JasonC SBB

My AEM will log at 20 Hz (>10 variables) using a laptop, and 200 Hz internally (8 variables).

My $29 4-ch logger will log 4 channels at 60 Hz each.

sjmarcy

Instantaneous throttle response "proven" by 5 (five) hertz or 1 (one) hertz logging and then posting about it on the internet just hurts haha.

JasonC SBB

Sav's posted log appears to be at 10 Hz.

sjmarcy

Which is too slow.

shlammed

iTrader: (8)

It is still fast enough to show a trend over half second. A laggy setup would take longer to spool at these rpm and he is trying to show that it is not in fact a laggy setup.

if we were talking about a 2554 on a larger than 2 liter engine where it would build transient boost in 0.5 seconds, your argument would be more valid.

Savington

iTrader: (31)

I disagree - I think showing that an unhealthy turbo car with a larger-than-average turbo can produce multiple correlated transient response changes within 0.1sec proves my point just fine.

18psi

iTrader: (76)

Who gives a **** about cold hard facts and datalogs when you can just make up excuses for a **** poor argument and reject evidence. The datalogs will always "be too slow" just like the people refuting them.

wayne_curr

iTrader: (8)

You're exactly right. This is just turning into a political debate.

shlammed

iTrader: (8)

m.net

blaen99

iTrader: (6)

Or was Sjmarcy calling you too slow, Sav?

sjmarcy

Sav, you are showing boost readings responding to TPS. That is not necessarily the same as making the same amount of torque that would show up on a dyno at that time at that or other throttle settings. Think about it.

Try measuring the vehicle's response to torque compared to the response at the boost sensor. They won't match exactly and this is normal. Clutch slip, mount flex, drive and halfshaft twist among many things affect this...

Here is an example of a car rolling along - see graph. Then the throttle is opened to full. This is a normally aspirated car at low RPMs that was proceeding at a steady speed before the throttle input. I did not log the air pressure in the manifold, but I am sure that it rose before the engine responded…and that the engine responded before the entire vehicle responded. This was logged at 100 Hz with 0.3 seconds smoothing.

See the sine wave after the car reaches it's maximum rate of acceleration? This is a characteristic that is best minimized for better car response at the cornering limit. Honda, for instance, oversized things like halfshafts and driveshafts on the S2000 to try to manage this issue. When you minimize the slop, the car is more responsive to the throttle when at the cornering limit. It's common to find a car nicer to drive with beefier drivetrain mounts - more responsive.

The logged car reached it's full rate of acceleration before the throttle was completely opened as it only needed X amount of air at the time anyway. From experience I know that the car reaches it's maximum acceleration such that this amount matches what it would at WOT for longer. Turbos don't always do that, they can't all the time.

Suppose you dyno a turbo from 2500 to 7500 Rs. If you were cruising down the highway at 3000 and then floored it, the car would respond but would not at first produce the expected amount of torque (from a dyno) at that RPM. Since the dyno chart involved the car already having been at WOT for sometime prior to the apply-throttle event.

Sorting out things like this to claim a certain throttle response might be best done by specifying the conditions. And doing tests over a range of conditions.

Another aspect of a car's response to the throttle involves engine braking. A high cube / high compression engine has a great deal of engine braking when you come off the throttle. Try driving a Cobra kit with a 7 liter 11+ CR lump as you come off the throttle. Compare this to a comparable weight car with a small engine running low compression pistons. Very different! The Cobra can practically lock up the rear tires. The boosted car won't even come close to doing so.

So…if you look into a car's response to throttle a little bit (as I have), you can see that there are a number of concerns. Things like how long it takes for the car to react. Does it misbehave (sine waves). Does the car overreact to trailing throttle events due to rear bump steer or compliance? What about lash? How strong is the engine braking effect? These things all contribute to the throttle response the driver experiences.

You could just compare the TPS signal with the boost pressure signal at a low sampling rate and call it a day. But I think you would miss some of the situation. See…all of these things are part of a system.

Laur3ns

This is news?

Lag decreases as rpm rises. While lag can be as much as a second or more at low rpm, the delay in boost rise virtually disappears at revs of about 4000 or greater, For example, in a properly configured turbo system, boost rise will fol¬low the position of your foot any time the revs are above 4000 rpm. Response here is virtually instantaneous.

Now, who wrote that?

sjmarcy

Here is a little graph I made to illustrate a response characteristic. If you are cruising along…and then floor it…what happens? Well if the car is boosted it can start responding decently…but it won't at first produce the output you expect at that RPM.

On this graph the green line represents the percentage expected TQ based on reading a dyno chart. For NA cars (blue graph trace), they tend to respond more immediately and then quickly stabilize right on the green 100% expected torque line. That is, they quickly start putting out what you'd expect. Turbo Cars (red trace on my graph below) don't immediately hit 100% of what a dyno shows. Many people do not realize this!!

Remember that a dyno test is favorable to turbos in that the RPM in question was reached with the turbo already at full blast since the test was started earlier in time and lower in RPM than the conditions shown in the dyno graph. Dynos ignore lagging response to the throttle. Since the throttle is already wide open and does not move.

You can also see the same thing in many highway runs with comparable output NA and boosted cars weighing about the same. At the 3rd beep, the NA car pops ahead. We just saw this the other day in the LS1 Miata versus Miata Turbo someone posted. Oh…here it is! ;-) Notice how the Turbo Miata does better after it has a chance to respond to its throttle. When the Miata falls behind a bit…well that is the yellow zone on my graph. It's yellow cuz the driver just pissed himself haha. Or do I have the cars backwards? ;-)

emilio700

iTrader: (3)

Hey Savington,

Are you actually engaged in a debate over the interpretation of datalogging results with sjmarcy?

Just checkin'

Faeflora

iTrader: (2)

ahh a ah ahhh
WHAT THE EVER LIVING **** ARE YOU SAYING?


HAVE YOU EVER DRIVEN A ******* TURBO CAR? IT'S SIMPLE. WHEN YOU GO WOT OVER 4000RPM THE TURBO RESPONDS QUICKLY. THE ******* END. IN YOUR SHITTY VIDEO, IF THE TURBO CAR STARTED THE PULL AT 5000RPM IT WOULD BE AS RESPONSIVE AS THE DAMN LS1. GO ******* KILL YOURSELF.

sjmarcy

What are you, 12?

Techsalvager

so for the turbo car that dyno from 2k to 7k and made say 140wtq at 4k rpms.
Say you are at 4k rpms in 3rd once you open the throttle all the way, you still will end up waitting somewhat before the power flows in couple hundred rpms, maybe thats extragating it, but thats what I think you are saying there. so you really won't be at 140wtq at 4k unless you started way lower in the rpms when you went wot.

Thats my line of thinking about it after doing my first autocross in the turbo miata when I dropped down to low rpms off throttle, sure on the dyno it may of said 130-140wtq in that area, but even than still took a while to get back into the power band. Wasn't like bam open throttle back in powerband, more like a delay and than bam.

That of course is not taking into consideration the rest of the drivetrain and connections to the engine\tranny\rear end and any other outside variables.

JasonC SBB

Why would torque output not follow MAP?

MartinezA92

iTrader: (4)

This forum is so entertaining sometimes.

sjmarcy

It does follow, after the brief intermission. You can see the same things happen with normally aspirated cars. If you are not using a sluggish logger, just compare the different signals. On my 97…throttle opens…vacuum is generated…air rushes in…you then see the MAF signal start to ramp up…and then the accelerometers indicating that the vehicle has started accelerating after another lag.