Data v. Whiny Idiots (Throttle Response Edition)
#1
Former Vendor
Thread Starter
iTrader: (31)
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 15,442
Total Cats: 2,104
Data v. Whiny Idiots (Throttle Response Edition)
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.
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.
#2
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.
#3
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.
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.
Last edited by JasonC SBB; 08-15-2011 at 08:04 PM.
#6
Former Vendor
Thread Starter
iTrader: (31)
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 15,442
Total Cats: 2,104
And that is not the best way to check throttle response.
#11
Former Vendor
Thread Starter
iTrader: (31)
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 15,442
Total Cats: 2,104
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.
#12
Tour de Franzia
iTrader: (6)
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,085
Total Cats: 375
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.
#14
Elite Member
iTrader: (4)
Join Date: Aug 2009
Location: Redwood City, CA
Posts: 1,784
Total Cats: 42
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.
#18
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).
#19
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.
#20
Elite Member
iTrader: (15)
Join Date: Dec 2007
Location: San Antonio, Texas
Posts: 4,847
Total Cats: 27
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.