turbo vs nasp engine sizes

[sanjsanj]

hello there
does anyone know how big a normally aspirated engine would have to be to produce as much power as a turbocharged engine (with all other variables kept pretty much similar) ?

[pgarner]

hey they can be similey sized
for instance my bora is supposed to be 180bhp from 1.8t engine so 100bhp per ltr
the civic 1.6vti gives 160 from a NASP engine again 100 bhp/ltr
current M5 504 bhp from 5ltr 100.25 bhp/ltr


what do you mean by al other variables ?

[HDi fun]

This is a simple question that is nowhere near as simply answered. I'll ignore my favourite soapbox, which is high performance diesels, but will cover that topic quickly;

I have yet to drive a NASP diesel with anything other than leisurely performance. If you have any ideas about useable performance then forget NASP diesels. You can also discount anything without electronic high pressure injection - even if it is turbocharged.

Petrol cars are a different matter. We'll discuss factory tune for now.

VW/Audi is an interesting research point. VAG's 1.8 litre 4 cylinder, 20 valve unit is available in so many flavours. The NASP engine delivers 125bhp and drives very nicely indeed. Yes, it's ploddy, but quiet and comfortable; in fairness, it gets on with the job in a pleasant kind fo way. It's also available in several other levels of turbocharged tune. 150bhp is the very modest one. In the Audi TT this can be had with a 250bhp spec. Yep, it goes.

Ignoring diesels (as the differences between NASPs and turbos is too wide to consider) in general you can expect, for example, a turbocharged 2.0 litre four cyl petrol to offer similar power and torque to a three litre V6 petrol. The turbocharged motor will probably be more economical in fuel terms than the 3.0 V6. The V6 will probably sound nicer, and will probably last longer, although lots of manufacturers are now designing engines with a view to offering them in turbo form only so cooling issues should never be a problem.

I depends really on how you like to drive - turbochargers can be exciting and offer some silly gains in performance on paper.

Personally, I still like the idea of a quad cam large capacity V8 with everything done in a nat asp kind of a way. With an auto box.

Yet, I drive a manual 2.2 litre diesel. And it's nowhere near as bad as you'd think.

[waynne]

The volumetric efficiency of a NASP engine can be anything between 40 and 70%. The highest power figure I have seen is from the Hondas at 100bhp per litre as P Garner says (the s2000 also fits this profile). When you add a turbo you dramatically increase the power of the engine but there is no real scale as each engine is different.

A Turbo 2.0 can produce upwards of 400bhp to a max of about 750bhp. For a NASP engine to acheive this it would need to be 4.5-8.0 litres and will typically produce around 80-90bhp per litre.

Did HDI really type "ignoring diesels"

[sanjsanj]

Originally Posted by HDi fun

in general you can expect, for example, a turbocharged 2.0 litre four cyl petrol to offer similar power and torque to a three litre V6 petrol.

That,^, is exactly what i'm trying to find out.

in the above example, the turbocharged engine needs to be 1 litre smaller to produce similar power/torque output to a NASP engine. Does anyone have a example of this for a car manufacturer?

Even though they produce similar power/torque outputs, why does the turbocharged engine use less fuel? Lighter engine maybe?

[HDi fun]

It's probably down to the engine being smaller, therefore lighter and with less internal friction. The car is also likely to be lighter as well. I do think that the gap would close quite a lot if you drive the arse off two similarly powered and weighted cars, even with a 2.0 four Turvo against a NATASP 3.0 V6. Ultimately, you've got to burn fuel to generate torque and therefore power.

I suppose if you really can afford a 6 litre V8 then fuel economy is not likely to be a problem. Hence they're not fitting quad turbo four cylinder units in their place.

I know VW has an interesting 1368cc unit at the moment. Petrol FSI unit with a supercharger and a turbocharger. Allegedly good for 168bhp...

Not driven one, so can't comment

[old-git]

Every engine design has different characteristics so I don't think that there is a straight NA/Turbo ratio.

Sticking to my realm of experience:
Ford Cosworth 4 cylinder YB 2 Litre
N/A - Struggling to get over 300bhp = 150bhp/litre
Turbo'd - Over 1000bhp has been achieved = 500bhp/litre

[pgarner]

Originally Posted by sanjsanj

Even though they produce similar power/torque outputs, why does the turbocharged engine use less fuel? Lighter engine maybe?

when holding a steady speed the turbos not on boost so the engines works more like its NASP equivalent in other words theres not as air going into the engine so not as much fuel is required and more economical.

as well as the lighter engine

Originally Posted by "HDI fun"

I know VW has an interesting 1368cc unit at the moment. Petrol FSI unit with a supercharger and a turbocharger. Allegedly good for 168bhp...

yeah the TFSI engine its supposed to be very nice to drive . i remember VW were talking about putting it in the passat as a possible replacement for the R36 engine as a GT car. its also turned up in the VW cup in a modified golf. it was doing well as it was much more economical than the R32 VR6 and 1.8t that were racing around with it so could carry less fuel, so less weight.

yeah the S2000 is where factory NASP engines are getting silly 240-250bhp from a 2ltr 120bhp/ltr and this from a factory tune engine

[waynne]

Interesting fact = the S2000 head is pretty much perfect flow wise. I've not heard of anyone who has managed to get any better flow from it! Way to go Honda.

The key arguement here with NASP and Turbo is volumetric efficiency. The turbo uses the engine capacity more as the air is being pushed in. The more efficient the engine the less fuel it will use for the same power as a less efficient one.

I can see the day coming where all cars have Forced induction as standard due to stringent emissions. (This will be a tuners dream!)

[pgarner]

well look at Renault with the clio theve turboed the 1.2 engine to replace the 1.4. you get roughly the same power but better economy and emissions

[garagestmarien]

I remember when formula 1 had turbos and to equal the power to the others, the engines were half the size. 1500cc turbo, 3000cc normally aspirated.

[HDi fun]

As OG says - there's no easy way to compare and provide an accurate ratio.

As for 1980's F1 cars, it's true the turbo's were limited to 1500cc but then the engine only had to last one race before a rebuild so it didn't matter if you ran at 24,000rpm with 3 bar of boost.

No manufacturer would consider this kind of brutal treatment for a road car.

Furthermore, the economy was not an issue as there weren't significant fuel limits. It was commonplace to overfuel the engine to reduce combustion chamber temperatures.

I'll stick to my guns though. If you have 200bhp on tap and use all of it all the time then you will burn fuel, whether it's diesel, petrol, NATASP or forced. There's no free ride really.

[waynne]

I read not 20 minutes earlier that a 1500cc F1 car with turbo produced 1500bhp! Hows that for a power gain.

[pgarner]

was that not a BMW engine ?

[waynne]

I think it was 1982 Brabham - BMW BT50 F1 car.