I just wanted to address a few of these issues, and sorry about dragging this back up. Also, I know I only have like 1 other post, but I'm a lurker and don't post much.
--------------------------------------------------------------------------------Originally posted by quick dsm For my sake in the arguement, i was starting a turbo with a spool time around 4300rpm, not 5k. I believe a 5000 rpm spool is at the limit of streetability.
With that being said, im most cases you are spinning the turbo in day to day driving, more fuel consumption in response to more boost.
Not necessarily, see below | \/
2. A lean condition in low rpm will not hurt engine longevity provided you are not detonating.
2.a Wrong again, lean conditions produce more heat the an ideal fuel mixture, running anything lean on a engine with forced induction will detonate. Higher heat causes premature breakdown of oils, and ultimately increased wear and tear on engines
ME -> Lean is relative to engine load is it not? Such as at idle, you don't want your a/f ratio to be 11 or 12, it will be somewhere at 18 or 19. Same with partial throttle operation, if the engine is under a light load, it doesn't need to be rich or at stoichmetric (sp), and your temperature will not skyrocket and reduce the life of your engine even if you drove around like this all day, which, amazingly, 95% of the population does. It doesn't hurt anything if tuned correctly. And thats what proper tuning will get you: good mileage by figuring out how lean you can make it and still not detonate and or reach too high of egt's. But even at partial throttle, your still not going to have as high of egt's as your are under full throttle, so what wears your engine out faster?
3. Driving around at lower rpms with a larger turbo will increase mpg-smaller turbos will spool sooner causing the engine to injest more air and burn more fuel.
3a. Newsflash, your not driving a CVT, your rpms wont remain constant, and regardless of where your rpms are your still spinning the turbine... even if your not fully boosting your ecu is still sending the signal for more fuel in order to keep the mixture decent, or in your case "lean". Dont tell me you'll never spin the turbo when your around town because you'll keep it down in lower rpms. It aint gonna happen. BTW whats the point of having the turbo if your not going to use it?
ME -> I don't know what town your living in, but even driving a 240 with sr20 w/ a t25, if you even hit 1 pound of positive pressure, your driving to fast and will be pulled over. Hell, with a stock ka24de and partial throttle I already drive faster then 90% of the people, and thats shifting at 3500. You don't need 15 lbs of boost to go between stoplights. You do to get to freeway speeds with confidence (love that phrase), but thats about it. After that, you only need boost to go fast, and to me that means your racing. And, if your racing, 1st gear goes by so fast, you probably wouldn't make full boost before you realized your hitting the rev limit. After that, your already in the proper range for 2nd when you shift, and away you go. On the other hand, if your doing freeway racing, if its to hard for you to downshift from 5th, the "lag" you experience is your own fault.
4. As far as a car "dumping fuel" the amount of fuel is calculated by the amount of air being drawn in to the engine. When the turbo spools, the engine will injest more air and ad the correct amount of fuel. This happens with any turbo, small or large. The larger unit may be moving more air and using more fuel but the ecu does not just dump it in there. That doesn't make sense. That's why people tune their cars.
4a. If you weren't trying to pick my post apart with your *** you may have noticed that people refer to adding fuel as dumping fuel. Your right, when the turbo spools it takes in more air, which "dumps" more fuel, which means... *drumroll please* you loose gas milage. So with that point down, onto the next.
ME -> Not to also pick apart your post, but I can see where saying "dumping" fuel would cause some confusion and make it sound like your wasting gas excessively just to further your point. Just because he called you on it because it does sound confusing, you just say "well, what I really meant was this", that just doesn't work. Saying something like using more fuel would be a little less confusing.
5. The turbine spins always, no matter what size turbo you have. That's the whole advantage of turbocharging-using otherwise "wasted exhaust energy. A larger turbo will even have less back pressure due to a larger turbine housing.
No thats not entirely true. The turbine vanes take up more space. That means that any extra room has been taken up by the vanes. The bigger turbine has more rotateing mass, making it harder to move/ spin. Why did you think it takes so long to spool? The houseing is not built simply to flow more air, it's built to speed up the air to increase effieceintcy. They are made to lower spool rates, increase pressure and response. Bernoulli would be proud of the turbo.
Now, explain to me, how much do you think you know?I was like you, thought i knew everything, came on here, found out the hard way i dont know squat, and compared to the veterans, Adam, Apexi, Freddy, AZ, Exar-kun, K Car, Maine... i still dont know squat... but i know something, and that something, is that your wrong.
-----------------------------------------------------------------------------
Now I don't want to ruffle any feathers, but I think quick dsm did make valid points and I just wanted, to me at least, maybe clarify them further.