Turbo's

[dbtk2]

ZZP put a turbo on an L67 with an M90. It has two intercoolers (one under the blower and a front mount for the turbo). They run a 3.4 pulley on the blower and it helps build up cylinder pressure so the turbo spools quicker. Once the turbo spools past X psi the wastegate for the blower opens to allow the air from the turbo to flow through there...or at least thats how I understood it when they explained it. The car makes insane power, although they still have lots more to do with it, they are still playing around with the turbo/supercharger combo.

 

Shawn

[Guest TurboSedan]

how does a wastegate for a supercharger work?

[mfewtrail]

how does a wastegate for a supercharger work?

 

"The Eaton supercharger system incorporates a specially designed bypass valve, which is actuated by a vacuum motor near the throttle body, and recirculates the supercharger air flow when boost is not required. During typical driving conditions, the engine is under boost around 5% of the time, which means the remaining 95% of the time the engine is under vacuum, allowing for better fuel economy and a quieter ride. In addition, the helix angled rotors, along with specially designed inlet and outlet port geometry, also reduce pressure variations resulting in a smooth discharge flow and a lower level of noise during operation. The associated ducting and mounting used in installing the supercharger can play a major role in reducing the noise emitted by the supercharger. "

[z34_nut]

Thanks again for all this great info!

 

I went to my local bookstore they didn't have it *go to hell waldenbooks* so it looks like I'll be buying it off amazon.com.

 

P.S. This thread is jumping around every-where!

[slick]

Maximum boost was only $23 at amazon.com. i'm going to try my local bookstore first. I just hate shipping.

 

It's a good read. I have it laying around here somewhere.

[z34_nut]

Bumped for an odd reason.

[Guest TurboSedan]

i better go out and adjust my overboost eliminator tomarrow.....

 

<-----noob.

 

why would over boost be bad and doesn't the waste gate protect from that?

 

i'm not intuned w/ FI....i know the basics though

 

well i went through this thread and didn't see anything that would answer your question about overboost Adam. so i'll try my best to explain it to ya

 

an "overboost condition" is a built in safety feature that is programmed into the chip from the factory so people don't raise the boost themselves, which could result in blowing their engine resulting in warranty claims....and auto manufacturers definately wouldn't like that! but first of all, i'll post some basic info before i go into what an overboost eliminator is....my apologies if i'm posting info you already know, i just want this to be as understandable as possible for others interested.

 

a MAP sensor is used on "speed-density" controlled engines (as opposed to mass-airflow [MAF] controlled engines). IOW it meausures airflow indirectly by using the crank posistion sensor to measure engine RPM (speed) and the MAP sensor to measure engine load (density). both my Cutlass and my GTS use the speed-density system of measuring airflow into the engine. a 1-bar MAP sensor (used on NA cars) cannot sense pressure - only vacuum. therefore its 0-5 volt output signal has a greater resolution than 2 or 3-bar MAP sensors which is beneficial to driveability (but anyways...i'm getting off topic here since we're talking boosted engines and not NA).

 

anyways, onto 2-bar MAP sensors....which are used on boosted engines utilizing a speed-density system. a 2-bar MAP sensor's 0-5v output signal doesn't have as much resolution as a 1-bar MAP sensor due to the fact that the 0-5v output signal must now be used to span both inches of vacuum and up to 14.7psi boost pressure levels. most factory turbocharged cars experience the factory programmed "overboost condition" at around 10psi depending on the engine of course. this overboost condition is used to limit boost level and it does this by cutting fuel to the injectors. this causes the engine to suddenly feel like it dies since it momentarily has no fuel (the overboost condition can sometimes be a very harsh feeling and can almost make your head hit the steering wheel!). the result of course is that since there is no more fuel, the engine has no exhuast gas to feed the turbine, and therefore boost cannot go any higher. the fuel supply is only cut off momentarily but long enough so the turbo has to re-spool all over again. cutting fuel to the injectors is a rather crude way of creating an overboost safety feature and can sometimes be damaging to the engine becuase since the fuel supply is cut off at a relatively high boost level, it could result in a momentary lean condition. but it does work.

