Turbo talk again.........

Well guys, I have yet to drive a turbo Porsche. However I have recently driven 3 turbo cars and need to comment. I never thought much about turbo cars in general, but this has changed.... They are fast!

First I drove a Volvo V40 T4 with 200 hp. Obviously too much power for this front wheel drive car. At 3000 rpm it really started to pull and struggle for grip. I could feel how the steering wheel pulled from side to side due to the power.

Then I tried a modified Volvo 850 Turbo with 265 hp. That's more than my Porsche !!! However the car ran on skinny winter tires (185/65x15) so I couldn't really explore the power. It had nice low end grunt and really exploded at 3500 rpm. At 160 km/h I backed off as the car "sailed" all over the road - scary.

For the last 2 weeks or so I have driven a Skoda Octavia 1,8 20V Turbo with only 150 hp. (I now work at a Skoda dealership instead of Nissan). This car has really got me convinced that Turbos are fun. Massive low end grunt with 210 Nm at 1750 rpm and nice smooth power all the way to 6000 rpm. No struggle for grip - ok maybe a bit, but not as the Volvos - and no power impact on the steering wheel. Also I don't trace that often mentioned TURBO LAG...?

So now I'm curious: How's it like to drive a non modified 911 Turbo 3,3???

BTW anyone near Denmark who owns one feel free to come by to take me for a ride

Mikkel

I haven't driven a 911 Turbo but to add to your comments about turbo cars in general, I have a (rear-wheel drive) Nissan 200SX (240SX in the US) with 197 bhp. I bought it mainly for the turbo - that big lump of acceleration that comes on at 3000rpm, but three years on and I am really fed up with the all or nothing power delivery. Below 3000rpm I have to floor the accelerator to get even modest acceleration, and then as the turbo spins into life I have to lift off otherwise I shoot towards the horizon. I spend my whole time see-sawing on the accelerator trying to get smooth power delivery. I learnt the hard way not to even look at the accelerator on wet corners!

I don't think this behaviour is what you would term turbo-lag - above 3000rpm there is no discernable delay between prodding the loud pedal and the car accelerating - but it is frustrating nonetheless. I would take an naturally aspirated 200 bhp over a turbo 200 bhp anyday. It is almost as if turbos are a mechanical "cheat" which you must pay for in a loss of driveability.

Having said all of that, the lump of acceleration at 3000rpm is really only a problem in day-to-day, city driving. If it were a weekend or even track car it would be fun rather than tiring, so perhaps I need a 911 Turbo for the weekends only and an NA for the work commute .

James

[This message has been edited by James Ball (edited 02-14-2001).]

Mikkel
I've had a fair amount of experience with turbos.
The advantage of a turbo is the phenomenal increase in torque, especially noticable in the mid-range). Torque x revs = horsepower.
The downside is very high fuel consumption. Due to the increased combustion temperature, the piston crowns are close to melting and have to be cooled by a rich fuel mixture. (the 930 engine is air, oil and fuel cooled).
You have to distinguish between old (first generation) turbos and new turbos. The older turbos suffered from antique engine/power management, which means that their power delivery can be on/off. The 930 is a typical example of that behaviour. In a slalom (autocross) competition they are absolutely crap, since you cannot accurately dose the power delivery. In this case a naturally aspirated car is far more fun to drive.
The newer turbos (993/996) has such a smooth power delivery (no turbo lag) that you virtually dont know there is a turbo (or two) on the motor. It's as driveable as an aspirated motor, except that there is a lot more grunt.
One more thing: the fact that a car handles bad or suffer from traction problems (like your Volvos do) is not the turbo's fault! The mistake is that the manufacturer put a powerful engine in a weak chassis.
Same as James, I had two Nissan 200SX's. I really loved their all-or-nothing power delivery (like being hit in the back every time you accelerate) and often found myself braking so that I can accelerate again (I was a bit younger then). Unfortunately their bad wet-weather behaviour caught up with me one day on a wet autobahn. It's no fun when you swap ends at 120 MPH and destroy everything in sight. The second one's motor snapped a con-rod at 6000 rpm (another downside of highly strained turbo motors).
Regards
Stef

moderators can kill this post if it's too off topic, but I drive a turbodiesel, as my company car, and it has 310NM of Torque at 1900 rpms, and it's 80-120 KPH times are quite impressive for any passenger car. It has a variable vane turbo, and suffers from no turbo lag. My plans are to get it chipped so the torque goes up to 325 NM. and get this, with only 145 Hp (I don't know the conversion to ft/lbs)

Turbos are great!

still no Porsche though...

Regards

[This message has been edited by Russla (edited 02-14-2001).]

Can anyone define 'turbo lag'?

Is it the time taken between pressing the accelerator and any real acceleration actually happening? And does it apply to times when the engine is above the revs required to spin the turbo or when the engine is below this point?

I have never noticed any problems in my Nissan 200SX if I try to accelerate when the engine is already above 3000 rpms and I doubt that there are many turbos less cleverly designed than the one in my Nissan (the whole car has a pretty basic feel to it).

