BC

Did I say the SC was more efficient then the turbo? Nope. Its like your arguing with the ghosts of previous threads where you got personal too. I'll get personal when provoked.... And from the way you write your probably short - napolean complex comes to mind.

We WERE having a simple discussion. Geo and I disagree... Any personal attacks? Nope.

Really - just Fvck off down your snipe-hole. I'm ouit until there is something intelligent said.

Geo

OK, come on. You need to know what you're talking about. Ever seen an engine on a engine dyno?

BC

NON-turbo Geo. Freeflowing headers? Yes, a few times in person, many in movies on the web - actual engine room runs.

Jack '84 928s

Driving a 1983 toyota supra at 130mph give or take for 30miles will make a exhaust manifold glow like that. The fastest CS car i have seen with my own eyes was a 1989 Mustang with complete forged internals, intercooler off of a ford powerstroke ( bumper was heavily modded for this to fit). Something like 4.11 gears, and slicks. This car would only run around 12.0-11.5 with tons of tuning it ran a 11.0... Of course he launched the thing at like 6k rpms, and had light wieght rims in the front.. He was using one of Vortechs biggest headunits also.. I know this person, i have been to his shop and checked out his cars, watched him race.

88BlueTSiQuest

Not argueing here, but I thought IHRA had a Turbo Class, which was where the Late John Lingenfelter ran his turbo cavalier.



Also, it seems that the biggest arguement between Turbo and Superchargers happens to be lag. Something that needs to be considered here though, is that lag is practically a thing of the past. Turbo's have become more and more efficient over the years, so the lag you'd see on the older 80's sport cars is nowhere near as prominent in the newest breeds of turbo cars. And lag can be easily removed with careful planning and tuning.

My Conquest suffers no lag at all, if driven properly. If you simply release the clutch at idle and give it some gas, sure, there's lag. But rev it up slightly and slip the clutch out(as most people tend to drive anyways), and lag is non-existant. I build 5psi of boost at 1500rpms with proper driving techniques, and if you keep the throttle open I reach 16psi of boost by ~3200rpms. Instead of lag, all you feel is a constant increase of G-forces up til redline.

If you plan the turbo install properly then lag won't be anything that you need to worry about. Lag is only an issue if you don't build the system according to how the car will be driven(street, track, etc..) I think the only cars that really suffer from lag now-a-days, aside from the early factory turbo cars, are cars built strictly for drag racing. As those applications usually use a large turbo(s)designed for vast amounts of boost, they tend to add N2O to help get those turbo's spinning, and those are generally not compressors you'd want on daily driven vehicles.

nine-44

I've had the privlage to talk with John, he's very knowelegable in the subject and had definately done his homework. I'm currently working on my own sequential turbo setup, much like the 959 has. I'm also attemting to design an intake manifold to open up some space to add two turbos to the engine bay and offering better performance. If you are saying that you CAN'T get a turbo up to boost as fast as a SC, you aren't utilizing up to date technology and are not engineering your system to it's fullest potential. The VNT, VGT and VANT turbos are definately today's technology. if they were an option when the 951 turbo vs 951SC little chart and tests was made, it truely would have ended differently. Think, a SC has to pump more than the engine's displacement per rotation to provide positive pressure. That means, either make a SC twice the displacement as the engine to make 10-15psi boost or make it spin faster to keep up, any gearing to overdrive the SC creates more paracitic load. in a turbo, there is no paracitic load, only back pressure on waisted heat going out the tailpipe. As I have read in multiple books, the backpressure between the head and the hot inlet of the turbo should bot exceed more than 2-3 times the boost pressure in reguards to efficiency. Back pressure, exhaust velocity and such in used with valve overla to createa scavaging effect to help draw intake air in when the intake and exhaust valves are simulatniously open for theduration of the overlap. In a boosted car wether it's SC or turbo, the boosted intake pressure will blow fuel and aire straight through during overlap and ignite when it meets the hot exhaust gases. This burns valves, heads and turbos. So, in short, back pressure is not necessariny a big issue in a turbo system other that for hotside turbo sizing. I know, you guys are saying yes it is, and it is in reguards to turboing, but for matters of significantly diminished performance due to increased backpressure of turbos, it is not.

It all boils down to efficiency, technology and design. The most thought, best components and not necessarily the most money is the key. Here's a little bit on my plans...

budget..no longblock mods in the budget at this point 2-3grand
standalone, sequential turbos, anti lag devices and plans, custom plumbing

my goal, NA powerband, mocking and improving the 959 turbo system using today's technology. 350-500 hp from a 2.5L
At this point I'm planning on 8V, 16 V is a possibility.

nine-44

May I also remind you guys of Eddie Bello that was running 9-10ETs in a 911 that was turboed and driving it to the track and also beating turboed Hyabusas on the street. Also, I forget all the details but the reason why turbos are not allowed at NHRA was because of a toyota V8 with twin turbos kicking everyones asses in his classrunning like 7 secs or something crazy with a few thousand HP. Not too bad as technology grows considering that lag in seconds was longer than this guys ETs 20 years later. It is true that you have to plan your system around it's intended use, I hope to build it for many...AutoX, Drivers EDs, bigtrack and street. I don't plan to drag, but I'll throw that in as well. Go ahead and laugh at my crazy ideas, to you they are crazy, to me it's a challenge and I hope to tear down the walls of your imagination. I have a plan and I'll see what I can do, it could all be junk in the end, I'll do what I can on a working budget. Wish me luck

Fishey

Your car is already plenty health on HP but with your plans it would be absolutly amazing.

Danno

"Also, I forget all the details but the reason why turbos are not allowed at NHRA was because of a toyota V8 with twin turbos kicking everyones asses in his classrunning like 7 secs or something crazy with a few thousand HP."

Those Toyota V8s are monsters! They stick them in the smaller 1/2-tonne trucks and add a supercharger. Instant 500bhp! Wow...

Geo

I could be wrong because I don't really follow drag racing, but I think turbos have been illegal in top fuel for a long time.

Z

Wow! Lots of posts. Who would have thought! Lots of stuff to reply to, so this is going to end up being long.

The two pages posted are from the book "Forced Induction Performance Tuning". Did you notice the last sentence of that second page?

Yes, any car including a supercharged one will have some exhaust backpressure. The amount is nowhere near the same though. A supercharged car with an adequately sized exhaust will have very, very little backpressure. On the other hand, a turbocharged car will have substantial backpressure if it's making a good amount of boost. In his post above, nine-44 mentioned that he'd read on multiple occasions that the backpressure between the head and the hot inlet of the turbo shouldn't exceed more than 2-3 times the boost pressure in reguards to efficiency. In that case, a turbo car running say 12psi of boost would be seeing at least 24psi of backpressure. That's a little higher than the test results I've seen for a 911 turbo, but not too far off. I know some of you have removed cats from cars and installed "offroad" or "test" pipes in their place, and noticed a performance improvement. That's with cats being responsible for causing a less than 1psi backpressure in the exhaust. Anybody with a normally aspirated car want to restrict their exhaust to the point of where it has 24psi of backpressure at full power and tell us how the power felt compared to when it had almost no backpressure?

Exactly. It's defined by how much the supercharger or turbo increases the temperature of the incoming air during the course of compressing it. It does not take into account higher air temperatures that may very well be going into or being created in the turbo initially due to high underhood temperatures from close proximity to hot exhaust plumbing, confined engine compartments, or from close proximity to the hot exhaust side of the turbo.

The book it's from was published in 2002. The Porsche test data is obviously older, because Porsche wouldn't have been testing on a 944 anymore very recently. Since the test specifically involves a 944 turbo vs supercharger comparison, I'd say the information is about as "ancient" as the turbos that are on the vast majority of 944 turbos on the road today. Modern turbos undoubtedly do perform better than back then, and so do modern superchargers. A modern supercharger would have done significantly better against the turbo that was used for the tests, and the turbos that are still on that majority of 944 turbos currently in operation.

That's a very good question, and one that comes up often in these types of discussions. Porsches are designed and built in Germany. (Well, at least they all used to be) Automotive wise, Germany is different than the United States. Gas is much more expensive in Germany, there are no speed limits in large areas of the Autobahn, and many cities and towns have very narrow and twisting streets and roads that were originally laid out hundreds of years before cars even existed. Many are cobblestone as well. There isn't as much opportunity to use big low end power, especially at the expense of lower power at the very top end at Autobahn speeds. On top of that, as the article mentions there would be the greater fuel consumption with the roots blower. For that application, as the cars would more typically be used in Germany, the roots setup would have been a big sales failure. Porsche realized that for the intended application, the turbo was the better choice, and was what consumers would be more likely to buy. The other question that some people always seem to ask when claiming turbos are always the ultimate answer is why are turbos used by Porsche and others in their race cars then? Many of the same reasons mentioned for the way cars are more likely to be operated in Germany are valid here as well. A race car like that doesn't particularly care about low end power, because it never sees it once it pulls out of the pits. Fuel economy is important because you can't win if you're having to stop and refuel more than the competition. You'll also have a harder time winning if you have to carry more weight in fuel than the other guys if you don't want to make those more frequent fuel stops. For that application, a turbo setup is obviously a good choice. See any race cars in traffic on your way to work today? Even on the track, it's not necessarily a clear cut choice though. Did any of you see the Acura NSX with the centrifugal supercharger that was racing in the SpeedVision series? When I saw it race in the SpeedVision race up at Road America, I think it was the only supercharged car in the field. It came in I believe third place, ahead of a good number of turbocharged cars. A good question to ask might be why are the majority of cars that Porsche has sold NOT turbocharged? If turbos are the absolute best solution in all cases, the way some people make them out to be, why do things like superchargers, nitrous, and even just normally aspirated engines even exist. If turbos were the absolute best solution in all cases, they'd be on absolutely everything from weed wackers to aircraft carriers and the space shuttle. Application, application, application.

I just knew you'd show up John. For those of you that don't know him, John owns a Callaway twin turbo 928. Callaway built maybe 5 or 6 of the twin turbo 928s back in the early to mid '80 before they abandoned the project. John's is one of the one's that are still left. The owner of one of the others that had the engine blow up still has his on the road too though. He installed a normally aspirated engine from a later model 928. That owner seems to be happy and claims the car is much faster and more reliable now.

John, I never said that the turbo wasn't good for top end power. I also never said that the centrifugal was always the way to go. What you apparently just can't comprehend for some reason is that the best choice depends on the specific application. Instead you always start to rant about top end power, race cars, and these strange "roll on in 4th gear at 3000 RPM" types of comparisons that you seem to think are the only way people actually drive, without giving much if any thought to how people get to 4th gear in the first place. You also repeatedly ignore dyno charts showing centrifugal superchargers starting to make boost at as low as 1,500 RPM where the dyno runs were started, and claim centrifugals only make boost up at the top end. Yes, the turbo may make more power up on top, once it finally gets there. One time you make statements about dyno numbers not meaning much, and another you start talking about how much more torque your car made on the dyno than a comparable centrifugal car. Why not tell everyone here the whole story John? Since this is a turbo vs supercharger discussion, it is relevant information. John's car is an early 5-speed 928 with a stock engine except for the twin turbo installation and a free flowing exhaust. Carl's car is an early 5-speed 928 with a stock engine except for his centrifugal supercharger installation and a free flowing exhaust. John brags about the greater peak torque dyno numbers of his car, but what are the on the road results like?
Some quotes from the 928 board:

Oh yes, I almost forgot to mention that the stock torque rating for Carl's engine is 15ft/lbs LESS than the stock rating for John's engine.

Since "a few pounds" could be interpreted differently by different people, there are an awful lot of supercharged cars driving around with 8psi or so of boost, pump gas, and around 9:1 or 10:1 compression ratios and no intercooler. There are a number of other factors that can influence those numbers for a specific engine though.

Absolutely not true about the CS guys bickering and flaming turbos. Going back and looking at any of those threads it becomes pretty clear where the negative and bashing type comments start. The main point that has always been tried to be made by some of the centrifugal supercharger guys was to consider the application and to have people think about that rather than blindly listening to someone that's trying to sell them something based on incorrect information.

There are centrifugal superchargers that are rated at and making 40psi or more of boost.

If you're going to be building an 18 wheeler, turbos would probably be a good choice. Fuel ecomomy would be a major consideration, the diesel engine would be delivering big low end torque, and the RPM operating range is what? Maybe 2K RPM or so? Lots of transmission gears to be able to stay in that narrow RPM range aren't there? Application, application, application.

I don't know about the 944 cams, but at least the later 928 cams have zero overlap. There is never any point where the intake and exhaust valves would be open at the same time for positive manifold pressure to move the exhaust gasses out. That also means that none of that pressurized fresh air/fuel charge is being blown out past open exhaust valves. As has already been stated, the exhaust backpressure on a turbo will be significantly higher than the boost pressure in the intake. If both valves are open at the same time for very long at all, which way do you think that the gasses are going to want to flow?

If you look at a few of the really big turbo horsepower dyno charts (not necessarily talking about 944 turbos here), you'll see that they typically show very little low end power, and then there's what looks almost like a cliff of an increase. I can't see an increase of sometimes several hundred horsepower within the span of a few hundred RPM being particularly easy on an engine.

There is no constant boost with a supercharger. During normal part throttle driving there's vacuum in the intake like with any other car. What's much more likely to damage bearings is high RPM operation, oil starvation, or detonation/pre-ignition.

I haven't really looked at any of that stuff for a while, but turbos, as well as centrifugal and twin screw superchargers were all illegal in top fuel. Turbos were legal in I think the Pro 5.0 category, but there were very few of them because they weren't competitive. The last I remember reading about it was that the weight limits were being changed to try to even things out more though. Turbo cars were being allowed to go down in weight, and centrifugal supercharged ones were having to up.

Drag racing wise, this is what's claimed to be the world's fastest pump gas car:
8 second Nova
It uses a centrifugal supercharger making 28psi of boost on 91 octane gas. I know of one daily driver 32 valve 928 that's been running over 20psi of boost, and has run up to 26psi, all with the stock engine management computers, no timing retard, no water injection, and pump gas. He also has a centrifugal supercharger on that car. I thought boost and octane numbers like those of the Nova and that 928 were pretty good. With the more efficient turbo compressor maps, you guys are probably all running even more boost on pump gas though, right?

I have to hand it to you guys, except for starting with John's very typical rants, the discussion here has been much more civil than I thought it might be, knowing that there would be a good percentage of turbo owners here. While some still might think that I'm bashing turbos, that's definitely not the case. They have a very real place, and if they didn't they wouldn't exist. The main point I wanted to make was that there is no simple "this is the best, period!" type of answer, and that each individual has to realisticly think about and decide what they want, and what will work the best for them to do that. It might be a turbo, a supercharger, nitrous, or even a transplanted Chevy engine. Okay, forget I said that last one.

944J

I don't know anything about drag racing so I looked up some stuff:

http://www.nhra.com/streetlegal/cars.html

Top Fuel
Top Fuel dragsters are the fastest-accelerating vehicles in the world. The 25-foot landlocked missiles can cover the quarter-mile in 4.4 seconds at speeds in excess of 330 mph. The engine of choice for most teams is an aluminum version of the famed 426 Chrysler Hemi. These supercharged, fuel-injected, nitromethane-burning engines produce an estimated 8,000 horsepower.

Funny Car
With aerodynamically enhanced carbon-fiber bodies that loosely resemble the production cars on which they are based, these supercharged, fuel-injected, nitromethane-burning machines travel the quarter-mile in 4.7 seconds at more than 325 mph. Most teams use an aluminum version of the 426 Chrysler Hemi engine that produces an estimated 8,000 horsepower.

Comp
Comp, which boasts 80 classes, showcases a variety of gas-burning dragsters, altereds, street roadsters, coupes, sedans, and trucks powered by engines ranging from tiny four-cylinder screamers to powerful V-8s. Some are supercharged, others turbocharged, but most are carbureted. A handicap starting system equalizes competition.


Sport Compact
Sport Compact cars are exotic four- and six-cylinder machines fed by turbochargers and nitrous oxide. Race cars in the fastest classes can cover the quarter-mile in as few as six seconds at more than 200 mph, but NHRA also offers novice and intermediate categories for every level of enthusiast. Many people think Sport Compact racing is only for imports such as Hondas and Toyotas, but there's room for the Detroit makes in this extremely popular scene.
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Like I said, I'm just learning here, but from the above data it seems like the absolute fastest cars use superchargers and the lower cost smaller cars use nitrous and turbo chargers. Why? Thats up to the experts out there. I only need 2,000 HP not 8,000, however

And here is a similar, but more hostile, discussion going on at another board:
http://www.automotiveforums.com/t150842.html

Dark Lightning

*cough* This is a turbo six cylinder... *cough*

pete944

Whatever your past history with John it is not appropriate to flame and name-call on the forums. John did not personally attack you. If misspelling your name was the problem, then you need a little bit thicker skin.

Watch the language too please.
You can edit your post now.

Got Me a Porsha

But the boost is NOT constant...as the BOV (blow off valve) releases the boost until a predetermined decrease in engine vacuum dictates it should close.