Quote:
Originally Posted by PoorMans180SX
I'm really talking about actually driving the car. While we can extrapolate some data from a consistent dynojet figure, it's really all about how the car actually goes down the road. Downshifting takes a lot longer than pressing down a pedal, and it's much easier to shock the drivetrain into wheelspin. If I can simply push the throttle down and accelerate, that's ideal.
Yeah I'm used to driving 300-800whp Evos and STis on the street. These guys aren't afraid to spent some good coin on sticky tires and awd makes the traction thing a lot less of an issue.
Speaking hypothetically, I get if you're on 235 400tw tires or something, but if that's the case I'd say build your wheel and tire setup for the power you're making.
On the other hand, maybe learn to control your right foot and the car? Breaking traction might be easy, but it's also not hard to learn some finesse. I'd rather be able to break traction at all times than to not have the power when I want it without having to make a gear change. There's always unexpected situations in daily driving, like you didn't see that car while you're pulling out, etc. You can't always account for being at low rpm.
I totally get the tuning window aspect of it, pump gas can be a fickle beast when it comes to big, low rpm torque swells and boost spikes, especially if the intercooling system is sub-par and heat soaks. I still think a conservative tune with nice low-end grunt is more fun to drive than something with an S2000 like powerband on the street. I've driven 450whp Evos that feel lethargic even though they basically have a linear powerband after ~4500rpm. The bolt-on 18K cars are much more fun, and make the same power when switched to E85. Then again, my friends 2.2liter 7670efr makes 450+wtq and feels like the perfect hybrid of the two. There's about $6k difference between the two setups though.
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Well first consider not all cars are manual. There is a very narrow window of manual transmission cars with a broad range of power used in a similar manner- I assume mostly street 300-500hp fooling around stuff.
I understand the scope is lightweight rwd 2L~ cars but the turbo specific behavior has to reflect the sort of use, whether it is indeed "street" car or used in some kind of racing. The racing efforts where rules are in use will need reflect the efficiency
range of the turbo used, with support from fuel quality in that range. While street stuff may not need to be perfectly dialed in since ever situation is random or can be random from light to light. And highway roll racing stuff can be 40mph or 60mph or whatever.
thats the issue with street setups- anything goes or can go. It isn't the same corner and downshift (or not downshifting with the right turbo) in every single race or trial.
This reveals an overwhelming issue of torque management, or simply boost control per speed or RPM or Throttle position. The faster a turbo spools the more difficult it is to control the boost with your right foot, the more important it is to control the power using electronics instead of your right foot. The more emphasis on modern closed loop boost control and wastegate operation becomes. Small, high flow turbos using high boost are excellent candidates for manual transmission cars when the boost control is dialed in properly to match the current use, per gear and terrain.
Boost control as that can be difficult for the average enthusiast, and anybody whos ever tried to hold the boost halfway between 0psi and 25psi to maintain traction with any kind of turbo is going to realize it isn't possible to keep boost pressure as a steady line with the right foot alone.
So it isn't really a turbo issue, its a control issue. High boost pressure is not bad for an engine- but the fact that it needs to rise so high in such a short time can make it difficult to control, and maintain through gears, its it's own problem and set of issues.
Whereas a larger turbo running less boost and spooling a bit more gradually is far easier to control, both from electronic point of view and with the right foot. It may be more 'civil' in a street application and predictable as well.
It depends on how far the owner operator is willing to go in terms of control theory, micro controller management, frequency response, that sort of thing will determine how well the small peaky spiky graphs will work for your car.
added:
In other words, if someone can conquer the issue of boost control to make exactly the amount of torque(boost) needed at any given instant, that is a real time traction control for max torque, ideal torque for any situation at random on a street
Most turbos and especially with alcohol fuels can boost 30 to 40psi to make any torque desired for it does not tax mass flow rate to make a high peak torque
also added:
personally I would not put a turbo less than 50lb/min on any 2L
the smallest turbo for any car is 50lb/min is my basic tenant for all 2L+ no matter how they are used in 2500-3500lbs vehicles.
Application sets the turbine. Drag racing buy the biggest turbine. Long racing situations, overdrive gears you want to keep the EGT as low as possible so the largest turbine lowest pressure wins at constant output. On the highway all the time, use a large turbine for those 80mph roll races. Especially in drag where the driver never lifts from the throttle, it just gets up and stays up, none of this talk about response makes any difference. The less strictly drag the smaller the turbine gets until its small enough to produce boost on the coldest day after a cold start at some freezing temp outside while not being on a highway, stuck in normal traffic stoplight stuff. Your coldest environment has the smallest turbine for those cold stoplights waiting for the heat to start working. The engine can light that thing off at some 40*F to give you boost with 2L on those days from the factory.
The environment (temperature) is critical design factor in cars which frequent those climates.