'Turbo Boost'

[Aerate]

Is there a good reason that a car cannot be fitted with a turbo 'isolator' switch?

We run a Forester XT. My wife loves it to drive, but is not a quick driver. I love the fact that it is quick, but I don't drive it often. The fuel consumption is fairly horrific for the size of car and it occurs to me that if it was a non-turbo we would save on fuel. Is there a reason why the turbo could not be used on demand rather than constantly (yep - I know there is such a thing as throttle control, but a big button marked 'Turbo Boost' would be cool!).

[eliot]

Fit a boost controller.
Can't see the point though, easier to not boot it everywhere.

[lostkiwi]

Modern turbocharged cars use a mix of mechanical (base boost) and electronic control.
Essentially the base boost is the boost pressure set by the mechanical wastegate which is then pulsed under electronic control to increase boost to the desired level'.
You could in theory hobble the electronic side but you'll still have the base boost present.

[numtumfutunch]

I think some M series BMW's have a function deep inide the idrive and Im also fairly sure that some early 90's Turbo Technics conversions had a staged boost switch too

In fact dont some serious current performance cars have a valet parking numpty mode too?

Cheers

[Sinatra21]

not really as the car is mapped for the turbo and the fuelling accordingly. If you disconnected the waste gate for instance so it just drained all the boost off the car wold still stick loads of fuel in (it might compensate a bit depending on how the ecu works). a full stand alone ecu could in theory be mapped for a car with no boost and then changed when you engaged the turbo but the cost of this would be way more than the difference in fuel for sometime. If you want a more fuel efficient car then buy one not a turbo monster.

[lostkiwi]

Place this under the throttle pedal....

[otolith]

Buy a VW and drive precisely to the NEDC?

[aka_kerrly]

Assuming that the OP has a Forester of the 2002-08 variety a XT turbo manages to average 26mpg with 226hp and the non turbo with 155hp manages 30mpg (info from Parkers)



Keep the turbo

[GC8]

Aerate said:

Is there a good reason that a car cannot be fitted with a turbo 'isolator' switch?

We run a Forester XT. My wife loves it to drive, but is not a quick driver. I love the fact that it is quick, but I don't drive it often. The fuel consumption is fairly horrific for the size of car and it occurs to me that if it was a non-turbo we would save on fuel. Is there a reason why the turbo could not be used on demand rather than constantly (yep - I know there is such a thing as throttle control, but a big button marked 'Turbo Boost' would be cool!).

Pointless - normally aspirated Subaru boxer engines are terrible of fuel too. Not an uncommon question on ScoobyNet for a decade, but the only answer is to keep it off boost. Easy with a TD05 but easier said than done with a TD04.

[DuckAvenger]

[jontbone]

aka_kerrly said:

Assuming that the OP has a Forester of the 2002-08 variety a XT turbo manages to average 26mpg with 226hp and the non turbo with 155hp manages 30mpg (info from Parkers)



Keep the turbo

My thoughts exactly, the non turbo models are not exactly known for brilliant economy. It'd take some considerable time to recoup the money spent on any mods (if at all possible) needed to gain this slight economic advantage anyway.

[eliot]

Sinatra21 said:

not really as the car is mapped for the turbo and the fuelling accordingly. If you disconnected the waste gate for instance so it just drained all the boost off the car wold still stick loads of fuel in.

If the car uses alpha-n that might be true, but if it uses maf or map that's not the case at-all

[Lowtimer]

If she's not a quick driver anyway, she won't be using enough boost enough of the time to make any significant difference to the fuel consumption. In any case, a petrol car with throttle valves is generally more fuel efficient running wider-open throttles at lower rpm than light throttles and higher rpm. If you really want to save fuel fit a rev limiter at 2500 rpm.

However, all of that said, no flat-four petrol Scooby is ever going to be economical. If you don;t drive it much, time to switch to a dag-dag.

[likesachange]

One of the best mods I have ever bought for a car was a piggy back ecu called a JB4 for a small BMW 135i coupe.
£325 delivered.
You could drive it along completely standard... And then at a flick of a button on the steering whee could add 100bhp or remove 100bhp ....
Along with so many other things that you could program in. But tbh driven gently on a run it would almost get 40mpg anyway .... So perhaps just put a block under the pedal so it only has an inch of movement ha

[Theophany]

likesachange said:

One of the best mods I have ever bought for a car was a piggy back ecu called a JB4 for a small BMW 135i coupe.
£325 delivered.
You could drive it along completely standard... And then at a flick of a button on the steering whee could add 100bhp or remove 100bhp ....
Along with so many other things that you could program in. But tbh driven gently on a run it would almost get 40mpg anyway .... So perhaps just put a block under the pedal so it only has an inch of movement ha

An extra 100bhp seems optimistic to say the least.

[Moulder]

They managed it in this so I don't see why it should be impossible...

[likesachange]

Theophany said:

An extra 100bhp seems optimistic to say the least.

Well fair enough, but it pulled 396 on the stage 1 map on the rollers and did go like stink, map 2 had more boost again and then there was others too
Regardless it completely transformed the car into a bit of a nutter and easy match for V8 m3's (on the straights)

[otolith]

We used to have a naturally aspirated 2.0l Impreza estate. Long term average for that was 29mpg. We're getting the same average mpg from a Saab Aero estate with a 2.3l engine, double the power and an extra 500kg to lug around. Either the 4wd transmission losses were horrendous or those just weren't very efficient engines.

[V8RX7]

aka_kerrly said:

Assuming that the OP has a Forester of the 2002-08 variety a XT turbo manages to average 26mpg with 226hp and the non turbo with 155hp manages 30mpg (info from Parkers)

Mine - short, fast trips manages 18mpg - it did when I had 220bhp and still does now it has 273bhp.

However it has LPG fitted which costs 50p/l so effectively I'm paying for circa 36mpg.

[Lowtimer]

Of course, simply preventing a turbo engine from boosting doesn't turn it into the normally aspirated engine of the same range. It will almost certainly have lower static compression and therefore be inherently less efficient off boost than the engine built for normal aspiration.