Turbo`s again ??

[zentac]

Ok, Ive got an idea to run a small turbo on the back bank GT15 and a larger one on the front bank GT17 or GT20, can any forsee and problems with this? I may have to run two boost controllers.

[valmes]

Why can't you just put 2 GT17 instead?

[Legnum Boy]

I did read somewhere that different size turbos, on different banks is a dodgy idea. So called sequential set ups on the Supra doesnt involve different size turbos, just a valve that stops one turbo from spooling up until later in the rev range. The two turbos are exactly the same size.

Would there not be a problem with the smaller turbo spinning too fast while trying to keep up with the bigger turbo? .... or am I thinking poo poo again..

[zentac]

I did read somewhere that different size turbos, on different banks is a dodgy idea. So called sequential set ups on the Supra doesnt involve different size turbos, just a valve that stops one turbo from spooling up until later in the rev range. The two turbos are exactly the same size.

Would there not be a problem with the smaller turbo spinning too fast while trying to keep up with the bigger turbo? .... or am I thinking poo poo again..

Yeah thats king of the conclusion Im comming to, looks like I will be going to 2 x GT15`s or 2 x GT17`s which ever I can get my hands on first.

[Nick Mann]

It would surely cause a pressure imbalance between the two banks if it was set up like that? Sounds like a major headache!

[ako]

I'd say it'd be VERY unhealthy - there would be different loads on each bank wouldn't there?

[Roadrunner]

So called sequential set ups on the Supra doesnt involve different size turbos, just a valve that stops one turbo from spooling up until later in the rev range. The two turbos are exactly the same size.

The turbos on my Legacy RS-B were definitely different sizes - the low pressure turbo was physically smaller than the high pressure one.

[Legnum Boy]

The turbos on my Legacy RS-B were definitely different sizes - the low pressure turbo was physically smaller than the high pressure one.

How were these positioned on the engine? The RS-B was a boxer set up, no?
Was each turbo fed by a different bank, or were both banks joined together before the turbos which were then attached to the same manifold and controlled by complex exhaust valves like the older Porsche set ups?



Enough questions....

The supra guys, with same size sequential turbos, either un-sequentiate (is that even a word?) their twin set up to non-sequential (like ours) for better response or swap to single big turbo for more power.
The RX7 guys, that have a small/big sequential set up just ditch it for the big single, full stop.

I personally think that bigger twins will involve just as much re-modding the engine bay layout, as the single big set up. I also think that bigger twins will impact on the total output due to the smallish displacement of each bank. (probably thinking and typing $hite again...)

FTOLTD was on to something with his last car....

[valmes]

The turbos on my Legacy RS-B were definitely different sizes - the low pressure turbo was physically smaller than the high pressure one.

But they were not run off the different banks... since there are none (engine is inline 4 on Legacy). One exhaust manifold with different set of "routes" to get spinning either of turbos...

[AllBeItMine]

well i see two problems.

without a valve, the smaller turbo would pressurize the whole system first, meaning the bigger turbo would need to fight against the pressure before spooling. worst case it could end blowing through the turbo and out your airfilter.

secondly, the different back pressures would cause an inbalance in the engine, the smaller turbo would have higher back pressures up top which can't be good for the harmonics...

[Roadrunner]

But they were not run off the different banks... since there are none (engine is inline 4 on Legacy)

Er, no ... Legacy uses the same flat-4 Boxer as the Impreza. I don't think Subaru have ever produced an inline engine - even the SVX was a flat-6.

[Roadrunner]

How were these positioned on the engine? The RS-B was a boxer set up, no? Was each turbo fed by a different bank, or were both banks joined together before the turbos which were then attached to the same manifold and controlled by complex exhaust valves like the older Porsche set ups?

All is explained below

Reproduced from AutoSpeed, anticipating their permission

[valmes]

Er, no ... Legacy uses the same flat-4 Boxer as the Impreza. I don't think Subaru have ever produced an inline engine - even the SVX was a flat-6.

Oooppps, sorry.... you are right! Really, what was I thinking of ... they do come in "boxers" !!!

[Legnum Boy]

All is explained below

Reproduced from AutoSpeed, anticipating their permission

Complex manifold and valves as I suspected.... not disimmilar to the way the supras turbos are set up (except for the massive manifold)

I see that the slight difference in size is only the compresser wheel.

[ako]

You're right. The legacy turbos are in fact identical in size - just different compressor wheel trims. And one hell of a complicated sequentialling setup... And an ugly 1500rpm powerband.

I just dont like TT legacys.

But anyway - the way I've seen all sequentialling setups done is always bloody tricky - I think on the RX7's it uses some of the feed from the primary's wastegate or something? I dunno. But they ditch it for a big single to save trouble anyway.

Sequential = waste of time

Simultaneous = Drives like a single turbo of comparable flow rate

Big single= You'll never go back to anything else

[Roadrunner]

Big single= You'll never go back to anything else

But you've time to go and make yourself a cup of tea during the lag while it spools up ...

[Legnum Boy]

But you've time to go and make yourself a cup of tea during the lag while it spools up ...

This could be reduced using a big shot of NOS.....

[ako]

But you've time to go and make yourself a cup of tea during the lag while it spools up ...

Thats just a misconception...

Put it this way. You want to go fast - in any car, would you just floor it at 3000rpm - or would you drop back a gear or two?

I thought so

I've driven a few cars with "large" setups - i.e 600cfm flow on 2L engines, bout a 4000 - 4500 spool up, believe me, once you try it, you'll wonder why you were so cynical in the first place. That kick in the back is awesome - and from a standing start, the lag isn't an issue, if the other guy pulls a car length or so through first - you MORE than make up for it in the next 2 or 3 gears.

[Roadrunner]

Put it this way. You want to go fast - in any car, would you just floor it at 3000rpm - or would you drop back a gear or two?

Yeah, but I don't like to go flat out everywhere, and the lag in a big single turbo setup is a pain in the ass if all you want to do is pass someone quickly without scaring the sh!t out of him. I appreciate (and note from your signature that you live your life a quarter mile at a time) that some people see outright acceleration as the only thing that matters but, for me, day-to-day driveability is much more important and a big single turbo, with its attendant lag, doesn't provide that.

[Smokinmasta2]

Here here m8 - i too like my cars driveable (but mainly for the cr*p roads that i have to travel on EVERY day!) with plenty of low and mid range - where really matters on a daily driver.
Torque is the thing i want more of - BHP is mainly pub 'torque' boasting..........he says, waiting to get flamed from everyone going down the BHP route............


Smokin...................