i don't think your problem is any of what has been mentioned, artguy. now bear w/ me. you have a certain amount of total exhaust energy going to the turbos. we'll call that total exhaust flow, c. now c goes to either spool the first turbo or to pre-spool the second turbo. the exhaust flow going to the first turbo we'll call, a, and the gases going to prespool the second turbo as, b. now a and b add up to = the total exhaust flow c. you only have a finite amount of c, so if you want high boost on the pri turbo, a, you'll have to take that from, b, your prespool. hence, when you close prespool all the way your a will be high, cause b will be zero. if you want less of changeover dip, you'll need more prespool, b, hence your a has to go down. so you can't have it both ways have high primary boost AND have good transition, because you only have a fixed amount of c, your total exhaust energy. what might help is if you leaned out the motor more at low rpms as this is the only way you can increase c. then it's up to you as to how you want to allot that total btwn a and b.

 

what you said sounds totally true.

the stock system have a 10 8 10 boost pattern right?...would that pattern not proportionally increase as you up the boost if the pills were increased proportionally?

I want a 16-14-16....perhaps the increased wheel size needing more prespool is the problem Im faced with

I think another issue is that the m2 set is built for 16-20lbs of boost and Im pushing 14....the secondary needs more prespool to ramp up and thus below the comfort zone is more of a bear...even if it is still faster than stock

perhaps we should just get the boost drop at transition solved and tune for 16.3 lbs of boost...we can then see if we need less prespool which would balance things out a bit more.


j

 

on a side not..fdracer...one aspect of the equation which the other FD Racer points out is that the wastegate vents differently during prespool in order to allow more flow during the primary boost...this should compensate for the prespool loss...but for some reason my pfc is not controlling that solonoid well. I will play with the duty cycle numbers some more and may try running different hoses as well.

I hope i said that correctly..haha

gotta get this figured out.

I appreciate the input

j

 

no it would'nt increase proportionally, your exhaust energy is not infinite. you can have the best spooling set up out there w/ no restrictions at all, but your turbo will not spool up instantaneously. it's not a matter of restriction at this point. the turbos need to be fed by exhaust pressure, of which you only have a certain amount.

 

***No I am not responding to myself....it's me the other guy.***
Anyways...

fdracer,

No offence, but your a+b=c logic has a couple flaws.

1.) You failed to include the wastegate (very important) into the whole equation. Contrary to popular belief, the wastegate does effect primary-only boost. You are right that there is only a finite amount of exhaust energy to work with, however there is plenty. artguy is not even close to using up all of it.

2.) Your formula is also missing the fact that the ECU controls the wastegate actuator using a solenoid to vent away pressure to REDUCE (not eliminate) the opening of the wastegate during primary-only boost since the precontol gate is using up some of the exhaust energy and therefore the wastegate does'nt have to open as much to achieve the same boost pressure as it does after the transition. This is how you get a nice even boost pattern (I.e. 13-11-13, 10-8-10, etc)

Without assistance from the ecu duty cycling of the wastegate solenoid before the transition, your primary-only boost will always be lower than your pri + sec boost, no matter what pressure you dial in. Trust me, I've tried it.

Let me take a crack at the whole variable thing:

For this example we'll call:
Actual wastegate opening amount BEFORE the transition = x
Actual wastegate opening amount AFTER the transition = z
Precontrol gate opening (for prespool) = y
Total exhaust energy = c
Primary boost pressure = p
Pri + sec boost pressure = s

p = c - y - x
s = c - z

 

Im going with FD Racer on this one...hahaha

THERE CAN BE ONLY ONE!!



j

great conversation guys...well done. Im learning a lot here. thanks.

 

on another note...ordered a profec b today..hopefully will be able to clear up some of the problem that way.

j

 

totally off the subject, but did you get the intake from louie on your car yet, artguy? i talked to him today (yesterday, cause i'm still up) and he asked who i heard about it from. yep, it was you. send 'em (pics) to me, please.
spoolin7@midsouth.rr.com

thanks

 

I dont have it yet...louis was busy this week so I havent had my car there...will be putting my profec b in with FD Racer and will hopefully have the intake soon...louis is going to replace my bushings in the rear end..will probably do it then. soon i hope...another week or two at the most.

j

 

As i said before, and FD Racer noted, u need different duty cycles before and aft transition. The profecB can't do it, unless u modify it so the manual A/B settings are triggered by bef/aft transition. The PFC has bef/aft cycle settings.

Another person suggested a conroller that maps boost vs rpm (apexi?) .... this would come close to even boost if duty cycle is also mapped in.

Do these '20 psi' M2 have clipped wheels? could contribute to primary response issues. At what rpm does primary boost hit the set point?

 

get a midpipe, and ditch the valves use only the PFC. if you keep vavles, raise teh duty to max on PFC so it does nothing.

