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Mike2J

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  1. On 8/2/2020 at 2:58 PM, Tsung said:

    Great breakdown of the setup for sequential. I have a few suggestions to see if you can improve upon your transition. I see the boost dip from map 27 psi to below 20 psi then back up to 27. That is a big drop and I believe you transitioned too low of rpm for the second turbos to spool up. In your ttc log, you don’t reach 27psi map till after your 3744rpm mark. I would like to see what your graph would look like if you move the sequential transition to start at 3900-4000 rpm and see if you still get that big of a drop in MAP during transition. I am curious because I am in the process of installing gt28r hybrid twins and I see big dips on dyno sheet between 3700-4200rpm as if the sequential went into ttc too soon. Another interesting idea is to keep the egcv transition the same and allow the exhaust gases to pass through the second turbo early to spool up the turbo and open the iacv later at 3900-4000 rpm so the second turbo is fully spinning when it opens.

    http://www.munroracingturbochargers.com.au/performance.2jzgteTransition DIP.html

    This site discusses taping into iacv vsv to help with better transition in their hybrid twins set up.

    Please do some experiment with delayed transition and come back!

    another issue I see is that ebv should only be active in prespool and turns off when the egcv opens as the exhaust air now travel through the second turbo via exhaust manifold and not ebv. 

     

    Hi.

    Recently had a chance to play around with another sequential setup (stock turbo's) using new G4X Fury. I saw your post and did some experiments. My findings are:

    - The RPM at which transition occurs does not have a major effect on the dip in transition. At 4000 rpm the dip was the same as 3500. The longer you delay the transition the more power/torque you will drop as you are working the first turbo past its effiency. In a higher gear like 5th, you can make transition occur at 3500rpm or slightly earlier for best performance. In a low gear like 1st/2nd, even if you signal the VSV's to open at 3500rpm, sometimes there is not enough exhaust energy to bring the second turbo online until 4000rpm+. I have not made any adjustment maps for VSV control based off vehicle speed & gear, but technically you could and you'd be able to tune the optiminal RPM to make transision occur in each gear. 

    - Opening the EGCV & IACV earlier/later usually only resulted in a drop in response for the second turbo to come online. The IACV in my experience needs to open roughly 100rpm after the EGCV for optiminal transition. However whilst experimenting with this I noticed that if I used PWM control to bring EGCV & IACV duty% in linearly over 100-150rpm, rather than having them turn on/off instantly. I was able to able to minimize the boost dip substantially. Now the boost only drops 20KPA whilst transitioning, which is not noticable whilst driving. I'm sure further improvements can be made, but this is as close to stock as I've ever had it before. 

    - EBV staying open or closed during/after transition period made no significant impact to performance. Once EGCV is open, the exhaust gases naturally will not want to flow down the EBV bypass as its far less restrictive to go down the exhaust side of turbo #2.

    Ive tuned two hybrid setups a while ago and my take aways from them were:

    - EBV can only bypass so much air with stock exhaust manifold. Typically airflow was enough to prespool second turbo to around ~70KPa. This is good enough for stock turbo with light cermaic exhaust wheel as response is very quick, but with heavier hybrid setups I noticed some lag as second turbo built boost, even with all the prespooling I could give it. I'd be interested to see if porting the EBV somehow would result in higher prespool boost. Or maybe using more gradual VSV opening as described above can help this issue. 

    - Both setups were using completely stock Jspec exhaust manifold setups, other than having large hybrid turbo's installed. Increase in power was nice, but it was clear from EGT's and manifold temps that the rest of the exhaust setup was restrictive. Didn't get too many pulls at high boost before temperatures were getting molten. UK/EU/US exhaust pipework is less restrictive than Jspec, so better to use those. Ideally I would like to see that pipework ported even further to help the bloody things breathe a bit. e85 is a must to help lower EGT's on such a setup if you are trying to shoot for big power. 

     

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