Fuel Economy, Waste Gates And Boost Controllers

[GTaaargh]

I drive my GTR like a grandmother to keep the fuel economy reasonably. Last tank was 430km around town, so it works, but it's a pain.

I have a wastegate that opens mechanically at 9 pounds. The boost controller is set to 12 pounds and 16 pounds. Most of the time I drive around with the boost controller turned off because 9 pounds gets me to work and back comfortably. When it's fun-time, the boost controller goes on and I live with the (drastically) reduced fuel economy. After all, that's why I own the car. I rarely use the 12 pounds though.

It occurred to me that if I had the wastegate open mechanically at, say, one pound pressure, I might improve the fuel economy and not affect the around-town driving performance too much. I could reset the boost controller to 9 pounds and 16 pounds, and use it when I want to drive a turbo'd car.

Is there any reason this wouldn't work?

If it's feasible, what is involved in reducing the pressure needed to open the wastegate?

[nuffin_werks]

To reduce the wastegate opening pressure you need to pull it apart and change the spring inside of it. However changing it to open at 1 psi would be the dumbest thing ive heard today. Your wastegate would be just about always open, and for instance trying to drive up a hill with no boost cause your gate is venting all your exhaust gases would drive you nuts.

Your drivablitiy of the car would go out the window as it would be a slug, you know like driving grandma's Hyundi.

[rb26s13]

if ya dont like the fuel economy.. buy a shitta that runs of the smell of a oily rag..

[R33S2]

In other words you want a NA car with the option of turbocharged to be dialed in on request. I had an idea using a BOV to do this but it never took off past thinking really.

[paulr33]

engine load uses fuel not boost, you may find if your plodding around the city staying in 4th may yield some better economy. when you drop in the load map by airflow meter and TPS signal the AFR's richen up a stack load and boost comes on. if your in a lower gear you wont need to load it up as much as it will be revving higher, so boost wont come on as much and the AFRS shouldnt drop to stupidly rich.

try it out

the fuel map is a 20x20 or 25x25 excel spreadsheet and as you move away from 1x1 diagnolly it richens up gradually. when you load it up you drop staright down the medium / high load axis, there is where your economy takes it up the ass. if you can stop in the top region you should be sweet

[GTaaargh]

engine load uses fuel not boost, you may find if your plodding around the city staying in 4th may yield some better economy. when you drop in the load map by airflow meter and TPS signal the AFR's richen up a stack load and boost comes on. if your in a lower gear you wont need to load it up as much as it will be revving higher, so boost wont come on as much and the AFRS shouldnt drop to stupidly rich.

try it out

the fuel map is a 20x20 or 25x25 excel spreadsheet and as you move away from 1x1 diagnolly it richens up gradually. when you load it up you drop staright down the medium / high load axis, there is where your economy takes it up the ass. if you can stop in the top region you should be sweet

I don't see it as a dumb idea Nuffin, it's what R33S2 said - I'm interested in knowing if it is possible to get turbo on demand. The car has reasonable torque, so it could probably run with no boost - and if it was a real problem, maybe I could set the spring to 3 or 5 pounds. Anyway, if I wanted the extra power up a hill, I'd switch on the boost controller, which was the whole point.

Thanks for the explanation Paul. Most of the time I drive around town in 5th, but back to 4th for hills. So you reckon I should drive with more revs in lower gears when accelerating, rather than putting it into a higher gear and keeping the revs down? I normally don't take it over about 3500 when accelerating in city traffic.

[paulr33]

well at least with my tune (pfc) my afrs are quite lean up in the medium rev area and light load. ie;

3000rpm with not much load is fairly lean

2500rpm with not much load is lean

2000rpm with not much load is lean lots

comapred to

1900rpm with lots of load is rich

2200rpm with lots of load is rich more

2400rpm with lots of load is rich more more

if that makes sense so plodding around in 4th *may* yield better economy, it depends on the tune. but i dont think its as simple as drive in 5th and yoll get best economy. as when im plidding around in 4th i can tell there is jack all engine load, but when in 5th i find myself pushing the pedal in more to maintain the same road speed, as load increases in 5th, revs begin to drop. so you need to gas it more to keep same speed

[ferni]

Also your boost controller will have to do ALOT more work if you want it to hold 15 pounds boost above the actuator pressure... boost would be very unstable and spike up and down..

As paul said i've found driving around in a lower gear at higher revs with less load on the engine is better for fuel... i don't use 5th gear unless i'm cruising at 100...

@60k 3/4th

@80k 4th...

[ODessA]

i always assumed lower revs less fuel ?

i didnt realise that if ur doing 60 in 5th, and u need to accelerate more to maintain speed its using more fuel because there is little reaction from the engine and less revs.

also in saying that whoring around in 5th uses less fuel but is better engine/transmission wear wise or not ?

ima try driving around in 4th instead of 5th for the next week or 2.

[hicas_posse]

I drive my GTR like a grandmother to keep the fuel economy reasonably. Last tank was 430km around town, so it works, but it's a pain.

I have a wastegate that opens mechanically at 9 pounds. The boost controller is set to 12 pounds and 16 pounds. Most of the time I drive around with the boost controller turned off because 9 pounds gets me to work and back comfortably. When it's fun-time, the boost controller goes on and I live with the (drastically) reduced fuel economy. After all, that's why I own the car. I rarely use the 12 pounds though.