 

now an overboost eliminator is simply a device that limits the voltage signal from the MAP sensor to the ECM. it's called an adjustable zener diode and sometimes referred to as a "MAP clamp". there are zener diodes that aren't adjustable but i wouldn't bother with them. by limiting the MAP sensor's output voltage, the ECM is essentially fooled by not 'seeing' the raised boost level (done by turning up a manual boost controller etc). so let's say factory overboost condition occurs when the ECM sees a 4.75v signal from the MAP sensor. with the overboost eliminator, you can limit the output voltage from the MAP sensor by adjusting it to a level just under 4.75v. adjusting the overboost eliminator to just under whatever the factory set overboost voltage limit is is very important because if you adjusted it to say....4.3v you would be limiting the max amount of fuel since the ECM would interperate that 4.3v as 9psi when in reality you have your MBC set to say.....15psi. that would obviously result in a lean condition and likely a melted piston or two. so if your factory set ECM overboost condition occurs at 4.75v (example), ideally you would want to adjust the overboost eliminator to something like 4.72v....giving you basically 99.9% of max fuel available to the injectors and of course, the ability to raise boost without hitting the overboost condition (which usually sets a trouble code and an SES light btw).

 

a VERY IMPORTANT thing to consider is that IF you raised the boost level past 14.7psi (IOW, above the maximum pressure a 2-bar MAP sensor can read) is that you still have done nothing to add extra fuel for the extra boost you are now pushing. since the overboost eliminator essentially fools the ECM, it has no way of knowing to add extra fuel past 14.7psi. adding extra fuel can be done in various ways, such as chip tuning, larger injectors, AFPR (adjustable fuel pressure regulator), RRR (rising rate regulator aka FMU), adding extra injector(s), or alcohol injection or a even combination of some (or all) of the above. some cars even have 3-bar calibrations available which makes things really nice and easy. a professionally tuned 3-bar calibration is probably the best way of adding fuel & boost (not to mention timing and everything else) if you want raise boost levels above 14.7psi.

 

adjusting an overboost eliminator is kind of tricky. i've done this a few times on my brother's cars (Bossman429 actually installed the one on my GTS). FIRST, go for a drive with TWO people in the car - one to drive (doh!) and the other in the passenger seat with a DMM (digital multimeter) with the DMM probes attatched to the output signal wire and ground wire off the MAP sensor. before you go for a drive, adjust the boost level just slightly higher so you know it will definately hit the overboost condition. you need to see what voltage setting the overboost condition actually occurs at on your particular car. then have the passenger take note of the voltage that is displayed the exact moment the overboost condition occurs. now install the the overboost eliminator inline between the MAP sensor output wire and the ECM and ground it of course. go for another drive and adjust the overboost eliminator by turning the trim pot screw until maximum output votage to the ECM is about .03v below where the overboost condition occured on the first run. this will likely take a few test runs to get it dialed in just right. IMPORTANT - DO NOT raise the boost level any more until you know you have enough fuel to support the higher boost, ECSPECIALLY if you are adjusting the boost higher than 14.7psi since that is the maximum pressure the 2-bar MAP sensor can read and the ECM would have no way of adding fuel past 14.7psi.

 

that pretty much covers it. every once in awhile a readjustment of the overboost eliminator may be needed to account for colder weather or altitude changes etc.

[kuntzie]

turbo sedan i didnt read your post but my car was getting overboost aswell cecause the stock boost conntrollere wasnt keeping enough boostt to open my wastegate

[Guest TurboSedan]

yeah i won't bother installing an overboost eliminator on my Cutlass since the stock turbo is no good for above 12psi anyway not to mention you can easily get rid of it via chip tuning (unlike my GTS). i think Jay raised or completely removed the overboost cut-out in my chip since i've run at least as high as 13psi and never did hit overboost once.