GR Yaris Intercooler performance and lag

sixtentouge said:
I didn't read through all four pages of this thread, so...

I've seen loads of calculations done by people showing that adding a larger intercooler and charge piping should increase lag, but in general, it's just not true. On just the surface, the volume of air the turbocharger produces makes adding a larger intercooler and charge piping a non-thing where "lag" is concerned.
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"Volume of air the turbocharged produces"

Lag isn't about volume, volume is fixed in displacement of the engine, it's about how fast pressure can be built. More IC system volume increases this time to pressure, as it increases the time in the reinforcing feedback loop of boost builds more boost.

That is why M/AMG/Porsche/etc use charge coolers, that is water cooled IC that don't need to be front mounted with resulting short piping, on top of much lower volume of the cooler itself. Because they value low lag in their previously large NA low lag applications.

But yes it is true that high system volume can help NA response a little but didn't notice this on the GRY.

Top end yes there is much less pressure drop on a larger system, but at this point lag is usually not an issue anyway. It's a mid revs ~3,5k rpm where it matters when you go on throttle out of a bend.

It is also true that once a smaller system is heat soaked it will lag more, and the GRY system is very prone to this - this is why I changed myself too, but I still got annoyed at lag at times as soon weather wasn't cold, and I noticed a clear increase in low down turbo lag (not NA). In that sense, e.g. a DO88 full height thin IC can be preferable to a thick front mount with more volume, although the latter will allow higher peak horsepower, in real driving the former is surely better if you value response, both by lower volume and much more area for quick cooling of any heat soak.

So there is no single answer, IC can be optimised for many variables of driving and also power level.
 
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Onehp said:
Lag isn't about volume, volume is fixed in displacement of the engine, it's about how fast pressure can be built.
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The more volume you can move, the quicker you can fill the fixed displacement.

The quicker you can produce exhaust pressure, the quicker the turbo begins to move air. In many cases, which is why I said "in general" increasing the intercooler and charge piping volume will lower the boost threshold. Of course there are outliers. The point is that there's more to the story than just filling the empty space.
 
Its like one cancels out the other to a degree. Increase the volume with pipes and a larger IC (with better end tank design) should mean less pressure drop, less resistance to flow and faster spool.
As far as the GR goes, the VB 43 turbo can reach max boost and I Call that 22psi here at least 1000rpm sooner but the OEM tune restricts the spool time. Probably to control the rise in torque as the boost builds or the dreaded LSPI.
 
sixtentouge said:
The more volume you can move, the quicker you can fill the fixed displacement.

The quicker you can produce exhaust pressure, the quicker the turbo begins to move air. In many cases, which is why I said "in general" increasing the intercooler and charge piping volume will lower the boost threshold. Of course there are outliers. The point is that there's more to the story than just filling the empty space.
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I did some analog testing in 6th gear at 2000 and 3000rpm in same road stretch/runtime/weather. Aftermarket IC+pipe (volume x2) definitely took longer time to build full/respectively 1 bar of instrument cluster boost, roughly... 2x as long. Not scientific but confirming with my subjective impressions.
Mostly cancelling any response gains from the HJS that improved turbine pressure ratio.

Still took it as I hate heat soak more...
 
Onehp said:
I did some analog testing in 6th gear at 2000 and 3000rpm in same road stretch/runtime/weather. Aftermarket IC+pipe (volume x2) definitely took longer time to build full/respectively 1 bar of instrument cluster boost, roughly... 2x as long. Not scientific but confirming with my subjective impressions.
Mostly cancelling any response gains from the HJS that improved turbine pressure ratio.

Still took it as I hate heat soak more...
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but if then you drive +4krpm its not much of an issue. I seldom drive sub 4krpm if giving any more throttle.
 
Its light.
IMG_1281.webp
 
11:28 in this vid, I thought about this thread. 3rd gear pull. Smallest engine with biggest turbo has the least lag and even beats the twice as big 4l NA. Why? Small water cooled intercooler (aka chargecooler) with very short piping is one important reason....

 
You're drawing a "long bow" aren't you.
What about power to weight?
What rpm are each engine running at during the roll-on test?
Where does each engine produce Max torque?
Saying that I do agree. Less volume equals less lag as long as the drag through the piping and IC remain the same.
Smaller IC cores usually mean more drag/pressure drop.
 
Sekred said:
You're drawing a "long bow" aren't you.
What about power to weight?
What rpm are each engine running at during the roll-on test?
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Just an illustration.
Not the fastest car by a margin here in acceleration.
Not too dissimilar to the others turbos to explain the big difference (Porsche is long geared though).

Agree there is a compromise and that's the point, rather then 'lag doesn't matter make IC as big as you can' approach.
 
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I don't think I would want to change the pipework for stock frame turbo.
 
ninjan00dles said:
Has anyone here actually measured lag
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It varies per rpm and gear. Point is that for me the relative absense of lag was and is a very important measure of driver pleasure and car control. E.g. driving a rally car with or without anti-lag is night and day. So it's imho important to discuss and take measures in engine tuning to reduce lag.
I would compare by going completely off boost and let the car roll untill rpm was at 3k rpm than WOT, and counted the time until I had 1 bar boost.

Up to each to decide how important it is for their driving.
For me it's so important I would counter lag by using left foot braking into bends so I could spool up the turbo even before I had a clear view out of bends. That worked too, but car was noticeably more fun when air was cold and lag was less.


PS: Now I have a lag free car and it's bliss to large part because of that...
 
My point being you can measure lag based on boost target vs boost actual. And maybe consider WGDC.

There is 5 pages of discussion here and no measurements
 
ninjan00dles said:
My point being you can measure lag based on boost target vs boost actual.
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As I wrote, that depends on gear and rpm. Also varies with air temperature and intake heat soak. Moreover there is no default logging tool.

I've measured it as described, don't have the exact results anymore (car sold), but at the time the HJS cat made a clear improvement. Which was basically eradicated by a bigger IC... Unless the stock IC heat soaked, then the bigger IC was a bit better. Lots of variables not so easily measured equally.

Be my guest to set up a comprehensive framwork for cross community reliable measurements, contributing with your own measurements.
 
Ecutek can log this, OBDfusion as well.

You measure boost request vs boost actual... the lag is the latency between the curves. Post the manifold IAT as a secondary axis for heatsoak reference. X axis is time.
 
ninjan00dles said:
Ecutek can log this, OBDfusion as well.

You measure boost request vs boost actual... the lag is the latency between the curves. Post the manifold IAT as a secondary axis for heatsoak reference. X axis is time.
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Still need to step on it at an agreed rpm 100% off boost to be comparable. 3000rpm?
 
Some might appreciate this D4A video on lag, don't think it has been linked-to yet.

A rear-mounted turbo is going to have absolutely horrendous lag, right...?

 
I haven't watched the video yet but I can guess at the volume of the system being all that matters with respect to how fast a given turbine can pressurise it. Absolute distance doesn't affect time to pressure if the pipe work diameter keeps volume optimal.
 
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