twin turbo....what do you guyz reconmend?
- Thread starter kaifiji
- Start date
tissimo said:
TTC just takes away power in the low end when a working seq. system would and should be supplying boost and power.
The turbos die prematurely because the system is not working correctly. #2 may not come online full until 4000 but it is being pre-spooled before then around 3500. If #2 comes on at 4500, something is wrong.
The sequential system is very complicated and all the parts must be functioning properly.
At a predetermined pressure from #1, exhaust gas is routed to #2.
There are some important parts that pertain to the failure of the 2nd or both turbos. One is the intake air control valve which is located in the intact tract for the 2nd turbo. It's closed before 4000RPM so the boost pressure from #1 does not travel back to #2 and cause it to spin backwards. #2 is pre-spooled around 3500 but doesn't join up until 4000. There is also the exhaust gas control valve which allows #2 to get spinning at it's full rate before joining in with #1. When that happens the IACV opens and they both join together and you're fully online then. The EGCV has to open before the IACV for the 2nd turbo to be safe. If the IACV opens before the EGCV, the pressure from #1 will travel backwards through #2 and will spin backwards if there is not sufficient exhaust energy to keep it moving forward. When the EGCV opens after the IACV, the 2nd turbo has to not only build up boost quick but it has to reverse direction due to the IACV opening causing it to spin backwards before it had sufficient energy to keep it going forward with full pressure. That's what puts all the strain on the shaft and bearings of #2 causing it's failure.
The exhaust gas bypass valve is what allows #2 to prespool at 3500 and is there to smoothe the transition between 1 and 2.
If any of those aren't working, quick death of the 2nd turbo usually occurs shortly after. A proper seq. system with all VSVs working as they should will not just kill the 2nd turbo.
If I had a 2J with twins, I would rather fix my seq. system and reap it's benefits than taking the easy way out and creating a powerband with the lag of a single but none of the power.
To the OP, it's your car... If you don't want to learn about the seq. system and would rather put it out of sight out of mind, that's your choice. I'm just trying to provide you with more info other than "yeah, seq. is better cuz it's kewl." It should not matter if your car is auto or manual.
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so #2 will surge until 4k when the iacv opens.. sounds like a winner to me..
Still doesn't do anything to counter act the #1 turbo overspinning to create 15+ psi in the intake
yes it does have more torque from 3000-4000 but its not that big of a difference..
Still doesn't do anything to counter act the #1 turbo overspinning to create 15+ psi in the intake
yes it does have more torque from 3000-4000 but its not that big of a difference..
@kaifiji, what are your hp goals?
If you stay near stock hp > stay sequential, nice early spool.
If you wanna get the most out of the stock twins > go true twin; you will need to tweak the engine with some sort of management to get up to the hp goal and the sequential system is a pain to tune. The transfer is not at a set point, it is dependent on load, so revs and boost vary. With the sequentials you get a flat spot on the power curve which moves around, so in certain conditions your tune will be right, but in other conditions your tune will be off. With ttc you don't get this and you can tune more accurate, won't need to build in reserves for the wandering transfer point. Also some ebc's don't like the sequentials.
just my 2ct
If you stay near stock hp > stay sequential, nice early spool.
If you wanna get the most out of the stock twins > go true twin; you will need to tweak the engine with some sort of management to get up to the hp goal and the sequential system is a pain to tune. The transfer is not at a set point, it is dependent on load, so revs and boost vary. With the sequentials you get a flat spot on the power curve which moves around, so in certain conditions your tune will be right, but in other conditions your tune will be off. With ttc you don't get this and you can tune more accurate, won't need to build in reserves for the wandering transfer point. Also some ebc's don't like the sequentials.
just my 2ct
NO. #2 is pre-spooling before the IACV opens. It is not surging.tissimo said:
If the IACV opens BEFORE the EGCV, then yes you will have problems. IF it opens before it may cause surging(not always) and #2 to spin backwards. If the system is working how it should this does not happen and the IACV opens AFTER #2 has sufficient exhaust energy and boost. So when the IACV DOES open, #2 is already pre-spooled and joins #1 just fine without any surge. The system would be a complete failure if #2 had to experience surge. But it doesn't.
tissimo said:
How is 15psi considered overspinning? If #1 spinning 15psi is bad, then both spinning 15psi is just as bad. 15psi is 15psi whether it's from 1 or both. Number one is not the commonly reported failure. It's #2 and for the reasons I wrote in my last post.
tissimo said:
Maybe not to you. The point is to provide the OP with enough information to make that decision for himself.
