I wonder if it would be possible to exchange the stock cats for hi-flow aftermarket cats and would this address the issues presented here....

 

I think race cats would address it a little, but as far as an even comparison, I think a SC will make power sooner than a turbo. Not saying that a SC is more powerful, just that a SC would have a jump start on the turbo just because of the way the extracts power from the engine, and the turbo waits on the engine to process the exhaust in order to spool. IMHO

Lee

 

Get High-Flow cats and it will spool faster. Or get them out completely, less back pressure is better.

 

I hope I don't step on any toes here. I know a little about turbochargers.
The poistive displacement blowers will have more initial torque than a properly designed turbo. As soon as they're turning, they're compressing air. Turbos obviously take longer.
Centrifugal blowers (Paxton, Vortech, etc) make boost dependant upon rpm. At 3000 rpm you get 3 psi, 4500 rpm gives you 5 psi, 6000 rpm gives you 7 psi, etc.
A well tuned turbo setup will always give more power than a blower making the same boost. The parasitic drag on the engine is substantially lower.

Judging by the dyno chart, it looks like this kit has fallen into the same trap that caught so many Supras. The turbos were laid out for top end power and have greatly sacraficed mid range torque.
If slightly smaller turbines were used, you'd see a significant increase is usable power due to higher boost levels at lower rpm.
If you can get full boost (11 psi) in by 3500 rpm, the mid range power would make the car much more fun to drive. That's why you see so many 600 to 700 Supras running 11 second quarters instead of the 10s or 9s that their power suggests. They simply have no appreciable power below 4500 rpm.
Peak power is nice but it's the area under the power curve that makes a car quick and drivable.
Someone else hit on a valid point. Have you tried disabling the VVTI to see how well the engine responds in the upper rpm? The torque falls rapidly after peak but power isn't hit quite as hard. This tells me that either the cam timing is fighting the boost or your'e running dangerously lean up there. The graph doesn't jump around too badly so I'm a wee bit hesitant to say that it's only fuel related.
A better flowing exhaust would pay great dividends in power. The best exhaust is no exhaust but that's not very practical on a Lexus.
When building my hot rod, I kept the turbines relatively small and used a somewhat low speed compressor to give good, efficient mid range boost. As a result, I have 8 psi of boost by 2800 rpm and 17 psi at 3400. The resulting power is impressive. A small increase in throttle responds with a nice fat torque increase. The price I pay is a bit lower power at engine speeds above 5000 rpm but you're only talking about 20-30 hp (5% of peak power).

All in all, it's an impressive setup that will surely lead to bigger and better things.
If you can bring up the torque between 3200 and 4000 rpm it would take a team of horses to pull the smile off your face.

Nice job and keep us informed on the progress. We all know that there's no such thing as too much boost.

 

You hit the nail on the head. Great response, this is why I got T61 turbo with .58 AR not the T78 with .80 AR for my supra. Bigger doesn’t always mean better.

 

My little 440 (7.2 liter) is running on hybrids. I've got T04 compressors with 60-1 wheels and T3 Stage III .82 A/R turbines with Stage III wheels. The wastegates are Tial 35 mm units. Some say they're on the small side but I haven't had any issues with them in the 20 months I've run 'em.

Here's a couple quickie (old) shots:



I've got an old, outdated page but it's still full of info.

http://www.pentastarpower.com/feets/newpage.html

 

Wow, 60-1 is smaller than mine, with 440 (7.2 liter) you could run 2 T78's. What do you put down with this thing. I mean each of them are good for about 400rwhp?

 

I dunno how much it's putting down. Last time I dynoed it was in January. It was dialed in at 8 psi and the el-cheapo no-name rear tires let go every time we got over 560 lb/ft of torque. That was right at 3600 rpm.
I don't have a cage in the car so full blast drag runs are out of the question. There's also the issue of 4 wheel drum brakes. You only get one good stop from 100+ mph and then you've got to let 'em cool off.
The dyno software says that my runs of 17 psi are kicking out something between 680 and 700 hp but I don't have any times or real world numbers to back that up. There's nothing special in the engine except my custom gound cam and it's kinda small. I even used bone-stock heads to keep the port velocity up to increase throttle response at cruise rpm. I rely upon big block torque multiplied by boost to get me down the road.

