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Discussion Starter #1
The car is a 94' 6-speed, and the only mod is a 3" catless downpipe. In sequential I will get about 10 psi out of the first turbo (give or take depending on gear/load) and then the second will prespool when it is supposed to, come online when it is supposed to, and peak to about 12/13psi depending on the gear and load. However, I tried temp TTC with the checkvalves, and if I floor it in third gear at about 3k rpms, the boost will slowly rise, and when it peaks it will shoot WAY higher than it does in sequential (about 16 or 17+ psi) and then shoot right back down to 12/13psi instantly. Does this sound like I have a sequential problem or is that normal? But even if I went permanent TTC I dont think it would be good to be spiking to 17 psi all the time with just a Dp installed and no BC even. What are your guys' thoughts? Any help is appreciated, thanks in advance.
 

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You mentioned that you hit a 16 or 17 psi spike while testing TTC on a 3rd gear roll. Did you try to see what the boost level is with TTC when starting from a stop? The reason that I ask, is because you will typically spike higher on a roll especially if you hit it right at a sweet spot in the power band, like you in fact did. Otherwise it doesn't sound like what you described is too far out of the normal range.

Try sequential and TTC each from a stop, and report back what the boost response is in 1, 2 ,3, and 4 gear respectively. That should provide enough data to judge how well your sequential system is working.
 

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if you do not have a bcc or something similar done. you are not hitting 17psi as there is a factory boost cut(fuel cut) at i believe 13.5 psi boost gauuges always read off and it usually is hihg. I thought I had the same problem then to test I pulled the hosses and sure enough I found boost cut maybe you should try this too.

If you already have done sometyhing to allowa you to boost beyond this point I dont know what to tell you.
 

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Discussion Starter #4
ama0787 said:
if you do not have a bcc or something similar done. you are not hitting 17psi as there is a factory boost cut(fuel cut) at i believe 13.5 psi boost gauuges always read off and it usually is hihg. I thought I had the same problem then to test I pulled the hosses and sure enough I found boost cut maybe you should try this too.

If you already have done sometyhing to allowa you to boost beyond this point I dont know what to tell you.

I dont have a BCC but you can still hit any boost level you want without a BCC if it spikes quick. The lack of BCC doesnt stop it from hitting that high of boost level, but rather once it senses higher than 13.5 psi for a certain amount of time, then it will trigger fuel cut, the spike was not enough time to trigger fuel cut.
 

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I think it should trigger the boost cut immediately.... I mean what reasonable amount of time could they have decided to start boost cut after?? 1/10th of a second?

I have a aem and my map sensor always reads from 2-6lbs less than my boost controller and my defi boost gauge the map sensor is supposedly medical grade so I always trust it. There usually seems to be 2lb incrments starting at map then blitz boost controller and finally the highest my defi boost gauge

Either way just trying to help out I dont really care what the answer is.
 

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Discussion Starter #6
ama0787 said:
I think it should trigger the boost cut immediately.... I mean what reasonable amount of time could they have decided to start boost cut after?? 1/10th of a second?

I have a aem and my map sensor always reads from 2-6lbs less than my boost controller and my defi boost gauge the map sensor is supposedly medical grade so I always trust it. There usually seems to be 2lb incrments starting at map then blitz boost controller and finally the highest my defi boost gauge

Either way just trying to help out I dont really care what the answer is.
No its cool I appreciate all your help and Crossways as well, I didnt mean to come off mean or something its just that I was always told boost cut would be triggered after 3 or so seconds of detected "overboosting" The best I can come up with as to this problem is this; In sequential, the wastegate vsv stays open to keep the wastegate closed for the first turbo under 4k rpms (give or take depending on many factors) After that, the wastegate vsv will close and allow the wastegate actuator to do its thing. With my setup, in TTC I will hit peak boost a bit earlier than sequential (37 or 3800 rpms as opposed to 4/4200) and the wastegate vsv is probably open at that point thus kind of like having a pulled hose on the wastegate, and the reason the boost shoots to 17+ psi and then right back down to 12 is because shortly after that the wastegate vsv is closing and allowing the actuator to open the wastegate. I ran a wastegate vsv that was not functioning or opening, and I did not get the boost spike, it would go up to about 12 or 13 (the same that I was peaking at in sequential) and that is about it, that is what leads me to believe my theory is correct.
 
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