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Originally Posted by bradyb
Sky Captain, your just flat out wrong buddy. Please don't be offended I like you and I'm not trying to be a jerk. Please remember that this is my back ground.
Not offended, but I'm definately not "flat out wrong". You are not the only one with this kind of background - and frankly, I'm not so impressed by your background, or more specifically, the company you developed that background with. Please don't be offended by that remark. But your background is primarily with STS and rear mounted turbo systems. I remember when you first came on here that STS and RMTSs were the second coming of Christ and the answer to all Solstice performance needs. But now that you're now longer in the STS camp things have changed, more than slightly. I was never impressed with STS and the RMTS crowd or the results, when compared to other kits available for a given platform. Although, I must admit, the ease of adding an RMTS is a meaningful point for the DIY installer.
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The parasitic power loss from a supercharger is much greater then the back pressure created by a turbo- I've measured both first hand. My car has a fairly small turbo and I see a horsepower gain of 20.5 horses per pound of boost.
While that is true for peak horsepower, it means absolutely zip before that turbo spools up. When your turbo isn't spooled up (for example when CRUISING as I said above) it's nothing but an exhaust obstruction. A supercharger, on the other hand, continues to force air through the system even at cruising speeds, causing the AE & VE to be above 100% in many applications but always an improvement, sans bypass systems. Hence: my very valid assertion that superchargers can increase your gas mileage at cruising speeds while a turbo reduces it in most applications.
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Comparing a Procharger Supercharger the Procharger gained 17.5 horses per pound of boost, 16% less power. The difference is the mechanical force used through the gear reduction to spin the blower. The turbo doesn't use any type of a gear reduction; it just spins with the exhaust pressure that is already there. A turbo feeds off itself, it uses back pressure to create boost and as it creates more back pressure it creates more boost. With out a waste gate a turbo would be more then happy to make 30 PSI and blow your motor.
I am probably the last person on this forum who needs any kind of forced-induction lesson. I am perfectly aware of how the systems work, and their advantages and disadvantages. But I quoted this so I could high-light your own words for use in just a moment...
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A supercharger is severely limited by slipping belts and volume. A magnuson supercharger makes decent power down low but totally falls off up on top end when you try and run more then 7 PSI. Why do you think the SS Cobalt has 200 horsepower with a supercharger and the turbo Solstice will have 245 horsepower with the exact same motor???
Now, this is where your weakness lies - your knowledge of superchargers is about as deep and impressive as the McDonalds receipt I just threw in the garbage. Firstly, slipping belts is a totally unrelated problem that has nothing to do with power output and is about as relavent as putting a potato in a turbo - which is to say completely irrelevant to the topic at hand. If you have either one of those situations, fix it. Secondly, magneson superchargers do not "totally fall off up on top" when running more than 7 psi. The "problem" is heat soak caused by the blowing rather than compressing of the roots blower (since a roots design isn't really a compressor, per se). Simply put, adding an intercooler to both applications in the comparison completely evens out the playing field again. I run ~11-12 PSI every day on my eaton, non-intercooled, no problems. GTP people have found that this is about the cutoff before seeing heat-soak. Furthermore, PSI is definately not the standard of measuring power coming out of an engine and your reliance on it as the benchmark for the comparison is fatally flawed. I can take a roots-blown engine and only modify cams, heads, and/or exhaust and it will make more power with less PSI than it originally had. It's actually much more about flow when dealing with roots. And finally, the ecotecs are not the exact same motor, as everything about the combustion chamber is vastly different.
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Essentially the supercharger needs 1.80 PSI just to get it back to where it was stock. A turbo needs .35 PSI to get it back to where it was stock.
Oh so true, but coupled with your statement that I emphasized above it becomes quiet obvious that at cruising RPMs the supercharger has no problem supplying the 1.80 PSI since it has a perfectly linear relationship with engine RPMS. While the turbo does nothing but sits there sucking away .35 PSI because it feeds off of its own load that isn't there until you get on it.
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Because the turbo creates a lot of torque sooner in the power band and because it doesn't add an engine load you get better gas mileage.
No offense, but this is where you need to put down the crack pipe. Go to ANY performance car forum that uses superchargers and make the statement that "turbo creates a lot of torque sooner in the power band" and you'll get laughed out of there so fast your grandchildren will be born as starving comics. I suggest any of the multitude of Mustang/Cobra/Whipple sites if you really want to see how bad a flame-fest you can ignite.
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For example the Porsche 911 Turbo gains 119 horses over a non turbo 911 with only a 3/4 MPG drop, the SS Cobalt has a gain of 55 horses over the regular Cobalt but it loses 2/5 MPGs.
And yet GTP's get better mpg than their N/A 3800 GT brethren. Since the displacement is the same on the 3800s it's a much better comparison than the Cobalt that changes out critical dimensions between engines.
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Top Fuel dragsters use roots blowers because of the required volume and cost. It wouldn't be too cost effective to build a 300 millimeter turbo to handle that much power.
Riiiiiiiiiiiigghht. Because top fuel dragsters have such small budgets... But hey, since I did purposely caveat my entire previous post with "dollar for dollar" I guess that means you admit that I was right all along! Maybe you missed that "dollar for dollar" part???
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The world's fastest door slammers are turbo cars now.
Oh I'll give you this one - I've never disagree there. You were spot on when it comes to the parasitic losses, so there is no doubt that in the end, if you're trying to make a "world's fastest door slammer", or peak power is your goal (aka 1200hp supras), then a turbo (and a big bill) is probably in your future. There are many, many more factors to consider, though.
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The world's fastest 4 cylinders are all turbo ecotecs.
Do some more research.