If the turbo is spinning and the compressor isn't flowing it will surge, just like your throttle body closed when the turbo spooled.OneJoeZee said:
Because 1 turbo is Flowing 15 psi. If you add in turbo 2 the flow is cut in half for each turbo. I probably shouldn't say overspin, cause I dont have a compressor map of the ct12b and cant tell for sure, But I'm sure its running extremely high rpm and causing accelerated wear on the turbo.
true
wrong Joe....
it doesn't even start prespooling #2 until 4K and then it kicks on fully at 4500. tissimo is correct. i prefer ttc.
The MKIV Supra's twin turbos operated in sequential mode instead of the more common parallel mode. The sequential setup featured a pair of small, equally sized turbos, with ceramic blades for the domestic Japanese market and steel blades for export (USA, Europe) markets. At first, all of the exhaust is routed to the first turbine for reduced lag. This resulted in boost and enhanced torque as early as 1800 rpm. Approaching 4000 rpm, the exhaust is routed to the second turbine for a "pre-boost" mode, although none of the compressor output is used by the engine at this point. Approaching 4500 rpm, the second turbo's output is used to augment the first turbo's output. This setup differs from other twin turbo designs which run both turbos in parallel. The sequential mode provides greater low RPM response and increased high RPM boost.
it doesn't even start prespooling #2 until 4K and then it kicks on fully at 4500. tissimo is correct. i prefer ttc.
The MKIV Supra's twin turbos operated in sequential mode instead of the more common parallel mode. The sequential setup featured a pair of small, equally sized turbos, with ceramic blades for the domestic Japanese market and steel blades for export (USA, Europe) markets. At first, all of the exhaust is routed to the first turbine for reduced lag. This resulted in boost and enhanced torque as early as 1800 rpm. Approaching 4000 rpm, the exhaust is routed to the second turbine for a "pre-boost" mode, although none of the compressor output is used by the engine at this point. Approaching 4500 rpm, the second turbo's output is used to augment the first turbo's output. This setup differs from other twin turbo designs which run both turbos in parallel. The sequential mode provides greater low RPM response and increased high RPM boost.
The Reaper said:
You are wrong... Turbo #2 prespools at 3500 and teh VSVs are switched open to allow #2 to join in with #1. I am pulling this info straight from www.mkiv.com.
ok well i got that from wikipedia so i dont see how they get two different answers
but you're a supra god and im not. my bad.
for the original poster i still say TTC but do whatever you want
but you're a supra god and im not. my bad.
for the original poster i still say TTC but do whatever you want
ahh Reading off mkiv simply have the valves wrong.. If the EGCV was opened without the IACV it would surge, with ebv the flow would be Fairly minimal but it really wouldn't spool up the turbo, maybe a few thousand rpm if that as the exhaust as no where to flow as the egvc is closed..
tissimo said:
#2 does not surge...
" there is also a 1 way reed valve within the same housing of the intake air control valve. as the #2 turbo starts to pre-spin at 3500 rpm, it will build some boost. if it builds enough boost, it will open the 1 way reed valve to allow this boost into the intake tract to join with the discharge boost pressure coming off of #1 turbo. at somewhere over 4000 rpm, the ECU sends a signal to the intake air control valve vsv, which allows manifold pressure to build in the intake air control valve actuator which opens the control valve. this allows the full boost pressure coming off #2 turbo to join in with that coming from #1 turbo and you are now fully on line. "
Taken straight from mkiv.com http://www.mkiv.com/faq/faqtt.html#turbosystem1
tissimo said:
Either way, turbo #1 is not the turbo that commonly fails when a seq. problem occurs.. It's #2 and that's what was being discussed a page or two ago when a few others gave their reasoning for TTC(to save the 2nd turbo).
Accelerated wear is something we have to live with when trying to push the stock turbos on our engines. I'm still not seeing that as a reason not to use the seq. system. If accelerated wear was a main concern, then we would all be running stock boost. Increasing the boost by 50%-100% adds a notable amount of accelerated wear on both turbos anyway.