This is a street car. I've driven from Dallas to Houston, Austin, Oklahoma City, Louisiana, and several other places on pump gas. It gets 17 mpg if I behave myself.

Major upgrades are in the works. I've got the front disc brakes and the rears are in transit to me now. I've also gathered everything excpet a few sensors and a throttle body for my EFI system. The 85 lb injectors are gonna be fun.

 

this thread is really good! i am trying to think of ways to help tune the valvetrain but its really hard because VVT-i is so advanced. Also since the V8 has 4 cams overal it could make it very expensive and the tuning would have to be perfectly even to have equal power on both banks.

i think a high flow downpipe / cat / 80mm japanese exhaust for the v300 would make a large different in spool times just because the turbos dont have to push as hard to start spinng.. basically shift your power curve over 500rpm or so to the left.

Have you guys tooled with the ignition yet? i know that an IS300 was using the HKS direct power ignition or whatever, so it does work on the advanced coil-pack ignition systems that we have, im sure that would yeild a large gain.

overall i am impressed with the system and you must be amazed to have the ONLY TWIN TURBO GS4 in the world.. that must feel awsome. Although soon there will be two of you hehe

please post more dynos once the exhaust has been freed up and / or the valve train opened up! are the heads ported and polished?

you've gone this far why not all out thats the way i see it oh and, how bout a Blitz Power Meter i-D to match your Boost controller!!

 

May I ask how old you are?

 

im 16.. did i say something inappropriate? im sorry if i have repeated what was already said.

by the way i love your supra

 

No you didn't say anything wrong. But it does look like you have a lot of knowledge about this subject at such a young age.

P.S. I watched some of your videos and have to correct you on the G force testing. You suppose to drive in circle to see what you can pull. Also you suppose to measure the distance from the middle. Usually it's 200 and 300 feet circle. You keep accelerating till the car starts loosing traction and starts to over steer. Someone correct me if I'm wrong.

 

I have the Power Meter with the Boost Controller. I am going to set up the boost for different mphs, so that I can get the most out of those turbos. I know that my exhaust (Borla) is probably restricting my optimial power, but again, I am not trying to break any HP records! I also have to pass emission too!! lol

This thread IS getting very informative!!!! Thanks fellas!

 

Isn't that for mustangs? I have seen nice exhausts for the gs in Japan, maybe you should look into it.

 

This subject can literally fill text books.

Turbos and centrifugal superchargers share the same type of compressor, dynamic. Below a certain rpm these comressors do not make any boost. It doesn’t matter if they are belt driven or exhaust driven they must reach a certain speed before compression occurs.

If belt driven, these compressors are completely dependent on engine speed to reach their boost threshold and then have a fixed ratio between engine speed and compressor speed. Depending on the amount of step up between engine speed and compressor speed (pulley sizing and internal head unit gearing) and the relative flow ability of the compressor vs the engines ability to flow… boost can be designed to begin at a VERY low rpm. This is done by using a drive pulley sized to spin the compressor very fast at low rpm. The problem is at high rpm the boost will be too high. This high speed also wears out the bearings and drive gears much faster. Restrictions and or boost bleeds can be used to prevent overboosting but the compressor speed is still very high and efficiency suffers.

Exhaust driven compressors don’t have the limitations of the belt drive. They use exhaust energy and can be operated at variable speeds and boost vs the engine speed. By using a more restrictive turbine housing the compressor can make boost virtually from 1000rpm (or less). This is rarely done as power is rarely wanted at such low rpm and the restriction hurts high rpm exhaust flow and reduces max power. Most factory turbo engines make boost by 2000rpm and reach peak boost by 3000rpm. The boost curve is dependent on component sizing and system flow capacities.

While it is possible to make boost at a lower rpm with a belt drive vs exhaust drive… this rarely happens. By nature the exhaust drive responds to exhaust flow and engine load.

Here is a fairly normal torque and power curve for turbocharged street engine:

Single turbo Chevy LS1 V8 at 4psi boost.
http://www.laker.net/magnus/tta/ttadyno.jpg