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Check out this graph from Hot Rod Magazine:
"Given equivalent vehicles, the turbo would easily motor away from the centrifugal in an acceleration contest......The turbo offered massive midrange torque production, the only system to exceed 600 lb-ft. Need more convincing? At 4,000 rpm, the turbo was more than 100 lb-ft. stronger than either the Roots or centrifugal." Richard Holdener, "Battle of the Boost"
For every article and graph you can post to prove your point, I can post another to prove mine. I'd LOVE to see this article, but as presented here there are just too many factors missing to say it's actually a fair comparison. The article would need to keep PSI
and CFM levels comparable (since you can "turn up" boost on a turbo, let the supercharger decrease pulley sizes). And to still be unbiased, you'd have to use different cams in the comparisons since turbo and supercharged applications respond to
vastly different cam specs. And just to be sure it's on the up-and-up, I'd need pulley sizes and SC model numbers to verify potential flow.
But hey, benefit of the doubt: lets take a look at what we got here. It's got pretty curves drawn there. Gee, look at that, they all are shaped pretty much like standard theoretical curves for the different types of systems. Notice how the turbo peaks high in the mid range, but has a much steeper ROA & ROD. Turbos are traditionally tuned to peak in the higher end, but more are showing up tuned for mid-range like this so the shape of the curve isn't unbelievable. The centrifugal is also peaky, just as it's always described. And the "lowly" roots blower? Nice and flat. Gee, I thought you said they fall flat up top? No sign of that here. Just a solid power curve from one end to the other. If this graph is showing any of them "falling flat up top", it's definately the turbo.
But wait! What's this? They left one out! The big-boy of superchargers isn't even represented.
If anything says this comparison is biased, it's the fact that a comparison with a twin-screw wasn't done. Oh twin-screw, my lovely twin-screw, how do I love thee? Let me count the ways...
Even if this comparison was validly performed, the twin-screw would have the same flat curve that the roots has (if not flatter), with better power across the entire rpm range than the roots - and peaking at about the same hp level as the centrifugal (certainly at a more mid-range rpm). It becomes apparent that even in this comparison, had they included the twin-screw, the turbo would be overtaken by the twin-screw in both the high & low rpms. Suddenly, even in this comparison, the power-under-the-curve is threatened by the twin-screw... Wonder what it would look like...
http://www.solsticeforum.com/forum/a...tid=2932&stc=1
The comparison would be even worse for the turbo if we could prove that it was somehow biased... let's see. You said yourself that you did comparisons between roots and turbos, and noticed a 16% loss per pound of boost. Assuming (uh-oh) that PSI was comparable and disregarding CFM (in other words, completely taking your idea of a roots
blower, as flawed as it is) There's quite a bit more than 16% loss from the turbo to the roots on that graph. I'm gonna guess since peaks aren't labeled at a turbo peak of ~625hp and a roots peak of ~475hp, difference of 150hp - a loss of 24%. Gee, that's an extra 8% loss over what you yourself claim. I guess you can tune for a supercharger better than these guys. The next flaw in the graph is the artificial limitation of "usable" horsepower into an RPM range that favors the turbo. They really should label it "used" horsepower. I use the 1000-2500 rpm range constantly to destroy opponents from streetlight-to-streetlight. No data under 2500 RPM? Yeah... pretty graph, but worthless. And ~500hp on the turbo at 2500 RPM? Something smells in the state of Denmark...
Now after all that, somebody might think that I'm all about the supercharger and I'm a turbo hater. Nothing could be further from the truth. Turbos rule the roost when it comes to peak hp (RMTS not included, save that for another day). And because of that, turbos are great in an application where you can select that chunk of the rpm curve where nothing else can touch the turbo. Autocross and road coarses instantly jumping to the front of the list, and even daily drivers with a manual transmission fit a turbo better. Heck, most rwd cars will fit turbo systems in the engine bay easier than a supercharger.
But you fail to give credit where it's due. In applications where you can't force the RPM range (high power drag racing, streetlight-to-streetlight brawls) or IMHO even daily drivers with auto transmissions (worse gearing responds better to broader curves) suddenly the supercharger gets the kudos. But I also suggest supercharged cars for beginners in the performance world, for other reasons. Roots cars respond well to most mods that apply to N/A cars, such as headers & exhaust. Superchargers with modular pulleys are less complex to tune and much easier to control a wide array of PSI/CFM levels for the beginner. Reliability used to be much better with SC's too, although water cooled turbos have pretty much evened that out (do RMTSs use water cooled turbos?). And yes, I stand 100% by my MPG claim for superchargers. I challenge you to find any turbo at my horsepower level getting my MPG. Oh, and price. Roots & centrifugal are notoriously cheap for OEMS to produce, not to mention you don't have to have a bunch of special exhaust parts. Just use the same ones from the N/A base car. Hence the reason that GM bean counters will Ok a supercharged platform before a turbo'd one.
But in particular to this thread, which is about CA CARB, a supercharger leaves all emissions systems unmodified. Trust me when I say that CA CARB seriously frowns on any kind of modification to the exhaust since they won't like any mod at all that changes the position or distance from the exhaust ports of the CAT, the oxygen sensor, or the EGR connection. I've heard so many CA CARB vs. turbo horror stories it makes me cringe and thank the Lord that I don't have to go through that.
So, no, I'm not flat-out-wrong. The truth of the matter is that there are so many different applications and variables that the truth cannot be covered in a couple of blanket statements.
As of yet, no one has completely answered my question. Apperently there are some companies that go to the trouble to register/certify their systems with the state. Are there any of these companys that do smog legal systems for the Ecotec? If so what do they offer?
