Project Thread SC470TT (VVTi) Twin Turbo Lexus SC400 with 4.7L Toyota Tundra Engine

[Lextreme II]

I am very happy with the results of the Project LS400T. As expected I am running 16 psi and the car is felt very strong. Dyno numbers will be out soon.

my next quest is Project SC470TT
Twin Turbo Lexus SC400 with 4.7L Toyota Tundra Engine

Here is what I named this system Single Sequential Twin Turbo System or SSTT:

I will be running two Garrett GT30R Ball Bearing turbos. The headers will be modified from the existing Toyota Tundra Headers. The headers are flipped upside down and the exhaust are facing to the front. The exhaust gas then routed to the front of the engine where two pipes meet in the center like a upside down Y configuration. After the joining of the two hot 2.5" exhaust pipes from the heads, then a single 3" stainless steel pipe divided into two 2.5". The two 2.5" pipes will go to two GT30R turbos. However, one of the pipe will be fitted with a wastegate/bypass (see below for pictures). At low boost, one of the turbo exhaust will be closed and allow all exhaust gas to power one GT30R. This design will generated almost instant boost. After 8 psi from the single turbo, the wastegate/bypass open up and both turbos get even exhaust flow.

The design of this turbo system gets little tricky. Basically, at low boost only one turbo will be working and at high boost, two turbos contribute like a typical twin turbo would. Why is this system so different? This setup is superior to the traditional single or twin turbo setup. As for single turbo comparison, regulator single that is capable of producing 1000 hp will take at least 5,000 rpm to start positive pressure (boost). Twin turbo is almost the same because you only getting half of the exhaust gas. Imagine our V8 4.0 liter is like running two 2.0L Honda motor. So when someone say twin turbo spool up faster than single is a fallacy or single makes more hp than twin. Its all depend on the size of the engine, size of the turbo and other factors. You have to compare an apple with an apple. Basically I am saying if you want high horse power, you will sacrifice lower end.

From the perspective above, people start fitting smaller turbo for low end street use, but lack of high end power. Here is my solution to the age long problem. SSTT is what I call it and I am sure someone call it something else. SSTT operate only one small turbo at lower end and utilize the second turbo at mid and high rpm range. Since only one turbo is working during the 8 psi or less environment, the 4.0L will spool the ball bearing GT30R turbo at very low rpm. Its almost instant due to the cubic and the size of the turbo.

The tricky part of this setup is the bypass. Here are some example bypass units I might use. The D-Celerator bypass wastegate is made diesel trucks or heavy duty RVs for increase back pressure during hill climbs. We can utilize these units for our applications. Here are some choices I have found. D-Celerator, E-Cutout and ATP Turbo VES system.

 

[poid]

i love the idea Lex...i guess you are going to have to control the opening of the bypass unit so that it comes on gradually rather than in on hit, yeh? It would produce an interesting power curve, thats for sure

I have pretty much settled on running a pair of GT30R's so will be keenly watching your progress

 

[1youZee]

hmm, it sounds very interesting. What happens to the exhaust after it gets to the "y" and there are two paths, a path through the small turbo, and out of the system, and one through the big turbo. say at 12-15 PSI when the smaller turbo's wastegate is open. Why would the exhaust "want" to flow through the bigger turbo, exert energy on it and then leave. What stops it from taking the easy way out, through the smaller wastegate? I think you would have to have two of the valve thingys and route the exhaust out of the wastegate of the smaller turbo, back into the bigger turbo. of course, some of it(exhaust energy) would have to hit the bigger one(turbo), because of flow restriction of the smaller one...

very intriguing, though.

 

[Lextreme II]

After a detail conversation with JBrady. He suggested route the primary exhaust to the secondary turbo exhaust inlet to pre-spool the turbo while the bypass gate open and share exhaust to the second turbo.

However, this setup my have restrictive flow for the primary turbo. I think the trick is the control of the wastegate for it slowly open and pre-spool the turbo.

