Jump to content
SAU Community

Recommended Posts

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

Link to comment
https://www.sau.com.au/forums/topic/371517-wastegate-held-open/
Share on other sites

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 by zoidbergmerc

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 :P)

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.

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.

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.

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 by D_Stirls

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?

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 by Space Goat

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

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.

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 by D_Stirls

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

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"

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 :P ... 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

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • For once a good news  It needed to be adjusted by that one nut and it is ok  At least something was easy But thank you very much for help. But a small issue is now(gearbox) that when the car is stationary you can hear "clinking" from gearbox so some of the bearing is 100% not that happy... It goes away once you push clutch so it is 100% gearbox. Just if you know...what that bearing could be? It sounding like "spun bearing" but it is louder.
    • Yeah, that's fine**. But the numbers you came up with are just wrong. Try it for yourself. Put in any voltage from the possible range and see what result you get. You get nonsense. ** When I say "fine", I mean, it's still shit. The very simple linear formula (slope & intercept) is shit for a sensor with a non-linear response. This is the curve, from your data above. Look at the CURVE! It's only really linear between about 30 and 90 °C. And if you used only that range to define a curve, it would be great. But you would go more and more wrong as you went to higher temps. And that is why the slope & intercept found when you use 50 and 150 as the end points is so bad halfway between those points. The real curve is a long way below the linear curve which just zips straight between the end points, like this one. You could probably use the same slope and a lower intercept, to move that straight line down, and spread the error out. But you would 5-10°C off in a lot of places. You'd need to say what temperature range you really wanted to be most right - say, 100 to 130, and plop the line closest to teh real curve in that region, which would make it quite wrong down at the lower temperatures. Let me just say that HPTuners are not being realistic in only allowing for a simple linear curve. 
    • I feel I should re-iterate. The above picture is the only option available in the software and the blurb from HP Tuners I quoted earlier is the only way to add data to it and that's the description they offer as to how to figure it out. The only fields available is the blank box after (Input/ ) and the box right before = Output. Those are the only numbers that can be entered.
    • No, your formula is arse backwards. Mine is totally different to yours, and is the one I said was bang on at 50 and 150. I'll put your data into Excel (actually it already is, chart it and fit a linear fit to it, aiming to make it evenly wrong across the whole span. But not now. Other things to do first.
    • God damnit. The only option I actually have in the software is the one that is screenshotted. I am glad that I at least got it right... for those two points. Would it actually change anything if I chose/used 80C and 120C as the two points instead? My brain wants to imagine the formula put into HPtuners would be the same equation, otherwise none of this makes sense to me, unless: 1) The formula you put into VCM Scanner/HPTuners is always linear 2) The two points/input pairs are only arbitrary to choose (as the documentation implies) IF the actual scaling of the sensor is linear. then 3) If the scaling is not linear, the two points you choose matter a great deal, because the formula will draw a line between those two points only.
×
×
  • Create New...