damian

iTrader: (2)

I would like to chat about a very specific part of the boost pattern, the transition and only the transition....

I hopes of trying to debug why mine is still a bit slower than it should be, i wanted to break the transition down to 4 states:

1) just before the transition dip (stock pattern this would be 10lbs)

2) the dip (stock pattern this would from 10lbs to 8lbs)

3) the rise (stock pattern would be from 8lbs to 10lbs)

4) just after the completion of the rise (stock pattern would be 10lbs to redline, possibly dropping to 8lbs by redline on some cars)

We all know about spiking, causing unfavorable numbers between states 4 and 5, and we know about a slow moving TCA (from lack of pressure or vacumm to its respective sides) that can cause a sluggish move between states 2 and 4....but lets pretend those are fine for now and just talk about the states 1 and 2.

What I see in my car is a slight decrease in boost right before state 1 and then a slow state 2 (slow dip), but then a quick state 3 (rise) and a normal state 4. I have done numerous debugging and all actuators 'seem' to be working correctly. Also, the easy answer seems to be that the secondary is not spooled enough, causing the sluggish transition...however, when I think about how the system works, it seems to me a non-prespooled secondary would cause a slow state 3 (rise), but state 2 (dip) would still be fast if all actuators are working as they should.

So, after a long stare at the diagrams, it seems like there are the only causes I could think for a late primary falloff and slow dip while maintaining a fast rise and otherwise normal pattern:

1) CCV opens a bit, allowing some of the primary to vent into the secondarypath and out the CRV valve, the primary can overcome the slight leak at first, but spins out by the time it reaches transition..thus the slight dip from 10lbs.

2) The BOV is slighly leaking, causing the same 'overcome in the start but spinout of power' condition as above


...any other takers on the culprit....
there is a lot of info already on boost pattern fixes, but not much on the 'slow transition dip' and 'pre-transition fade' yet...

damian

iTrader: (2)

wow, no one likes this thread (heheheheh).... so i guess ill post to myself...

so self....yes, self..... be sure to mention to yourself that you are also getting a very small spike on the rise part of the transition so the secondary is definetly getting spooled up...good note, to self :-)

rynberg

Wish I could help you Damian as I am experiencing an odd behavior at transition myself. I get immediate full boost on primary (10-11), the boost drops to 5 psi at transition but IMMEDIATELY jumps back up to 10-11 psi and holds 10 psi til redline. This is on a 95 with no pills in the lines and using a Profec B hooked up only to the wastegate (as per usual install).

I have noticed this problem since I got the boost gauge and Profec B (installed at same time). The dip is low to 5 psi but so fast that it doesn't even really register on the dyno. Any ideas?

Sorry to hijack your thread. Perhaps some knowledgable individual will help both of us.

damian

iTrader: (2)

hey rynberg,

hmm, interesting, if it goes all the way to 5 i would say it is the secondary not spooled up enough, but you say it IMMEDIATELY jumps back up to 10-11 psi....that contradics the secondary not being spooled up because it would be a slower jump up top 10, not quick...

well, after transition each turbo is effectivly making 5 lbs of boost...so what i would guess is that the TCA opens as it should (making the exhaust path open to both) but the CCV opens late, thus not adding the secondary at the exact time the TCA has opened, making a condition where both turbos are sharing the exhaut but only the primary is providing boost (half of 10lb = 5lbs), but it only sticks for a moment and then opens, giving you a very quick rise to 10lbs again (since the secondary is actually spooled up nice by this point)

im just speculating though..... have you made sure the CCV isnt sticking and is operating as it should

so just to clarify, the dip is really quick, just relly deep...right? the needle just blips down, but instead of to 8 it goes to 5?

damian

iTrader: (2)

ohh wait, you have no pill in the PC line either?

rynberg

Yep, it just blips down to 5 and then shoots right back up to 10. My experienced FD mechanic is baffled but I haven't exactly paid him to go searching around.

As good as the Derek Vanditmars TT troubleshooting page is, it doesn't cover either of our issues.

I will check the CCV. Thanks for the advice.

