Homemade Boost Controller

[Gannon]

I have been working on an electric circuit to emulate the factory boost control on the EA82T

It is a simple duty cycle generator that produces an adjustable output of around 15Hz to drive the WGDS (Wastegate Duty Solenoid) and thus control the bleed air to the wastegate.

It even has a built in dummy resistor to fool the ECU so it thinks its still controlling boost.

It cost me less than $15 to make, but im gonna make another one that is smaller and neater (this is just a prototype)

Here is a scematic


Its based on this Jaycar unit The Nitrous Fuel Controller

And some pics of it being tested with a 10W globe
At 100%


At 50%


At 10%

[PeeJay]

I made a similar thing using the basic circuit from the chepo Jaycar boost controller that just expands the duty cycle after it comes out from the computer. The problem is that the computer (EJ20G) seems to "learn" around it so after a while the effect is minimal.

I'm currently working on designing something that's a combination of the digital fuel adjuster and the independent boost controller, except hopefully mine will have closed loop boost control.

[discopotato03]

Why ? If their boost controller references off MAF meter signals (and these compensate for temp/density) its going to be accurate anyway .

[PeeJay]

Because I can I'm also a bit of an electronics nut.

[steptoe]

Duffus here, don't you just whack in a boost controller in the vac line from turbo to waste gate , what is this electronic intervention for ????

[discopotato03]

Another long post .



Steptoe the idea of electronic boost control is two fold .

Firstly it's possible to get a little more torque and a slightly earlier boost onset because the waste gate stays shut until just before the target boost pressure is reached .
The conventional pneumatic system works like this . As the engine builds revs and load the exhaust gas speed through the turbos exhaust housing rises spinning the turbine (and compressor) fast enough to make positive inlet manifold pressure . Most OEM turbos have a waste gate actuator which is a spring loaded diaphragm connected to the push rod and waste gate flat valve . The springs preload keeps the valve shut until the rated boost pressure overcomes it and the gate cracks open to give a variable bypass so that the turbines speed can be throttled . If you can control the compressor wheels speed you can control boost pressure within the capacity of the wheel .
Being a straight pneumatic vs spring load thing means it's impossible to keep the waste gate shut virtually until the target pressure is reached . What they do is start to crack open at about 2/3 to 3/4 of the intended pressure which makes for a gentle climb up onto set boost pressure .
To have more accurate control means using an electronic means of measuring pressure and having an electrically controlled valve in the circuit to block boost pressure from reaching the actuators diaphragm . Now because electronic controls are far more accurate and faster acting than diaphragms you can prevent pressurised air reaching the actuator until just before the target pressure is reach and then let it open the wastegate .

Secondly you can raise the boost pressure above that regulated by the diaphragm spring by keeping the solenoid valve shut a bit longer so the waste gate remains shut and boost pressure climbs higher .

The Ugly side of boost control done badly .
Standard fitment production turbochargers are sized wheels/housings/wastegate/actuator wise to work properly with the std engine meaning its ability to breathe in/reject heat/breathe out .
As soon as you raise boost above std the engine develops more heat and a greater volume of exhaust gas and its systems often don't cope very well because of it . To raise boost by keeping the WG shut means the pressure between the exhaust valves and the turbine rise out of proportion to inlet manifold pressure but who bothers to measure it ? Most people understand the value of a boost pressure gauge but just as big if not more of a worry is the exhaust side pressure . It's not unusual to have 2-3 times the boost pressure on the exhaust side and it goes through the roof when the std boost pressure is jacked up .
The warning sign is when the exhaust manifold pressure (aka turbine inlet pressure or TIP) gets that high that it physically forces the waste gate valve open and steady boost pressure cannot be held . High TIP means high exhaust gas temperature (EGT) and it's not impossible for it to bake the turbine/turbine housing/exhaust valves etc .
The other ugly side of excessive TIP is this .
With TIP so high and the valve timing having some overlap the exhaust pressure being higher than the incoming boosted inlet air means some of the exhaust stops and goes back into the cylinders via the exhaust valves and is known as reversion . This is really bad because firstly the spent gas is not combustible and secondly it's really hot so it preheats the incoming air and lowers the engines detonation threshold .
Production turbo pistons are usually hardier than NA ones but can only live with so much heat and then they literally melt and collapse around the ring lands . If they don't and the engine is detonating this usually hammers holes through them .

If you want to know about power through volume rather than in theory pressure ask away but it means another longish post .

Cheers A .

[steptoe]

Aw, what the heck Adrian, let 'er rip

[discopotato03]

You asked for it ...

Turbocharging the piston engine is all about getting bigger engine torque from the existing engines size ie 1800-2000 etc cc .
It works by pushing more air into the cylinders than atmospheric pressure can . BTW engines cannot "suck" , they can create an area of lower than atmospheric pressure on the inlet stroke and then its up to good old atmospherically pressurised air to fight its way into the cylinders .
When you place an air pump between the atmosphere and the inlet tract the engine acts as if atmospheric pressure is higher than normal because on the inlet side it IS under boost . Higher pressure means higher density (greater mass of oxygen molecules) going into the cylinders to which we can add more fuel to make more horsepower .

To quote Corky Bell (Maximum Boost) one of the greatest obstacles to overcome when looking for more performance is heat , air pumps whether they be rotary (turbo) or constant displacement (roots blower) impart heat into the air being pumped so intercoolers are used to waste the heat and maintain the inlet airs density .

