Boost control and turbo stuff - how it works in normal words

[Marky]

Ok, the internet is full of these but I thought I\'d do a quick write up since... well since I\'m bored and it might be useful.

Alrighty - this is a real "how to suck eggs" for a lot of people but it this might help some understand things better

Ok - first off - the difference between "turbo lag" and "boost threshold"

Boost threshold is easy to explain, and is normally called lag instead. If you drive in say 4th gear at 60kph, in 90% of cars you can put your foot down and load it up on the brakes, and you will see full boost at X rpm. Below X rpm it will not make it all the way there. In an ideal situation, anything past X rpm your boost will neither climb nor fall from target boost. Larger intercoolers, whatever you want, don\'t change this RPM (see below)

LAG on the other hand is the opposite and has nothing to do with RPM - lag refers to the transition response between when your foot goes down, and when the car hits that full boost number. Dyno charts can completely confuse this issue - it\'s possible with the same car to show a sheet where it doesnt make full boost till 4000rpm, or another where it gets loaded up for 5 sec beforehand and make the same psi from 2500. For example - in some cars they don\'t even have time to make full boost in first, but will make it with a flick of the ankle at 100kph in 5th. Bigger turbo = normally more lag. Bigger intercoolers & more piping = more lag, though to be blunt a big deal is made out of it on subarus and most are hard pressed to pick the difference (unless they\'re part cyborg /drift monkeys on and off the loud pedal 8 times a second and/or measuring lap times to 10ths of a second).

The boost THRESHOLD generally can\'t be improved on much - generally. It\'s a function of how much gas flows through the motor and spools things up. If you can free up the intake path, flow more exhaust, then you\'ll move more gas, wake it up sooner, off you go. Spool up can also be improved through slightly retarding the ignition - do it enough and that\'s basically what anti lag is. Hence why one gets confused for the other - faster spool up / less lag = lower rpm full boost in the lower gears

The other one which is often confused is Compressor surge

- PROPER compressor surge is a result of a turbo spooling up faster than the engine can physically swallow (there\'s totally some innuendo there) - it\'s common on some cars, such as a GTR with big turbo, cars running mismatched combos (say td05 rear with 25g front / T3 rear T04 front) or people running these crazy efficient new tech turbos on evo/wrxs - it\'s NOTHING to do with the chatter you get on throttle lift off. Surge is a "chuffchuffchuff" sound on part throttle or as a car comes on boost (with full throttle), it has the ability to munch a turbo eventually, even more random is the effect it can have on the engine - the shuddering it can create can chew up engine mounts, in extreme cases the shock loading can smash gearbox components. Random as. On AFM metered cars it plays absolute havoc with driveability as it\'s air going in, out, back & forth but with WOT... you can imagine it\'s not great

THIS is compressor surge -

- that chattering in mid RPM, not the BOV noise as he lets off

The chattering (or "zu-tu-tu-tu-tu" noise silvias make) you get on lift off is purely down to a BOV not doing it\'s job well enough, and is air chuffing it\'s way back out the turbo inlet. See: your average nissan with no BOV / aftermarket BOV with too heavy a spring / not enough venting area. Youtube "Dose Pipe" for pages full of epic examples. It can, eventually, over time hurt the turbo (you\'ll find an internet full of arguments back and forth) - some cars didn\'t come with one from factory (late 80\'s turbo models etc) and still run fine, that said for the $20 a decent BOV can cost (late model evo BOV\'s are pretty ideal for example) is it worth the risk just for a random noise?

Vid for proofses -

or

So much lols

Onto the fun bit - boost control. I have to say here that the use or lack of use of factory control has ZERO to do with your misfire / pinging issue / ex GF leaving you / whatever. All the function of it is, is to use and fool a pressure signal into making a turbo work at a certain rate, what happens from there on is a separate issue. Anyway....

Now how any boost control operates is quite simple. Think of the wastegate as a bucket, think of the wastegate hose as well.. a garden hose. If you punch a hole in the hose, the water while the same VOLUME comes out, you\'re bleeding some off and fooling the bucket into thinking there\'s less water, filling it slower. (In my sentient-bucket example anyway) In air terms - less pressure makes it to the WG, this means it takes more pressure in the hose to push the actuator open = more boost at manifold. It\'s a simple spring loaded thingy, which pushes a rod when it has X pressure on it (normally around 7-10psi), that\'s it.

