Sequential Turbos... worth it?
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Joined: Apr 2003
Posts: 128
From: Maui, Hawaii
Car Info: 2004 WRX STi
Sequential Turbos... worth it?
I'm trying to find more info about squential turbo setups, and so far I've found very little, and what little I've found has been about RX-7s and Supras.
From what I have read on most sequential setups there is a rather large dip in power when switching from the primary turbo to the second. Is there any way to overcome/lessen that or is it a physical impossibility?
Secondly, how does a sequential setup react when you go from crusing at say 3000 rpm to WOT? Does the first turbo ever spool up or does it just start spooling the second turbo?
Sorry for the n00bish questions
From what I have read on most sequential setups there is a rather large dip in power when switching from the primary turbo to the second. Is there any way to overcome/lessen that or is it a physical impossibility?
Secondly, how does a sequential setup react when you go from crusing at say 3000 rpm to WOT? Does the first turbo ever spool up or does it just start spooling the second turbo?
Sorry for the n00bish questions
Guest
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It's pretty much pointless on a car with the kind of low end torque that a Subaru has. They have 600hp kits with single turbos available, that will have been much more thoroughly researched and tested than an experimental sequential set-up. But if you got $$ and time to blow, keep me updated, as I'd love to hear how it goes. Good luck.
7
7
Thread Starter
Registered User
Joined: Apr 2003
Posts: 128
From: Maui, Hawaii
Car Info: 2004 WRX STi
Well... I sure as hell don't have the money to blow right now... but in a year I'm planning to have a pretty large chunk of change stored away... but... yah never know... it's all just speculation.
The only problem is that... even if I can come up with the outlandish amount of cash... I'm in Hawaii and there are no good Scooby tuners out here.
What I'd like to do is this... I wanna do a FMIC, but I think getting rid of the TMIC is morally wrong to do...
So... I was thinking, what if I do both, rig the FMIC up to the second turbo and leave the TMIC for the first turbo. I don't even know if it would be physically possible to do with the piping and all... but... that's what I'm gonna be doing research on.
I talked to a friend of mine who's a Porsche mechanic and he said that a properly tuned sequential setup can be amazing. The primary turbo could be fully spooled around 1700rpm and transition over to the secondary turbo at around 4000rpm.
Granted, I didn't really get to talk to him for long and he's only one person... so... it might all just be buttkiss...
Somewhere else on the net I was reading that as long as you have the proper setup of "vacuum valves"(talking out my *** here, don't know yet) then the transition from one turbo to the next can be virtually transparent. Once again, this would take some serious tuning, which we are lacking out here.
So it's pretty much all a big pipe dream, but hey, doesn't hurt to dream.
P.S. If any of this ever comes to fruition, it will be on the 2.8Liter Short Block from I-Speed. Which will also take plenty of research in and of itself, I don't wanna demolish every aspect of my drivetrain the very first time I let the clutch out
The only problem is that... even if I can come up with the outlandish amount of cash... I'm in Hawaii and there are no good Scooby tuners out here.
What I'd like to do is this... I wanna do a FMIC, but I think getting rid of the TMIC is morally wrong to do...
So... I was thinking, what if I do both, rig the FMIC up to the second turbo and leave the TMIC for the first turbo. I don't even know if it would be physically possible to do with the piping and all... but... that's what I'm gonna be doing research on.I talked to a friend of mine who's a Porsche mechanic and he said that a properly tuned sequential setup can be amazing. The primary turbo could be fully spooled around 1700rpm and transition over to the secondary turbo at around 4000rpm.
Granted, I didn't really get to talk to him for long and he's only one person... so... it might all just be buttkiss...
Somewhere else on the net I was reading that as long as you have the proper setup of "vacuum valves"(talking out my *** here, don't know yet) then the transition from one turbo to the next can be virtually transparent. Once again, this would take some serious tuning, which we are lacking out here.
So it's pretty much all a big pipe dream, but hey, doesn't hurt to dream.
P.S. If any of this ever comes to fruition, it will be on the 2.8Liter Short Block from I-Speed. Which will also take plenty of research in and of itself, I don't wanna demolish every aspect of my drivetrain the very first time I let the clutch out
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From: Reno, NV
Car Info: 1993/2000/2001 GF4 mostly red
Originally posted by verc
all i know is that rx7 tt's hit full boost by 2500 rpms! now that's some major anti-lag!
all i know is that rx7 tt's hit full boost by 2500 rpms! now that's some major anti-lag!
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Just somthing to keep in mind. Simpler is always better. The more complicated setup you have, the more libel it is to break. And usually complicated stuff is expensive to replace. Just find your happy spot between torque and top end and enjoy your fast *** street car.
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Well I don't know if you know or not but
Subaru has had a sequential twin turbo for the last ten years.
The JDM Turbo Legacy has been in production since 1993.
The first series did about max 183kw (250hp) and the 2nd and third were good for 206kw (280hp)
The primary turbo was pumping out 240nm of Torque at 2000 rpm and peaked at 310-330nm at 5000 rpm. For comparision the latest WRX does about 300nm peak.
Sequential setups are great for daily driving, the feeling of good low down torque is great for just cruising around. Unlike a single turbo power is always on tap.
Here a little article about the Sti 401 the ultimate Twin Turbo Legacy.
http://homepages.ihug.co.nz/~1amiga/s401.htm
However Subaru never really mastered the setup unlike the Toyota Supra.
Interestingly for the new Turbo Legacy Subaru have turned their backs on the sequential twin in favour of a twin scroll turbo. Which does the job on a twin but with a single turbo. To keep it light (thus ensuring faster spoolup) the turbo is made out of titanium ~ strong as steel but half the weight sort of stuff.
