Since you have the big cams and heads I'd go with the smaller turbos to start with. There might be unforseen big problems if you try to run 9000 RPM with high torque output. Make sure nothing is going to break with the "smaller" turbos first.

 

i agree, there has been so much effort put into this car that i would think there is a more optimal turbo setup. given the two choices, i would opt for the larger turbos. in a sense, to take the smaller turbos and run out of the compressor's efficiency range near the top end is not taking full advantage of the engine's potential, and all the effort which went into it to make it rev safely at such high speeds. there has been so much work which distinguishes this motor from those of other 996tt's, that it would seem kind of pointless to not utilize the full rpm band. but, the motor is staggering nonetheless - it's a win-win situation. if the smaller turbos are used, put things into perspective, to be able to produce such power with such minimal lag and boost is amazing.

 

It's interesting that this is always the critical issue to decide; quick respons or high power. Volkswagen has announced that most of their future models will use supercharger/turbocharger combo. The supercharger will provide power lower in the curve and the turbo will spool up in time to give the power up high. I know you can't add a supercharger to your engine right now so it's a tough decision.


What is really odd to me and maybe you can shed some light is why is this decision being made now? Trhoughout the last couple of years you've mentioned that you are using a hybrid turbo that will spool up faster while still providing top end power. Most of the work done in the past year appears to have been to make the engine capable of revving very high and handling the 1200+hp power. Now after all that work, a couple of weeks before the end, the question is being asked of what type of turbo you want to go with. Why is Rob just now suggesting that you go with the smaller turbo. It's like getting a real estate broker who helps you buy a gorgeous lot in Miami and then coordinates 3 years of building the perfect house. Finally, a few days before moving in the two of you start talking about where you want to live, to which you reply - definitely someplace cold, I don't like warm climates.

Whatever you decide, I really appreciate all the work you and Rob have put forth and your willingnes to share the journey. I've followed this from funcars to rennlist to here and I've learned a ton. Thanks, good luck with whatever the choice.

 

carnut,

Rob hasn't changed ............ I have. I was the one pushing for the added power. Rob says 900 rwhp with quick response throughout the bandwidth is a better car. I am now tending to agree with him.

As for the build for 1200 to 1400 hp. It will always be there and ready to tap simply by changing turbo's, headers and re tune.

On the flip side a 900 rwhp bullet proof motor with good longevity and almost instant power on tap throughout the whole rpm range isn't all bad. Rob says these turbo's will spin well through 8100 rpm's.

 

twin charging has been in the tuning industry for a loong time now, an example of this si the first gen., mr2 superchraged.. hks came out with a turbo kit for twinchrgaing it.. s/c for low turbo for top.. but it was not generating the expected hp and performance that they wanted.. hoad problems wit he sequencing of the two diff. systems...too much avirables that can easily lead to problems..


i cant rememberwho said it but someone suggested sequential type turbo system, i.e. small turbo for low end and big turbo for top.. it is hard to do it with the flat six motor... since there are 3 exhaust ports on both side.. the placement of the turbos will be hard especially since the excess air generated by the smaller turbo when it"spins out" must go to the big turbo to start it's spool up.. also the tuning of this type of system will be a nightmare...


if i can give my opinion cjv, from reading your thread throughout the years it seems to me that the better fit would be the type A version.. it wil be generatin 900hp but at a lower rpm which is better at the type of driving you will be doing (i.e canyon / mountain) a big *** turbo'd car is hard to control on mountain roads bec. of the unexpected rush of power when the turbo kicks in.. " i have almost lost it taking a turn in my old car bec,. the to4e kicked in during mid turn" the big turbo is suited for high speed runs... and top end power...

i hope you finish this bad boy .. and i wish that one day i may actually see this marvel of a car in person...
i have a question.

the hot sid ethat you are using in the version a is that the only one available? maybe u can custom make a set of impellers with a diff size so u can still have the manageablility of low end power and get some respectable top end hp?maybe a slightly bigger impeller than the one being used in version a.

sorry if im throwing more variables toyour quest of speed...

hope to see it on the road soon

 

if you are interested in multistage-turbo-setups:

mercedes developed an experimental car with three turbos. it is a diesel with v6 engine and has two small turbos for low rpm and one big turbo for high rpm.

it is the same system as bmw uses in its 535d, but due to its v6 enging layout, they were not able to copy bmw's system with just two turbos.

but i think i am getting a little ot ;-)

 

You know the more I think about it though.. I mean with your larger displacement and better heads, you'll have considerably less lag than a car like mine with 3.6L etc.. Come drive mine (I'me getting some new headers) and see what you think... Even though it's a tip you'll at least get a feel for it Craig will tell you the same thing, there's more lag with these guys but man when they go... the GOOOO.

