RotorMotor

iTrader: (5)

well i just got my boost gauge in the mail so i decided to go hook it up and go for a spin.... i learned some very disturbing things.

first of all... boost patterns seem to change depending on the gear im in... i thought it was supposed to be constant.

second, if im at say 3.5K rpm in 4th and step on the gas, im getting a pretty quick spool up to 14PSI!!! can this be correct? also while the car is spooling it doesnt feel like its pulling much... after it hits 14PSI the boost drops to about 12psi, then drops to what seems to be 7psi at transition, then hops back up to 12 (this is at 4.5K rpm)... then it slowly drops to 8 or 9 psi up till redline. strange thing is, sometimes it stays at 10, sometimes it drops to 8 and stays there. anyway, all of this seems to change slightly depending on the gear that im in. (i can go into further detail later when i have more of a chance to play around and see what the turbos are doing when)

also as far as vacuum is concered (i dont know what a healthy vacuum is)... but im getting 25in/hg when the car is fully warmed up (the is before i went on my run)... and then after i got back i was getting 15in/hg. i dont know if its normal for vacuum to change that much after a half hour run.

the other thing that im noticing that could possibly be related is my stock IC is quite hot to the touch.

as far as modifications.... 94 touring, original motor w/ 82K, sock sequential turbos, ported wastegate (but the housing has a small crack in it), downpipe, knightsports metalit highflow cat, some unknown catback exhaust, k&n filter in the stock air box, efini y-pipe, and thats about it. new plugs/ wires, new intake gasket, vacuum lines redone (who knows if i did them right... but i was failrly meticulous w/ them) ... hmmm the o2 sensor is old and needs to be changed... but thats everyhting that ive done that i can remember. any help is appreciated as always. -heath

FDjunkie

If your still using the factory pre-spool and boost controls, then the boost behavior you described is probably to be expected with the mods you've listed. I've often read that the turbos produce more boost in higher gears and that's why most recommend testing in 3rd gear (or higher) so you get a more accurate reading. A fall-off at higher RPM's is also commonly reported; again with the stock controls.

The amount of vacuum change is a bit strange. Did the idle RPM's change, too? I've seen other cases where the idle will drop for a while following spirited driving. Another likely possiblity is that a vacuum connection came loose. If one was already leaking it might also help explain some of the strange behavior.

With the mods listed I'm not surprised that your boost is strange. In fact, I wouldn't have been shocked if you saw much higher spikes & boost than the 14 psi. Since I don't see where you have an ECU to feed the proper amounts of fuel for the higher boost levels, I think you're REALLY are taking a risk of blowing the motor.

My recommendations are that you:

1. Switch to manual controls for both boost and pre-spool. There are lots of approaches, but I think the best by far is Damian's https://www.rx7club.com/forum/showthread.php?t=178136 and with this mod you will always see the same maximum boost, regarless of gear, temperature, etc.
2. Inspect for loose/leaking vacuum hose.
3. To get all the benefit from the K&N you need to open up the air inlet to the stock air-box. To understand more or test yours https://www.rx7club.com/forum/showthread.php?t=347603
4. Consider testing your exhaust back-pressure which can also cause boost fall-off at higher RPM's. Here's how I checked mine https://www.rx7club.com/showthread.p...t=backpressure

RotorMotor

iTrader: (5)

ok for vacuum i did notice a higher idle after the run VS before... 900rpm after (seeing 15in/hg) vs 750 before (seeing 25 in/hg). id think a loose vacuum line wouldnt produce that much change in vacuum (if there in fact is a loose line)... but who knows. maybe the intake gasket is leaking again... i dont know.

as far as backpressure... id like to think there is minimal back pressure at this point... brand new metalic substraight HF cat, DP, and some annonimous cat-back (the catback is the only thing i can think would be suspect).

now... for boost control... the boost seems to be all over the place... and im really worried about the 14psi spikes... and the 12psi that holds till 4.5K. untill today i assumed everyhting was ok as the car seemed to run fine. would i just be better pulling the HF cat off? there just seems to be so many problems im not wure where to start. (FDjunkieL: ill read the articles you posted about manual boost control and pre spool control... thanks for the links!!)

another thing that i forgot to mention was ive noticed that the car just looses power suddenly (feels like boost just drops out or some other thing is happening)... maybe it is the computer and fuel cut/ignition cut/or whatever the stock ecu does when it sees extrordanarily high boost. this rarely happens... but when it does it seems to do so when i shift.

thanks everyone for the replies... and keep them coming... i have a feeling there are a multiple problems with the system. im going out tomorow to do some more testing with the gauge.... but it just started raining here so ill just read up on it tonight. -heath

iluvmy3rdgen

VACUMN HOSE JOB. Time to troubleshoot.

RotorMotor

iTrader: (5)

^already did the vacuum hose job... troubleshooting and their associated fixes is why im here

RX7Wishing

check valves functioning properly? test them, i had a defective check valve and it caused some interesting vaccum/boost related problems.

RotorMotor

iTrader: (5)

ill test them again... but when i did the vacuum lines i replaced the 4 green check valves

iluvmy3rdgen

Did any vac lines melt on something hot by anychance? Did you possibly break any wires going to the solenoids? It could be many things. You may want to take the solenoids out and apply a mity vac to it and apply 12VDC to the solenoid and see if it works properly.

