Overboost, gimmick or feature

[Exorcet]

I was reading a Motor Trend article on BMW 335, and came across another mention of overboost. Yet again I found myself rolling my eyes. It's not quite as bad launch control I guess, but I still can't see myself liking the concept much.

It could certainly make things interesting in an autocross or amateur racing, but I find the old constant power engine system more appealing. I'd rather set up for the pass over the long run rather than push a button and suddenly be the fastest car on the track (not to say that boost systems would make strategy pointless). Of course my mind could change if I were able to use it at some point, but that's not happening any time soon.

Am I the only one who doesn't like it?

 

[Rotary Junkie]

I don't like it either in cases where it is only there for a boost to the midrange.

Makes me wonder why they didn't just map it that way initially, considering if it's not going to blow the motor up it's not going to blow the motor up

 

[McLaren]

I was reading a Motor Trend article on BMW 335, and came across another mention of overboost. Yet again I found myself rolling my eyes. It's not quite as bad launch control I guess, but I still can't see myself liking the concept much.

It could certainly make things interesting in an autocross or amateur racing, but I find the old constant power engine system more appealing. I'd rather set up for the pass over the long run rather than push a button and suddenly be the fastest car on the track (not to say that boost systems would make strategy pointless). Of course my mind could change if I were able to use it at some point, but that's not happening any time soon.

Am I the only one who doesn't like it?

I'm pretty sure this kind of feature has found its way to every manufacturer whether it's Corsa Mode, or Power Mode.

If I were to guess, I'd say most manufacturers have these modes as an optional button instead of leaving it standard so that ride comfort, or gas isn't affected by an additional "sport-mode" (firmer suspension, little extra power at WOT), unless you choose to.

 

[neanderthal]

There are considerations (heat, durability, fuel economy, warranty, budget etc) that may have a bearing as to why a manufacturer can make a car with higher power but chooses not to.

As far as I cam concerned, it boils down to them being able to charge you more to uncork the engine.
Case in point, most Porsches with the standard exhaust sound like crap. Buy the uber expensive sports exhaust and it sounds sexy.

 

[Philly]

Put a piece of duct tape over the button and you have the world's cheapest 20 hp boost...

Which, according to my calculations, is a better hp/$ ratio than the equivalent GReddy sticker.

 

[niky]

Partially that, mostly this:

Makes me wonder why they didn't just map it that way initially, considering if it's not going to blow the motor up it's not going to blow the motor up

It depends on how long you need to be in overboost for the motor to blow up.

The overboost setting is usually one which they've determined will generate un-necessary heat/stress/pressure/wear/etcetera if it's left on too long. And yes, that does happen... modern, high compression turbo engines already run pretty "hot". Having a default boost pressure that's lower helps them maintain the warranty for the vehicle for much longer.

It's the same as with ignition and fuel maps. Even high-strung high-revvers can see a bunch of extra ponies from retuning, but tuning as such would make them too sensitive to octane, heat, etcetera.

 

[Bones Brigade]

i think the whole thing is a gimmick. its no secret that the current 335 makes more than 300hp. my honest opinion is that the new the n55 actually does make 300hp and the n54 is now uprated in print, but still produces exactly the same numbers, outside of "overboost." great marketing.

 

[niky]

Well... dyno results are conflicting. Dynojets claim a big number... around 270-280 at the wheels. Brake dynos show around 250-260 whp. I'd trust the brake dynos more, as a sweep test on an inertial dyno will be affected more by such factors as torque, gearing and drivetrain inertia since it measures only drum acceleration, not actual torque. A loading dyno will not be affected. It measures actual torque.

Numbers for the 335i are about 90 whp lower than M3s on the same dyno. The numbers all seem to point to around 300 or so HP. BMW didn't have to under-rate the 335i. They simply had to program the electronics to limit the power. You can chip a 335i for up to 400 bhp, but this obviously voids the warranty BMW wants to maintain and gives you less reason to buy an M3.

That said... a 335i, even with a good exhaust at full howl, doesn't sound anywhere near as good as a stock V8 M3.

 

[Murcie_LP640]

This is the same with the new Z4 (sDrive35is or w/e the **** it is) but I thought it was a boost to torque rather than power? I read about the Z4 in Motor Magazine and its torque output was rated at 450Nm (~332lb-ft) @ 1400rpm with an overboost to 500Nm (~369lb-ft) for "brief bursts under acceleration".

But as an answer to the original question I think it's a bit of a waste of time. There's probably going to be two groups of people: one that doesn't bother with the overboost, and another that doesn't bother WITHOUT it.

 

[niky]

It boosts mid-range and low-end torque... hence... boosting horsepower in those rpm ranges.

Overboost is fun. And it's practical. It allows you to run a highly strung turbocharged engine safely and economically when you're not "getting it on"... which is why more and more manufacturers are using it.

Although it's nicer to have a feature like the "M" button on the M5, where you could select a completely more aggressive engine map for times when you want to have fun.