Wastegate Held Open

[Space Goat]

G'day

I have always thought about the idea of holding the wastegate open on a standard rb25 (or any turbo car for that matter) to see how it affects the fuel economy.

Here's my theories-

-wastegate open turbo wont make boost

-no build up of pressure will be read through boost sensor and therfore adjust fuel mixtures to suit

-less pressure = less fuel but is it still at the right mixture???

I have designed a Simple circuit that will do this with the flick of a switch (pneumatics background). My guess is on open roads you wont notice any difference in fuel economy as 95 percent of the time you are off boost anyway. But driving through the city even if you are light on the old pedal it still comes on and off boost fairly often.

The only thing I am not clued up on is the detailed workings of the ecu, how it calculates correct fuel delivery and the long term effects of running continuously like this specifically any possible damage to the turbo and engine. for now lets assume its a pretty standard setup i.e. no fuel or turbo mods, standard block and ecu and maybe an exhaust/frontmount (ive got a rb25det neo in a stagea rs4 which is stock standard).

Also please dont start with the whole "if you dont like paying fuel bills for a turbo car then buy a friggin hybrid" talk because I dont pay for my fuel so at the end of the day it doesn't bother me a great deal. Honestly its a simple mod that could be done to any stocker in about 2 hours with a switch and everything and would cost under 400 bucks for the whole setup.

Thanks in advance

Cheers Rick

[zoidbergmerc]

I don't think it'll help fuel econ at all, because you're still moving the same mass to the same speed over the same time so boost or no boost.

Air going into the engine is measured though a mass air flow meter so yes with less boost you'll be flowing less air but you're still moving the car around with the same engine so I doubt it'll make a difference to fuel econ.

If you want better fuel econ, get a nistune daughter board for your ECU and get it tuned and tell your tuner you only want better fuel econ, not more power, get rid of that stupid dual stage boost thing that stags have and you'll live the fuel econ dream.

Edited July 19, 2011 by zoidbergmerc

[Randon_I_Am]

You could also drive light footed... another way to keep it off boost.

[GTScotT]

Drive an SR20 with a T28. They seem to have this awesome balance where they can spool quick or with the control of your right foot be extremely economic and good offboost for drivability.

IMHO you want the turbo spooling to some extent, you just dont want it making positive pressure without reason.. The situation is more dynamic than 'less air = less fuel' unfortunately.

A very senior CAMS official once told me one of the group A teams let him drive their MA70 supra while it was in development. He told me when they went from the stock turbo to their race item the car became MUCH better to drive and multiple times more economic.

I think the trick here is the right turbo.. Having something that has some nice offboost spool but ready to take action with half a hint (50% throttle )

[R31Nismoid]

THe trick is just right foot. IF I can get 450-500km around town in a 360rwkw 1700kg+ car... No O2 sensors either... Then you are doing it wrong if you can't get better.

IF you use low amounts of throttle, youll barely come near boost.

If you intend to have the gate open 100% of the time, and use more throttle... You will still eat fuel boost or no boost as its all about right foot control and a DECENT tune. not a 250 mail order special.

[GTScotT]

The trick is just right foot. IF I can get 450-500km around town in a 360rwkw 1700kg+ car... No O2 sensors either... Then you are doing it wrong if you can't get better.

However true, 360rwkw out of a twin turbo 2.6L is also a lot of off boost flow under the pedal. In my experience, even the stock turbos on the R32 GTR are a whole lot of play before you need to worry about boosting unnecessarily.

A factory turbo RB25, I believe, is a very different ball game. A useless SOD of an item IMHO.

Also, the mail order Toshi tunes definitely seem to be quite successful. I mean, its not like Nissan tuned an ecu for every individual car.

[R31Nismoid]

You could do it with a stock 25 too I'm sure.

Well Nissan didn't get decent economy either now did they?

[The Mafia]

lol at this thread entirely.

I love the way people think that they have a better idea over a few beers than years and millions of dollars in R&D.

If this is such a great idea, nissan would have thought of it. Back in the 1980s.

[islade]

Pretty sure the new BMW turbo 335i does this. Wastegate is open always, unless you put your foot down, then it closes, and then regulates boost.

This way, it fails "open" so you would never accidently get an overboost situation

[gotRICE?]

You could do it with a stock 25 too I'm sure.

Well Nissan didn't get decent economy either now did they?

At 100km/h in a stock RB25 it will make boost in 5th gear with 1cm of throttle. lol

[D_Stirls]

so how you going to pressurise the actuator to hold the gate open? you going to have a pressure cylinder somewhere to store the pressure.