Most OEM turbo engines have small turbine (exhaust) housings and turbines so that boost and torque can be had at reasonably low engine revs .
They can also have low static compression ratios and small or non existant intercoolers . Sound familiar ?

If you are prepared to go inside the engine you can increase the low OEM CR and do a bit of porting in the head(s) , maybe make or port out OEM exhaust manifolds , find ways to get better exhaust flow through the hot side of the turbocharger and the exhaust beyond it .

The increased CR means your compressing the induced air to a higher pressure so the resulting combustion pressure will be higher and the engine will make more torque . The enlarged ports in the head(s) means there is less restriction to the "atmocharged" air so you get more complete cylinder filling . On the exhaust side there is less pulse energy lost to restrictions in the ports and manifold so more to excite the exhaust turbine with .
All of the above is aimed at reducing the air in and exhaust out flow restrictions so that the engine can make more torque .

The idea of doing things to the turbo like going up a size in exhaust housing and or turbine means that it may not start boosting as early but if the engine has more grunt without boost it probably won't need boost as early .

Many an engine has had a worthwhile performance increase purely by reducing restrictions on the exhaust side and advancing the ignition timing .
With less turbine inlet and exhaust restriction the engine suffers less reversion and pumping losses and often will make more torque per pound of boost pressure than it did originally .

Subaru exhaust headers . There are many urban myths existing about flat fours and exhaust gas velocity - small pipes are bad news .
What we have to remember is that exhaust gasses exiting the cylinders want's to expand (increase volume and reduce density) but it can't do so if the only path to atmosphere is via inadequately sized tubes . If the passages are large enough to let them expand you get a series of high and low pressure areas (pulses) between the cylinders and the exhaust housing/turbine . As we know an area of high pressure will flow to an area of low pressure faster if the pressure differential is large . If the gasses are forced through a small passages this dampens the pulse effect and the average gas speed is LOWER than it would be if it were larger . The restriction also means the spent gasses can't exit the cylinders as fast as it wants to so some crank energy is lost by pushing these gasses out with the rising piston - known as pumping losses .

This I have to confirm but I suspect that Subaru have screwed us on cam lobe phasing and the weird firing order . I think these flat fours fire the adjacent cylinders in each bank every 180 crank degrees rather than one from each bank every 180 degrees . If this is the case you would get two inlet draws from each head (and exhaust events) which screws up inlet air pulsing and exhaust pulsing .
I think its this that gives these flat fours that stupid off cadence exhaust sound because of the two exhaust shots 180 deg on one bank then the other . Half the exhaust events overlap and half don't making the alternating grumbling sound . Must be terrible for reversion and very likely why Subaru never quite got the consumption figures that other similar sized cars/engines got .
The twin scroll EJ20 turbos don't do this because the manifold phasing allows an exhaust event into each engine pipe at regular intervals .

I have read that the 1400 twin carb engines used a different cam to the single carb ones and I wonder if they got it righ on that one .
Also the twin scroll EJ engines link the front and rear sets of exhaust ports where they could have linked each adjacent pair of cylinders if the firing order had been changed .

Enough for now , cheers A .

[Suby Roo]

Man Disco, Have you ever thought about writing a book??

[PeeJay]

air pumps whether they be rotary (turbo) or constant displacement (roots blower) impart heat into the air being pumped

I should point out that air heats up naturally when compressed. For a demonstration try pumping up a bicycle tire with a hand pump, and feel how hot the little hose attachment gets.

But I imagine a turbo housing at a few hundred degrees would also heat the air a tad!

[Gannon]

I made the device so i can control my boost easily from in the cabin. If i wanna give it a thrashing, i'll turn the knob up. If im gonna let someone borrow my car, i'll turn it down. Easy as.

So to summarise what Disco said in his 1st long post..

If you are looking at making more horsepower than the factory designed, just increasing boost is not the best way. If you are pushing more air though the original sized inlet/exhaust components, you are creating in-efficiencies because higher density air creates more friction and heat and thus more pumping losses ect. Not to mention high exhaust port and manifold pressures from pushing lots of air through a little turbo.

The smart way to increase horsepower is to increase the amount of air flowing through the engine by increasing the size of the intake/exhaust ports, the exhaust pipes and the turbo, whilst keeping factory boost levels.

Unfortunately, the first way (increasing boost) is by far the easiest and cheapest option for 99% of us.

[steptoe]

Good read Adrian, thanks

[discopotato03]

Compressor housings are usually aluminium castings and if air is flowing through them at a fair rate it's not there long enough to absorb much heat .

Yes boost hikes are easy but the prob is lots of people try this and lunch turbos or engines .

Have a ready of Corky Bell's book Maximum Boost , it's a little dated (10 odd years) but it does more than just render you cabable of identifying which hair driers have a 240V inlets and which don't ...
It's a good reference for those interested in turbocharging car engines because it goes into all the things that need to be considered ie cooling/lubricating/intercooling/manifold design and gives a couple of example conversions .

Other interesting things it delves into is working out approximate engine airflow requirements and how to go about getting the turbo sizing about right for a given sized engine .
Also exhaust flow and exhaust pipe sizing .

If you like automotive books and turbocharging then consider this one a bit of a classic . Car bookshops usually cary it so if your going past one have a glance at it .

Cheers A .

[brumbyrunner]

Pitstop usually have it for $76.90
It's a very good read.
http://www.pitstop.net.au/view/products ... /plu/8396/