Cowhorn

...during my around-town driving, I rarely accelerate enough to call on the turbos for boost. My question is what are the qualities of the engine when it isn't being boosted? Is it similar to a GT3 engine or one of the other 3.6 liter powerplants?

I hope that makes some sense.

dianic

hmmm i think you "think" you dont use them...
I recently upgraded by exhaust, and I can tell you that the turbos work a lot more than you think. I can hear them spool all the time, across all ranges. From coming up my driveway in the garage, to even cruising and just applying the gas a bit more...
Trust me they do turn...

Z06

It has lower compression so it's slower/less power then a NA engine.

Cowhorn

You are probably right. I am going by the boost gauge on the dash. Only when I hammer it do I see the boost register.

Cowhorn

This is the feeling I get.

So when do I actually get the benefit of the 480 hp and 450 ft-lb of torque? With wide open throttle only?

dianic

no, consider this as a slope rising, just like the chart of a dyno. Full trottle will get you 480hp towards the upper end of the rev range. Before that, its a smaller amount of hp that you get. Max torque comes much lower. Also there are ridiculous speed levels where high revs wont get the turbos to register boost, but you will be flying with over 100 mph...

The biggest advantage of the turbo in my view is the 50-60, or the 80-100 or any sort of acceleration between two points where a turbo car is dramatically faster than a NA engine. I may not be getting 480hp there, but I am getting my money's worth!!

Eric - Plug Guy

My turbos get exercised every time I drive....and that's mostly street driving, not racing, not pucker inducing, but exhilarating.

foreplay

yep less compression

Cowhorn

Can somebody expound on the significance of compression and how it effects the way the car feels? I'm not very clear on the concept. Thanks.

Leigh2

Compression increases cylinder pressure which = torque. So an engine with a 12:1 compression ratio will have way more torque and better throttle response than a comparable engine with a 9:1 compression ratio. Once the turbo kicks in it forces more air into the cylinder effectively raising the compression ratio and increasing the torque.

Cowhorn

Got it. Thanks.

Macster

To make an educated guess as to the answer to the question you ask one I think needs to have before him the torque/HP curves for the 997 Turbo engine and the NA 996 or NA 997 engines to be able to say.

IIRC this is provided in the owners manual, but I do not have my Turbo handy to consult its owner manual for this info, to at least confirm it is present in one of the 996 car's owner manual.

The factory service manual I have for the 996 Turbo gives the max engine power (as per 80/1269/EEC) of 309 (420) in kW (HP) and the net power as per SAE j1349 of 415 in HP.

Max torque is given too.

Then after net torque as per SAE J1349 is given (415 ftlbs) this is followed by an rpm range of 2700 to 4600 rpms. Thus the engine produces 415 ftlbs of torque from 2700 to 4600 rpms.

This last bit of info if one has it for the various engines under consideration can help one develop a sense of how the engines compare.

The 997 Turbo's torqe/rpm curve that most closely matches that of another engine, then one can I believe develop a feel of which engine the 997 Turbo morely closely mimics.

But as I stated above, I do not have this info for the 997 Turbo engine nor for any of the NA 996 and NA 997 engines.

The 997 Turbo engine's lower compression ratio means the engine's not going to have quite the off idle responsiveness the NA engines have.

However, the compression ratio is pretty high (for a turbo-charged engine) which does help some and I'm sure valve timing (and variable valve timing) and variable valve lift and other things are chosen to compenstate for the Turbo engine's lower compression ratio.

I point out too the 997 Turbo has variable turbo vane control which means the engine controller can select a turbo vane setting that allows the turbos to develop boost at a lower rpm than that of a non-variable turbo engine (aka the 996 Turbo), which helps this compensation.

The saying is the car owners buy HP but drive torque, so car makers (at least Porsche) strive to provide competitive HP numbers but also strive to provide an engine that supplies a good torque curve, with torque kicking in at a low(er) rpm, reaching max torque as soon as possible, and the torque output remaining as flat as can be to as high an rpm as possible.

Thus my guess (or WAG) is there's little difference between the 997 Turbo engine and the NA 997 engine off idle, that is even though they are different engines, they have similar personalities cause most drivers would be turned off by a flat feeling Turbo engine, but of course once the Turbo engine begins to make boost then two engines begin to diverge considerably in their personalities.

Sincerely,

Macster.

Cowhorn

^^^ Thank you. I will try to look up and compare those hp/torque curves.

ELMEL

Great thread.

I have a 996TTS, so perhaps the algorithms used to display data on the display are different than the 997, but I very frequently see turbo action even under light to moderate acceleration. Low bars, but there nonetheless.

eclou

Having had a 2007 GT3, I can tell you the 997 turbo has far more grunt at any given rpm. The Gt3 felt like a beetle until it hit 5500 rpms