Also by doing this you effectively have a low compression 2.5 litre that still has a reasonable exhaust restriction, the cam profiles aren't optimised for what you are trying to do and due to the low compression your fuel economy will not be good. The reason manufacturers use high compression engines is to increase efficiency to increase fuel economy.

Edited July 20, 2011 by D_Stirls

[R31Nismoid]

Pretty sure the new BMW turbo 335i does this. Wastegate is open always, unless you put your foot down, then it closes, and then regulates boost.

This way, it fails "open" so you would never accidently get an overboost situation

Could be emissions related too?

[jiffo]

so how you going to pressurise the actuator to hold the gate open?

Yep. Going to need something completely different to the standard setup, external air source like the big diesels......

or just forget the whole idea and drive with your foot.

[Space Goat]

so how you going to pressurise the actuator to hold the gate open? you going to have a pressure cylinder somewhere to store the pressure.

Also by doing this you effectively have a low compression 2.5 litre that still has a reasonable exhaust restriction, the cam profiles aren't optimised for what you are trying to do and due to the low compression your fuel economy will not be good. The reason manufacturers use high compression engines is to increase efficiency to increase fuel economy.

Makes sense when its said it this way. the actuator actually opens with vacuum its simple using a 3/2 solenoid valve and a check valve 400 dollars in my first post is a little off the mark... the solenoid valve is about 120 dollars and the check valve is about 50 dollars add your electrical relays, switches a bit of wiring ect. thats all you need. I can get from penrith to jindabyne fully loaded with ski gear, 4 adults and a roof pod and have just under a quarter of a tank left.

I have tried it out driving up and down the street and it works a treat... all I am worried about is getting wrong fuel mixtures and damaging something cause of a bad mixture

Edited July 20, 2011 by Space Goat

[paulr33]

if you are bringing the engine onto boost you are well past TPS being basically closed, ie %20 TPS

so if you find its coming on boost, then you are pushing the pedal too hard

you could have a T88 big single RB26 and still get 450kms+ to tank like ash said

its all how you drive the car

imho wiring the wastegate open or shut achieves zero for fuel control

the airflow meter drives fuel injection control so wastegate open or closed, its the same

you pushing the pedal more than needed is what drives more airflow meter load

[Space Goat]

imho wiring the wastegate open or shut achieves zero for fuel control

the airflow meter drives fuel injection control so wastegate open or closed, its the same

you pushing the pedal more than needed is what drives more airflow meter load

I would have thought that if your car is off boost the pressure of the air that your engine is using is at atmospheric pressure (or under vacuum close enough). if your car is on boost then the air your engine is using is under pressure... wouldn't this mean to achieve a desireable air/fuel ratio when your car is on boost it must use more fuel... wouldn't this mean there is less air passing through the air flow meter??? a standard rb25 at say 7 psi (.5 bar), needs 1.5 times more air to run at the same revs as one that was running at atmospheric pressure.

[D_Stirls]

the actuator actually opens with vacuum

Sure about that? Unless your pulling from that other side of the diaphragm, but even then where the shaft leaves the can isn't sealed in 90% of actuators. You talking waste gate actuator or some other actuator in your setup?

I have tried it out driving up and down the street and it works a treat... all I am worried about is getting wrong fuel mixtures and damaging something cause of a bad mixture

The mixtures will be fine.

Edited July 20, 2011 by D_Stirls

[paulr33]

you are going way too technical for something that's not a problem

all for trying new things

but on light cruise

ecu is in closed loop feedback

TPS is usually around %5

wastegate is closed

pressure is around -200mmhg

when you open the throttle

ecu is not in closed loop feedback

TPS is usually around %15

wastegate is closed

boost pressure may be zero or may just sit around 0.0kgcm2, ie past vacuum

[paulr33]

when you are on light cruise the turbocharger is effectively a paperwork

there isnt enough velocity to make boost or as we call it "to tell the computer - hey throw in tons of fuel were making boost"

[Space Goat]

Sure about that? Unless your pulling from that other side of the diaphragm, but even then where the shaft leaves the can isn't sealed in 90% of actuators. You talking waste gate actuator or some other actuator in your setup?

The mixtures will be fine.

Sorry my bad your correct otherwise it will over pressurise and could not regulate ... i think it slightly built up boost the first time it was on and then with the check valve configured correctly it held pressure in the wastegate from then... I might give it a try and see how it goes with a full tank of city driving