This article will attempt to describe the whole thing in a simple yet precise and understandable manner. This isn’t exactly rocket science and all of the effects of wastegate adjustment and boost controllers are fully understood and have been measured. Sufficient information is available on the operation of the car’s Engine Management System for us to avoid the common pitfalls and modify the car while keeping operating parameters within safe limits.

The Turbocharger

In order to increase the engine’s performance the turbocharger feeds compressed air into the engine. The pressure of the air has to be limited in order to prevent damage to the engine which simply is not strong enough to withstand the additional stress caused by too high a power output. 

In the 850 T5 the “stock” pressure (set by Volvo) is 10.3 psi. This may be increased in various ways to a (generally accepted) maximum safe level of approx 13 psi. More than this and the pressure can become dangerous or the engine may start to “knock” or “ping”. The car’s engine management system (known as the ECU or Electronic Control Unit) will then cut off fuel to safeguard the engine from damage. 

Before this situation arises the ECU needs to reduce the boost pressure. It does this by opening a device called a “wastegate” which is an integral part of the turbocharger. It is simply a butterfly valve operated by a pressure controlled “actuator” - which allows exhaust gas to bypass the turbocharger’s exhaust turbine and vent directly into the exhaust system. This allows the turbocharger to slow down and decrease boost pressure from the compressor.

The simplest way to add a turbocharger to the engine would be to operate the wastegate actuator directly from the boost pressure from the turbocharger. The wastegate would simply be set to open at the maximum required boost pressure of 10.3 psi. Why didn’t Volvo do this? Because the designers of the car wished to maintain ECU control over boost pressure for safety and flexibility of operation. The ECU continuously monitors engine and transmission sensors, and if any adverse effects are noted, such as “knock” or “pinging” (perhaps due to change in fuel properties between manufacturers) the boost can be reduced. Without ECU control serious damage could result to the engine.

The ECU does not directly measure the boost pressure. It measures only the mass of the air entering the engine, which depends on many factors - including the boost pressure and air temperature - which can vary considerably.  At “wide open throttle” (WOT) the ECU disregards input from the O2 sensor(s) and runs “open loop”. 

The ECU takes a finite time to measure a change in airflow due to the increased boost pressure and to compensate by opening the turbocharger wastegate. As a result of this delay the boost pressure may rise briefly under some operating conditions to a level which might be considered dangerous. This condition is called “spiking”. On a “stock” system the effects are minimal and can be handled by the ECU. However, when boost is increased in the search for more power these spikes become more serious and the ECU will act by shutting off fuel to the injectors.
 

Now for an explanation of how ECU control is added to the wastegate. 

An electrically operated solenoid air valve is placed between the turbocharger boost output and the wastegate actuator. Now consider the scenario where the valve is fully open. As the engine rpm increases the valve passes boost pressure directly to the wastegate servo. At some preset level, the pressure is sufficient to overcome the spring pressure of the actuator and it will open the wastegate and limit the turbocharger boost pressure. In practice the manufacturers set a “baseline” boost on the turbocharger wastegate actuator of approximately 3 - 4 psi. This is done by adjustment of the actuator spring pressure. Hence, under these conditions the car would build boost up to a maximum of 3 – 4 psi at which point the wastegate will open and limit the boost to that level. Note that since the ECU is not in line, the system reacts almost instantly to any boost spikes. The car is actually very driveable like this - but lacks “sport” performance.

Now this is where the ECU steps in. Under control of the computer program running in the ECU the solenoid valve can be pulsed from fully open to fully closed depending on the mark/space ratio of the pulse. When more boost is required the ECU pulses the solenoid closed, reducing the pressure at the wastegate actuator and thereby closing the wastegate. By this means the ECU can safely permit the turbocharger to develop a higher boost pressure. In a stock 850 T5 the maximum boost is set to 10.3 psi - which is approx. 70% into the white line portion of the boost gauge. 

How does the ECU know when to limit the rise in boost? By monitoring of the engine/roadspeed/transmission sensors and especially the engine’s Mass Air Flow sensor, which tells it how much air is entering the engine.

Adjusting the Wastegate.

Now to one of the most common controversial modifications carried out by enthusiasts all over the globe to increase performance by adjustment of the turbocharger wastegate. Removing the heatshield over the turbocharger will reveal the wastgate actuator, and the rod connecting it to the wastegate valve. This is adjusted by the manufacturer to a “baseline” setting of 3 - 4 psi. Before any attempt is made to change this setting it is interesting to see what the setting actually is, and how the car “feels” at that level of boost pressure. 

