88BlueTSiQuest

The difference is compressor efficiency. You use a wastegate to limit the speed a turbocharger is spinning, the supercharger's only limit is it's gearing/pully and engine speed. If you spin either a supercharger or turbo past it's efficiency it practically becomes a heat-pump. So even if you vented off the excess PSI's, you are still getting a vast amount of heat(hot air) into your intake. Even using an intercooler or aftercooler won't be able to compensate for the heat of running a turbo/supercharger past it's efficiency.

For the second part of your reply. I believe what they are saying is that if you started with a car that had 240hp, and added a supercharger. In order for that car to engine dyno at 300bhp, that supercharger would be required to boost performance by 120hp, as turning it requires 60hp(but you'll never see that extra 60hp on an engine dyno, as it's consumed by the engine). I don't believe that superchargers are that entirely un-efficient, but the load of a supercharger could be compared to the power robbing load of the A/C compressor with the A/C switched on.

slinky

My Corrado is supercharged. I get more of a sense of "constant power", but nothing compares to the feeling of driving the Porsche when the turbo kicks in.

Lead Foot 944

Dah.........

Go with the turbo....You know what car company was the first to put a turbo on a mass produced.......and what year.....?

Damian

jp944

I have a supercharger, and if the cost were the same, I'd have gone with a turbo. I got a GREAT deal on mine, so it was much cheaper than buying a 951. You can only get so much out of a supercharger before the typical ribbed belts start to slip. Ask Turbo Tim about his stage III SC kit and belt slippage. An SC get's you close, but its really tough to get the same horspower put down by a 951 with only chips and a MAF.

The supercharger definately makes a very predictable powerband, lots of low end grunt and never any unwelcomed surprises on corner exits.

ttwirz

I have an SC. At the moment I have a 5 psi pulley. When I install the upgraded injectors and fuel regulator I will be able to go to 8 psi. I have never been in a 951 so I have no comparison, I have driven other turbos. There is definitely more low-end power with the SC. Foot down in first yields major wheel spin. I am hunting for some wider phone dials to combat that problem. At about 3000 rpms my boost gauge shoots to the 5 psi mark. The increase in power is through out the rpm range. I have a centrifugal SC which is like half a turbo. I hear the roots based SC’s are the ones that give full boost right from the start. Based on my experience that would pose a problem getting the power to the road. The “con” of a centrifugal SC is the boost comes on later and is dependent on the rpm of the engine. Since there is already a traction issue I don’t really see this a con. I am happy so far with the results. It is an expensive upgrade but I think worth the out come. I also like the uniqueness of having a SC. With the SFR exhaust the whole set up sounds incredible, nothing subtle about it. I have pulled up to guys with big V8’s that would probable stomp me but the little red 944 that sounds like a Ferrari on steroids scared them away. J What ever you choose talk to Tim a SFR. He is extremely knowledgeable and can explain the differences and what to expect from the different options.

loonyjuice

Drive your Corrado on part throttle until 3500 rpm then floor it, and you can pretend you have a turbo

Turbo lag doesn't seem to be as big a problem these days as they seem to be bringing in the turbo earlier. I heard a diesel spool it's turbo as it started! I guess they work like a super-charger in that you get more boost as the engine speed increases?

Still, I always think that turbo/super-charging is cheating. I'm more impressed by the 911 gt3 engine. And BMW should be applauded for not using turbo's at all (except on diesels, of course, but diesels are useless otherwise!)

Luis de Prat

Yet many of Porsches most legendary racecars have been Turbos.

trebor_quitman

The 911 has two extra cylinders! Thats Cheating! I don't think any form of forced induction is any different than increasing displacement or adding cylinders in regards to "cheating". You are increasing the amount of air per rotation, and a certain amount of engineering and tuning is required to run properly. NOS could be considered cheating because of it's ease, but the same argument persists, it's just adding more "air" into the cumbustion chamber per stroke. Now if you used an aircraft carrier catapult, or a TOW rocket, or went down hill, or had taller front tires to recorded your 0-60 times, than yes, you would be cheating...

I personally think turbos are better than S/C's because they are more efficient, and therefore produce more horsepower verses the amount of wear and tear. Not saying that S/C's are unreliable, just that for the same amount of dyno HP, the SC'd engine will actually be doing more work than a turbo... BUT, I don't like the concept of allot of boost instantly coming on at some magic RPM number though. Sure it might be fun to get that kick in the seat, but I'd rather have allot of power on tap, as in at my discretion, rather than when I don't expect it, in a curve... At the San Diego get together I was able to go to, a guy in a 951 was racing with a guy in a 928 on the street. They were coming around a turn and the 951 hit boost, spun the rear end, and went through the inside guard rail and dropped down the hill. Luckily him and his GF were ok. Not so fun of an idea anymore...

