Hypothetical TT vs T question.

[FST4RD]

Been thinking about this and was wondering...

If you took a BG5 Wagon, TT, manual, completely factory and say 100k on board.

Also take a completely factory BP Wagon, turbo, manual, completely factory and also 100k on board.

They both had same gearbox and diff ratios and motor condition.

If you were to put them both in 4th gear, driving along at 1000rpm around 25kmph and then put your foot flat to the floor, which is going to hit redline first?

I know with my BG5 Wagon the boost starts building around 1100rpm, builds really quick, hits secondary and goes onto higher revs pretty quick.

I\'ve not driven a BP before, so would the turbo lag be such that by the time it got a wriggle on that the TT would be gone?

[Drunkenmonkey]

The twin scroll turbos come on smooth and early you can barely feel it when driving. Would be an interesting comparison

[Marky]

While your turbo in the BG might be making "some" boost under 2 grand, it\'s still not doing anything productive (boost pressure does not equal power made) - at switchover time most TT\'s in factory trim are lucky to be making 80-90kw @ wheels (this is at 4500ish) where most single T motors are getting up to 80% or so of peak power at that point - under 3k rpm the difference would be negligible between both cars regardless of how much psi is being pushed through

The single turbo one might take maybe 500rpm more to make the same PSI, but then once it is, it will proceed to make more power the whole way up, to then peak at a lower RPM than the twin turbo, meaning it would build speed faster

The TT peak torque and power are both upwards of 6k rpm - they are quick if you\'re rowing gears and keeping it on the boil, however in a roll-on scenario they fall over bigtime in the midrange (as we all are familiar with) and that\'s where it all goes wrong

Short answer - while it might make a touch more boost a tiny bit sooner, it will be missing out to the tune of a good 30-oddkW until the secondary wakes up, during which time the BP would be pulling ahead happily

[Joker]

4th gear redline in a BG? need to remove speed cut 1st

THEN it still wont go anywhere at 25kph, thats a 1st gear speed, good luck

[FST4RD]

 JoKer said:

4th gear redline in a BG? need to remove speed cut 1st

THEN it still wont go anywhere at 25kph, thats a 1st gear speed, good luck

I have a BG5 Wagon. Completely factory, no motor mods at all bar a boost gauge and no speed cut. It will easily pull from 1000rpm in 4th. The primary turbo starts building boost immediately and it will go on to redline pretty quick. Tried it on a private road, so know there\'s no speed cut

[Marky]

This is the first couple of graphs I could find which show comparable peak figures - (what you\'re looking at is the massive difference in power between them at around 3-5 thousand - talking 80-100hp difference at some points)

TT graph for ~200kw @ motor -

And single T graph for the same - (it\'s a forester... but anyway)

Same peak figure, single T wakes up that much faster it\'d be getting mucho ahead-o before the early model has a chance to even start spooling the secondary

Same theory as say a vtec vs a big v8 - both might make say 150kW @ wheels, but the difference in when torque and power is available means that in a roll-on race the bigger motor always pulls ahead (weight & gearing being equal) - and if the power & weight is equal then it doesn\'t matter how much of a top end rush one or the other has, first in wins and the other one is playing catch up

For what it\'s worth jesus yours sounds like it wakes up the primary fast

[FST4RD]

 Marky said:

This is the first couple of graphs I could below shows comparable peak figures - (what you\'re looking at is the massive difference in power between them at around 3-5 thousand - talking 80-100hp difference at some points)

TT graph for ~200kw @ motor -

http://i7.photobucket.com/albums/y262/80XXR/Forester2_001.jpg

Same peak figure, single T wakes up that much faster it\'d be getting mucho ahead-o before the early model has a chance to even start spooling the secondary

Same theory as say a vtec vs a big v8 - both might make say 150kW @ wheels, but the difference in when torque and power is available means that in a roll-on race the bigger motor always pulls ahead (weight & gearing being equal) - and if the power & weight is equal then it doesn\'t matter how much of a top end rush one or the other has, first in wins and the other one is playing catch up

For what it\'s worth jesus yours sounds like it wakes up the primary fast

Yeah it seems too. Just been out in it again before and tried it. Definitely starts to build boost between 1000-1100rpm and pull quite hard. The exhaust has been replaced from the cat back as well due to failure of original exhaust, but nothing special, just press bends etc

So on a rolling start say both in 3rd gear at enough speed so the TT is above vod the single turbo would still have it all over the TT?' alt='>So on a rolling start say both in 3rd gear at enough speed so the TT is above vod the single turbo would still have it all over the TT?'>

