vf turbos

[rustyford84]

im looking at getting ither a vf 21 or vf 27 X2 in my legacy i have found some but was wanting to know if i can use 2 secondry turbos or if i need both primary and secondry as im wanting to set up a twin set up

[SilverSuby]

I may be wrong here I don't claim to be an expert but I'll give my input. The reason for the primary and secondary is the spooling similar to say a transmission. you don't run a car going slow at a high gears just like the turbo the bigger one spools later since its bigger. The smaller turbo is just to keep the boost up in the system so the thing doesn't lag like crazy unless you have a Vf 34 where its set to spool through the who shabang. Thats what I think is right, and if I am wrong someone will correct me and well will both learn something lol.
-Logan

[MonstarMotorsports]

Silver, your not far off by any means, but it depends on your set up.

Say your a v8. you run two turbos, but both are the same size. You dont want to spool one side of the motor faster than the other.
If your running a inline 6, and run a compound turbo set up, you run a smaller turbo and plumb it into the bigger turbo. the smaller turbos will spool quick and hard at lower rpms, but runs out of steam fast. Where the large turbo will make the big power numbers at the high rpms, but it takes for ever to spool. So basically the little turbo kicks in the power, and spools the bigger turbo faster, keeps the boost coming in lower and carries it all the way up. Super popular set up with cummins diesels.

now with the subaru motor, technically you can treat it like a v8 and run two of the same turbos for each side of the motor, or you can run it more in a compound set up, in which case you would want a smaller and a bigger.

[Telemekas]

im looking at getting ither a vf 21 or vf 27 X2 in my legacy i have found some but was wanting to know if i can use 2 secondry turbos or if i need both primary and secondry as im wanting to set up a twin set up
*Will this be for a parallel twin turbo set up?
*EJ2.0L or EJ2.5L engine?

[Reuben]

The smaller turbo is just to keep the boost up in the system so the thing doesn't lag like crazy.
-Logan


Nah, sorry, that's not how subaru TT's are!!! Most of the time they are actually the same size primary and secondary turbo. Nor do factory subies run a turbo per bank, but i don't think that's monstar was meaning.

Regardless, both you guy's should go have a read of this, I tried to make it easy to understand! But it's a bloody complex system that is a bastard of a thing to understand regardless. But the short version is the primary gets used as a single turbo for the first part of the rev range, then after a certain ECU controlled point, the exhaust valve opens up allowing the secondary to be used, and the two turbsos (which are the same size) then start working as a twin parallel. Both turbo's are TINY, but combined on parallel boost about as much as say, an ordinary ol VF24...

viewtopic.php?f=59&t=10991 (http://www.sl-i.net/FORUM/viewtopic.php?f=59&t=10991)


And as a parting shot, do not touch twin. It's about 100 times more effort, and expense, to achieve a final goal that is not as good as a twin scroll. Why do you think subaru dropped TT in favour of twin scrolls!!!

I know yamazaki disagrees with me, but he's running a bloody S401, which essentially perfected the TT system to the point of it being a work of art and pleasure to drive. It only took subaru close to a decade to get to that point, and even then, still dropped it in favour of twinscroll :P

[SilverSuby]

Like I said not an expert lol, but Monstar are you talking about a biturbo system? I'm still trying to learn about forced induction myself.
-Logan

[MonstarMotorsports]

Theres about half a dozen names people use to refer to it as. In my world its a called compound turbos when one smaller feeds into the larger.

As reuben said though, subaru TT's are a little different of a monster. I've never paid much attention to them, nor have any experience with them since they arent a US thing. Just saying with the way a subaru motor is set up, you have options to run different styles of TT set ups.

[lord flashheart]

If the twin scroll interests you you should chexk out the Variable geomety turbo. Vgt for short. I am very excited to see one on a gas engine.

[Cervantes]

Unless you have a TON of money to do it right, I would t recommend a twin funk setup.

[Mark in NZ]

Twin primarys, then you get twin wastegates - most secondary turbos (apart from the very first RS/GTB's 1993ish?) don't have a WG on the exhaust housing.

Run them on a stock TT manifold or make something to suit (sometimes syms parallel manifolds come up second hand)

Run them in parallel on a WRX ECU

You'll see full boost around mid 3k ish, I see full boost on a parallel converted std setup at approx 4k rpm depending on gear

And it will sound nothing like a subaru

This is treating as the same setup you see in a 300ZX / 3000GT etc, no reason it can't work if you want to be a bit different

The sequential setup is pretty average, not terrible different to that in an RX7 or supra (it is different... but ends up the same)

If the timing and sizing of everything is done right, it's a good system - the new BMW's run a sequential TRIPLE turbo for example

[rustyford84]

oh cool guys lots of help thanks im looking at a single vf25 atm im running a ej22 single cams (1 per side) goes hard with out the turbo but i like to be different dose anyone know if the exhaust manifolds are the same as twin cam as these motors dont come factory turbo?