Quick question for the knowledgable out there Yesterday, I was a bit naughty and had to put my foot down to avoid a hazzard before the usual 10/15 mins that I normally like to give the car to warm up. It seemed that the car was not acelerating with as much vigour as usual: even the turbo seemed quieter! (I have a standard -apart from a H&S backbox- MY99 Turbo)

Worried, 5 minutes later I put my foot down again at a safe overtaking opportunity. Wooooo Hooooooo, big turbo rush! That's more like it!

I was just wondering if the engine management system retards boost whilst the engine oil is warming up in order to prevent hard acceleration too early. It was also rather hot yesterday, could it just have been that the intercooler needed to gulp in more cool air before the car could accelerate at its potential? I understand that turbo engines work best when cool.

Forgive my mechanical ignorance!

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Probably the turbine housing was not that hot on the first throttle application. There can be 20 BHP difference on power testing depending on whether you cruise at 5000 RPM for a minute before to get the EGTs up.

There is no boost retardation written into the engine management on your model, it would be possible on some new age STi ECUs based on coolant temperature, not oil, but again is not actually used.

 

Thanks John, Thought it might be something like that, just that when you get used to the turbo rush, you tend to notice any deficits in power very easily! It did feel like more than a 20bhp deficit though, more like 50bhp! It was only for the first serious prod of the accelerator in second though, and I did do it much earlier than I'd have liked and would have normally; I treat my engine with Kit gloves and always warm it up and let it cool off before enjoying it's power.

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You weren't hanging around in 2nd gear for any preiod of time when you booted it by per chance?

May have triggered the boost cut which halves the boost level when you hold in 2nd gear for a while off boost then floor it, something to do with emissions control.

 

Ali B,

Bingo! That's exactly what happened mate! I was lagging behind a very slow vehicle in 2nd and a couple of chavs behind me were getting very impatient and really tailgating! There's no way they could have safely overtaken me and the car causing the obstruction in their 1ltr Nova, I had to get past the slow moving vehicle pronto before they did something very silly. I pushed my foot to the floor and didn't get anywear near the same kind of acceleration I know my Scooby can deliver. In fact I'd estimate that the boost was only about half as aggressive; felt akin to a 1.8T Audi A3 (my mate has one)

Nuts to the environment.....how do I turn it off!

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Use 3rd...then change to 2nd when you need to move quickly - only way around it I'm afraid Unless you want it re-mapped or an aftermarket ECU

 

Or you can lift off and reapply the throttle when in 2nd, or use a Dawes.

 

Just found out that apparently it's not emmissions related (at least not entirely anyway) It's to reduce the strain on the transmission!

I guess that makes sense; I know that some cars engine management systems restrct the torque in 1st and 2nd e.g. Ford Focus RS probably for the same reason, at least the scooby doesn't do it all the time, and you can drive around it.

Gotta have that second gear hit that evokes the clasic understatement from passengers: "Quick, isn't it?"

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It is drive by noise regs, not for transmission as you can at other times get full boost in 2nd, so it wouldn't be a good transmission protection mechanism.

 

John. Really?? Even with the the standard exhaust?? So, the theory is: if we program the engine to deliver only half boost when ambling around in second gear they'll change up a gear and keep the noise down? I guess they're not going to like my sports silencer then are they!

I actually think this is quite dangerous. There are occassions when you might be relying on your car delivering its full potential to -for example- make a safe overtake only to be caught off-guard by this mechanism. It really does cut the performance significantly and backing off completely or changing up then down again makes for untidy and clumsy progress.

Bummer!

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You only have to lift off the throttle a fraction, and stamp it again.

It only does it when you have been in 2nd for a while.

 

ive kinda noticed this too, but never really been able to pin it down.

However hanging round in a gear then flooring it i have noticed that effect, u think come on, get a move on, and it doesnt really do it! weird! But saying that it still accelerated pretty darn quick so it could just be ma imagination

not happened enough though for me to bother posting about!

 

P20SPD Thanks for the tip; got the impression you had to lift off entirely, which would make for very jerky progress! Codek, it seemed like quite a pronounced reduction in power and torque to me; feels more like a good GTi (which isn't exactly slow) but compared to the "OOOhhhmygawdddd!!!" aceleration the car normally generates at 3000rpm, it's a noticable step down.

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PS Does anyone know how much power and torque is cut by (i.e. BHP and Lbs feet?) under the above condition?

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No, it is specifically so that when the car is tested for the drive-by noise regs during type approval etc it will pass. I believe the test involves a full throttle 2nd gear run past a noise meter, I guess that in order to do this they will have to run along in 2nd for a bit then floor it past the noise meter, which will trigger the half boost feature and keep the noise down. It has nothing to do with trying to encourage particular driver behaviour.

 

It halves the boost, normal boost is aroun 0.9bar, the cut out drops it to about 0.5 bar. A wild guess of about 40bhp

 

Thanks for the info guys! Very interesting. I still find it hard to believe that a scooby with a standard exhaust would generate enough noise to fail these tests! Mine was way too quiet til I got the H&S backbox. It's lovely now! I'd say 40-50 bhp feels about right, I wouldn't be at all surprised if there was a similar reduction in torque as well; the thing that is most noticeable is that the car's acceleration doesn't pin you to the seat anywhere near as much.

Are there any other "power reduction" features I might like to know about in order to drive around?

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