It occurred to me that if I had the wastegate open mechanically at, say, one pound pressure, I might improve the fuel economy and not affect the around-town driving performance too much. I could reset the boost controller to 9 pounds and 16 pounds, and use it when I want to drive a turbo'd car.

Is there any reason this wouldn't work?

If it's feasible, what is involved in reducing the pressure needed to open the wastegate?

hey 430km around town-that's very good. My GTS-t comes in the 370km mark in the city. RReally ugly!

only launch her a bit on occassions.

[ferni]

i always assumed lower revs less fuel ?

i didnt realise that if ur doing 60 in 5th, and u need to accelerate more to maintain speed its using more fuel because there is little reaction from the engine and less revs.

also in saying that whoring around in 5th uses less fuel but is better engine/transmission wear wise or not ?

ima try driving around in 4th instead of 5th for the next week or 2.

Its also about the load on your engine, higher load = more wear and more fuel...

If you ever feel your engine struggling at low RPM's (1-2k) then drop back a gear...

[dkonig]

If you really want to run no boost you can just remove the circlips holding the actuator rods to the wastegate flaps. Simple.

Take you two seconds and the thing will make pretty much no boost.

Though at the end of the day, if you want a slow economobile sell your GTR and buy something else. They are not meant to be a car for penny saving!

DK

[paulr33]

You shouldn't need to restort to stupid changes to get economy. Running 0 psi hacks and bypasses is the wrong way to do it.

I have a HKS EVC set at 12psi all the time and I never change it or run 'hi' or 'low' boost settings. I use my right foot to control how fast the car goes. This week I got 403kms on a full tank (54 litres) of premium.

This was simply achieved by a good tune and some normal driving. If I spank it non stop on the street my economy drops, as one would expect. Load affects fuel economy not simply revving.

[chrissso]

^yeah, he's right bout controlling boost with your right foot.

If you are driving aroung town like a granny, the chances are that your not putting more than one 1lbs boost into the engine anyway.

So, putting on a one pound actuator wont improve your enconomy at all, if you granny drive it. It will be the same.

If you have a boost guage, you can see how much absolute pressure is in the manifold, and you can reduce or increase it by controlling the throttle.

Also, you need to bypass alot of exhaust via a wastegate to acheive 1 lbs boost. So your wastegate is probably not be big enough to cope with all that flow.

[Cubes]

Get it tuned better, most tuners drop straight to a high 11-mid 12 once its making some boost, there's no need to run so rich at such low boost levels.

Lean the bugger out.

There's a good thread floating around that discusses economy tuning.

I've found low rev's, higher load is better than little load higher rev's. i.e short shift it, even if it means you need to accelerate more to get you moving.

[Race__24]

^^^^^ but how much more torque do you have over us 2.5 to 2.6L midgets?

[Cubes]

yes so it may not be applicable.

The 3ltr does give you a lot more acceleration and shove in the back before the needle hits 0 vacuum. Enough so that you leave traffic driving in vacuum, but only just.

and the torque question... an rb30det making around 200rwkw makes roughly the same 'peak torque' as an rb25det making 300rwkw.

[R33S2]

Thanks to Paulr33's advice I've been watching the AF 's on the micotech, I assume these are what the ecu is doing, not the actual ratios, at 78ks in 5th 14-15, in 4th 11 flat, this all depends on load as both rise on a hill but in 5th its much more up to 17, while in 4th not much at all. At 58ks in 3rd/4th its the same.

I now drive a bit different to before, where I hardly went above 3000rpm, as thats when boost starts, but now I understand that to acheive boost the ecu loads on fuel just as I was backing off and wasting that. Have I understood this correctly?

What I try to do now is keep the AF's in the 11 zone and to do this I take it that bit futher than before.

[mad082]

the way i see it is that the more you push the accelerator down the more fuel you use....to a certain degree. using lower gears at higher revs only works in certain circumstances. depends on how high revs you have to use. if you have to push the accelerator down 15% in 3rd or 20% in 2nd to get the same speed then you are better off using 3rd as it will be at lower revs, using less fuel and forcing in less air.

being a turbo car it is about what boost is going into the engine. the more boost that goes in, the more fuel that has to go in to keep the afr's right. it is fine to say that the afr's are 11 or whatever they may be, but that is only a ratio, not an amount of fuel or air. you could tune the car so it has an afr of 11 at full noise at 12psi at 6500rpm, and have the same afr at 2000rpm and not even be in positive boost. does this mean that the same amount of fuel is going into the engine? no, it means that ratio of air and fuel is the same (hence the name air/fuel RATIO). 100cc of air and 5ml of fuel has the same ratio as 1000cc of air and 50ml of fuel.

as people have said its more to do with load.

[Cubes]

Believe it or not the old 4stroke motor is more efficient as in makes more power from the fuel supplied when the throttle is open rather than almost closed.

A butterfly/throttle body that is almost closed causes the motor to work hard in order to suck air in, this is known as pumping loss.

If you were to drive at a lower rpm with a greater throttle opening in theory you should be a little more fuel efficent, providing its not tuned to go rich as soon as you open the throttle up.

So, give it some nice open throttle low in the rpm and have that area tuned to stoich. Even if its making 1-2psi still tune it to stoich.