 

[verylost]

I believe what you described is how a stock twin turbo supra works. You may want to steal some ideas from the supra and possible some parts to get your project working.

 

[cribbj]

David, what you described is almost exactly the way the sequential twins operate on the MKIV Supra. The JDM version did not have this option, IIRC.

On the Supra we have four VSV's that have to operate their actuators in a very orderly fashion in order for the transition from single to twin to happen without a flat spot in the torque curve. There's even an old-fashioned one-way reed valve on the intake side to smooth the torque curve when #2 comes in, but even Toyota couldn't get it exactly right as a flat spot is evident on any stock USDM twin turbo Supra dyno graph.

Not to dissuade you from this project, but nearly everyone who has chased higher HP with a MKIV Supra has pulled the sequential system off, and gone with a large single turbo. Far easier to control, and the only downside is the slight loss of torque from 1500 to 2500 RPM or whenever the larger turbo comes on boost. The little CT12 "peashooters" that Toyota put on the MKIV spool incredibly fast - especially #1 when "all" the exhaust is going to it.

I can PM you a control diagram of the MKIV system if you'd like, and there are numerous writeups on its operation at www.mkiv.com

John

 

[R-Jay]

Actually, JDM TT supra's are the same as the US ones except that there is no evident flat spot... then again, you guys get slightly larger injectors (550), and steel wheeled turbo's, while we get smaller injectors (440) and slightly smaller (exhaust wheel) ceramic wheeled turbo's....

the smaller size makes spool instant off idle and there is no flat spot (none that i've ever felt in a stock JDM tt at least).

IMO a sequential twin turbo setup would be beneficial if you used 2 different sized turbo's. The first would be smaller to reduce lag time off idle, and the second would be for mid-top end power.... a combo like a gt2840 as the first and a gt42r as the second would see you have instant (practically) response with over 1200hp capability (depending on the gt42 trim).... there would be a noticable transfer point when the second turbo kicks in, but would be alot smoother than just one big single....

 

[cribbj]

Not to turn this into a Supra thread, but I'm curious which 2JZ-GTE came with twin turbos, but setup in a true parallel configuration? We have been told it was the JDM model, but never having seen one, I'll stand corrected if you owned one and confirm that it had the sequential system.

John

 

[skid]

I greatly admire what you are trying to do, however is low down torque really that important to you?

I'm going to be running in a lighter car and a manual box and best driving will always be between 3000 and 6000 rpm, nicely in a big single, or equal twin turbo systems effective rev range.

If low down torque really is required why not try a supercharger/TT mix as did Ferrari with the amazing F40? I know we have seen recent pics on here of an Eaton and a turbine (turbo or centrifugal blower???) which had a mixed response, but a straight forward TT system blowing into a plenum as an Eaton or Whipple is loosing boost would be amazing!

Has any one the know how on how to effectively clutch off a SC and manage SC and Turbo boost into the same plenum allowing them to work together closing off the lower pressured source and opening the higher accordingly at what ever rpm???
M

 

[R-Jay]

cribbj, apparently, all 2jzgte's came with twin sequential turbo setups.... this includes the USDM, JDM, and EDM supra's, and the Aristo v300 (GS300)...

i know that the 1jzgte ran twin ct12a turbo's in parallel (2jz ran ct12b's for anyone curious)... maybe that's what you've heard.

Skid, as for switching between sc/turbo's at certain rpm, the electric clutch setup is common in parts such as ac compressors and thermo clutch fans.... to control, any ecu/piggyback that has auxilary outputs matched to revs/afm signal can be used.....

the hardware is readily avilable, it just takes abit of work to set up... not terribly difficult i don't think.

Tan.

 

[turboandrew]

Nice project. I would not go with different sized turbos unless you did them in a compund fashion (one feeding into another). I have never seen two different size turbos on a facotry sequential system, and I am sure there's a good reason why. There's no point in using a second larger turbo when you can have both (same, medium sized) turbos running together at high rpms, flowing just as much, if not more air then a single large turbo. I would study very carefully the sequential systems on the RX7 and the Supra. They have some similar, some different techniques.