BTW, I just noticed from your "old" website that you had a 79 RX-7. Me too. I miss the red bomber. So much so, I got a red 95...

damian

iTrader: (2)

heheh, yeah, i loved that yellow 1st gen...and the yellow r1 3rd gen.

i have to admit, your 10-5-10 pattern wiht a quick blip transition is baffling me too..it seems like its woul dnot be possible to go all the way to 5 without having a slow transition (TCA slow from missing pressure or vac, or secoindary not spooled up enough) ... did the CCV suggestion make sence, or does it seem way off...just when i think i know how it all works, my car proves me worng (heheheheh)

Alien7

iTrader: (1)

i have the same issue as you rynberg

my profec is installed the same way, and my transition dips to 5 or 6 and goes back up to 10 (or whatever i set it to).

I still have my main cat, and it could be clogged up. Could this be the issue? I know that I had a 10-6-8 pattern before I removed my precat, and immediately after the dp was installed I had 10-8-10 pattern. After a few months I noticed that my pattern was getting funky again until i recently installed the intake, cb, and profec.

Alien7

iTrader: (1)

oh...sorry about getting off-topic from your thread Damian. Unfortunately I have nothing to add that can help you, other to say that I was trying to help my friend tune his boost with the HD manual valves this last weekend, and he had an intermittent slow dip problem at transition.

Right now his pattern is 8-6-10. Changing his wastegate valve changes the boost after transition, but we couldn't seem to do much messing around with his pre-control valve. He has a streetported engine and a ported wastegate....would this account for the lower primary psi due to less backpressure?

LAracer

Now this is my kind of thread !

I'm in a hurry right now so I skipped over a few replies, but I wanted to post a link to the results of my T-tests because it is probably relavent to this discussion. The link is here:

http://www.geocities.com/laracers_vr_r1/boost_plots

Note that (in case you've never read any of my threads before) I'm at 7000ft.

es

I would say the 10-5-10 pattern is caused by the fact that you have no Pre-control restrictor pill! Why did you pull it out? You did the right thing by replaceing the WG restrictor with the boost controller, but with no restrictor in the PC you're directing too much of the 1st turbos exhuast through the 2nd turbo while the Y-pipe butterfly is still closed (this is the pre-spool state, & at this time the CRV or whatever the rear blow off valve is called is venting all of the #2 turbos boost).

Damion, I'd say You should try to adjust your PC rod. If it's cracked open your routing the exhaust to the #2 turbo all the time, & routing too much exhaust to it during prespool causing the slow transition, but a very powerfully spun up rear turbo...

But, like anybody else, I could be wrong.
Eric.

911GT2

LARacer, that is awesome info. I don't know if anyone else has ever done that before, but kudos for the idea if it's yours.

How would those change as altitude got lower?

DaedelGT

Erm, in order for the turbos to make 10 psi over all they have to BOTH be making 10 psi. They are just not working as hard to do it.

I also get something like what you guys are describing. I attributed it to the crappy autometer guage I have, but it sounds like it may be common. The transition is really fast (like less than half a second).

redrotorR1

damian, it seems like the slow secondary response should be solely a function of the TCA. From Derek's site:

The Turbo Control Solenoid / Actuator is one of the more complicated actuators as it requires both vacuum and pressure to operate properly. This actuator is controlled by two solenoids, (both are wired together to the one ECU output) one solenoid applies pressure to one side of the actuator and the other applies vacuum to the other side of the actuator. With pressure on one side and a vacuum on the other side of the actuator, the speed of the actuator is improved. A typical problem is loss of Secondary boost in 1st or 2nd gear at 4,500 RPM, but reliable operation in other gears. This points to one side of the Turbo Control Actuator not getting it's pressure/vacuum, so it will still operate but not quickly enough.

So, I'm thinking your transition issue may be a problem with the pressure and vacuum of the TCA. I highly doubt the actuator rod is offset or moved somehow. (Has this car been in a serious wreck? Has anyone been jacking with the turbo assembly a bunch?) Perhaps, the rate of rise in pressure is too slow/not enough vaccum at first ... which might cause the the prolonged transition. Then, as pressure rises and/or the vacuum increases, the return spring compresses quickly, resulting in a very fast 'spike' to said boost pressure.

Then, there's the primary problem. That should be mostly a function of the Turbo Pre-Control Valve. If it were to open early, that would explain the early dip. But, here's the tough question ... why would the TPC open early? It's a pneumatic valve, so it would have to be pressure related. So, why would there be pressure in the line before 4500 rpm? I dunno ... you got me.

