will provide whatever high end / high rpm boost you would want. There was a series of articles on this in Turbo Magazine, using a Toyota V6 with a TRD / Eaton supercharger and a Garrett T series turbo. They have very good results with it, and it is far simpler than a sequential system.

IMO, the ultimate for the 1UZ would be a supercharger and twin turbos, using a water to air intercooler .

 

[Pro]

I read an article (similar to that in Zoom that Edz mentioned) and they compared a stock sequential setup, to a well thought out ballbearing single turbo
The single had better response, smoother and made more power
Not to mention was cheaper and simpler to setup
But then again dont let me stop you, I just think you could save some time and money (which could be used to purchase a better turbo e.g. garret as opposed to purchasing 2 lesser turbos and all the neccesary extras)

Logan

that article was on a 13BREW - a system reknowned for having problems with cracked exhaust housings, valve operation problems etc etc. the cosmo version of the same engine had a better design layout, but the RX7 was mazda's test bed. hence why there are so many problems with it.

that said, you can't compare a manufacturer's design for a sequential turbo setup to a custom design. the supra's twin turbo system is a work of art and has very few problems (here in OZ anyways) so copying that (or close to) seems a logical way to go.

you could use an external wastegate to re-direct exhaust flow to the second turbo. using a large first gate like a 60mm would be a minimum, so you could control boost on the first turbo and have it dribble into the second. when the first turbo is producing boost you could have the 60mm gate open to provide flow to the second turbo. off this pipe you could run a second, smaller (say 42mm) gate to bleed gas into the exhaust system off the second turbo to stop it overboosting too.

it wouldn't be too hard to make, you would just have to very good with a tape measure and your vacuum lines.

you have me interested in this now...

 

[Lextreme II]

I think is great to let our ideas and visions share. This is an very interesting thread and would like to explore more about it. If we used a large waste gate, once the WG open, the primary turbo will surfer and there will be few seconds lag between the transfer of boost. If we can some how do a progressive wastegate/actuator, then it would be more smooth between the primary and the secondary turbo.

 

[Pagong]

It can be done... R u interested?

I was actually going to do it when I had the spare motor in my garage, but a lack of welding skills, some parts (i.e. pipes), and funds stopped it.

I was going to use twin 14b turbos from an Eagle Talon TSi AWD. Since the Talon has a 2 liter engine, using two 14b's for our 4 liter engine sounds feasible.

 

[Lextreme II]

As from my personal experience. DO NOT USE USED TURBOS. Use turbos usually leak oil from seals. I would get a new set of turbos and it will back up by the seller and manifacture.

 

[TundraEddie]

Turbo Performance Center in MD did a seq. system in one of their 911s years ago (1994 or 1995). There was a pretty large article in Turbo magazine about this car.

Turbos were different sizes. The primary turbo is plumbed normally,its wastegate's discharge was used to spool up the secondary. It wasn't that easy though,Mike Levitas also had some actuators controlled by engine management (Electromotive). I have the issue somewhere here,will post up details once I find it.

 

[Lextreme II]

Eddie..

I have been thinking about the same idea too, but using the discharge gas/heat to power the secondary turbo might be ineffecient and restrictive.

 

[LEXUSV8NZ]

What about doing a twin turbo set up, where the smaller primary turbo spools and provides you with low end, start to bleed exhaust gas to the 2nd turbo, and then completely bypass the primary turbo? so that it doesnt restrict the system?
Do you think that that could be feasible and made to work?

Logan

 

[jdchmiel]

The exhaust part of a true, well done sequential is the easy part. You use a small turbo as the primary, with a massive wastegate. Set the massive wastegate to something like 10 psi so that it opens up and provides plenty of exhaust gas to spool up a massive 2ndary turbo ( 4.0 liters at 10 psi is about equivilant to 6.75 liter motor)
The 2ndary turbo has another wastegate set to your desired boost pressure, like 25 psi for example. Since the vacuum line feeding the first massive wastegate is at 25 psi, but is set to 10 psi, it will be VERY open, providing no exhaust restriction.

The difficult part of the true sequential is how to route the compressed air. You cant do them in parallel or the boost will back out of the unspooled 2ndary turbo and it will never spool up. you cannot do them sequentially or you will have compressed teh air two times, and compressing at 70% efficiency and then 70% efficiency again means you end up with 49% efficincy overall.. so you need multiple intercoolers and such to maintain thermal control. The best bet is to have the primary turbo flow through the 2ndary turbo while only the small primary is spooled, but as the 2ndary spools up, a bypass valve opens up for it to suck in more air than the small primary can deliver. At this point the primary is not compressing air anymore, and overspinning is a concern... but with the massive primary wastegate, it will be getting less exhaust energy and might not spin excessively. The unltimate goal is small turbo spooling early, providing enough gas to spool up a big turbo earlier than it normally would, thereby allowing you to use a larger and more efficient turbo ( so long as compressor surge is not an issue, and a 4.0 liter motor with compresser surge issues is nothing I have ever heard of before lol) And the transition to happen smoothly to only the 2ndary turbo being spooled up. It is a nice engineering exercise, but it all boild down to a single turbo being so much simpler that a single can be set up very well, where a complex sequential takes a LOT of know how and extra $$ to get set up..

 

[42GAMI]

Bailey says "Carry me please".

I agree with jdchmiel, on the (just use a big single turbo) issue. sure thers is huge lag, but it is so much simpler and cheaper.



now im kinda stupid when it comes to cars, so dont everybody shoot me down at once.



just my suggestion: go with the twin turbo setup. use one for the low end, one for the high end. i dont know sh!t about turbo matching so go figure make the 1st turbo take care of business from the start up to somewhere around 8-12 psi. 2nd turbo to take care of biz, or shall i say wake up at that transition point. im sure you understand the concept.



instead of plumbing one turbo into the next, run them parallel. i know what your thinking, when turbo 2 comes on, it will force back pressure on turbo 1. Now the trick is to figure out how to keep turbo 1 from being damaged when turbo 2 takes over for the real work. try to employ ((wastegate technology)) here.



Fabricate some kind of vacuum actuated bypass valve (wastegate), and plumb it just after the compressor outlet on turbo 1. use a 12 psi spring to gradually close the actuator valve as it approaches 12 psi, but not any sooner than 8 psi.



if there is any concern about turbo 2 being damaged from the same scenario, install the same type of wastgate just after the compressor of turbo 2. use a 10-12 psi spring to gradually open the valve.



What to do with the leftover air coming from the bypass/wastgate on the compressor side of the turbos? I don’t know. Route it back into the exhaust after the exhaust wastegate or just let it purge to the atmosphere.



The actuator valves can be any kind, they don’t have to be vacuum operated, could be electronic, but a pneumatic system will ease more headaches. Issues with compressor surge? I don’t know.



Of course you should be using a pressure sensor type of system or some other means to measure the airflow because I don’t think an airflow meter would work unless both turbos where fed by the same inlet pipe.



Isn’t this “sequential” turbo concept already employed in Toyota’s 1G-GTE and 2jz?