Naturally Aspirated

[ESfour]

Will someone explain to me what exactly a "Naturally Aspirated" engine is[confused] Sorry for sounding like a nob.

[Imperial]

An engine that isn't turbo or super-charged [:)]

[S4audi_SD]

B6 S4 = naturally aspirated

B5 S4 = forced air induction (turbo)

[Anthony]

Also known as "Normally Aspirated". The boys above explained it well. Basically just an engine that isn't force fed, but rather relies on its natural displacement to make the power.

B5 S4 = only 2.7 liters, needed two turbos to make the 250 ponies.

B6 S4 = big ol' 4.2 liter V8, packs plenty of punch. 340 HP worth, baby! [:D]

[ESfour]

Here's an excellent explaination I got from a guy at germancarfans.com


There are several differences between (FI) Forced Induciton (Supercharged/turbocharged) engines and (NA) Naturally Aspirated engines. From the drivers point of view it all comes down to power delivery.
FI engines don't necessarily make more power than a NA engine there are many other variables. Displacement of the engine (bore/stroke), rev-range, timing intake/exhaust configuration, etc. all play a role in how much power the engine makes. That said in general a decently tuned FI ingine will make more power than an identcal NA engine. The shape of the power curve on a dyno graph will be very different though.

C4S driver is right on the money with his quick and dirty description of FI. More air into the cylinders. Therefore more oxygen to burn + more fuel = more power.

The reason some people prefer NA engines is because they do not have the lag and/or chunky power delivery associated with many FI cars. For example most high pressure turbo cars desgined to put out lots of power (like any single turbo supra) has something called turbo lag. A turbocharger works by using exhaust gasses to spin a turbine which in turn spins an impleller that compresses intake air. But since there is no direct connection between a turbo and the engine it take some time before enough exhaust pressure is built up (This is called spooling the turbos) and the turbos can create pressure on the intake side. This little bit of delay is called turbo lag. On bigger turbos it takes longer to reach the boost but once it hits it hits hard. A car with this system will start off slow but will haul @ss from mid revs or from a roll once pressure is built up.

Superchargers work very similarly to turbos but instead of being driven by exhuast gasses there is a direct connection to the engine by way of a belt. When the engine turns, it turns a belt, which turns a pulley on the superchargers which turns a compressor (there are many different kinds). The advantage over turbos is there is far less lag since the connection to the compressor is dircetly related to engine speed. Disadvantages are that in general it is more difficult to obtain very high boost from superchargers (most SC are below 20psi while turbo's can go up around 40psi on extreme street applications). Also because of the direct connection the engine uses a significant amout of hp to actually turn the compressor in the first place. The results in an initial reducation in power balanced out by a higher addition of power due to the FI effect resulting in (hopefully) a net gain of hp.

NA performance engines are smooth and seamless in power delivery. In a good NA engine there are no places where the power suddenly "kicks in" like in a turbo car. There is a nice long wide range of power across the full range of RPM's. For the hardcore performance enthusaist or track enthusaist who is unwilling to compromise throttle response for high end power or low end torque NA is the best bet. Throttle response and linearity of power delivery is unmached by FI engines with the only disadvantage being that the actual maximum power generated is less than the FI equivalent.

A typical comparison of FI versus NA can be seen in AMG vs M. Take the Type 12 AMG 65 series of engines 6.0L twin turbo 612hp 730+lb/ft . The power is phenominal, but turbo lag is there and the engine has a small rev range of less than 7k rpm. The E60 M5 V10 on the other hand is smaller NA generates 507hp and 383lb/ft less power but a much wider powerband ~8500rpm. Power deliver on these two engines could not be more different as well. I haven't been luck enough to drive either, but my money would be on the M5 when it comes to linear deliver of power to the wheels.

Sorry for the long rant but I just love this stuff and I hope this answers your question!

[SBGirl]

I've driven the B5 S4,I have a B6 S4 currently. I also owned the 3.0 A4(NA) and had a loaner 1.8(turbo) for awhile. I personally do not like a turbo. I do alot of mountain driving and the lag on the 1.8 and B5 S4 suck. On steep climbs it was impossible to get any real power. My 3.0 and S4 are seamless in the mountains. The difference between the 1.8 and 3.0 was incredible. The 1.8 was a complete dog. It was almost embarrassing. The 3.0 would pull the hills with no problem on the same road. Only the curves limited me.

[dukez]

Naturally aspirated means it doesnt need artificial aspirations.

** as·pi·rate Audio pronunciation of "aspirated" ( P ) Pronunciation Key (sp-rt)
tr.v. as·pi·rat·ed, as·pi·rat·ing, as·pi·rates

2. To draw (something) into the lungs; inhale.

[B6NogaroS4]

IMHO the B6 S4 in under-powered. It needs about 475 F/I hp.

[Gzo17]

Originally posted by ESfour

I haven't been luck enough to drive either, but my money would be on the M5 when it comes to linear deliver of power to the wheels.



well you would be losing money b/c the M5 is not nearly as fast as any of the AMG 65s........but I think we are talking about 2 diff things........M5 will probably run high 12s and the 65 runs in the high 11s

[jimmyrecluse]

^ agreed.

It sounds like you know the difference know between NA and FI. I wanted to add the parts about the power curves being different.

FI motors are generaly low compression. Lowering the compression allows you to run higher boost without detonation. For instance a ratio of 9.1 and 15 PSI would work out. 12.1 and 15 or even maybe 8 PSI on an average engine would be disasterous. SO... low compression high boost makes more power than high copression low boost and is safer. Because of the low compression and that big ass turbo sitting in your manifold restricting exhaust flow power sucks before your turbo spools. So I guess you could say the cons of a turbo are Lag, because the engine alone doesnt do anything.
Superchargers although they dont slow up exhaust flow because they are not powerd by exhaust gas, draw thier power from a pulley. This puts an extra load on your enigne... Its like the supercharger has to make a total of 40 HP just to make 30. It makes up for the power stolen and then puts out. the good thing about SC is that ther is no lag. Most start to boost at 1500 - 2000 RPMs and the boost increases as RPMS get higher and the crank turns faster. Niether turbo or SC are REALLY efficient...

NA is cool because you have a really nice even power curve. Turbo motors start low and then make high power, even with SC's you dont get the same response out of a well tuned NA motor. NA = high compression, cams, headwork yup that includes valves and good cold air.

What makes power is sparks, compression, gas and air. Spark ignites the gas fire needs air. FI shoves the air in the there is plenty to burn with NA engines you have to get creative and while you are not forcing air in you are making it easier to flow in as much as you can.