I was going to do something like this on the 2JZGTE with aftermarket turbos -HKS 2835R turbos. I eventually gave up, as making an efficient turbo header was almost impossible. It sounds like the 1UZ would be a little easier to do this because you have a lot of room up front.

All that being said, I would still not recommend going this route, as I have never seen a sequential system, which runs high boost, not have some sort of awkward transition persion bewteen single and twin turbo operation. Low boost, yes, you should be fine, but then you might as well go with a 60-1 turbo and call it a day. If you want boost all over the rpm range, I would go with a compund setup with a blower and turbo like you already have. You can then keep your existing header, and all you need is something like an eaton to get you low rpm boost.

 

[Lextreme II]

I am not sure if you guys have the same picture in your mind and i am not sure how the supra and rx-7 system work. As for one large and one small turbo. I assume u guys are talking about turbo #1 goes on, than the second turbo goes on. While the second turbo goes on, what about the first? My setup when at low boost, only one turbo will be working and at high boost, two turbos work together.

The turbo of choice would be GT30R (.60 A/R). Each can provide about 500 hp. This system only run one GT30R at low to mid end and both turbos at mid to high end. I need to do some drawing so we can have the same wave length.

 

[skid]

I need to do some drawing so we can have the same wave length.

Get the crayons out Dave!

 

[cribbj]

i know that the 1jzgte ran twin ct12a turbo's in parallel (2jz ran ct12b's for anyone curious)... maybe that's what you've heard.

That was it Van, thanks ; my memory just isn't what it used to be.

John

 

[Lextreme II]

Here is a picture of the SSTT. Thanks to Cribbj (John) for the Supra Sequential Twin Turbo drawing. The below picture is a modified from Cribbj hard work.

Thanks John.

 

[SCV8]

Wouldn't a torque convertor get you out of the flat spot and allow you to run the turbos synchronised/together/normal?
The system sounds complicated to dial in and get the wastegates to repeat exactly the same each time you run; sounds like it would be tempermental to try and tune.

 

[1youZee]

if your smaller turbo's wastegate opens a 8psi will it hurt itself when it's big brother hits 8+ psi, like around 25. won't it try to force air backward through the small one. if your turbo's are going to work in conjunction with each other they would have to both be making 25 psi, unless you completely shut off the incoming air to the smaller one.

as far as the exhaust goes, i think if you route all the exhaust through one, then take all the exahust coming out of it, including wastegate eaxhaust, into the second it would have the best affect. This is how Sequentila Twin setups work on diesels. but they do the same (kinda) with the intake and are capable of 50+ psi. -that's a lot.

i think running 100% through both, one after the other, at all RPMs and putting a valve of some sort to "switch" between the two compressor housings may work and not be to tempremental to tune. hmmm.. except for the twin intakes to each turbo... definately an interesting project.

 

[skid]

... definately an interesting project.

..... but a sh*t load or weight in excessive plumbing. I've gathereed you're running auto now, so surely it would be more effective to run a normal TT set up and work the power band in with the gear box settings?

I know you want to experiment but it is a lot of work in a complicated set up that could end up working aagianst you? I admire your balls for fronting up on the challenge though!

M

 

[R-Jay]

That was it Van, thanks ; my memory just isn't what it used to be.

John

John, the name's Tan, hehaha... Andrew, when i suggested different sized turbo's i was thinking about it in a compound system... wasn't too clear, sorry.

Now don't you wonder why none of the big supra or rotary shops do this? it's damn hard is why... Especially if you're using 2 externally gated turbo's, that would make manifolding a nightmare. That is why i suggested 2 different sized turbo's... at the least, the first should be internally gated... garrett have some mid sized internally gated turbo's (gt30, possibly larger)... then the secondary can be as large as you want and run an external gate... this would make the total compound package easier to fabricate...

 

[Lextreme II]

Here are the three prototypes: