Turbo lag and intercooler location

prizrak

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Had an argument with my co-worker over turbo lag, he used to drive an STi and was adamant that the TMIC has less lag than a FMIC, his reasoning is that because there is less piping in the way (it basically sits right on the engine's air intake) it would take less time to pressure the entire system. What I was saying is that while it's true that more volume will take longer to pressurize the difference would be negligible because of how quickly the air moves through the system at the kinds of engine speeds required to build boost in the first place. I couldn't really find any info one way or another, everyone who mentions turbo lag is generally talking about the boost threshold (aka RPMs at which turbo spools).
 
While technically it's correct that the smaller volume will pressurise more quickly as you say, I highly doubt you'd notice the difference in this case. I fitted a bigger intercooler that also requires longer hoses as it sits further forward, and I haven't noticed more lag at all.
 
Well FMIC does cool better but the actual point was that it would take longer to charge the system rather than quality of air coming in.
 
Well, there are two factors on this case, tubing lenght and better cooling (piping air that shrinks tighter thru longer tubes) So better cooling => more lag.

Best way to improove here, is to fit more powerful turbo, but set it up for same pressure (and channel exesive exhaust into the KAT, instead of intake, so it woun't heat up the inlet air)

That way, turbo would always work with spare boost up the sleeve, and bearing resourses.


I also like the "bus boost", presented on latest heavy diesels, where they upped turbo idle revs from 15 to 60~80 thousands/min, so the turbo has like... half-a-boost even at engine idle revs, only you touch the loud pedal.
 
I also like the "bus boost", presented on latest heavy diesels, where they upped turbo idle revs from 15 to 60~80 thousands/min, so the turbo has like... half-a-boost even at engine idle revs, only you touch the loud pedal.

AFAIK that's variable vane tech, they use it on turbo Porsches as well, basically the fins change their configuration (through magic as far as I can work out) so that they can put out boost at almost any RPM.

But on the actual subject, I get that more pipes will mean longer time to compress the question is how long are we really talking about. If say a TMIC takes 1ms to get from compressor to intake and a FMIC takes 5ms then it really doesn't matter.
 
I can't give you any actual info on Tudaroos, but as ex-dieselwacko, i can tell that ANY lag is just the matter of pedal timing. You get used to pre-boost the thing, even if it takes half-an-hour to pump.

If you're interested in lagless shifting, easiest way is the fuel cutoff button on the wheel.
 
This is a topic often discussed in relation to Volvos of my vintage. The stock intercooler setup routes the hot air to the bottom of the intercooler first, and then the throttle body is connected to the top side. Stupid idea, but it makes for easier packaging. Aftermarket setups reverse the routing (hot air to the top of the intercooler, throttle body hose attached to the bottom), and shorten its overall length. Their official tests claim a 12C decrease in temperature air at the inlet, and an improved throttle response as a result of the shorter tubing.

But as you see, I can't really answer your question :) You are right that both shorter tubing and colder air are better. Ideally you should find a setup that doesn't sacrifice either. Something that isn't very easy with Subaru's top mounted setup. Here is an innovative solution though:

10649561_10153110112047112_302630494968797388_n.jpg

10612679_10153110112062112_8084525631294576809_n.jpg


Before someone asks about rocks going into the turbo, he designed to place a filter there:
1622216_10105786695567630_5626527438520309968_n.jpg
 
I see few issues here (like what'll happen with the turbo, when you hit a small puddle) but the key problem here - Noise. Which leaves it with "only trackday" option.
 
Well, there are two factors on this case, tubing lenght and better cooling (piping air that shrinks tighter thru longer tubes) So better cooling => more lag.

Best way to improove here, is to fit more powerful turbo, but set it up for same pressure (and channel exesive exhaust into the KAT, instead of intake, so it woun't heat up the inlet air)

That way, turbo would always work with spare boost up the sleeve, and bearing resourses.


I also like the "bus boost", presented on latest heavy diesels, where they upped turbo idle revs from 15 to 60~80 thousands/min, so the turbo has like... half-a-boost even at engine idle revs, only you touch the loud pedal.

please define "more powerful turbo"
 
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please define "more powerful turbo"

I meant get turbo, designed for larger engine, capable of delivering more air with barely same/little more pressure, and channel exessive exhaust pressure into exhaust with induction valve.

Results => boost stays the same, but less lag, and longer use resourse of turbo (cause effective load on it never reach the "normal" point)
 
I had to google to figure out where my intercooler was.



That's the back of the engine, btw. Here's the front:



Then again I'm so used to driving automatics and various turbo diesels that I don't mind it anymore. It's probably been years since I last drove a naturally aspirated car. In the company van (manual turbodiesel with 90 raging hp) that I just floor it when I cut the street corner and hit boost when I've straightened out the wheel. :p My current car doesn't really have much turbo lag but it's a DSG which needs to figure out what gear to pick based on my throttle input, so it's not instant unless you have it in sport mode.... which you probably don't, because it's a nuisance when all you want to do is drive to work.

It took me a while to figure out my first drive-by-wire car though. V70 2.5T with a FMIC and slushbox. You had to give it some throttle and wait for stuff to happen. I wasn't used to that, so I instinctively gave it more, and then when stuff finally did happen, everything happened at once. But that was still the DBW and not the turbo.
 
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I meant get turbo, designed for larger engine, capable of delivering more air with barely same/little more pressure, and channel exessive exhaust pressure into exhaust with induction valve.

Results => boost stays the same, but less lag, and longer use resourse of turbo (cause effective load on it never reach the "normal" point)
That's just an anti-lag system that uses boost, you still need to get boost in the first place for this to work.

@Narf, looks like a normal air to water intercooler, S4 uses same tech as well. Also that turbo is tiiiiiiny and 90hp that's hilarious.
 
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It took me a while to figure out my first drive-by-wire car though. V70 2.5T with a FMIC and slushbox. You had to give it some throttle and wait for stuff to happen. I wasn't used to that, so I instinctively gave it more, and then when stuff finally did happen, everything happened at once. But that was still the DBW and not the turbo.

Unless you had an upgraded intercooler, the V70 doesn't have a true FMIC. It sits behind the radiator and condenser.

Also, if you thought you had turbo lag in the 2.5T (low pressure turbo), you really need to try the T5. It's an old-school turbo feeling of nothing, nothing, still nothing, holy shit where did that come from!
 
That's just an anti-lag system that uses boost, you still need to get boost in the first place for this to work.

@Narf, looks like a normal air to water intercooler, S4 uses same tech as well. Also that turbo is tiiiiiiny and 90hp that's hilarious.

the link narf posted, talks about 90KW (=120hp)
 
you still need to get boost in the first place for this to work.

No you don't. Cause when you haven't enough pressure - wastegate is closed and you have exsessive turbo. Belive me, even with less displacement, there's always enough exhaust, to start a self-loop. (well, not with the mopeds case, but anyway)
 
the link narf posted, talks about 90KW (=120hp)

My bad, didn't pay attention to the unit, that is pretty respectable out of a 1.4 motor.

- - - Updated - - -

No you don't. Cause when you haven't enough pressure - wastegate is closed and you have exsessive turbo. Belive me, even with less displacement, there's always enough exhaust, to start a self-loop. (well, not with the mopeds case, but anyway)

I don't think you are right, when you are running with throttle open any air that is being moved by the turbo is being put into the the air intake of the engine (boost or no boost won't matter in this case). When you close the throttle (take foot of the gas pedal) then if you are making boost it has to go somewhere so its either vented into atmo or recirculated back into the intake (more common). There are anti-lag systems that will take that boost and recirculate it through the turbine to keep it spinning above boost threshold so that you don't lose boost, but you still need to build boost at least once before it works. You can't spin up the turbine using non-pressurized air, it plain doesn't have enough energy to overcome it's inertia.

P.S. Yes the turbine is always spinning when the car is on, even at idle but its not making any boost until it reaches certain RPM (the turbine itself).
 
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