Disconnect the hose from the solenoid valve to the turbocharger actuator.  Using a short length of hose, tee the actuator input into the boost gauge pipe. Now take the car for a spin. It will feel very driveable but low on power, as the boost pressure is set to 3 - 4 psi maximum. Look carefully at the boost gauge and remember the setting in case you want to set the baseline back to this point later (it’s a little hard to get an exact reading as the gauge is rather small. A more accurate gauge can be used if available).

Allow the engine to cool and then release the lock nut from the actuator rod. Next, remove the circlip holding the rod onto the wastegate valve. Lift the rod off. Rotate the rod, shortening it by 3 to 4 turns. Replace the rod onto the wastegate and also the circlip. Now again take the car for a spin. It will feel a little livelier than before. Note the psi setting on the boost gauge. Try to set the wastegate to 6 psi on the gauge. (Centerline is 0 psi and full scale is 14.7 psi – aim for just over one third of the white area of the boost gauge).

Now replace all the hoses back to their stock positions and again take the car for a run. The full turbocharger boost should cut in earlier and with more ferocity. Take the car onto a stretch of open road and boot it. The gauge should rise to approximately 12-13 psi and hopefully the ECU will not cut off the fuel supply due to any adverse condition being detected. Repeat this test under cold ambient temperature conditions to make sure this won’t happen – the turbocharger becomes more efficient on cold days. If any cutting out or hesitation is noticed, back off the adjustment a little. The number of turns of the actuator rod to achieve the setting will vary from model to model but is usually between 3 and 5 turns. When satisfied tighten the locknut on the actuator rod and replace the heatshield. [Note that sometimes misfiring may occur due to poor engine maintenance especially fouled or incorrect gapping of plugs. It pays to check that your car is in good shape before modifying the wastegate setting].
 

So now you have a “tweaked” turbocharger – what are the advantages and disadvantages?

The “base line” boost of the turbocharger has been increased to 6 psi – meaning that the impeller blades are allowed to “idle” faster than before on part throttle opening. This means that  boost is available sooner when the throttle is opened wide - hence it has the effect of reducing turbo “lag”.  However, as the baseline boost is now higher and the turbocharger can build boost much more quickly than before, it can also spike more easily before the ECU has time to make corrections. 

So the delay introduced by leaving the ECU in line means that it is now much easier for a boost “spike” to exceed safe parameters and the ECU may react by cutting off the fuel to the engine. Secondly, the ECU is still measuring the output of the Mass Air Flow sensor. It will react to the higher volume of air entering the engine by reducing the boost pressure via the wastegate solenoid valve. The onset of “knock” will cause the ECU to retard the ignition and also to back off the boost level. Luckily it does take a finite time to do so - therefore there is an increase in boost but only for a short time, until the ECU returns it to what it considers to be “normal”. [This isn’t as bad as it sounds – carefully study this extract from one review on the T5R. 

“The R's engine management system has been programmed to allow the turbocharger to kick boost from 9.6 psi to 10.9 psi in 7-second bursts during maximum acceleration. This ups the horsepower rating to 240”.

Manual Boost Controller

(Dawes device, g-valve, Hallman controller, or ball & spring (BSC)).

Tighter control of boost pressure may be obtained with a device known as a Manual Boost Controller (MBC). It is essentially a ball check valve kept closed by a spring. This is commonly placed in a line from the turbocharger boost output to the wastegate actuator. (On the 850 the lines from the solenoid valve are disconnected and plugged onto the MBC but the solenoid is left in circuit with the ECU). Pressure from the turbocharger opens the spring at a preset level allowing air to pass to the wastegate actuator. The tension of the spring is varied to set the boost to the maximum required level – e.g. 12 psi.

What is the disadvantage? The ability of the ECU to close down boost to protect the engine in the event of knock, excessive engine charge etc has been lost. Most auto engineers on the various discussion boards therefore state a preference for retaining ECU control (as do I). Placing the MBC in the line from the ECU controlled solenoid valve to the wastegate actuator allows one to control peak boost and also retain ECU control of boost. BUT we are still left with the problem of spiking due to the slow reaction time of the ECU.

There are many articles on the internet discussing boost controllers but there has been little thought as to how these Boost Controllers can be used to set the desired boost and eliminate spiking yet still retain ECU control over boost pressure. 

The answer is to use two MBC’s.

MBC1 is placed in the line from the ECU controlled solenoid valve to the wastegate actuator. It is set to open at the desired maximum boost e.g. 12 psi. However the ECU can still close the wastegate by pulsing the solenoid valve open and applying boost pressure to the actuator.

