Turbos

[ManDownUnder]

As I understand it - turbos, use a little more fuel - and give of HEAPS more power (i.e. the power added is dispoportionately higher than the fuel used...)

I assume the same is true of mechanical blower?

1) Is that the case...
2) If so, why don't all vehicle have 'em. It's good for power and good for the environment (smaller motors, same amount of power - works for me!)

Or am I working with false premises?
MDU

[FlyingDutchMan]

The theory behind turbos says that is true (higher compression blah de blah gives higher efficency), but in reality they use shite loads more fuel for the power they produce. A mechanical blower (supercharger?) is similar but doesn't suffer so much from turbo lag - i.e. you open up the throttle and it will give you the power right then and there... depending on the type of supercharger you've got of course. Some pump more air at low rpms, some need heaps of rpms. They're huge amounts of info out there, but in general a normally aspriated vehicle is more efficent, even if it produces less power. Anyway production turbo cars generally produce the same hp/litre as a sports bike (around 180 hp/litre).

[scumdog]

As I understand it - turbos, use a little more fuel - and give of HEAPS more power (i.e. the power added is dispoportionately higher than the fuel used...)

I assume the same is true of mechanical blower?

1) Is that the case...
2) If so, why don't all vehicle have 'em. It's good for power and good for the environment (smaller motors, same amount of power - works for me!)

Or am I working with false premises?
MDU

Things NOT good about turbos: they add weight, they take up room, they create lots of heat in a small area, they require lots of plumbing/wiring, they do not give much grunt until they 'spool-up' (turbo-lag), when under boost the engine takes a hammering - ergo need stronger components.

Thins NOT good about superchargers: same as turbos generally but also not so 'flexible' when it comes to where they can be located (mostly driven off the crankshaft), greater 'parasitic' loss of power (i.e. the s'charger takes 20hp to drive so to make 100hp at output shaf it has to put out 120hp at crank). One good thing about s'charging is there is no 'lag', it makes hp. straight away

My 2 cents worth

[ManDownUnder]

Thanks Dude. Kinda explains why it seemed wrong for all vehicles to be non boosted, but the performance stats suggested they should be (to me anyways...


MDU out!

[bugjuice]

The other problem with turbos is that when you've got it, you use it more, so you go thru more fuel anyway, just cos you spend half the time dickin around making the turbo spin up. From what I understand, the turbo is forcing more air into the engine, more fuel is added, thus creating your extra power boost. The turbo is driven from exhaust gases, so the exhaust has to be pumping out hard before the turbo spins up to compression, hense your turbo lag. To reduce the lag, you use a smaller turbo, but that's smaller power, hence 'twin turbos'. One is a smaller one to get off the lights, then they cut over to the larger one where the bigger turbo is more effective higher up the rev range. You can bodge this to be two big turbos on things like V6s etc. But turbos can often out-spin most engines, so the boost lasts and lasts most of the time.

Compressors (mercs call 'em Kompressor), super chargers, blowers etc, whatever you call 'em, work mechanically and often belt driven, so it works straight off as the engine spins up. These don't have any turbo lag. But they don't have much top end.

What I want to know, is given the theory of how both work, can they both be bolted to one engine? The supercharger will give you the boost off the lights, the turbo will give the power up the rev-range..

I'd love to fit a small turbo to my bike, not for the power increase, but just to hear the whoosh from it..

[vifferman]

Some truths there, and some untruths. Turbos use more fuel when being used because they're forcing more mixture through and creating more power. However, turboed vehicles often run lower compression ratios, so when they're being run below the range where the turbo kicks in, they are more economical than the same engine without a turbo.Turbos give 'free' power in a sense, in that because they're using exhaust gases to drive them, they're not sucking any power from the engine. As has been stated, superchargers suck lots of power as they are a mechanical compressor driven off the crankshaft. Some more sophisticated models are disconnected when the extra boost isn't required, thus not provided a penalty at lower throttle openings.