The Reaper said:
Because wikipedia is hardly a reliable source of info. It is regulated but anyone can edit the information in there. The editors of wikipedia aren't going to know the difference between a few numbers regarding the MKIV Supra.
I'm just supplying concrete information to help the guy make a choice instead of just unsupported opinion. He will draw his own conclusion and decide whether to ditch the seq. system.
I am still standing by my option to keep it. After 4000, it's doing the same thing TTC does. Below 4000, it's supplying more power than TTC.
well ACTUALLY
i wouldn't do either. i'd single it before i put it in the car. seeing that you'll have to pull the whole motor JUST to remove them when you ARE ready to go single it'd be wise to single before the swap.
plus stock twins suck at controlling boost. one minute 12psi next minute 18 psi its stupid. i'd go single from the beginning just like i told tissimo
i wouldn't do either. i'd single it before i put it in the car. seeing that you'll have to pull the whole motor JUST to remove them when you ARE ready to go single it'd be wise to single before the swap.
plus stock twins suck at controlling boost. one minute 12psi next minute 18 psi its stupid. i'd go single from the beginning just like i told tissimo
tissimo said:
I give up. I already refuted that. #2 dies because something is malfunctioning in the system. It does not die simply because you are running sequential. This is like the 1J myth about boosting over 1bar. If seq. truly caused the 2nd turbo to die, everyone running sequential would have a dead 2nd turbo. It is true that many have experienced failure of the 2nd turbo running sequential. It is also true that many people have faulty sequential systems.
Correlation does not equal causation.
What are you going to tell people who ask about how to raise the boost on their 2J? Run stock boost... keep #1 and #2 alive?
Do as you wish, as long as you're enjoying your car.
hahahaOneJoeZee said:
But seriously what would not function correctly on the Sequential system to cause it to be more prone to blow #2? Only think I can see is if the timing on the EGVC and the IAVC arn't right cause surge or IAVC opening too early or maybe even the EBV not opening so the turbo is at 0 rpm when the ebvc opens. You can not control any of this, the ecu does. Now if the VSV doesn't work or is broken then yea, but you will notice something is up doe to abnormal boosting.
Now sequential might not blow your turbo any time soon, it may last several years, it just simply causes more stress on it.. I didn't want to risk it, as I didn't want to pull the engine to get the turbos off (I highly doubt you will be able to get them off in the car). Lag isn't that bad at all (I'm making 300 ftlbs of torque by like 3500 rpms), and I can gain a few extra HP from removing the valves all together. So I went TTC.
tissimo said:
I already explained the causes of the 2nd turbo failure. The opening of the IACV before the EGCV will cause the pressure from #1 to backtrack against #2 and surge it backwards if there is not sufficient exhaust energy for #2 to continue spinning forward. This should not happen. The EGCV opens first and the IACV 2nd, there is no surging, and #2 is already up to speed.
OneJoeZee said:
tissimo said:
Why do you keep backtracking to the save your 2nd turbo point? I already spoke about that at least twice. It's a non issue. If you were really concerned with preserving your turbos for a more extended period of time, you would running stock boost which you are not.
If you simply did not want to risk it, well that's fine. This is the point I've been trying to make all thread. The system will not kill your turbos anymore than the higher boost you are running if it is working fine but if something is out of working order, you may experience turbo failure. There are reasons for a possible 2nd turbo failure as already stated at least twice. Even if one dies, who is to say it was because of seq.? You might have had a completely perfectly working system. It could have been because you were running higher than stock boost. Even 1Js that are 100% true parallel often experience only failure of only 1 turbo. What happens if your TTC twins start smoking and you find out it was only the front one that is blown? Again, correlation does not equal causation.
It's up to you to decide whether or not you would rather not fix the problems with your seq. system if you had any. I have been saying this all thread. It's a choice that should be based on sufficient evidence, not just "some guys told me my 2nd turbo will die." or "it feels like a single."
I don't believe you picked up any hp because you removed the seq. system. The VSVs are either 100% open or 100% closed. Again, this is assuming everything is working the way it should. If not, maybe you could have partially closed VSVs. I do not know. Only you would know that after troubleshooting your system.
Why do I keep having to repeat everything I'm saying?
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the ecu controls the timing on the valves, you have no control over it. You can only control to make sure then work.
I was talking gaining power from removing the valves, I have no egvc or iacv anymore
I was talking gaining power from removing the valves, I have no egvc or iacv anymore