MBC2 is placed in a line from the turbocharger boost output to the wastegate actuator – bypassing the solenoid valve. It’s function is to eliminate spiking - it is set to a slightly higher pressure than MBC1 - e.g. 13-14 psi. 

All hoses between the various valves and actuators must be kept as short as possible for best reaction time to spiking. The MBC valves should therefore be mounted close to the wastegate actuator and solenoid valve. The “baseline” value of the wastegate setting should be left at the original stock position for quickest reaction time - there is no longer any point to adjusting the wastegate rod.

For those whose car may be used by the family on shopping trips you might like to “tame” the car a little by using an extra solenoid valve to bypass MBC2 allowing boost pressure directly to the wastegate actuator. This will limit the boost to the “baseline” value of 3 – 4 psi and the car will become less aggressive. A High/Low Boost switch in the passenger cabin allows a switch between the two modes of operation. It may be possible to operate the solenoid valve  from the “Normal/Sport” transmission switch, [easy if this switches 12 volts] but I have not yet investigated this. If this can be done it would be a nice touch.

When boosting, the ECU monitors many things and in particular the onset of knocking, pinging (or whatever you want to call it). It retards the ignition and slightly backs off the boost level via the boost controller solenoid to compensate for this. In fact some people install a bright LED in the cockpit and have it wired such that it comes on as the ECU pulses the solenoid. This would give a visible indication of the ECU attempting to retard boost under near full throttle condition, i.e., it's detecting knock!! 

With only the MBC controlling the turbo, NO BOOST SIGNAL is passed to the wastegate actuator until the preset cracking open level is reached. This stops wastegate creep occuring and therefore the turbo spools up very quickly, even on light to part throttle input. When the MBC opens the wastegate is driven fully open and stops further boost rise. This set up gives consistant boost irrespective of the weather etc.

So the computer will know if additional air is going to the  engine and should increase fuel accordingly? True to a degree (that is also which can trigger a check engine light as the ECU measures a too great amount of air going into the engine according to it's programming), but the normal map will reach it's maximum injector opening time and thus maximum fuel amount a little over stock maximum boost/air intake levels. After that it can't compensate any longer unless a RRFR is used to force more fuel in the same time. At WOT this can especially be required since the ECU will run in open-loop mode, so it disregards the O2 sensor output and can't detect if the mixture is leaning out or not. It should be running rich at WOT, but if the boost is upped it may not completely reach that state. The ECU will try to compensate for quite a lot of factors, but it will be running at or over the upper limit of it's regular mappings. It's all very possible to do it this way and not touch the ECU, but some tools (accurate boost gauge, A/F meter and possibly an exhaust-gas thermometer) and time are required to tune it properly and keep it running reliably. 

Bye, Arno.

However the Dawes Devices website explains the installation of their MBC's and does so such that it by-passes the ECU controlled Boost Control Solenoid. They suggest raising the boost level to a point BEFORE the fuel mixture and EGT values begin to alter drastically ie O2 goes LEAN and EGT rises rapidly. Their instructions make important reading for anyone thinking of doing this sort of mod.
 

The low 'baseline' boost setting is used to give a controllable boost-rise. As the boost is building up the ECU will start to mostly open the pressure line to the wastgate actuator once it reaches about 80 to 90% of the 'final' boost level. This will slow the boost rise and it will 'level out' at the factory spec where the ECU is constantly opening and closing the valve to the actuator to keep the pressure at the factory limit.

If you look carefully at the boost gauge at WOT and keep it there for 30 to 60 seconds or so you will see it fluctuate constantly around the factory boost limit. This is the ECU in action while it pulses the valve.

This is also the reason why *only* screwing the wastegate rod tighter (without boost-controllers and such) only has a *temporary* effect on a stock Volvo turbo pressure. What it does is raise the baseline boost, but the ECU still only supplies pressure to the actuator at about 80 to 90% of max boost. But now it takes more pressure and time for the wastegate to open because the baseline boost has been increased. This causes the boost to 'overshoot' it's maximum (the boost-spike) until the wastegate has opened enough and the turbine is slowing down enough (the wastegate only bypasses the exhaust gasses around the turbo and does not 'vent' pressure) for the pressure to drop to it's factory maximum again after about 30 seconds or so.

So the wastegate mod in itself will give you a better/quicker pickup and initial 'push' as the ECU can't control the rise of the boost as well, but if you stick it at/near WOT for longer you will see it drop back to stock levels.

