8 replies to this topic

[Nathan]

Sorry for the poorly worded title, but I cant think of any other way to properly word this.

I was wondering how one would compare the equivelent of a turbocharged engine, with a certain engine size and boost level to a normally aspriated engine?

I have read that you multiply the bar (pressure) with the engines liter size. Eg...a 2-liter turbo engine running 2-Bar of pressure is the same as a 4 liter NA engine (2.0*2=4) when both engines are tuned to there mechanical and mathmatical maximum's. I was just wondering if this is the correct way to compare one type of engine to another???

[Richard Border]

You may want to try this http://www.turbofast...alc.html#readme

[f40nz]

For motor racing you multiply the engine capacity by 1.7 to get the equivalent naturally aspirtated capacity for class ratings, so 2 litres becomes 3.4 litres:)

[Halfwitt]

Originally posted by f40nz
For motor racing you multiply the engine capacity by 1.7 to get the equivalent naturally aspirtated capacity for class ratings, so 2 litres becomes 3.4 litres:)

How did you arrive at this pearl of wisdom?

In the turbo F1 days the 1.5l turbo engine were easily more powerful than the 3l NA engines. Therefore at its limit this factor would be AT LEAST 2.

[bukusuma]

1.7 was (is?) an equation originated by the FIA in Rallying.

If I'm not mistaken, the multiplier was 1.4 back in Group B times.

Regards,

Bram

[BRG]

There have been various Equivalency Formulae used by the FIA etc. In the 3-litre F1, it was 2 (ie a 1500cc turbo engine = a 3000cc n/a one). The British MSA use 1.7 so to be in the up to 2000cc class, you cannot exceed 1176cc if using forced aspiration.

But these are notional formulae - when the F1 rule was written, people were thinking about supercharged engines and it was meant to effectively rule out forced aspiration. But technology moved on and Renault proved that a 1500cc turbocharged motor could outperform a 3000cc n/a one and the rest is history.

The truest way to compare is probably by measuring how much power can be produced for a given flow of fuel. Then you might be comparing a 1400cc turbo with a 6 or 7 litre n/a. Group C Sports Cars sort of went down this route by using a maximum fuel allocation per race.

Ultimately, a turbocharged engine should be more efficient (or rather, in the case of petrol or hydrocarbon-burning reciprocating engines, less inefficient) than a normally aspirated one because it recylces energy otherwise lost down the exhaust as heat and noise.

[palmas]

Well, try it in this simple way:
The power you would get depends on the capacity of fuel burning (in correct conditions). And the fuel you can burn depends on the oxigen you can put inside the cilinder.
Well, for a perfect gas, for the same temperature, if you have doble pressure, you will have doble mass. So basicly for 2 bar(a) you would have doble power. There are however other details to consider:
turbocompressors increase air temperature
the flowing of compressed is is a little different fron NA air
thermal load of engine (and smaller surface to cool) will avoid using very high turbo pressure
the conterpressure turbochargers make on the exhaust will diminuish the power output

etc, etc, etc...

So do not believe those who tell you there is a fix relation on power output/engine capacity between NA and turbocharged engines.

[Ray Bell]

The present FIA equivalency formula would seem to be 1.7:1. This is mentioned above, and is also the figure used by CAMS in Australia, which usually follows most of these things fairly closely with the FIA.

It was 1.4:1 for many years, however, and I don't know when it changed, but change it had to... as shown by the F1 experience. The 1.4:1 ratio was used worldwide, too.

When the 3-litre formula was proposed, it was not expected that a supercharged 1.5 would be any more powerful that a naturally aspirated engine of 3.0 litres. But times change... remember that N/A engines came ahead in leaps and bounds in the F1 supercharging void of 1952-1965?

Well, the pendulum swung, largely because of the introduction of turbocharging...

[Halfwitt]

Well, if you believe the figures:

1.5l turbo: 1500hp, 1000hp/l

3l NA 600hp (late 80's) 200hp/l

Therefore equivalency ratio (in this case) is 5:1