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Old 07-30-2005, 12:54 AM   #1
Nocturn
 
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Note, don't ask what the best mod is, or what color GTO you should buy, those arn't the type of questions to ask. Instead if you don't know what AWD means, or how a DOHC engine differes from an OHV one, or perhaps something as simple as what M6 and A4 mean, ask them here and I will answere them for you. If not I will find someone who will, or at least point you in the right direction.



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Old 07-30-2005, 03:25 PM   #2
04GOATGERM
 
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Good idea Noc.
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Old 08-14-2005, 01:54 PM   #3
MajorMajor
 
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I know the high reving inline Import motors have gotten huge boosts from Turbo Technology but why Havent Turbos made their way under the hoods of more cars with V-8s?
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Old 08-14-2005, 07:09 PM   #4
mldavis
 
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Turbochargers have some potential problems. The idea of any "forced" air, either turbo or super-charging, is to increase the amount of air (hence oxygen) inducted (or packed) into the cylinder. If you get more oxygen, you can burn more fuel and more air/fuel equals more power.

A supercharger, like the GTP uses, is a parasitic device. It requires a belt to run it that is turned by the engine and so uses some of the engine's power to produce more power. The advantage of a supercharger (as used on most racing engines) is that it doesn't require special cooling.

A turbocharger, on the other hand, you might think of as a dual "water wheel" device on either side of a common shaft. One side is directly in the red-hot exhaust stream and is spun by high velocity exhaust gases, the other side is in the intake where cooler air is inducted. Being in the exhaust stream creates some flow restriction, but the biggest problem is that it's HOT! The Grand National (and most turbocharged engines such as diesels and tractors) use an oil jet spraying onto the common shaft to keep the bearings from frying. Some, like the Volvo, use an intercooler with antifreeze to help bring temperatures down.

Passenger cars suffer from some ignorant drivers. On a tractor, most farmers know to let the engine cool down at idle after a hard run and the oil jet continues to cool the bearings until the temperature are low enough to prevent the cooked oil from congealing on the bearings and freezing up the turbo. But your wife is more likely not to know or care, and come flying in off the turnpike into a gas station, shut off the engine and the oil cooks on the bearings while she is filling the tank and taking a whiz.

Another problem with turbochargers is turbo-lag. Since the turbo boost relies on the speed of exhaust gas flow, you have to rev the engine up to generate more boost. The bigger the turbo, the slower the acceleration of the turbine and the more lag time you have before the boost comes up.

A supercharger, on the other hand (on my GTP for example) always generates a positive boost pressure so there is pressure on hand when needed. A waste gate, controlled by the ECM dumps unused boost to the atmosphere, while a little bit is used to bring the otherwise low compression engine up a bit. When you hammer a supercharged engine, it responds more quickly than a turbo.

SO....a turbo is slower to respond, and it's more likely to be abused by ignorant owners. Too big a risk for most American manufacturers warranty coverage.
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Old 08-15-2005, 03:41 AM   #5
Nocturn
 
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Thanks for giving a good discription of TC/Sces MLD.

I think the main reason that most V8s havn't used SCes is because they don't need to.

For example, the 2003-2004 SVT Cobra Mustangs made 390 HP out of a 4.6L DOHC.

Caddilac is now making a supercharged Northstar engine, its a 4.4L making 469HP.

Mercedes Benz has been making strong numbers with "kompressors" since god knows when.

For the general buying public high horsepower numbers just arn't needed.

Both the Cobra, and STS/XLRVs of Caddilac are made in limited production.

Turbos do require more maintenance, and care to be put into your driving habits. Depending on the turbo, it can have little to no lag at all, or you may not be making your power untill 1/2 way through a gear...I know many a Supra don't make peak power untill 4-5000 RPM.

Because of that Superchargers have generall been more often applied to V8s because they compliment the low end power better, and are easier to drive. If you were to take the Northstar engine, and change it to a Turbocharger isntead of a supercharger, it would probably push the power up to around 500-520. But on a 65-70 thosand dollar car, a person doesn't want to have to let their car idle to cool the turbos.

That being said, there are a good number of cars that DO use them. Audi/Volkswagon use them. Audio made a BADASS car back in 2000 I think called the RS6, which had a twin turboed 4.2L V8 making 450HP or so. It was a good performing car, but also was a big sedan so it took out some of the performance. Mercedes makes a couple of turbo V12s in their AMG cars, but those are another story.

I think it boils down power, the turbochargers extra power provided just doesn't outweigh the advantages a supercharger gives on a V8, mainly in driveability. (From a manufactorer that is, these can be solved in the aftermarket).

As for the imports, the have benefitted more from a turbocharger because instead of larger displacment engines, they use higher reving smaller engines. As MLDavis said, a supercharger uses power to make power, and the faster a engine revs the faster it has to turn the supercharger, meaning the higher a small engine revs, the more power is sucked from it, and the less power the supercharger gives to it overall. This is why a turbocharger is usually better on a smaller displacement engine, because the supercharger doesn't have the advantage it has for a larger engine that doesn't have to rev as high. In the high revs it draws to much power to be a big advantage, and since smaller engines have a peaky powerband anyways, the turbo can actually comliment the engine perfectly with simply increasing the power, and not altering the powerband that much.



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Old 08-15-2005, 07:06 AM   #6
MajorMajor
 
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Thanks that explained alot! I know a good bit about all the stuff before hand about parasitic and such but now that I think about it your right a high reving OHC motor is more suited to something that has to wind up like a toy! lol
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Old 08-15-2005, 06:36 PM   #7
mldavis
 
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One additional comment here probably isn't needed, but I'll add it anyway.

Turbochargers can be made to greatly reduce turbo lag by making them very small. Saab does that with their turbo model. The turbine wheel is so small and light that it doesn't take all that long to whiz it up to speed when you romp on the throttle. Bigger turbos push more air and generate more power, but that translates into bigger top end and more sluggish off the throttle initially.
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Old 08-19-2005, 11:55 PM   #8
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Alright next question...Nocturn and Mldavis on the job... :afro:



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