normal...even though the WG is open it still spins the turbine a bit... I've seen this on the DBW cars on the highway...block 114 WG duty cycle is 0, but block 115 reads above ambient...

 

I thought the N75 fails in the shut position... allowing no pressure to reach the wastegate actuator, and thereby allowing the turbo to spin up uncontrollably. (fail-unsafe?) :???: The wastegate is normally *shut*, until the N75 allows pressure to the wastegate actuator, right?

Perhaps the N75 fails in an open or semi-open (safe) state, allowing the wastegate to open fully at a reduced load?

Do you feel like tapping into the pressure line between the N75 and the wastegate actuator with a pressure gage, to see what's getting through to the actuator?

EDIT: replaced closed with open :banghead:

 

Correct if I'm wrong but the way I understand it is:

The turbo is still going spin and push air into the engine, but without the N75 the wastegate is held wide open. Although boost pressure can't be built up, at heavy loads the turbo is going to push more air than the wastegate can release.

 

without the N75 the wastegate is held wide open.

I thought the wastegate was normally shut... airflow restriction via the throttle plate prevents uncontrolled spinup at low load, then [boost pressure --> N75 --> wastegate actuator --> wastegate] prevents uncontrolled spinup at higher engine loads.

 

Well, here's what I do know:

The wastegate is normally shut.
The wastegate is opened by buildup of boost pressure.
If you mechanically disconnect the N75 (i.e. remove the boost line from the wastegate), the boost will build uncontrollably.

When my motor was stock, electrically disconnecting the N75 resulted in zero boost (well, maybe 1 lb max). Under 5th gear load, I can get 4 lbs now. But I get 2 lbs easy. Light loads.

I'm inclined to think it's what Scotty said...

 

Based on what you added, I agree. When unplugged, the N75 must "fail" in a mostly-open position... effectively becoming a "bleeder-type" MBC with the dial set to 4 psig.

 

What about what happens when the engine hits limp mode (which my H valve does from time to time)? The boost gauge will show 3-4 lbs under heavy load. Since the N75 serves as an electronic actuator for the wastegate, what is it doing under a limp condition? Is it opening the wastegate sooner or keeping it open to prevent the build up of boost pressure in order to protect the turbo from damage?

Incidentally, I tried bypassing the N75 and going straight MBC (Boostvalve) one time. Man did the turbo sound scary for the few seconds it spooled up before the computer went into limp mode. Not going to try that again.

 

Perhaps, due to the exhaust backpressure, a portion still gets diverted to the turbine even with an open wastegate. Does it do this only from a stop, or does it do this when you are rolling and then stomp on it?

Not to mention, your increased intake flow has got to go somewhere.

-Mark

 

Perhaps, due to the exhaust backpressure, a portion still gets diverted to the turbine even with an open wastegate. Does it do this only from a stop, or does it do this when you are rolling and then stomp on it?

Not to mention, your increased intake flow has got to go somewhere.

-Mark

It does it under all conditions (well, anything above 1400 or so). It's like it just naturally has 2 lbs boost.

A WOT run in 4th gear at this natural 2 lbs boost (and another one at stock 7 lbs boost) was an eye-opening experience. Here's the knock retard (taken from the cylinder with the highest knock at each RPM increment):

rpm ... 2#..7#
1500 .. 3 .. 2
1750 .. 5 .. 4
2000 .. 8 .. 5
2250 .. 7 .. 7
2500 .. 5 .. 8
2750 .. 5 .. 8
3000 .. 3 .. 7
3250 .. 2 .. 7
3500 .. 4 .. 5
3750 .. 5 .. 7
4000 .. 2 .. 7
4250 .. 2 .. 6
4500 .. 2 .. 10
4750 .. 6 .. 11
5000 .. 7 .. 11
5250 .. 8 .. 10
5500 .. 8 .. 10
5750 .. 10 .. 10
6000 .. 11 .. 11

These high numbers I attribute to the Holey MAF, but it was still a bit of a :icon_eek:. As a first-cut fuel map in my PCIII (yes, I installed it this weekend!!! WOO-HOO!!! shhhh... install writeup is coming...)(I'm so thrilled I can hardly stand it...)(YAHHOOO!!! Yippy-ky-yay!!!), I'm adding 1% fuel for each 1 degree retard. So you're looking at my first fuel map. Will be logging today during lunch to see how that does. The trick will be not disturbing the LTFT, which is now at a near-perfect -0.8% with 2-bar FPR and 380cc injectors. The transition to open-loop was 4750@2#, 4250@7#.

 

Rusty, did you have that much retard before your baro mod? I'm figuring those are mostly cylinder 2 numbers, how do the other three cylinders look, or what is an average?