If you want to know just how fast your car can spool up, ultimately, go outside, take the hose off the wastegate, and floor it in say 3rd from as low an rpm as you can BE FRICKEN CAREFUL WITH THIS - IT WILL WAKE UP AND KEEP GOING TO RIDICULOUS PSI AND YOU WILL VENTILATE THE BLOCK IF YOU KEEP YOUR FOOT UP IT. As fast as that wakes up, that\'s as good a spool up as you can ever get, and no amount of electronic doohickery is going to improve on that without physical changes to the exhaust/intake/blah. What you want to do is pay attention to just how fast it does spool up - is it faster than you had before? If yes, then there are improvements to be made. If no, woohoo you have fast spool up I guess?

By the same token, if you run a hose direct from the turbo outlet, to the wastegate, that\'s as low a boost as you can run, no debating it, unless you physically change the wastegate actuator itself. You should have dead rock steady boost like this. Some cars will see a drop at high RPM - this can be alleviated by changing where the WG feed comes from (manifold + a one way valve) or in some cases the turbo/s are just too small for the motor (see VR4 legnum / GTO / TD04 equipped wrx with breathing mods) - you can force them to hold it if you\'re feeling masochistic. At the same time a RISE with rpm indicates undersized (or poorly located) wastegate - this is called boost creep, fix is uh, larger wastegate - either porting factory to larger OR going external (or moving it to a better place if already external)

What they have in the factory arrangement is a T junction with an electronic open / closed solenoid at the end of it. Before this T is a restrictor "pill" - a tiny metal ring with a pinprick of a hole in it. The function of that is to a) restrict flow to the WG actuator and bring boost on quickly, and b) to mean the solenoid has a smaller flow of air to bleed off, giving finer control so to speak.

If you remove this pill you won\'t break, or harm anything - you\'ll just have a slightly slower spool up, possibly less boost spiking if you have that problem now, and lower boost overall.

The reason that this isn\'t as fast to spool now is that the wastegate has a partial pressure being fed to it as you spool up - before full boost - this opens the gate *slightly* and slows down response a touch - there are gains to be had with ball & spring controllers OR 3 port solenoids (see below) - the pill is a halfway measure of this. Same effect can come from the super DIY method of using a 3 foot long WG hose, the slight delay can give enough initial handicap to cause a faster boost rise, at the expense of less accurate control (slight spike for some)

The factory solenoid then pulses at a certain rate for a given RPM and throttle position. That\'s it. There\'s no fancy trickery, it doesn\'t watch what boost you have and try to maintain something - it\'s a simple pulsing solenoid mapped to a certain pattern out of the box. "Chipped" ECU\'s or what have you simply pulse faster - bleed off more air - and this lowers the amount getting to the wastegate, therefore you get more boosty boosty. This is a "Open Loop" system, in that it isn\'t monitored by anything, it just blindly does what it\'s told based on info it was fed in the factory. This is why boost rises with freed up exhausts etc etc/ The main and to be honest only benefit of keeping this is it means the factory ECU now has a "lower boost" mode, where it can shut off the solenoid and run WG pressure only if the situation requires it, say excessive knock or limp mode occuring. (Or in a GTS25T where it bumps it up halfway through the revs, or TT legacy so it can run less on one turbo rather than 2 but with only one wastegate).

SOME cars - say late model audis for example - do run a closed loop boost system, where if you fiddle with it, it will try and work around what you\'re doing to maintain the pressure it wanted in the first place and would you please put ze bonnet down sir you are not ze mekanik. XR6T is an example of just plain ignoring boost levels too - wind it up with a bleed and it just retards igntion to stop you gaining power anyway cause it\'s a dick and wants to ruin all your fun

Luckily most of us have much more stupid cars with no idea what\'s going on, so that doesn\'t matter

A *cheap* electronic controller is literally exactly ^ that, just without being mapped to RPM. It simply gets told by you "pulse at X frequency" - it can be fiddled with slightly (gain) to start off slowly, or tail off up top to try and maintain falling away boost numbers, but at the end of the day it\'s a simple device and only operates blindy from what you have told it to do.

