991 3Turbo

GrantG----I am strongly disagreeing with your supposed facts also. Your explanations are full of info but wrong. There are many types of superchargers out there----roots, centrifugals, etc. Turbos depend on rpm to build boost also and are NOT independent of engine speed since they don't build boost at idle either and have lag also.

Centrifugal superchargers are basically belt driven turbochargers spinning at tremendous speeds when in boost.

The ZR1 being a roots supercharger of the Eaton/TVS variety, which build quick boost and more powerful on the low end of RPM(superior here to anything but the smallest turbos) and centrifugals building with RPM and having tremendous mid and top end.

I like turbos for their flexibility, but everything has its advantages and disadvantages.

Once making boost, the engine knows not what is giving it boost

GrantG

Turbo will lose FAR less than SC at altitude. I'll be happy to discuss it with you offline.

Grantg10@aol.com

Petevb

In WW2 you'd often see aircraft with 2 stage superchargers- the pilot could change gears once the aircraft reached a certain altitude in order to increase the speed the supercharger was spinning for better high altitude performance.

The ZR1 will lose slightly less power than a normally aspirated engine at altitude, however. This is due to the high effective pressure the intercooled supercharged motor runs at. The effective compression ratio does still fall off linearly with altitude (unlike a turbo). However since power falls off non-linearly with effective compression (a 4:1 compression motor makes effectively zero power) and an intercooled ZR1 starts very high (something like 16:1) the ZR1 will lose less power at altitude than a normally aspirated motor. It will still be far below where is is at sea level (or a turbo) however.

Grant is correct I'm afraid.

The Eaton is a positive displacement supercharger. Every time it turns it compresses a fixed volume of air. At sea level the incoming air is at 14.7 psi and the supercharger is turning that into 14.7 x 1.85 = 27.2 psi. At altitude with lower pressure incoming air that drops, however- 13 x 1.85 = 24 psi absolute in the intake. Hence power drops off. You can gear the supercharger up to make up the lost power (pulley or the WW2 fighter above).

If the turbo boost regulation is absolute, it's simply going to spin the turbo faster until it hits the target pressure, ie 28 psi at sea level stays 28 psi absolute at altitude. Only pumping losses, etc come into play, so the power loss is minimal with altitude. Of course lag is increased, as mentioned.

TrackFan

Ok, I understand what you're saying. Just so you can see my side of it. I had a choice of a ZO6, or ZR1. I chose the ZR1, because of more HP, but also keeping more of it, because of the blower. A turbo wasn't in the picture.

991 3Turbo

GrantG said turbos are independent of engine speed which is completely untrue---they don't have boost at idle either, since it runs of exhaust flow/pressure, and superchargers do not. Boost is built on RPM's just as in a supercharged motor hence the lag. One pound of boost is one pound of boost no matter what the source. Obviously they build boost different depending on the style, and yes turbos give more area under the curve and spin tremendously fast but boost is boost.

Roots superchargers are positive displacement superchargers so lets not split hairs here. Turbos are generally more efficient, but modern centrifugals have efficiencies approaching 70 percent and have the advantage of less heat formation, which is the enemy of turbos and roots superchargers which are inherent heat sinks. Modern centrifugals have step up gears built in also.

Apples to oranges, disadvantages and advantages, but a pound of boost is a pound of boost.

Remember that the quickest cars in the world run roots superchargers not turbos!

I will agree to disagree but whatever you like.

TrackFan

We all had our points. If we put them all together we have the answer.

I know the ZR1 was a better choice than the ZO6, but the GT3 is an even better choice.

Maybe not at my altitude. The GT2 is a better choice.

GrantG

Yes, the engine has to be running and under load to make boost, but the turbocharger speed is far from proportional to engine speed like an SC.

Have you looked at the boost curve for the BMW 3L twin turbo - makes max boost under 1500rpm. Ever see a supercharger do that on a motor that redlines at 7k?

sunnyr

Autobild TTS vs GT3 article. I don't know German but maybe someone who does, can translate what they concluded.







Credit to DeDe@Germancarforum.com

991 3Turbo

Yes I had one--335 turbo. Very small TWIN turbos with quick spool and in a location to minimize lag, but not much on the top end. This is the reason they are using smaller twins not big singles . Great engine, one of my favorites, the new M3 should be awesome.

You can overdrive/underdrive superchargers to do whatever you like them to do. I wonder why Top Fuelers and Pro Mods not running Turbos? Cuz they take too long to spool up and then dump the power, break parts and glaze the tires. Many times massive abrupt boost is not good at all. Superchargers also a lot easier to work on and less complex.

As I said I love turbos, buy my Novi has tremendous mid and upper range power. My GTR was great too---the best actually!

Centrifugals build boost exponentially very similar fashion to turbos. A turbo with a belt, abeit massive and overall slightly less efficient and less top speed RPM spin, but very similar.

TrackFan

Was your GTR tranny as clunky as the one I drove? The one I tried sounded like it broke, but I was told it's normal. Pretty fast car.

TrackFan

Have you got the link for that? Chrome will translate it on a site, but not in a thread.

I'd love to read it.

I can see the tt is much faster. Look at the 0-200km/h times.

991 3Turbo

The only reason I sold the car was the fact it was noisy inside and rode rough as hell. The DCT did surge unlike PDK DCT at low speeds but at speed was phenomenal as was the rest of the car. They could refine it but they have chosen not to.

I sort of liked the whirring and sounds of the GR6, as it fit the car---big, fast, and brutal. I just didn't like the brutal part. I want refined brutality!

Mike in CA

Those appear to be factory performance figures. Also, note the <12.0sec "time" for the GT3 0-200kph. I think this was a "first drive" comparison feature as opposed to an actual test.

sunnyr

All I have is the link to the thread on another forum where the person originally scanned the magazine and posted the images - http://www.germancarforum.com/commun...parison.49294/

They are images, so I doubt you can auto translate them.

TrackFan

Yeah, the forum is in English, so Chrome doesn't see a need to translate.

Thanks anyway.