Now it really does produce some low down torque putting out at 2400 rpm 343nm !
If u want to read about the new Turbo legacy hear are some links.
The version due for the US may not have the twin scroll as it'll probably have a version of the US Sti 2.5 lt engine which has better torque than a 2.0 lt due to size.
http://homepages.ihug.co.nz/~1amiga/gtspecbreview.htm
But if u want ultimate top end power a big single turbo is the way to go. But beware the lag probs.
I think however a twin scoll setup could be a possible compromise.
Subaru has had a sequential twin turbo for the last ten years.
The JDM Turbo Legacy has been in production since 1993.
The first series did about max 183kw (250hp) and the 2nd and third were good for 206kw (280hp)
The primary turbo was pumping out 240nm of Torque at 2000 rpm and peaked at 310-330nm at 5000 rpm. For comparision the latest WRX does about 300nm peak.
Sequential setups are great for daily driving, the feeling of good low down torque is great for just cruising around. Unlike a single turbo power is always on tap.
Here a little article about the Sti 401 the ultimate Twin Turbo Legacy.
http://homepages.ihug.co.nz/~1amiga/s401.htm
However Subaru never really mastered the setup unlike the Toyota Supra.
Interestingly for the new Turbo Legacy Subaru have turned their backs on the sequential twin in favour of a twin scroll turbo. Which does the job on a twin but with a single turbo. To keep it light (thus ensuring faster spoolup) the turbo is made out of titanium ~ strong as steel but half the weight sort of stuff.
Now it really does produce some low down torque putting out at 2400 rpm 343nm !
If u want to read about the new Turbo legacy hear are some links.
The version due for the US may not have the twin scroll as it'll probably have a version of the US Sti 2.5 lt engine which has better torque than a 2.0 lt due to size.
http://homepages.ihug.co.nz/~1amiga/gtspecbreview.htm
But if u want ultimate top end power a big single turbo is the way to go. But beware the lag probs.
I think however a twin scoll setup could be a possible compromise.
Last edited by EJ206DX; Sep 12, 2003 at 09:19 PM.
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i don't know what you are looking for but if a twin turbo is what you want here is a link to a site that makes twin turbos for imps and legacys www.forcedairtech.com it is there stage 4 turbo check it out.
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Joined: Dec 2002
Posts: 242
From: Good ol oregon
Car Info: 02' WRX
For a 4 cylinder engine, sequential turbos is pointless and stupid. These days, at least with small displacement engines, twin scroll turbines can acheive similar performance, but take up half the space, weigh half as much, and are half as complicated. Sequential turbo's only exist to make big engines with big snails driveable in the lower RPM range. On a 4 banger, a twin scrool turbine like on the JDM STi pretty much does the same thing. Pretty soon, except on V geometry based engines where it's obviously easier to fit twin turbos rather than plumb a single one, we'll see variable geometry turbo's take over. Variable geometry turbo's actually change their A/R on the fly, which really lets you have the best of both worlds. Other cool stuff that is gonna phase out sequential turbos is electric assist turbo's, which is essentially a turbo with a high speed electric motor/generator incorporated into the compressor housing attached to what amounts to a big capacitor. The capactitor holds enough charge to spool the turbo at low RPM's giving the car a kick in the ***, and once it's taken into the higher RPM range the flow is reversed and the turbo charges the cap.
Last edited by Br1t1shguy; Oct 5, 2003 at 11:54 AM.
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I have been doing some study on sequential turbos, and I am not sure where the gain in using such a setup. My thoughts are that both turbo are drawing energy from the same source. Turbo 1 spins up and drives turbo 2 which in turn feeds the intercool that feeds the motor. Basic law of nature, you can't get something from nothing. From the air flow generated by turbo 1, turbo 2 is spined up, but this acts as a resisting factor. Result in lower total compressed air in the intercool compared to a single turbo setup.
Then I though well maybe it for lower turbo lag time. But if Turbo 1 & 2 have X amount of lag time then total lag time would be X1 + X2. So that means greater lag time. So where is the benifit to sequential turbo? Am I missing something? Even is it is setup up in parallel. 1 source splite into 2 at the sametime, that still yield less total compression. Someone please set me stright.
Then I though well maybe it for lower turbo lag time. But if Turbo 1 & 2 have X amount of lag time then total lag time would be X1 + X2. So that means greater lag time. So where is the benifit to sequential turbo? Am I missing something? Even is it is setup up in parallel. 1 source splite into 2 at the sametime, that still yield less total compression. Someone please set me stright.
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You are correct in your thoughts in regards total power.
If u want the highest peak power then u slap on the biggest single turbo your engine can cope with.
Good for the drag strip or dyno but not daily driving. Your talking lotsa lag and peak power at very high rpm.
Really twins are more for getting power at lower revs and better drivability. For the real world drivability is much more important.
Parallel twins try to do this by having 2 smaller turbos. Being smaller they spool up quicker.
Sequential goes a step further by having a v small turbo and spool up v quick to provide initail boost then a second unit chiming in to bring in peak power.
Twin scoll is nice way of achieving both - The EVO has been using one for years to good effect.
If u want the highest peak power then u slap on the biggest single turbo your engine can cope with.
Good for the drag strip or dyno but not daily driving. Your talking lotsa lag and peak power at very high rpm.
Really twins are more for getting power at lower revs and better drivability. For the real world drivability is much more important.
Parallel twins try to do this by having 2 smaller turbos. Being smaller they spool up quicker.
Sequential goes a step further by having a v small turbo and spool up v quick to provide initail boost then a second unit chiming in to bring in peak power.
Twin scoll is nice way of achieving both - The EVO has been using one for years to good effect.
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