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Discussion Starter #1
All right lets say you set your boost controller to 1 bar (17psi) max. Should both turbo's reach that at WOT or should the first be less?
Thanks
 
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#1 boost less then #2, that is why it is called sequential twins. first one boost around 2500-300 and then second one boost after that. so you go fast and then you go faster.

if you just want to go faster you can turn it into true twins where both turbos boost at the same time but the #1 turbo will still make less boost that the othet one.
 

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#1 boost less then #2, that is why it is called sequential twins. first one boost around 2500-300 and then second one boost after that. so you go fast and then you go faster.

if you just want to go faster you can turn it into true twins where both turbos boost at the same time but the #1 turbo will still make less boost that the othet one.
He's correct that's how they work. But to the original poster how do you know how much each turbo is boosting do you have two different boost gauges??
 

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Logically, Can't you just read the boost meter at when the first turbo comes on to get the full boost of the first turbo... then read the full boost after 4100 rpm subtract the initial and you get the second turbo?
 

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Discussion Starter #5
Let me make it simple. With a BCC & BC, when you stomp the gas in an auto what will the first turbo spike at if your BC is set at 17 psi?
 

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#1 and #2 are identical turbos once you start making more than 7 psi boost, they are both making the same. Sequential refers to the fact that all exhaust flow is ported to one turbo first, then once that is fully online, the second turbo shares the exhast flow and they make the same flow and pressure as they share the full exhaust flow.

TTC gains you nothing except for removing the slight restricion that is the reed valve between the turbos. It adds lag - the purpose of the sequential twins is to eliminate the lag of a single turbo while giving the performance of a single turbo.

Ingenious and defeating it to go TTC seems pointless to me.
 

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When I turn up my boost controller, my first turbo seems to boost to about 11psi then full boost is around 17psi. I don't know if there's a way to turn just my first turbo down and it seems to me that 11psi is probably bad for it.
 

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Discussion Starter #8
When I turn up my boost controller, my first turbo seems to boost to about 11psi then full boost is around 17psi. I don't know if there's a way to turn just my first turbo down and it seems to me that 11psi is probably bad for it.
OK, that is starting to make sense then. At WOT boost should rise to approximately 11 to 12psi and at approximately 3800-4000rpm should reach 17psi or there about? So basicly there is no possibility of hitting 17psi on the 1st turbo before 4k rpms?
 

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That's how mine works anyway. Like I said, I'm not positive #1 should even be hitting 11. That's above stock boost just on #1.
 

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yes, while the first one is online alone, it cannot make the volume so the pressure is lower, but once they are running toghether, they make the same pressure, just each has 1/2 the volume that is required to produce the pressure.
 

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Discussion Starter #12
yes, while the first one is online alone, it cannot make the volume so the pressure is lower, but once they are running toghether, they make the same pressure, just each has 1/2 the volume that is required to produce the pressure.
Mark,
If you keep explaining why my 1st turbo isn't blown as I thought I won't buy your single kit:x: !
 

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Just to clarify.

There are two valves that control exhaust flow across the turbos. You have your standard wastegate, and you have an exhaust bypass valve.

I won't go into to much detail here, but at low RPM both the of these valves are diverting exhaust away from the turbos.

When you install a boost controller you attach it to the wastegate. At low RPMS your boost controller is telling the Wastegate to stay closed, however the Exhaust bypass valve is still diverting exhaust gases away. This is the reason you are only getting stock boost.

After transition the exhaust bypass valve is no longer a factor when controlling boost, only the wastegate. Hence you can produce more boost.

There is a modification performed by Stu Hagen that allows you to tweak the EBV, and have more boost down low. The drawback to this (and this may cause some debate) is that it causes a poorer transition, ultimatly making the car slower.

HTH,

Howard
 

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nope...

There is a wastegate (WG) that dumps exhaust to control boost pressure, an exhaust bypass control vale (sort of a reverse wastegate that is used to prespool the number 2 turbo) and an exhaust gas control valve that closes off the exhaust tract of the number two turbo so that all exhaust flow is routed thru #1.

At low boost pressure, all three are closed. All exhaust flows thru #1 turbo. As you increase pressure, the bypass opens up to spool #2, spinning #2 up gently. As you increase pressure, the EGCV opens up and exhaust flow is shared fully between #2 & #1. Once you start making enough boost that the computer wants to limit boost, the WG opens up. #1 does not spin #2 in reverse because there is a one way checkvalve between them (the reed valve that makes that elephant sound sometimes).
 

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nope...

There is a wastegate (WG) that dumps exhaust to control boost pressure, an exhaust bypass control vale (sort of a reverse wastegate that is used to prespool the number 2 turbo) and an exhaust gas control valve that closes off the exhaust tract of the number two turbo so that all exhaust flow is routed thru #1.

At low boost pressure, all three are closed. All exhaust flows thru #1 turbo. As you increase pressure, the bypass opens up to spool #2, spinning #2 up gently. As you increase pressure, the EGCV opens up and exhaust flow is shared fully between #2 & #1. Once you start making enough boost that the computer wants to limit boost, the WG opens up. #1 does not spin #2 in reverse because there is a one way checkvalve between them (the reed valve that makes that elephant sound sometimes).
Which part of my explination did you disagree with?
 

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Hwilli at first I thought both descriptions are accurate, but I think the part that gets the "nope" is when you said that "at low rpms the valves divert away from the turbos" Air is diverted through #1 not around it, as 98 describes

.... to the original poster, there is no point in worrying about your #1 turbo seeing 11 psi, since when both turbos are online at 17psi, #1 is seeing that pressure too. All us BPU's are in the same boat. luckily the pea-shooters can usually take it for 100k miles give or take:) :)
 

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you left out one valve.... WG, EBV, EGCV.... you only mention WG and EBV.
 

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98MKIV,

I see what you are saying.

My intention was to give the original poster a dumbed down account of why he was seeing what he was seeing. Basically the reason he can't get more than 11psi at low RPM is because the EBV is letting some of that exhaust energy escape.

I didn't want to overwhelm him with the whole sequential operation.

beezupra,

I would have to doublecheck, but I believe the EBV dumps it's exhaust into the #1 Downpipe section. I am fairly sure it is post exhaust wheel, so the #1 doesnt see this exhaust energy. The #2 obviously sees it before it is diverted, but it's not enough energy for it to equal what the #1 is pushing.

I've done a lot of research because of the way the AEM handles the sequential operation. I almost have it behaving like stock, but it's taken a lot of work.

Anyway ac556, it's normal what you are seeing :)

Howard
 

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so say the second turbo is not turning on at all for some reason, can the first turbo boost up to .8bar all by itself?
 
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