 

The profec b will be used for better / easier dialing-in of boost presure. The PFC will still need to be used to control the solenoid that bleeds pressure from the wastegate actuator before the transition. The duty cycles on the PFC will most likely be very high on the Pri setting and very low on the sec setting. We will experiment with capping off the bleeder hose / solenoid on the precontrol and continue to use the needle valve for the signal going to the precontrol actuator.

 

right now the pfcs duty cycle numbers and the changes I make do jack nothing...raise it up...boost stays the same...lower it down...boost stays the same. we can try to log it using the datalogit and see what the situation there is as well.

Im not sure i have a lot of faith in the pfc to control boost.

Ive heard nothing but bad news about the apexi boost control unit and honestly Im not really happy with their products. the n1 dual melted my bumper and if it wasnt for the datalogit Id have dumped this PIA ecu already.

am i going the wrong direction with the purchase of the profec b or what? its the most reliable from what i have heard and like ray said, Im hoping the pfc will do the rest of what it is supposed to do.

thanks again for the help guys...this is all great info and has made me think alot about the issues Im faced with.



j

PS...the wheels arent clipped on the m2 turbos...they are garrett gt30's. the housings were machined out to fit the larger BB internals.

 

Just get a Z06 and call it quits.
From all the trouble you have had, I think that single is the way to go now.

 

Artguy,

I don't have the M2 turbos, but I had a similar issue with the stockers and the profec (low primary boost and full secondary) . Solution was to T off the PCA and wastegate to the profec and I got early response and full boost on both turbos. I drew up a diagram you can find on the attached thread. This is a very cheap option that you can try and reverse easily.


https://www.rx7club.com/forum/showth...hreadid=105959

MCF

 

ok, so let's say artguy's able to shut the wastegate completely during primary only boost, so that he's able to get 16 psi on the primary, at what rpm is it going to reach that? then take into account some of the exhaust flow will be diverted to pre-spool, quite a bit if he wants a good transition. i'm saying maybe the wastegate doesn't open as much as you think, maybe it just takes time to build up that much boost, but at that point the changeover occurs and the second turbo kicks in, so you can't get all the way up to 16psi. remember, it'll take longer to reach full boost w/ 16psi vs. 10 psi, so maybe your just running out of rpm's before the secondary kicks in.

 

You may be right about the RPM's required to reach that boost... To your other point, my experience is that the transition is pretty seamless, contrary to what logic may dictate.

 

I have plenty of rpms left...they are bb turbos and the boost hits peak in no time...full boost by 2800 rpms...aint no worries there.

after 2800 rpms it simply holds to the 12lbs until switchover...but when i set it with no prespool it hits 15 by 2800 rpms too...no difference in spoolup time that i can see...will datalog it to be sure.

Thanks mcf for the diagram...we will try that out.

my profec b came today...will put it on the car this weekend hopefully.

j

 

well then do what mcf did and get back to us

 

will do...

thanks

btw glassman...the problems I face(d) stem from my inexperience in this...Id have the same BS problems if i went single...cant find a tuning shop for fuel who i can trust locally and would have had to do it myself.

got the fuel 98 percent done and now get to tune for boost.

My car should be finished this week if all goes well...I wont trade that for a laggy single at all.

j

 

This thread should be brought to the top - just because it has some valuable content.

 

to note....the problem was solved....replaced all solonoids again and am now able to boost 15-14-16 lbs

I tried running a profec b but have gone instead with the pfc solonoid kit for 3bar control.

I also quit the stock cat and ended up on the midpipe.

neither myself, FD Racer, RRR, or XS engineering was able to pull more than 15psi off the primary.

15psi seems to be the maximum boost that the primary is capable of putting out before it hits transition....

anyone else ever try to see how far the primary can go?

I believe I am at the cieling.



jason

 

Jason,
Those numbers don't SOUNd like they should be so tough.... I remember when i first bought my PFS purple computer, and installed it, someone wired the 3-way switch wrong, and "low" was actually "high". My car EASILY made 15 psi on both turbos, and we're talking a stock motor/turbos, and just a downpipe/IC/intake/catback.

shouldn't be ANY problem for you to make 1 psi more... something else sound amiss.

 

artguy- just had my car tuned, but the tuner couldn't get my primary past .76-.8 bar even though the pfc was tuned to .9 and a high base duty 82% or so. He said he thought the primary might be going bad (21k orig miles past 1500 miles or so with mods). I suspect it is something to do with the precontrol.

Do you have any insight or suggestions?

Thanks!

 

you should be able to boost more on the stockers since my m2 set flow more at that equal boost...am i right in this thought?

you might be getting too much prespool and the boost from the primary would then be leaking into the secondary to keep it spinning.

Im assuming you are tuning boost with the pfc? I didnt have much luck doing that....though xs was able to do it. I personally had better luck with both the manual boost controller and with the profec b.

you could try putting on the home depot controller and then adjusting prespool manually....try running it with no prespool at all...if you get full boost on the primary then its not the turbo.


j