Kevin

I didn't say accelerate the turbine wheel, NO.. The factory design does aid in keeping the RPM's higher than if one vents to atmosphere. It keeps the wheel speed higher in this design. And this feature reduces lag.

"You then shift your car, the turbine wheel is still turning, the bypass valves open directing the compressor side air back to compressor wheel, which actually keeps the rotating assy spining without drag from the engine RPM drop from the shift"

"For breif moments you can have you high boost pressure levels at the compressor wheel inlet. This pressure brief as it is aids in keeping the rotating assy moving."

" In this application the bleeding down is used to keep the rotating assy speed up.. "

The internal wastegate design can be mechanically aided to prevent it from opening prematurely.. If someone is concerned about it, you and put a elect-servo on the gate similar to large diesel applications. So you wouldn't have any backpressure opening the gate.. Where the internal wastegate shines and has a advantage over the external wastegate, is it's ability to quickly modulate the turbine wheel sooner and faster than a external gate. And many time due to design issues, the external wastegate is placed upstream of the turbocharger. The exhaust is vented to a given point. When the gate closes, the exhaust has to re-pressurize the piping from the gate to the turbine housing. This takes time, the time is often translated as "lag"

Geoffrey

I just checked some datalogging I have and shifting from 3rd to 4th gear full throttle, a single turbo turbo with external wastegate takes .06 seconds to recover full boost from the point the throttle is reapplied after the shift. I then checked a twin turbo 993 with your Stage 2 turbos, and it also takes .06 seconds to recover full boost from the point the throttle is reapplied after the shift. Even if you double or triple those numbers, I would not call that measurable lag and I would bet that you could not notice .1 seconds of lag. In fact, some of the paddle shifted N/A cars take .3-.5 seconds to fully recover torque during a shift.

Kevin

Motec system, single turbo, custom headers, basically a built race engine, vs a stock Motec engine with your programming.. And those are from your figures.. So, Porsche in its wisdom is going back to single turbocharged engines. They had the opportunity to put external wastegates on existing KKK turbochargers.. It is done for a purpose..

Rick DeMan

I agree the internal wastegates were done for a reason....but not because of faster recovery times or shorter wastegate piping. Just simplicity of design. External wastegates would also require thier own small cats as per the 965 turbo cars...

Air Kuul TT

Thanks guys, this is all very informative

Kevin

I have many other tech sheets from Borg Warner & KKK, IHI, and Garrett.. Here is a brief paragraph from Garretts Online tech section. I chose the Garrett site, since people might think that only BW or KKK might share these view..

"Internal Wastegated Turbocharger

A wastegated turbocharger includes an integral device to limit turbo boost pressure. This consists of a pneumatic actuator connected to a valve assembly mounted inside the turbo turbine housing. By connecting the pneumatic actuator to boost pressure the turbocharger is able to limit it's maximum boost output. The NET result is increased durability, "Quicker time to boost" and adjustability of boost."

TB993tt

You've said this about four times now - and whilst there may be a theoretical disadvantage, I can't see it affecting performance in actual use. Any "premature" opening (if it actually happens as you say) will have negligable effect since it is happening when the turbos have wound up and have no problem delivering the required boost.
IMO this (if it happens) is NOT a disadvantage and external W/G holds no benefit in this area, and from what Kevin says seems to have other disadvantages which make the internal layout superior.

Rick DeMan

Since this is a theoretical discussion, any "theoretical disadvantage" will be a disadvantage.

Geoffrey

I'm not debating internal vs external wastegate design, each has its uses and merit. I'm also not suggesting anyone replace the internal wastegates on a 993tt with external ones. The data shows that there really isn't a difference in lag during a shift between the two designs. However, as the turbocharger is building boost, the internal design does open prematurely, bleeding off exhaust pressure and therefore not building boost as quickly as it should or can with other designs. This is the same issue an external wastegate has without a controller and it has been well documented by others that adding a controller adds to the torque curve. I was only addressing the statements about cracking wastegates as imprving performance when they don't.

Jussi

Is this Stage 3 package ready yet? Could you tell more about it, like what kind of torques are expected? How much these cost? Should these be good for 520hp/700Nm levels when using 98 oct (RON)? Is this package "bolt-on" type, so it can be installed by customer?

pstoppani

Do you consider changing the rods and heads a bolt-on? Personally, I'd have a trusted mechanic do the work.

Acropora

The stage 2 is good for about 480 hp/650 nm and its bolt on. If you go 98 oct and cat bypasses, on a cool day, you probably get more. This winter, after the ECU got used to the cold air, acceleration has been great.
Anything more and you're looking at big bucks to get more performance as the engine needs to be rebuilt. If tracking the car, you'd go a lot faster spending the cash on suspension mods and driving lessons.

Kevin

Stage 3 is very close.. I am actually working on 3 engines configured for Stage 3.. It is not a bolt on system.. It will have new rods, stepped flame rings, camshafts, twin plugged heads, larger cats, clutch, and a 102mm option with welded heads.. Turbochargers will be "Very Special" There has also been recent developments into intercooler options.

My Stage 2 system does limit the torque output. Stage 3 will dish out level over 800Nm..

Jussi

Kevin
800Nm, sounds like you are buildning real monsters!
How their torque compare to RS-tuning cars below 4000 RPMs?
What do you estimate for cost that stage 3 with 102mm P/C options?
Are these using RS spec cams?

Kevin

JS since the introduction of Zero clearance options for turbochargers I can build more boost=torque sooner on any Apples to Apples engine project. The Stage 3 102mm option will be based on the K24 platform... One can call it a K24/26 but in reality the compressor wheel is larger.. The turbine housings will receive extensive porting to increase the velocity of airflow. There will be a K16 version of the the Stage 3 kit for those that do not want the extra cost of 102mm. Camshaft selection is not going to be a RS per se, but with more lift and less duration.. The exciting thing for me is the introduction of different maps for fuel grades. Street vs Race..

Email me for cost...