NA vs. Turbo

[Riker]

Let's say we have similar weight cars, one is NA and the other is Turbo. And they have similiar HP.

Is the turbo in advantage, and why?

[AJLintern]

The NA car will be better as it has a smoother power delivery and there are less things to go wrong

[edc]

You could have a highly tuned 2.0 16v on throttle bodies perhaps but it will be a screamer and probably well down on torque compared to a 2.0 turbo. At the same time you could have a big capacity engine with relatively low power but big torque. I can't see a real advantage unless you are comparing specific engines.

[350matt]

If you've got two engines producing identical torque curves say 2.0ltr 4 cyl turbo vs 3.5Ltr V8 NA then chances are the choice of which is 'superior' will boil down to packaging advantages, although the turbo should offer slightly better fuel consumption this will be very marginal with todays engine designs.
Throttle response may be better with the NA lump but with modern fuelling requirements mabye not.
Horses for courses etc etc.

Matt

[Sparks]

350matt said:

If you've got two engines producing identical torque curves say 2.0ltr 4 cyl turbo vs 3.5Ltr V8 NA then chances are the choice of which is 'superior' will boil down to packaging advantages, although the turbo should offer slightly better fuel consumption this will be very marginal with todays engine designs. Throttle response may be better with the NA lump but with modern fuelling requirements mabye not. Horses for courses etc etc. Matt

But the V8 sounds sooo much better

Sparks

[annodomini2]

It depends on the engines in question and the vehicles, generally a medium capcity turbo'd engine in comparison to a large capacity engine. the turbo'd engine is generally lighter and therefore suited to a smaller vehicle hence lighter still.

A naturally aspirated engine is generally more responsive at low revs and generally pull away better (so in first gear a large capacity engine has more chance (assuming same gear ratios))

The turbo engine can have more potential for power to weight ratio than the na engine.

The NA engine is generally smoother to drive (dpepending on state of tune)

[Mr2Mike]

350matt said:

the turbo should offer slightly better fuel consumption this will be very marginal with todays engine designs

A turbocharged petrol engine will always have a higher brake specific fuel consumption than an NA of equivalent power. The turbo will have a lower compression ratio which hurts thermal efficiency, and the restriction of the turbine itself leads to higher pumping losses.

With a diesel engine things are a little different as you don't need a low CR to prevent detonation (but pumping losses will still be higher).

[GreenV8S]

But off boost, the lower displacement should reduce friction losses? Don't know how significant this is compared the lower CR, but I thought this was one of the main reasons bigger engines are less economical under part load.

[Mr2Mike]

GreenV8S said:

But off boost, the lower displacement should reduce friction losses? Don't know how significant this is compared the lower CR, but I thought this was one of the main reasons bigger engines are less economical under part load.

The displacement remains the same, irrespective of load. Engines are less efficent at part throttle due to the very low dynamic compression ratio. The engine i sucking in less air, but compressing it to the same volume, hence lower CR and lower thermal efficiency.

The turbocharged engine takes a double wammy as it's CR is already lower than that of an N/A engine to start with.

Frictional losses increase with RPM, and to a limited extent with load.

[GreenV8S]

Sorry, I meant that the turbo engine would presumably have less displacement that the NA one, and hence when the two engines were off load, the turbo engine would suffer lower friction losses than the NA one.

[boosted ls1]

Riker said:

Let's say we have similar weight cars, one is NA and the other is Turbo. And they have similiar HP. Is the turbo in advantage, and why?

Apples for apples, the turbo car will produce 30-50% more torque if you retain the stock compression and it's not excessive. So for an engine on 9:1 c/r you can safely use 7 psi boost. It will have stock atmo qualities off boost and be very satisfying on boost. Been there so I know it's really good on an 8 cylinder!
Off boost the engine just stays the same, as it was!

[accident]

bhp is a made up number that means little or nothing in the real world of performance.
the only true mesure is put the different engines in the same car on the same day with the same driver and then you might get a real answer.
other than that you have to take personal experience.
i had a sunbeam that with 250 atmo was easilly quicker than my 3dr sierra 350 turbo.
i have a 893cc atmo car that would easily beat both of them.the only real truth is .DRIVE THE CAR YOU HAVE,HARD!

[350matt]

Mr2Mike said:
'A turbocharged petrol engine will always have a higher brake specific fuel consumption than an NA of equivalent power.'
Yes when its on boost /full load but when just cruising / part load then you tend not to need as much fuel as the Big NA engine consequently the average fuel use is less. Not much less mind you but less.
Which is why manufacturers of large NA engines are now looking to switch cylinders off entirely when not required.

Matt

[boosted ls1]

Yep, a turbo engine will make you grow horns and you will be tempted to hit the gas. It really is a good idea to stick to atmo compression and use low boost so you get the best of both worlds. If you drive normally your fuel costs should be very similar to as before

[GreenV8S]

boosted ls1 said:

It really is a good idea to stick to atmo compression and use low boost so you get the best of both worlds.

Good man, that's exactly what I wanted to hear!