RotorMotor

iTrader: (5)

ok i read damians post on the manual boost control... why is this preferable to say an electronic boost controller like the greddy or apexi, or others? is the reaction time better with the ball/spring setups?

the other option is to simply remove the HF cat etc., in an attempt to bring the boost back into a safe pattern. i do have a ported wastegate... so im not sure how that will affect the the factory boost controls... i ported the wastegate when i rebuilt the turbos (as i thought id be building this car up)... but a short time after that i ended up purchasing another 7 which i am working on... long story short, im going all out on the other car, and id like to keep this one as close to stock as possible and prolong blowing the motor as long as possible. considering my plans/situation what would everyone recomend?

RotorMotor

iTrader: (5)

ok i read damians post on the manual boost control... why is this preferable to say an electronic boost controller like the greddy or apexi, or others? is the reaction time better with the ball/spring setups?

the other option is to simply remove the HF cat etc., in an attempt to bring the boost back into a safe pattern. i do have a ported wastegate... so im not sure how that will affect the the factory boost controls... i ported the wastegate when i rebuilt the turbos (as i thought id be building this car up)... but a short time after that i ended up purchasing another 7 which i am working on... long story short, im going all out on the other car, and id like to keep this one as close to stock as possible and prolong blowing the motor as long as possible. considering my curent plans/situation what would everyone recomend?

FDjunkie

By my count you've got 5 mods, so even removing the HF will still leave you at 4, meaning you'd still probably have boost control problems, plus the cost of replacement cat, etc.

Damian's approach is preferable IMHO becuase it is one of the cleanest and easiest methods to install while giving great control and stability. Also, I'm not sure that you'd be able to control the boost with just bleeder-style valves. Clearly boost control is an area where there are lots of other opinions. If cost is an issue, though, you don't necessarily need the high-dollar valves used by damian. Other ball & spring type controlers will work (home-depot, etc.) but they just take a little more time and effort to adjust. On the other hand, once they're set you probably won't be messing with them much anyway.

Many others have reported success using electronic boost controllers. For good transition performance you'll need something that can handle both pre-spool and wastgate which I understand limits your options. I have no experience with these so I can only suggest searching the posts for recommendations.

RotorMotor

iTrader: (5)

thanks... well if i pull the HF cat, id be down to 2 mods really... i wouldnt consider hte K&N filter in the stock box, or the efini y pipe a "power mod". i have an extra cat lying around (and really the cat on there now is meant for my other car... i just threw it on there to see how well it flowed,, apparantly pretty well).

at this point my main concern is the ported wastegate and what effect that will have on the stock turbo controls. ive read about the WG actuator duty cycles etc etc... but i still cant understand why it would be allowing +4 psi.... if the wastegate actuator sees 8 PSI its supposed to start moving... and keep moving all the way till 14psi where it (supposedly) will be fully open. since my WG is now larger id think i would end up w/ LESS boost, as more would be venting VS a normal sized WG. this leads me to believe that something else is wrong/functioning improperly...

RotorMotor

iTrader: (5)

^bump^ anyone? sorry my questions are long winded and all over the place... im still trying to understand all of the ins and outs of the stock sequential system... its pretty complicated

my main question at this point is: how would a ported WG affect the stock turbo controls? thats really the only i cant UNDO at this point...

WaLieN

You mentioned that you are pulling 25in/hg of vaccum with a motor that has ~88k miles. This sounds waaaaay too high for a motor with so many miles (let alone any motor with a normal idle). The only way you could pull that sort of vaccum is if you let off the throttle at around 3,000rpms. Are you measuring that vaccum at idle or after you left off the throttle?(you should measure it at idle)

Given your boost gauge is correct (if you're pulling 25in/hg @ 850RPM, then it probably isn't), 14PSI is way too high to run on the stock ECU. The stock ecu runs pretty rich, but not rich enough to sustain 14PSI. Before you remove that high-flow cat, try rigging up a Home Depot boost controller just to see if it will be able to tame your boost issues. It doesn't seem like you are creeping since the boost tapers off towards redline. It really sounds like your wastegate is not opening enough with the exhaust mods you have when combined with the stock pills.

RotorMotor

iTrader: (5)

Wailen: yes thats at idle... after the car was warmed up (but before my 1/2hour on the turbos). yes i did see 24-25in/hg... i was quite surprized. the gauge is a brand new defi d-gauge (mechanical) and it reads 0psi without the motor running (but the gauge COULD be bad... who knows... i should get a mightyvac to test it or something). its temporarily plugged in to the extra nipple on the manifold. this motor has 82K on the clock and is the original motor... the vacuum readings seemed a bit odd to me too. while i was on the run i was getting 20in/hg as the lowest value i saw, and after i got back i was getting 15in/hg. i havent gone out to test again because its been raining here... but once the rain stops ill see if i get the same results.

for the wastegate... could the rod possibly need adjustment? i did rebuild these turbos and something could concievably be off... (well ignoring the initial 14psi spikes that i see) i am getting a constant 12 psi on the primary, and a constant 12psi on the secondary which tapers off toward redline. logically id think one would be able to set boost values by altering the WG rod length.

also if anyone knows the answer to this question PLEASE post: if i have a ported wastegate, how will this affect the operation of the stock wastegate controls?? i assumed it would work as it normally does (regulating the same boost pressures), but would have the extra capacity to bleed off larger AMOUNTS of exhaust gas, or possibly react faster since the opening is larger... but would ultimatly function the same as a smaller one in regards to boost levels

thanks again everyone for bearing with me, heath

RotorMotor

iTrader: (5)

just went out to test vacuum again... im getting 20in/hg at idle (now it only hits 25in/hg when i let off the throttle at 3k)... and if i step on the brake at idle i get 15in/hg.... im confused... but this is the least of my worries. please look one post up if you are knowledgeable about the stock wastegate controls/ wastegate rod