Low transition dip and slow building secondary boost
 

Help! I have tried a lot of things and I am unsure what to do next. Plus i have read a lot of threads and none that I have read seem the same as mine. I have good primary boost and good secondary, however the drop at transition is way low and secondary take a long while to build, as if it is not prespooling or some thing is not closing when it should allow boost to build after transition. I even have adjusted the precontrol arm only to lower primary boost. So I shortened it again. My boost pattern is as follows - 1st gear it is not so bad, 2nd gear gets worse, 3rd gear even worse and 4th is pretty bad - never tried 5th, only gone into the transition and it is a dog! On my boost gauge (manifold pressure) i see 13.5 psi in primary, then it drops to 6 psi at transition then it has to slowly build back up to 16psi which takes almost 1,000 rpm, which in 4th gear is quite a while to go without power - it acts as if it is venting the air through the wastegate or the CRV or BOV. 3,300 rpm = 13.5psi, 3,900 rpm = 6psi, 4,200 rpm = 10 psi, 4,500 = 12.5psi, and then by 4,900 rpm I am at 16psi manifold (0.92bar absolute). I am located in Utah at around 4,300ft. so there is a couple a lb difference between manifold and absolute pressure. Any ideas? Thanks!

Living at high altitude will result in low boost at the switchover point and a slow-buildup on the secondary. I lived at 7000ft in CO for 4 years, so I've seen this first-hand. Most likely, what you are experiencing is the result of altitude.

However, with that said: you may want to check vacuum lines and solenoids just to be sure you don't have another issue compounding the problem. Most likely, if you had an issue, it would be related to the TCA. There are two solenoids (vacuum and pressure) that operate the TCA. Check these, and all your vacuum lines.

Also, watch that 16 psi. If you're relatively stock, that's WAY too high (even at altitude). You didn't mention any mods, so I'm assuming you're close to stock.

Rob

You may find some help here:

https://www.rx7club.com/showthread.p...boost+altitude

Good luck!

dude, quit screwing around and go single :stick:

thanks! it is not stock, it has just about everything without going single, Power Fc, Intake, Intercooler, high flow cat, apex dual n1, 1300 cc secondary injectors. I also just had it dyno tuned with a datalogic, a/f ratios are safe and knock levels were low. it made 332 rwhp at 6,000rpm and 303.4 rwt at 5,600 at .92 bar (absolute) - there was a time when my transition was better, the boost would come back fast, throw me in the seat fast. Actually the first day i installed my Power FC my transition was perfect 10-8-10, never saw it again.
I will do some more checking, i am hoping/wishing for a quick fix :D

I have been trying off and on to fix it over the last 4 1/2 years - maybe oneday I can go single

Sorry for assuming you're stock. Ignore my 16psi comment then. Nice numbers. Those are SAE corrected?

You would obviously not have to worry about transition with a single. However, you will still get more lag and slower boost buildup than you would at sea-level. Just one of the perks of living at altitude I suppose. Boost builds slowly. I went through the same thing. Car is much quicker now that I've moved back to low-altitude.

One thing I did to help correct the slow transition is that I installed ball-and-spring boost controllers. This made a noticable difference. Try some. Or better yet, get a Profec B (again, this is assuming you don't have a boost controller).

no problem saxyman990 - i should have posted my mods - i was in a hurry when i wrote it. I just installed a ball and spring controller sunday night - it did help a little. I have not had a whole lot of time since. The major thing it did was allow me to reach .92 in more than just 4th gear - before the contoller i would see .74 bar in 2nd gear, and maybe .86 in 3rd if it were colder out. Now I hit .85 in 2nd gear and .9 in 3rd - I will do some more testing tonight - another thing i asked the tuner to lower my transition point with a datalogit, which he did to 3,850 rpm - helped with more power/time in twin mode but maybe made the building of boost slower. Tonight I might up the point a couple hunder rpm. - thanks and yes altitude sucks:mad:

Try shortening the TC actuator rod, it improved the speed of my transition.