Nathan, we have strayed a bit off-topic, but I consider this a relevant discussion whenever someone makes broad statements about the pros and cons of turbocharged engines, so please bare with me.
Nsxsupra, sorry, I don’t know your name. Mine is Steve.
First of all, I’m sorry that my comments were taken personally. I didn’t mean them that way, but they turned admittedly sharp after the first exchange. As for your language skills, they were not the target of my sarcasm, your posts are more intelligible than many for whom English is their native language. I envy your multi-language skills. I’m not sure what wise-guy posts you read, but I’ll admit that I’m not around much the last couple years and post even less. When I do I’m generally motivated by something like this, annoyed at the dissemination of inaccurate or incomplete information that is an ever more prevalent part of this, the most spectacular tool for communication ever conceived.
I’m sure you have heard and read advertisements claiming that “More doctors recommend…” and wondered “More than what?” The whole turbo/SC/torque/lag issue is complex, and repeating the cliché statements about them without more information is not just incomplete, it is at best extremely misleading. FWIW, I probably owned my first turbo car before most members of this forum were born, and I’ve seen them evolve from very crude to very sophisticated. The crude ones would kick the crap out of most after-market SC options today.
Let’s stipulate that there are several types of superchargers with different strengths and weaknesses, and while those differences are significant they all share similarities that make them distinct from turbos. There have been and continue to be attempts to build SCs with variable drives and other ways to get boost earlier, but at best they are not perfected much less widely used so I’m ignoring those in this discussion. Let’s also stipulate that if your only goal is to crank maximum peak dyno HP out of a small displacement engine by bolting on a turbo pulled from a Cat diesel, there is a price to be paid in response. Naturally not everyone uses their NSX in the same way, but other than bragging rights or serious drag racing (not my cup of tea), there is little sense in building a street legal one with more than 500 rwhp even if you spends weekends lapping road courses. So my focus is cars with about 400 rwhp with stock internals and 500 with the appropriate upgrades.
If there is one thing that tubos do well it is torque, especially low and mid-range. Look at the power curves for two well prepared cars, one turbo and one SC with similar peak boost levels, and tell me which one has more torque. And that’s on a dyno, typically from steady “pull” which is a fine measurement tool but not the best imitation of real-world driving. It’s hard for me so address the misconceptions about lag and torque separately because people seem to think of the latter as an extension of the former, which of course it is not. I trace the exaggerated perception of turbo lag to the early turbocharged Porsche 911 derivatives. An already tail-happy car with extremely low compression and a big slow turbo, they did suffer from significant boost lag and when it did come on with a rush exiting a corner it could send you pointing the wrong direction in a hurry. Fast in skilled hands, but hard to drive, and deadly in the wrong hands. A lot has changed since then.
Back to the “compared to what?” question. If your idea of fun, or measure of performance, is to cruise along at a few thousand RPM and suddenly stomp on the throttle, nothing beats a well-tuned normally aspirated car. The typical CTSC using a rising rate FPR for fuel enrichment is a bit lethargic by comparison, falling somewhat flat as the throttle plate opens and the engine tries to suck air through the SC and the bypass closes. It is brief, but noticeable in from-a-punch races. I would expect that to be minimized with a well tuned standalone ECU. Do the same thing with a turbo designed for all around performance and it will certainly take time to build boost, but in the blink of an eye it will match the boost of an SC. After that it is no contest. Compared to the mechanically driven SC, a turbo builds boost from load rather than RPM, with more load creating more boost, creating more load, feeding itself. Typical dyno pulls don’t even begin to show the differences, but drive the two back-to-back under various conditions and they are obvious. In daily spirited driving the most dramatic difference is probably going up hills, where the link between load and power is maximized. A rush, literally.
Lag. Both SC and turbo cars typically exhibit a minor decrease in off-idle and low RPM throttle response, but that isn’t really the same as lag. I would define lag as the time it takes to transition into positive boost. Like I said, if you get kicks from jumping on the gas from a cruise then technically a turbo will transition to boost more slowly than an SC. How much longer? That depends, but don’t try to catch it on a stopwatch. In comparable systems it is very slight with a stock compression engine, and only marginally more for one built with higher boost in mind. More importantly, at times when power matters to me the lag is effectively non-existent. When the car is being driven hard through the gears or around the track where shifts are fast and engine RPM is kept up, max boost is regained about as fast as you can complete a shift. So much so in fact that many people use the latest technology to suppress the rate boost comes up. Actually, that’s been done in production turbos for a long time to keep Joe-average driver from losing control. In other words, too much torque too fast at lower RPM! Not a complaint you hear about SC cars. When not “racing”, I love the way a turbo responds. If I’m cruising along and decide to pass someone or sprint up to the next corner, I roll in the throttle and boost builds at an exponential rate, very different from an SC, offering huge torque with low revs and no unwanted drama. Experience that just once in a properly built car and you will never again say that turbos lack low-end torque.
My point with all this is to help debunk the myths and misconceptions about turbocharged engines. People looking for information to help make important and expensive choices are inundated with the out-dated, over-simplified and sometimes downright false clichés that get repeated again and again, often without any other details or attempt to put them in real-world context. Pretty soon they join the crowd of people repeating the mantra that turbos are crap for low-end torque and suffer from “lag”, even if they don’t really understand it. I liken it to ethnic and gender stereotypes that may or may not have sprung from a kernel of truth but are grossly exaggerated and not at all representative of reality as a whole. (Not that I put those on the same level. I do have a sense of perspective and relative importance, but the symptoms are similar.) My initial response in this topic was a polite attempt to coax you or someone into expounding a bit on the subject and fill in some of the details, to which you replied in part “Low end torque and turbo lag is well known downside of turbo.” It occurs to me that the Internet is to “common knowledge” what a turbo is to boost, building at an exponential rate rather than the more linear model of mouth-to-mouth communications. Unfortunately it does not discriminate between fact and fiction, so we all need to do that by asking more questions and insisting on supporting evidence because even “common knowledge” is sometimes wrong and often out of date.
There are lot's of terms that most people don't really understand.
