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Originally Posted by rez333
I'm still unclear which is better: SC or TC. Ultimately it's a cost/benefit issue, but American performance cars usually have SC, and European performance cars usually have Turbo, so I'm confused.
A Super Snake with 750HP at the crank makes about 650HP at the wheels, at 17PSI. According to your video, a 5.4 PSI Hellion on a 5.0L engine can make almost that power. I don't understand then why Ford/Chevy use superchargers that appear to be inferior? I am obviously not seeing the rationale that the Ford/Chevy engineers are using to justify their use of a supercharger over a turbo.
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Theoretical: Turbo is hands down better. It's taking energy (heat) from the exhaust and using it to compress the incomming air. This can boost the efficiency of the engine, as well as the engine is not under excessive strain to produce it's horsepower. Simple way of saying it, 6psi of turbo boost may create a 600whp engine, maybe 700 at the crank.
SC is parasitic on the engine and crankshaft, it may take 8-9psi for the same 600whp, all the while the engine is enduring the stress of 850 or more HP at the crank, because some of the engine's power goes to compressing the incomming air, nothing is gained from the exhaust. The engine components see more stress due to this.
Both require more fuel being put into the cylinders, but SC usually requires a little more because not only is there the heat and detonation issues with compressed air, there's the additional factor of it has to make a lot more horsepower than what goes to the rear wheels. Both usually require forged engine components (or relatively low boost levels), but again the "limit" is going to be higher with turbo due to not putting as much stress on them.
The issues are these: There are a lot of "bolt-on" SC kits out there. Obviously whatever you get has to be well designed and not wreck your engine. Tuners are familiar with these and how to tune them, and so on. The turbo kits are not quite as numerous, and sometimes require more "custom" parts to make them work. All of these statements are generalizations, so you'll find exceptions.
It used to be that SCs robbed lots of power all the time, and that they pushed a lot of hot air into the engine. Now with bypasses and water and air intercoolers, they only use more fuel some of the time, and only push mildly hot air in there. The only reason I say it like this is most SC systems usually don't have a big air-air intercooler, which simply can't be beat for cooling the air charge into the engine.
As for which is heavier, it's probably a wash. The big heavy metal superchargers are NOT light at all, and then there's the water-intercooler and any other associated systems you put on there. Two decent turbos+intercooler+piping is probably going to be about the same.
Other turbo issues include matching the turbo size to your engine. A turbo that is too big will require very high RPMs to activate and build substancial boost. There are even some SC systems that work like this. A turbo that is too small will build up boost very fast, but "drop off" as it can't keep up with the engine and loses it's efficiency, so high RPMs become useless and shift timing becomes a pain. Turbo technology has allowed some of these things to improve and get "the best of both worlds", but any time you take the tuning to the extreme, these tend to show up again.
Heat is also an issue, somehow you gotta keep the turbo from frying itself. It's a little bit more of an issue than with a SC. If you've ever owned a turbo car, you'll see how "conservative" they come from the manufacturer, because they want to cover their bases and make sure it doesn't do anything crazy like grenade the compressor wheel, or melt the cats. While GM could definitely design turbos into the system, it may be much more cost prohibitive to do it with the level of safety/reliability that a manufacturer wants OEM. The OEM turbo parts on my car were super heavy cast-iron bits that couldn't possibly fail. Downtube was then wrapped in some kind of metal heat shield. Turbo has it's own heat shield (that most people took off). Hood insulated. Coolant system (in addition to oil) designed to cool turbo and operate via evaporation after car shuts down. Relatively large injectors to dump tons of fuel in there and keep everything cool (and tuners got to be careful with this, because when "unlocking" power you can quickly end up with WAY too lean of a mixture, even though it seems like it's still "rich"..etc. It's most likely significantly more cost prohibitive to design the entire care like this from the beginning.