[Marky]

Well if both cars are making the same power / torque and have same weight & gearing in theory they\'d be identical, the 10hp difference or so up top would be hard to pick up the difference on the road. In your example the split second quicker spool up for the single t motor vs the twin waking up would probably equal things out anyway

The TTs do best at higher speed when they can be spooled up and make the most of the high rpm power peak etc, but really they\'d be pretty much equal. To be blunt there\'s no advantage the tts have over anything single - they can be fiddled to equal it but you\'re always starting from a handicap

To be fair they do perform well up top - I remember thorpys stock ish legacy overtaking my 12 sec vr4 at "open road speeds - but end of the day its still a simple equation of power vs weight and under 5k the early cars have lots of one and not much of the other

[B4 2000]

from very low rpm, id guess 4th gen would be quicker (max torque 343nm @ 2400RPM)

from higher rpm, then TT might have the advantage (max torque 343nm @ 5000RPM) < 3rd gen legacy -BE/BH-

[FST4RD]

Nice, it is a pity the TT setup in the legacy doesn\'t work as well as the GTR or Supra setup.

Although there\'s nothing like putting your foot down in 2nd, the primary spooling up instantly, then vod, then the secondary kicking in and taking it right up to red line. The noise of the secondary, the kick of the secondary... To be honest I had thought about going to single, but I do enjoy the TT.

[Joker]

same : had mine 10 years

[FST4RD]

I am assuming that to get it to run more like a GTR or Supra setup you would need to run 1 turbo off each bank of cylinders, both fed by the same afm, running into a 2-1 intercooler and then into the intake manifold?

You would also assumably need 2 turbos the same size?

I would also assume that the factory ecu would have to pack its bags and hit the old dusty trail?

[telemekas]

"Nice, it is a pity the TT setup in the legacy doesn\'t work as well as the GTR or Supra setup."

The supra sequential TT system has no prespool intake dumping, like the Subaru sequential TT system. Plus the inherent delay with the DPS--->IACV opening which this creates.

Replace the IACV with a passive valve and remove the SPRV dumping set up.

[Jord]

If the TT came fitted to EJ25 then it would be a different story.. Both a supra and GTR have a big displacement advantage.

[94 Leone]

 Jord said:

If the TT came fitted to EJ25 then it would be a different story.. Both a supra and GTR have a big displacement advantage.

not to mention run parallel twin turbo, rather than sequential bi-turbo.

Different system for different intended applications; the Subaru sequential bi-turbo systems were designed to be played with on tight roads where you might not have the high RPM ; so more boost down low. vs parallel twin turbo where it\'s like no boost...."ZOMFG I CAN\'T FEEL MY FACE!"

It depends what you want as to what you will perceive to work better or not.

[Marky]

 94 Leone']

[quote name='Jord said:

If the TT came fitted to EJ25 then it would be a different story.. Both a supra and GTR have a big displacement advantage.

/quote]not to mention run parallel twin turbo, rather than sequential bi-turbo.

Different system for different intended applications; the Subaru sequential bi-turbo systems were designed to be played with on tight roads where you might not have the high RPM ; so more boost down low. vs parallel twin turbo where it\'s like no boost...."ZOMFG I CAN\'T FEEL MY FACE!"

It depends what you want as to what you will perceive to work better or not.

To be honest I\'d say it was more of a marketing tool than anything, and joe bloggs who doesnt know cars can get a real kick out of feeling the second turbo kick in - a tight winding road is where the legacy TT system is at it\'s worst to be fair

Twin vs single is an argument which never stops with regards to supra / gtr type applications - it used to be that twin gave the quicker spool due to less inertia waking up two little huffers vs one large one so you chose response or top end

These days turbo tech has advanced so much it\'s gone out the window a bit and a properly sized single will walk all of the old gt2860 (or what have you) combos people ran, ditto for sequential applications being worked *properly* now by the like of the BMW turbo motors and a lot of diesel applications etc

In some applications it just makes sense to have parallel twins - say the likes of a V6 (300zx, legnum/vr4, things like that) where the packaging demands it. But even then - it\'s a marketing thing I suppose. The 300Z would have been better off with an RB, the legnum needed a 2.5 to be in the "next bracket up" compared to a 2L, when a 4G63 makes the same power & torque anyway

On the other hand they\'re probably the cheapest way you\'ll get a 300hp import these days so you takes what you gets

[kamineko]

quality post

[Divine]

This is an interesting thread, will keep watching for moar stats