A *good* electronic controller will use "closed loop" control, where you say "give me 20psi", it will watch and "learn" what it needs to do to make your car run 20psi. This is brilliant - they can compensate for the difference of 30 degree weather and being altitude on the desert road, vs a 0 degree day at sea level where an open loop system will most likely run higher numbers due to denser air. See the likes of AVC-R and E-Boost2 for proper, good boost control. The idea of a 3 port solenoid as opposed to just two (as factory) is that the solenoid literally blocks *all* flow to the wastegate, giving the fastest possible spool, it can gradually open it and avoid any spiking, and can then shut down flow progressively up top if boost starts to fall away (through turbo not maintaining OR wastegate being a bit weak and being forced open). This is also doable on later model (reflashable) cars since they can have the WG signal mapped to RPM, load, throttle position etc. Another thing is that if you set 20psi, it will just run that regardless of what you do with the car - bigger exhaust dont care, exhaust leak? dont care.

This is a gizzmo MS-IBC trying to control a mitsi GTO - stock or open loop would see boost fall to 10psi or so (the blue line), this is it trying to force it to hold boost via closing the wg... kinda works? Up top the thing is literally freeboosted and the turbos can\'t maintain any more flow hence boost falls over.

Example of how a 3 port solenoid works, more or less - imagine when it wants to let boost through, it lifts the red bit - boost can go in - when it doesn\'t want boost to go through - red bit drops - easy. To fine tune, this pulses up & down at a rapid rate and maintain whatever needs to happen (like, very fast).

Bleed valves - I relate these to a cheap electronic controller. All it is is a simple valve, this can be a 50c garden sprinkler fitting, a brass T or welding tip soldered over and drilled to suit, or one of the cheap & cheerful boost taps you see on trademe. SOME of these are a very simple bleed - where the more the knob is turned, the more an internal hole is opened up, bleeding more air and raising boost. To be blunt if the car has no boost control problems then most of the time this is literally all which is needed - for most, the $300 they spend on a cheap electronic controller is wasted.

Some of the better ones are called "Gated" boost controllers (for example the hallman controller, latest turbosmart Tee or the GFB atomic, see below), which have a small ball & spring inside which seals the wastegate off from any signal - this improves spool up, then generally maintains it pretty much rock steady. The marketing blurb with these is genuine, they do improve spool up even run at the same boost level as factory, and will bring boost on faster with smaller throttle openings (faster "feeling" car without any actual extra HP). Same theory as the 3 port solenoid just a bit more crude and obviously not closed loop so prone to slight variations with temp & altitude.

Gated controller very simply explained (though, not much more to explain!)

Might edit this later on... but hopefully it does help some a little bit? If I\'m off on things feel free to say so or just plain edit me haha

[funkytown]

nice write up... i want some one to go and do this...

 

If you want to know just how fast your car can spool up, ultimately, go outside, take the hose off the wastegate, and floor it in say 3rd from as low an rpm as you can. As fast as that wakes up, that\'s as good a spool up as you can ever get, and no amount of electronic doohickery is going to improve on that without physical changes to the exhaust/intake/blah

lolol i think perhaps you should caution this a little more in the write up coz if you dont know what it will do....

[Marky]

wreck all the fun, jeeze... good point though haha

[lachlan]

lol @ acknowledgement but not telling everyone to stop flooring it when it reaches normal boost level

also

"By the same token, if you run a hose direct from the turbo outlet, to the wastegate, that\'s as low a boost as you can run, no debating it, unless you physically change the wastegate actuator itself. You should have dead rock steady boost like this. "

observed boost(being taken from the intake manifold) will probably taper off slightly . well in direct relation to however much of a restriction your intercooler and piping and T/B are

boost will be rock steady at the point of pressure source being the turbo outlet in this case

[funkytown]

if your wg is too small it will do the opposite laclan...

[lachlan]

talking bout subaru motors here . not toyota supras

[funkytown]

yes... our two creep at wg pressure.

anyway it applies equally to any turbo application

[Marky]

Edited some shiz

Feel free to do it too

Needs pictures... and dinosaurs

[DacerX]

and a unicorn, i mean who doesnt like a uniform. Well that and a puppy

[lachlan]

 dacerx said:

and a unicorn, i mean who doesnt like a uniform. Well that and a puppy

ykhikyg

[Marky]

Googled it - laughed

WhyTF do I spend so much time typing these things up

I\'m like a grumpy elderly person writing letters to the editor or something

[Guest]

 Marky said:

Googled it - laughed

WhyTF do I spend so much time typing these things up

I\'m like a grumpy elderly person writing letters to the editor the MAN or something

[lachlan]

you type it for the same reason i would . if it saves explaining it just one more time to someone it was worth it .

yeah it needs googling but is well worth it

[Guest]

So no sticky then?

