Savington

iTrader: (31)

I saw this while going through my data from Willow Springs on Saturday.

This is T2 at Willow Springs, a 92-94mph 190+ degree sweeper (~1700ft of distance covered between turn-in and track-out). The latter half is uphill - in the last 700ft you climb about 50ft vertically. I can typically run through at 1.2-1.3 lateral G's, 92mph on entry building to 94mph mid-corner. It's a 5th gear corner in my car.

The technique for 2 is to carry a lot of speed in, trailbrake until the car begins to stabilize, and then add throttle and throttle-steer the car the entire way through. The idea is to build a bit of slip angle to maximize corner speed - if you just drive through without any slip angle, you're giving up a bunch of time.

This is what the "throttle response WHARRGGARBL" crew whines about the most - the supposed "inability" of a turbo car to make fine throttle position inputs which are directly linked to manifold pressure/torque output. As with most things (low-end torque, efficiency, midrange torque, quantity and frequency of perfect 10 sexual partners), though, the hard data is on the side of the turbo:



This is a trace of throttle position (blue) vs manifold pressure (red). Every single time the TPS goes up, the manifold pressure IMMEDIATELY follows it with virtually no time delay (way less than 0.1sec). If there's a lack in throttle response, I sure don't see it or feel it. Every time I flexed my foot, the turbo note would change instantly, and the slip angle would increase slightly. Lift off, the note drops, and the car tucks back into line.

My turbo is a 52-trim 2871R with a .86a/r housing, aka the "housing with less response", lol. The turbine wheel is also damaged, from last year when the CHRA bolts failed (for the second time) and shaved 2+mm off the turbine blades. If I had a healthy CHRA, the response would probably be better than perfect.

I'll throw some video up this week - I was playing with a new camera and it needs a better mount to knock some of the vibrations down, though.

Before the keen-eyed members jump on me, TPS EBC is on my short-list of things to do, too.

spoolin2bars

iTrader: (1)

the idiots are thinking in terms of drag racing in a straight line and/or comparing somebody's poorly tuned, improperly sized, laggy turbo setup. most of them don't track their cars either and don't realize that in the middle of a corner (or anywhere on a road course really) you aren't @ 2000 rpm when you go to full throttle. i don't think i'm ever under 4k and my turbo has instant response.

JasonC SBB

Be interesting to see this same datalog with a Rotrex with the same output power.

One could argue that the "problem" your datalog shows is not a lack of speed in rate of rise of MAP, but a lack of one-to-one correspondence. This would be more evident with an XY plot using TPS as the X axis and MAP as the Y axis.

For example, looking at about 15.5 seconds and 17.5 seconds, where the TPS is just below the 100 line, you get 2 very different values for MAP; ~110 kPa in the first case, and ~140 kPa in the 2nd.

Also, for some reason the rate at which MAP drops is much slower than your right foot - look at how quickly you lift at 14.5 and at 17 seconds, and the MAP somehow slopes down.


I'm not saying these effects present issues for the driver; I found that my supercharged M3 was a lot more difficult to modulate at autox than my turbo miata even though they have similar torque to weight ratios.

sjmarcy

Your graph seems to indicate a crummy sampling rate. Do you have anything at around 50-100 Hz, instead of "let's check from time to time if we are not busy"? And that is not the best way to check throttle response.

Joe Perez

iTrader: (8)

Andrew, everybody knows that naturally-aspirated engines have better throttle response than turbocharged cars. Don't go trying to cloud the issue with facts and truth.

Savington

iTrader: (31)

Nope, I think the above graph is more than enough to demonstrate the tight link between TPS and manifold pressure on a less-than 100% healthy turbo car.

What's the best way, then? I think that loading up a turbo car mid-corner at 95mph, then modulating throttle and watching boost (and thus hub output) change at the same time, is a pretty good way myself, but I'm sure you'll be along shortly with a fresh new definition of throttle response that sufficiently skews the results far enough into your favor that you can sleep soundly this evening.

Faeflora

iTrader: (2)

In other news, the sun rose in the east.

95mph in 5th means you're around 5500rpm which is nicely above boost threshold which means insta-response.

I guess that's your point ha ha

hustler

iTrader: (6)

Mine does.

hustler

iTrader: (6)

If we had "ALMS money" we wouldn't run "Continental Cup money" data stuffs.

Faeflora

iTrader: (2)

This is why I opened my throttle screw to idle my car at 5000RPM. Instant response. off the line and in between all shifts. I start my car and it just goes.

Savington

iTrader: (31)

You were kidding, but this is literally an integral part of rally-style anti-lag. You run the throttle plate 20-30% open, and use a rolling ignition/fuel cutout to regulate idle. When they're on course, they shut the rolling cutout off, and when they lift off the throttle, it leave the plate open and retards the timing, which keeps the turbo spun up and making boost even while the driver is off-throttle. Once they open the throttle, the ECU re-advances timing and away you go with absolutely no delay (and like 500+lb.ft at 2500rpm from a 2.0 liter turbocharged gasoline engine).

Google "jacked throttle" and "roving idle" and you'll get some more hits. Or you can look at the F1 version (blown diffusers), which is the same idea (throttle remains open under braking) but probably a bit different on the ECU/tuning side since it focuses less on exhaust pressure and more on exhaust velocity.

hustler

iTrader: (6)

Negative, pressure actuated valve-train, how does it work, Renault F1?

EErockMiata

my favorite analogy in a long while. thanks for the post, always cool when people share data and post it up for discussion.

MartinezA92

iTrader: (4)

I knew they did the whole retard timing to keep the turbo spinning but wow. That must make for an interesting sounding idle, not that they care.

Back on topic, I myself get pretty tired of hearing "dude your car must lag so bad from that turbo you should have done a crazy N/A build bro", especially when I have a peashooter 2560. I have had no problems with modulating throttle/throttle response obviously.

JasonC SBB

Listen to WRC cars just before they start off the line. Staccato misfiring exhaust note, sort of like chines dragon fireworks.

stinkycheezmonky

This is most likely launch control, not just an idle.

JasonC SBB

Antilag is active during launch control.
Their sequential boxes shift so fast you don't hear the antilag.

stinkycheezmonky

Ah, I misunderstood what you were saying. However, antilag being active during launch control is redundant; launch control is controlled throttle opening while stopped. The presence of antilag doesn't matter, because the engine is revved up anyway. One way or the other, launch control sounds like what you describe. Sort of like standing on the rev limiter (which is essentially what is being done).

JasonC SBB

It does - running a revlimiter at say 3000 RPM (for launch control), will produce a different turbo shaft RPM if it is combined with retarded timing (which increases exhaust gas energy). More so if there is some unburned fuel. The popping you hear from WRC cars before launch is unburned fuel.

ZX-Tex

iTrader: (15)

If that. I'll bet most of us are not logging anything faster than 5 Hz.
research time: MS3 logs in 5ms intervals? That is 200 Hz. Whoah....

Anyway ditto using my former (now parted out) GT2871 setup albeit with the 0.64 AR turbine housing. As soon as RPM was above 4K, and even in the 3.5K range, throttle response was quick enough not to matter, and modulation was no problem.

I'll bet RLogan (who now owns my turbo setup) will report the same thing once he starts tracking his car. Considering his last track car was a FFR Cobra with a serious NA V8, he has a decent basis for comparison. Plus he is fast.