In terms of the WG, I'd say it's within a normal range. Probably something you could eliminate by messing with the actuator rod position, but I think you were asking more for theoretical purposes, right?

 

No, actually cylinder 2 is easily my best cylinder. Those numbers come from cyls 1, 3, and 4 - they're all about the same, and all about twice as bad as cyl 2.

I never logged this data (2lbs and 7lbs, no Cartech, 380's) for the baro mod. But when I did log the baro mod (15 lbs + Cartech + 440's), the knock retard at WOT was unchanged.

 

No, actually cylinder 2 is easily my best cylinder. Those numbers come from cyls 1, 3, and 4 - they're all about the same, and all about twice as bad as cyl 2.

I never logged this data (2lbs and 7lbs, no Cartech, 380's) for the baro mod. But when I did log the baro mod (15 lbs + Cartech + 440's), the knock retard at WOT was unchanged.

I'm not sure of the exact correlation of retard to knock sensor voltages, but typically cylinder 2 knock voltage is slightly higher than the others because of the position of the sensor, or at least that's what I always understood. You are reading off maps for 110 g/sec max MAF readings or something like that right? That could be the whole answer.

 

When I had my N75J installed a week ago I blew some air through the middle connection (boost). It went out to the short outlet (WG). This would mean WG open IIRC when boost applied.

To open the WG you need some boost, this is the measured 2-4 lbs.

 

When I had my N75J installed a week ago I blew some air through the middle connection (boost). It went out to the short outlet (WG). This would mean WG open IIRC when boost applied.

To open the WG you need some boost, this is the measured 2-4 lbs.

I'm betting this is the answer - if the WG fails closed when you pull the hose, then you need some pressure to open it up. This will vary with RPM (should increase with RPM) since the flow through your exhaust causes higher back pressure at the WG as RPM increases, which requires higher boost pressure to open the WG.

The other interesting thing is that the WG is a bypass valve - i.e. it doesn't stop the flow to the turbine, it just routes the flow around it. Simple fluid dynamics (now if that isn't an oxymoron!) says that the pressure drop through parallel paths (the WG bypass and the turbine) will be the same and the flow through each path will adjust to give the same pressure drop. This means there will always be flow through the turbine since the WG is only so big. You will notice this more at high RPM than at low RPM, but because your compressor flow is higher, you won't notice the boost as the compressor drops down its curve and produces less boost.

 

if the WG fails closed when you pull the hose, then you need some pressure to open it up

By "it", you mean the wastegate, not the N75, right? I don't believe pressure opens the N75. I believe the solenoid valve in the N75 has a "normal" position, and it only varies from that position when a voltage signal is applied by the ECU.

Also, I dont think backpressure directly affects the wastegate's position. I think there is very little leverage that backpressure can put on the wastegate. Intake pressure, as transmitted through the N75 to the actuator, is the pressure that drives the wastegate's position.

I agree there should be a relationship between RPM and "unplugged" spool-up. More displacement per second = more air flow across the impeller

I wonder why Rusty is seeing more "unplugged" boost in 5th gear than in the others? There really should be no direct relationship between "unplugged" spool-up and gear selection. Maybe the higher vehicle speed (for a given RPM) is producing a "ram air" effect? Hmmm.

 

More load in higher gears. The AEB's is a load based system without boost sensors, etc. Correct?

-Mark

 

With no sensor feedback, no DBW, and an "unplugged" turbo, what's left to affect engine load other than the "ram-air" effect at higher vehicle speeds?

 

Bottom-line it's still what Scotty said.

Heh-heh - I just loaded my 2nd-gen map into the PCIII. It's already running smoother and stronger. yeeee-haw. :beer:

 

By "it", you mean the wastegate, not the N75, right? I don't believe pressure opens the N75.

Yes, I meant the wastegate not the N75 (unplug the wastegate from the N75, it stays closed, apply pressure to the wastegate and it opens)

 

When the N75 is unplugged available boost is applied to the WG, if there's no boost the WG is shut and stays there. When boost rise the WG opens. Measured boost is settled at a certain point were boost and WG-opening are balanced. It has become sort of a self-balancing system.

 

here's some diagrams:

http://www.boostvalve.com/tech/1.8T.html

my earlier statement was "kinda" wrong...dutch-mountains has it exactly right

 

When the N75 is unplugged available boost is applied to the WG, if there's no boost the WG is shut and stays there. When boost rise the WG opens. Measured boost is settled at a certain point were boost and WG-opening are balanced. It has become sort of a self-balancing system.

Cool, thanks, that makes perfect sense.