Dsalillas

1973


The BMW headquarter in Munich is occupied and the Dingolfing works officially opened. The BMW 2002 Turbo from Munich is the first mass-produced turbo in the world. BMW is European Formula 2 Champion, European Touring Car Champion and World Sidecar Champion for the
twentieth time. The BMW motorcycle division celebrates their fiftieth birthday - 500,000 have been built. The first European subsidiary is opened in France and BMW is founded in North America. The autumn witnesses the first oil crisis.




This was the second listing in a simple Google search.

loonyjuice

I don't deny turbo's have their uses and successes within Porsche, I just prefer naturally aspirated charateristics, and an engine which doesn't need to be wrung out before it moves, which is why I loathe Japanese engines. The Japs don't seem to be able to make a high powered engine without sticking a turbo on it. However, I digress...

roadrunner

Here's my two cents worth, since I have both turbo and Roots supercharged cars. In addition to my '89 951, I have a supercharged '97 Integra GSR that put down 251 Hp / 181 lbs-ft at the wheels at 10psi, up from 140 Hp / 110 lbs-ft stock. It uses a Jackson Racing/Eaton blower and it has completely transformed the character of the engine. The blower sits between the engine and the throttle, and there's a bypass valve that links the intake and output of the blower so that when vacuum is high, as in cruising and idle, no boost will be produced. There is now enough torque that I can pull from 1500 rpm in fifth gear (I also installed an LS transmission, taller gears) and I get decent pull. I still get extra helpings at about 3500 rpm and 6000 rpm, and it makes good power beyond fuel cutoff at 8500 rpm. My research and experience with the different blowers is that the positive displacement blowers tend to fatten up the entire torque curve, appearing to taper off at the top end because of diminishing returns between engine power increase and parasitic blower drive power. The centrifugal blowers tend to exaggerate the torque curves more at the top end, as they are usually sized to produce peak boost very near redline. Since they are dynamic devices, boost will not be constant and thus torque increases will feel peaky. There are, of course, pros and cons with either system.

I've only had limited experience with centrifugal blowers but I can give insight for Roots blower characteristics. I like the near instant torque the blower gives, as when I used to drive in the summer with the A/C on, I would have to rev the hell out of it and engage the A/C compressor cut-out programmed into the engine computer to get decent acceleration in traffic. I can now roast the tires from 10mph with the A/C on and I've deleted the cut-out until a 6000 rpm+3psi boost condition exists. The engine pulls with at least a 6000 rpm wide powerband, so although it's not a big block, it's many times over more flexible than in it's stock configuration. Also, the fallacy of being under boost all the time is simply wrong. The throttle controls the amount of air reaching the blower so power/torque is very responsive to one's foot, nearly as quick as on an N/A engine. Lastly, the 62 cubic inch blower on my car consumes about 15-20 hp at it's max design pressure and speed, according Eaton's website on that design.

However, there is a common saying that centrifugal blowers have the worst of both of both belt and turbo driven devices -- the lag of a turbo because you don't get full boost quickly enough, and the losses of mechanical driven blowers. Bigger engines such as the S2 or domestic V8's can mask the near stock torque when using centrifugal blowers, but smaller engines struggle with those. You CAN get amazing power from centrifugal blowers, but again, any existing limitations with the intended engine application will only be magnified. The turbos tend to strike a good balance between reasonable lag and great power, and that is why they are usually much more popular among people looking for power adders, but don't forget, they do have much more complicated plumbing and underhood heat.

For a daily driver and autocross car that require immediate response, a roots blower would be my choice.

For cars that tend to stay at constant high rpm such as Bonneville speed cars, centrifugal blowers and turbos tend to be the choice.

For most road racing, turbo, hands down, as the fatter than centrifugal torque and higher than Roots power gives you the most area under the torque curve.

roadrunner

'91 NSX made 270 at the crank with 3 liters, S2 made 208, 968 made 240...

loonyjuice

...ok, there is always an exception, but it's got 2 extra cylinders than the Porsches,

Eyal 951

" A turbo conversion will cost cosiderably more but is more efficient as it uses 0 power from the engine and just wasted exhaust gas to turn the compressor to create energy. "

Not so, it takes a tad of power for the turbo. Count on about 5-7 loss. Its an extra componant in the exhaust, it has to spin. You'll lose on that.
~Eyal

roadrunner

Not too many instances of 3 liter engines with only four cylinders, and I'm not sure I would prefer that configuration either, but there are some 2.2 liter Preludes out there of early to mid 90's vintage putting out 200 bhp in the US, and 220-240 in Japan. The only n/a production Porsche engine with very high specific output would be the current GT3, otherwise it was obvious Porsche were always trying to get the highest and broadest torque figures while trading off peak power. You have to hand it to the Japanese, with their crazy motorcycle engine experience, to create small engines with high power at dizzying revs, and that can bought by the average Joe. Porsche decides to keep that stuff only for their Platinum members that can afford the $120K+ GT3. Don't get me wrong as it'll take a hell of a car to make me sell my 951, but I wouldn't characterize Porsche engine technology as unique and all conquering. Heck, they even copied a version of VTEC for the 911 turbo...