[B4 I was 250T]

F**K you guys are so smart it\'s scary! WTF am I doing around such bright people? Lol

[Roo]

Fuck that is a huge write up, I got to the part about free boosting, lol\'d at the nostalgias then scrolled down looking for funny replies

Good work though very thorough, idk how to convey how happy I am that more people might learn what real compressor surge is

[tydon]

Ya learn something new everyday lol awesome write up

[Marky]

Just cause I made a thing I thought I'd write it up here in case anyone feels the need to follow suit

I got jealous of all them folks with their fancy 3 port solenoids and their e-boostses and all that nonsense so I made my own povo budget spec version instead

I got one of these:

And one of these:

Okay so my photos are sh*t

ANYWAY

What I wanted to achieve was the same as having a relief valve inline, or a three port solenoid, where boost pressure is completely shut off to the wastegate during spool up, meaning fastest possible wake up time due to no wastegate creep

So, what I did was very simple:

Solenoid placed inline between my pressure feed, and my boost control / wastegate itself

Solenoid is activated at a certain pressure by the pressure switch

...

Profit??

IF your desired pressure is too close to the switching pressure, it gets a bit of a wiggle on - as the solenoid opens, gate opens and dumps too much boost, solenoid closes, gate closes, boost rises too fast, repeat X forever. About a 5psi difference seems to keep things smooth and rock steady.

What I have now is it setup so the switch closes at 11psi, and my desired boost is about 16psi on secondary. the net result is about a 500rpm improvement in the boost "threshold" (like, what psi I make when loaded on the brakes at X rpm) and it makes a substantial amount more pressure on lower throttle opening, basically making the thing "feel" quicker I guess, wakes up and comes on boost noticably faster.

This can all be done for about $20 with a pickapart mission for what it's worth, and I hazard would work just fine in concert with the factory boost control setup too. Just need to find a suby being parted ideally - the subaru boost control solenoid is no restriction to airflow when open, most of the other ones are a very small orifice and impede airflow a bit. The pressure sensor is about $40 for an adjustable one (also called a "hobbs switch") or you could maybe just use an oil pressure sensor, the factory type used to switch on a low pressure light?

Only downside if you can call it that is it's a blanket rule everywhere, so cruising at 100kph you just have to breathe on the pedal to wake it up - probably not superb for fuel economy, ditto for trying to keep it off boost when warming up etc. Could be worse?

[lachlan]

interesting .

have you ever read this marky ? using a pressure regulator to controll boost

quite a solid idea . and this was published in 2000 apparently

http://www.autospeed.com/cms/article.html?&A=111348

http://www.autospeed.com/cms/article.html?&A=111350

another thing that has crossed my mind is to have a pull knob choke cable thing hooked to a spring that pulls on the waste gate actuator in the same way a external spring hooks on a wastegate . except its cabin adjustable . and has all the simpleness and stableness of running wastegate pressure alone .

im allowd to be a hori coz i have an original apexi avcr . pretty much the best boost controller ever . yes a eboost has more tunability but why wants to fk round with all that shiz ans gears and $900

oviginal avcr . up = up . down = down . propper closed loop as it should be . no guessing numbers and telling it the duty cycle . if you have to tell your boost controller what duty cycle to run then you are a schmuck and you have an "electronic" boost tap

[Marky]

Yeah, I've used that system a few times, (it's where I got the idea from haha), it does exactly what it says on the box. Really handy for VR4 / legnums etc which lose pressure up top, that setup forces them to hold whatever is dialled in - they have no probs with spool up time but won't hold psi past 5k or so. Would probably be a good idea to get some of the smaller VF's to hold pressure too?

This is just an electric version of the same, I found the pneumatic one had a bit of wriggle room and variation with temperature (like when the engine bay got really heat soaked it seemed to climb a bit?), 1 or 2 psi might not mean much normally but this car seems to be a ping machine if boost goes too high so thought I'd try it

Plus this works out cheaper, haha