 

sharkster,

I plan to take you up on the offer. I have no doubt your car goes when those turbo's come on boost. My question is, you enter a turn with as much speed as your brakes will handle. Your rpm's drop as your brakes scrub the power down. You push the accelerator coming out of the turn ............. what response do you have.

I don't want a car that can pass in the straights and gets clobbered in the turns. I would rather have a car that dominates in the turns enough to fend off on the straights.

 

Hehe no I know what you mean.. I guess I drove my car around a bit yesterday and tested out your scenario (yes that was naughty)... Looking back at the shoot out too, during the practise session (when I had a MAF lol) the car posted the fastest mph down the straight but also the fastest lap When the MAF went and the drivers had no ABS or PSM they still managed a 3rd... Neither of them said the car lagged or anything... It had the largest turbos out there during the day since Todd's didn't run.

 

Chad,

IMHO this part of your post indicates that choice A is the better one.

Greg A

 

Greg,

I am leaning that way. I quizzed Rob regarding the specs of the 1995 GT2 hots and the Garrent compressor side. He didn't know exactly. He said the 24's hot side were machined and the compressor side was Garrets. Tial did the work so I asked him to call Tial and get the exact specs of housings and impellars for both turbo's. Will have more information soon.

 

Take your time and think about what you want and what you expect out of the car. Both turbos have their pluses and minuses and it's hard to choose between them. Can you re-gear again to take advantage of the large turbo's upper horsepower? What I meant was reducing the lag by beeing in a higher RPM band. I'm just brain storming here.

 

Information on turbo "A."

Garrett - GT3071R 700382-20
--------------------------------------------------------------------------------



* Ball bearing
* Oil & Water-cooled bearing system
* The GT3071R wastegated units are the highest-flowing ball-bearing turbocharger in our range employing the "T25"-style wastegated turbine housing
* Actuator not provided
* Turbine stage is outline interchangeable with GT2554R (471171-3), GT2560R (466541-1), GT2860RS (739548-1)
* Excellent for applications w/ packaging constraints
* Ideal for single turbo applications making up to 460 hp or twin-turbo applications up to 900 hp
* Compressor housing kit options available
Front:

Inlet
102.0 mm
Outlet:
50.8 mm
Side:

Oil Flange
Watercooled
Rear:
Wastegated

Inlet
T 25

Outlet:
5 Bolt
Stats:
GT3071R Compressor Turbine
Turbo CHRA Ind Exd Trim A/R Ind Exd Trim A/R
700382-20 700177-4 53.1mm 71.0mm 56 0.50 56.5mm 90 0.86
Housing Option Part # 756021-1 Compressor
Ind Exd Trim A/R
2.75 3.58 0.50
Compressor Map

Turbine Map

 

Turbo "B."

Garrett - GT3582R 714568-1
--------------------------------------------------------------------------------

Ball bearing
* Oil & Water-cooled bearing system
* High Performance BCI-18 Compressor and UHP Turbine
* Perfect for high horsepower, but responsive engines
* Works well as twins for large V-8 engines
* T3 turbine inlet flange and 4-bolt turbine outlet flange
* Turbine housing is cast from high-nickel "Ni-Resist" material for extreme applications


Front:
Inlet
103.61 mm ( 4 in )

Outlet:
63.5 mm ( 2.5 in )
Side:
Oil Flange
Watercooled
Rear:
Free Float
Inlet
T 3

Outlet:
5 Bolt
Stats:
GT3582R Compressor Turbine
Turbo CHRA Ind Exd Trim A/R Ind Exd Trim A/R
714568-1 706451-5 61.4mm 82.0mm 56 .70 68.mm 84 1.06
Compressor Map

Turbine Map

 

More complete information can be found at www.tialsport.com Then click onto "Products" and then "Turbochargers" and then "Garrett Turbochargers."

TiAL is the turbocharger that many of the tuners are currently using in their packages in one forum or another. This company was one of the secrets used a few years ago by Wilbur, Tyson and myself and their respective tuners. Since then many have learned about them and their use has become much more wide spread in the 996tt world.