The lag can be gotten round by making the turbo impellor smaller, by using a 'twin-scroll' turbo, or by using two turbos, one which kicks in at lower revs, and another larger one that kicks in later.

The latest superchargers use a system that is driven by a 'magic fluid' that doesn't slip when under pressure, so that at low revs it slips, then locks up when revs (pressure) increase. Instead of gears or vanes, they use planetary rollers that multiply the input revs by 5 or 6 times. These are very effective on small engines like bikes, as they are compact and efficient.

[Ixion]

..

What I want to know, is given the theory of how both work, can they both be bolted to one engine? The supercharger will give you the boost off the lights, the turbo will give the power up the rev-range..

I'd love to fit a small turbo to my bike, not for the power increase, but just to hear the whoosh from it..

In theory yes. Some car maker did it but I can't remmeber who. I think maybe it wasn't a great success.

[scumdog]

I'd love to fit a small turbo to my bike, not for the power increase, but just to hear the whoosh from it..

Why bother, look up Trademe, Ebay and buy yourself a Suzuki XN85.....

[TonyB]

One good thing with turbos is once spooled up they give you huge amounts of torque over a very wide rev range, so while the maximum power may not seem that great, the engine will pull like nobodys business from the moment the turbo kicks in, not just at the top of the rev range like a normally aspirated engine does. For instance the latest Legacy GT 2.0 turbo makes 205kW at 6400 rpm and peak torque is 343 Nm at 2400 rpm. While the Legacy 3.0R SpecB makes 180kW at 6600rpm and 297Nm at 4200rpm. So despite having a 50% bigger engine, the 3.0R SpecB makes less power, but more importantly, significantly less torque at much higher revs.

[Suney]

What I want to know, is given the theory of how both work, can they both be bolted to one engine? The supercharger will give you the boost off the lights, the turbo will give the power up the rev-range..
it..

In the ausie Hot4s magazine, there a red corolla sporting both turbo and supercharger, so it's definitely possible

[bungbung]

However, turboed vehicles often run lower compression ratios, so when they're being run below the range where the turbo kicks in, they are more economical than the same engine without a turbo.

Isn't that arse about face?

When operating in the off-boost situation, they are less efficient than the equivalent na engine running at a higher compression.

[bugjuice]

Why bother, look up Trademe, Ebay and buy yourself a Suzuki XN85.....

cos it isn't sexy orange, and doesn't look menacing like mine does..
I just wanna hear some whoosh..
like this, but not as much power 499bhp (~12.7mb)

[TonyB]

Or how about this:
Current Ford XR6- 182kW @ 5000rpm, 380Nm @ 3250rpm
Current XR6 Turbo- 240kW @ 5250rpm, 450Nm @ 2000rpm
Current XR8- 260kW @ 5250rpm, 500Nm @ 4250rpm.....no wonder they feel so bloody peaky when you drive them- all the power and torque are at the top of the rev range. The XR6 Turbo is a much betterer car.

[scumdog]

Isn't that arse about face?

When operating in the off-boost situation, they are less efficient than the equivalent na engine running at a higher compression.

Dead right, a lot of the time the first bit of turbo boost is just getting the engine into thinking it's running at 11:1 comp instead of 8.5:1.
A hi-comp engine under lightish load is going to be more fuel efficient than a low-comp one under the same load i.e. will run a higher vacuum.

[chris]

What I want to know, is given the theory of how both work, can they both be bolted to one engine? The supercharger will give you the boost off the lights, the turbo will give the power up the rev-range..

The Lancia Delta S4 had both fitted during the heady days of Group B rally cars. I presume the turbo was fited to compensate for the superchargers inability to provide decent boost at high RPM.

Turbos do not necessarily have to suffer from lag. The newer ball bearing models tend to spool up much quicker and just about eliminate lag. The other way to eliminate lag, as the WRC cars use, is an anti lag system that injects and then ignites fuel directly in the exhaust system when the driver is off the throttle. Doersn't do much for the life of the turbo components though.

Superchargers are great, but my choice would be turbo.