Quote:
Originally Posted by Kingtal0n
Load and time spent under load is an important aspect to this discussion. With a load dyno you can hold a engine at low rpm and load it for as long as it takes to build to some huge boost number and then say look I made XYZ at 2500rpm or something stupid.
So when we start looking at dyno graphs and trying to compare response or spool character, it must be done using the same exact dyno situation and dyno electronics and dyno roller weight and vehicle tires/drivetrain/etc and gear ratios. Otherwise the load will be inconsistent and the turbo will look better or worse on paper because if the load is reduced the engine will accelerate more quickly and the turbo will appear to spool slower. This is why 1st gear spool is always terrible looking on paper and why a 5th gear overdrive dynopull can make the turbo look like is spool really fast on paper.
All my dynos are always done on dynojet. This keeps load from the roller weight consistent at least. And dynojet calculates power from roller mass so there is no fooling it. To compare cars more equally.
I recommend anybody interested in 'turbo spool' consider these things carefully.
Now- about the response and fast spool behavior, I don't see that it makes much difference for daily drivers or drag cars anymore, maybe some other racing applications where exact gear ratio situations (coming out of a specific corner) require fine tuning that last 500rpm of spool from the turbine... but in most daily driving situations you can just downshift or avoid being at a very low rpm in the first place. A stock turbo can blow the tires off of first gear, response is unwanted after some point. The onset of boost should be tire sparing and keep the car from spinning so a slower rate of boost building is desirable and fine-tunable in the best situation. IMO daily driving favors a larger turbine lazier spool when the power at 2L is around 400rwhp+ because it ensures lower EGT and wider tuning window, safer on gasoline especially.
|
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.