I was also thinking that the two issues might be inter-related. The transition-TCA thing sounds like a pressure/vacuum problem. That or the actuator itself. (Does the return spring wear out over time?) Added to that, perhaps the early TPC opening is somehow throwing off the pressure/vacuum balance of the TCA. My thinking is replace the TCA and possibly the two solenoids involved in transition. See if it that helps. The early dip issue ... well, I'm stumped.

Mahjik

iTrader: (1)

I seriously doubt it's your gauge (unless your line running to the gauge is crimped somehow). Unfortunately, I can't help with these problems, but I have an Autometer boost gauge. It's been on the car for a little over 2 years and no problems.

If you really think your gauge is off, just by a cheap gauge from an auto store (doesn't matter if it doesn't have vacuum). Run the line into the car and either 'T' with your Autometer or just disable your Autometer for the test and see what the readings are... I'll bet you'll find they are the same.

LAracer

I would love to know.

It would be great to see these results repeated on a perfectly healthy near-stock FD close to sea level. Then anyone with problems could just repeat the tests and compare - any problems should be obvious. It took me about half a day to get all the hoses set up for the tests, but that is nothing compared to all the time I've spent trying to troubleshoot.

Do we have any volunteers with healthy near-stock cars to perform these tests? Then Damian can do the same and the problem may reveal itself.

reza

I think for LARacer, you need to prespool the secondary more. Imagine this, if the secondary is only producing 5 psi during prespool, then after transition, it would still have to spin up to produce 10psi, thus showing the delay on your graph after 4500rpm.
On a correctly spooled secondary, you will have 10 psi after 4500rpm probably at around 4800rpm counting the dip.

reza

Damian,

What rpm does the primary, state 1 starts to drop off? Perhaps you need more prespool.

On mine, it holds 10psi until 4500rpm, then drop off quickly to around 8psi, and back up to 10psi by around 4800 to 5000rpm. Then my problem starts here, it hold 10psi until around 6000rpm, then slowly drop off to 8 psi to red line.
I am using HD boost control, and ported wastegate. I think the stock ECU open the wastegate fully after 6Krpm.

Reza

LAracer

Well, I wasn't really posting those plots to get help (don't want to be a hijacker), more for comparison, but any help is welcomed. I have needle valves installed on both the pre-spool and wastegate actuators, and no amount of adjustment affects the transition point. Notice also that the jump in the primary side of the CCV corresponds with what I feel as the transition point (5500rpm). Several other people living at high altidude have also experienced late transition, so I'm putting the late transition down to an altitude effect until I learn differently.

I'd really like to see these types of plots done for a healthy car. Even a database of them from all different cars to help us diagnose problems (dreaming, I know).

damian

iTrader: (2)

good note, ill check the PC rod out too.

damian

iTrader: (2)

good info on the post redrotor, I will check all those things you suggested.

damian

iTrader: (2)

I dont think so daedelgt, based on where you are looking at the pressure.

I am not sure on this but I would think that after transition they both only need to make 5psi, because they get added together after the y pipe junction, making 10 psi total, so 5 psi in there respective chambers.... right?

However prior to transition the primary does have to make 10psi itself because it alone has to make the 10psi after the y pip juction wiht the secondary not helping yet.

damian

iTrader: (2)

It starts to drop at around 4000, it just fades a bit from 10, then dip down firther for the transition at 4500, then pops back up after the transition dip. It is almost as if the turbo spins out right before transition, causing it to fade down a bit (venting somwhere it shouldnt or somthing)

DaedelGT

It's physics. It's sorta like turbos at lower vs higher temperatures. The reason you boost higher is because the turbo has an easier time making that amount of boost.

I don't have the words to explain what happens. Let me see what I can come up with.

Primary Turbo:
Compressor wheel spins at x rpm creating 10 psi of pressure.

Boost Transition:
Exhaust volume increases and the exhaust becomes even less restrictive, slowing the velocity of the exhaust gasses and creating lower pressures. (Psub1*Vsub1=Psub2*Vsub2)

After Boost Transition:
The pressure of the entire system is 10 psi, meaning it is the same within the turbos. Both are making 10 psi, but because there are two compressors creating the pressure, each works less hard.

I hope that makes sense. School has been out for a while.

I see your point about both turbos only making 5 psi, but it is not technically true.

damian

iTrader: (2)

ahh ok, i see what you mean now DaedelGT