What are the dis advantages of Turbo?

[sasha055]

A lot of my friends got themselves new cars for christmass (non porsche)

And while discusing it I noticed them most of them have around 220-240 HP (1.8-2.2L with turbo)

Why is porsche makes only 1 model of turbo? are there any dis-advantages of turbo.. other then cost?

Thanks
Sasha

[Flavor 987S]

Originally Posted by sasha055

Why is porsche makes only 1 model of turbo? are there any dis-advantages of turbo.. other then cost?

Thanks
Sasha

Only 1????

Let's see, in their recent/current line-up:

1) 911 Turbo
2) 911 Turbo S
3) Panamera Turbo
4) Cayenne Turbo
5) Cayenne Turbo S
6) GT2

[jmatta]

Porsche has a long history of producing turbocharged cars...first proven on the racetrack, the technology found its way into street cars back in the seventies.

Don't look too hard for new models being turbocharged, as Porsche appears to be focusing on the hybrid market presently. That being said, Porsche may introduce a smaller two seater or perhaps even an updated Boxster with a turbo four. This could really come into play if Porsche re-enters F1 as an engine producer, as they were extremely successful the last go around (partnered with TAG).

Turbo lag is often quite difficult to deal with...my '88 930 turbo was a pig "off boost" and would turn into a raging maniac when the boost kicked in.

[ekam]

NA engines in general have flatter torque curve and this is especially true for our flat 6 engines. In a track car you want steady power not power spike from hitting boost in big turbo units mounted on little 4-cyl engines. You'll often read about turbo lag on WRXs and they're slow on a tight track because it's hard for them to stay in boost.

Turbo engines also require bit more care than NA engines.

[blue2000s]

In general turbocharged engines require lower compression ratios to accomodate reasonable boost levels without preignition. This results in "lazy" engine response when off boost and a serious lack of torque off boost. The throttle response isn't particularaly great either. Direct injection is improving all of this, but still not eliminating it.

Often it's difficult to have a turbo system that can spool fast enough for low end torque yet still provide satisfactory power up to redline. Turbos just don't have the wide operating range that an engine requires. This is why Porsche has the variable vane turbo and Mazda had the twin sequential turbos. I can attest to the earlier statement about the powerband of the WRX. There's no power until 3000 RPM. Low speed turns in 2nd gear are frustrating. I find a 3 liter normally aspirated engine much much more satisfying to drive than a 2 liter turbo of equal power.

Turbocharged engines are more highly stressed, they run hotter, the combustion chambers see significantly higher pressure. Because of this the cylinders and pistons must be more robust and therefore heavier and more expensive. The former lowering redline. The turbo, piping, intercooler, ect add weight and expense as well. In general the turbocharged car is heavier and more expensive Kthan the naturally aspirated equivalent. All the extra stress means the engine and other parts won't last as long and need to be serviced more regularly. They are also more expensive when serviced.

Depending on driving conditions and habbits, there might be a fuel economy advantage to the turbocharged car. For exampleq, highway driving is off boost so consumption of a small 4 cylinder is better than a larger 6. But if the driver uses the car's powerband, the turbocharged economy will be worst than the non-turbo. Tubocharged cars tend to run more rich under boost to keep the intake charge cool.

[laphan]

Also, turbo performance is much more dependent on ambient air temperature and charge air cooler performance. In high elevation, turbo engines perform better than NA (pressurized intake and low ambient air pressure).

On the bad side, turbo engines have more moving components means their long term reliability might not be as good as NA engines.
DI adds into that issue too; high pressure fuel injectors and high pressure fuel pumps with all those turbo complexity (e.g. BMW 3.0L turbo has all kinds of issue with high pressure fuel pump and DI injectors).
It also needs better cooling for turbo components (turbo blade and bearings), many manufacturers run coolant or oil to cool the turbo components. The charge air cooler dumps a lot of extra heat, this usually translate to higher under hood temperature (for cars with front engine) which is usually not good for components such as battery, alternator, belts, etc.

[Flavor 987S]

Originally Posted by jmatta

Turbo lag is often quite difficult to deal with...my '88 930 turbo was a pig "off boost" and would turn into a raging maniac when the boost kicked in.

No turbo lag here! But, yes in a 930 I understand your point.

[sasha055]

Ekam, it's funny.. my first words to him were " racing you in a straight line is dumb"

Well, he's a good friend. and he's been bugging me for over a month now.. what can I do.. we have playdates with kids every other day and that's all he talks about

It seems that his car would make 6 sec 0-60 in tests, and I have 2000 base which should be 6.5 sec...

Time to finally install that underdrive pulley I've been putting it away for way too long (it's cold in my garage)

Thanks
Sasha