James

How would one rank an '87 930 turbo vs. '91 C2 turbo each with 45k miles. For purposes of this analysis let's assume everything else is equal (i.e. condition, options etc.).
The price differential is roughly $8k. Both cars are black on black and in excellent driving condition. Is it obvious the '91 is a better value or am I missing something???

It sounds to me as if you already know and understand turbo lag.

This definition is simple and straight forward, When you step on the gas, of your turbo, and your car moves, thrusting you back into your seats, you don't experience lag. If you step on the gas, you car doesn't move so fast, and then takes off very suddenly giving you whiplash,or breaking the wheels loose, you've experienced turbo lag.

more technically, and as you surmise, it probably refers to the time required for the engine to rev enough for the turbo to provide enough boost to make noticable power for additional acceleration. If you're already above this minimum RPM, then turbo lag shouldn't be an issue and you've already demonstrated this behavior to yourself.

I had an earlier turbo sports car, where I upgraded the turbo, more boost,more air,more fuel required,more power, more fun, but also a bit more lag down low.

Regards

To elaborate on Turbo lag, the exhaust turbine on the turbocharger is driven by exhaust which is attached via a shaft to centrifugal air compressor wheel that pressurizes air into your intake...several things:

1) at very low rpms, many engines do not produce enough exhaust to accelerate (spin) the turbine to get the compressor up to operational speeds (i.e. producing ANY significant boost at all)

2) there is rotational inertia (which can be translated into the resistance of the turbo to spin up because of the mass of the turbine, compressor, and shaft) which varys depending on the turbo. Some turbos have smaller and lighter wheels, and some are made of lighter materials (i.e. ceramics). Why doesn't everyone use smaller lighter turbo wheels? Well the smaller the turbo the less power it can make, i.e. that's why there are twin-turbo engines...two smaller turbos spin up faster than one big one and can make just as much power.

3) Centrifugal compressors don't have a linear rpm-boost ratio, it is exponential, so a turbo may not produce much boost at all until it is past 50%-60% max operating speed, and then wham it really goes. Those smaller turbos on the newer cars you drove have similar maps, but they spin up to their operating speeds in the blink of the eye. They have lag, but its not easily percieved.

4) After all 3 above points keep in mind that an engine off boost is well...essentially a motor without a turbo. Taking that into consideration, most high hp high boost engine designs have reduced compression ratios to allow for greater boost pressure. The early turbos have 7.0:1(3L) to 7.5:1 (3.3L) compression ratios. I think this is the primary reason why the early turbos are quite notorious for their lag. Try driving the 3.3 with a 7.5:1 compression ratio WITHOUT a turbo...it would be a dog no matter what RPM...thus the thing goes from one extreme to another (DOG to MAD MACHINE) when the turbo kicks in...as opposed to later turbocharged engines that use higher compression ratios (8.5-9.5:1) and are stronger engines off boost (instead of DOG to MAD MACHINE, you're going from SEMI-WIMPY to HOLD ON TIGHT).

The best recipe to get rid of lag in a 3.3L turbo is to rebuild the engine with higher compression pistons, open the exhaust, get a new turbo (like a K27), and maybe play with the cams a bit.

Then again, you might like that crazy rush. Ever let somebody drive YOUR fast car? Feels faster when they stomp it than when your'e driving because you don't quite expect it. Same with turbo lag

Brad

The diesel torque power is well known. I tried an Audi 100 2.5 TDi with massive torque. Can't remember how much. Even with 5 grown ups in the car it felt strong. However the diesels are slow and don't like revs. It takes away the fun I think.

To me the perfect engine has lots of torque and low end grunt and at the same time it loves revs. The 993/996 Turbos that Stef mentioned sounds like they are close to being perfect. The Skoda I drive feels a bit like that, but of course it's not as mighty powerful as a Porsche. Still it's fun to drive. Very flexible.

Three comments:

1. The 3.3 turbos (at least up to 89) also have 7.0:1 stock compression, not 7.5:1. They are dogs below 3500 rpm, in my opinion. Exciting between 4000-6000.

2. The stock 930 is a ***** to drive around a track, since you've got to figure how to keep the turbo spinning pretty much all the time, or you'll get eaten alive. Transitions between off-boost and boosted driving can be a real bear.

3. The 930 can be modified to cure its "problems". There is no question about that. Just bring cash.

whoops, 1/2 point off, the 3.0L was 6.5:1 and the 3.3L was 7.0:1, sorry

Brad

Larry, you can obviously make an older turbo just as fast as a newer one, but it takes $$$. The C2T's have a completely different fuel, turbo, as well as intercooler and spark management system to fix some of the problems with the older models. My bet would be to get the C2, better to have factory HP and engineering out of the box. Which is why I chose one. You can always modify it also!
Marc
'92 C2Turbo

Marc: They also have something else out of the box, an extra 375 pounds over the 78-79 and an extra 264 over the 87.

Keith
79 930