How will installing a bleed-off valve cause a lean condition, considering that the injection is done on a MAF (Mass Air Flow) basis, so the computer will know if additional air is going to the engine and should increase fuel accordingly?

> If that is the case, is there any way to increase boost pressure
> other than putting on a new turbo or buy a turbo boost?

There are 2 options:
easy way: chip tuning

hard way: bleed valve(s) in certain lines + RRFPR

The boost in FWD volvo's is controlled by the ECU using a valve in the pressure line going to the wastegate. The wastegate itself is set to a low pressure setting, so it would open very quickly if this valve was not in place.

By quickly opening and closing this valve can the ECU force the wastegate to open and close and this way control the level of boost.

To get a permanent boost increase (not just a bigger initial spike as with the wastegate rod modification) you need to change this behaviour.

A chip tune will change the boost settings permanently and also makes sure enough fuel is injected (lean running under boost is quickly fatal to the engine) and the ignition curve is adapted for he higher boost setting (ignition spark under boost is also more difficult).

Using bleed-valve(s) in the lines going to the wastegate can yield the same result (it's not real easy as proven on the board here when someone installed a bleed valve and the ECU still managed to keep the boost pressure at stock levels!), but it's harder to get 'right' and you run a few risks.

The first risk is that the engine management will find discrepancies in the sensor inputs it gets and if this exceeds a certain limit it will trigger the 'check engine' light.

Another risk is that you may be leaning out the mixture under boost as you have not changed the fuel input for the increased boost. Potentially lethal for the engine. Adding a rising-rate fuel pressure regulator may help, but again needs some tweaking and checking to get it 'just right'.

Hope this helps..
Bye, Arno.

This is good to know. So, if I understand this one right, all that I'm doing is bringing the turbo online earlier?
If that is the case, is there any way to increase boost pressure other than putting on a new turbo or buy a turbo boost?
Thanks for the input.
 
 

Note the max boost is not changed. Basically
you are allowing the turbo to idle at a higher RPM so it can
build boost sooner -- the max boost is still unchanged. Just
don't overdo the wastgate mod or you can get some problems
with engine surging and drivability.
 

Ok, I did the "4.5" turn thing as recommended and boom, accelerate and the turbo kicks in. Additionally, the boost now goes to with 1/8th of max.

Questions:

* Generally speaking (ie I know I need a real boost gage) Is 7/8ths of max safe? (the white line on the stock turbo boost gage)

* Can one have too much turbo up time? IE, my turbo kicks in when ever I accelerate. Obviously the lighter I accelerate, the lower the boost. And the turbo does not come online when I'm just cruising around.

* Do I run the danger of burning pistons etc.

* What happens when I do the IPD ECU?

* There seems to be a lag in boost at about 3500 - 4000 rpm, then pow. Is this just the EC trying to figure things out? or is there something else going on?
Thanks folks.
Scott
 

Re: Mod to increase boost on 850 turbo 850 1996 posted by someone claiming to be Scott Campbell on Thu Apr 26 16:14 UTC 2001 That's great information. I'll stick with the wastegate and watch the turbo uptime so as not to run too lean. It also sounds like I need to save my pennies for an ECU. Thanks

Just to add to that, adding a bigger downpipe will also richen the fuel mixture, due to flow rate differences.
 

I just bought a Dawes Devices MBC and I've been reading posts on how to install them, but I was wondering: is there any way to "fool" the ECU boost control valve so that the MBC actually has full control over boost? (Maybe some funky hose routing or something?) 
 

Remove all the hoses that connect to the boost controller solenoid. This takes away control of the turbo boost from the ECU. 
Leave the ECU connector plugged into the solenoid so the ECU thinks all is okay.

Plug the blow off hose inlet on the hose leading from the MAF sensor to turbo inlet.

Insert the MBC in the correct direction between the hose that comes from the turbo compressor housing, and the hose leading to the turbo waste gate actuator.

Whilst using an accurate turbo boost gauge set the boost level to what you want, within reason of course. 

with this type of setup, will the ecu still deliver the correct fuel/air mix and ingnition timing? Won't overheating and/or detonation become an issue? I would love to find an inexpensive way to control boost, but dependability and longevity are more important to me. 
 

--------------------
1998 V70 T5 my advice would be to NOT override the ecu... because i'm assuming all of us are not pro's at this, we should at least leave it to the ecu to protect our engine...

i too have a dawedevices manual boost controller and have it inline w/ the solenoid and the wastegate..i have a boost gauge for tuning....
I ran 15.2 stock(K&N), w/ my 95 850 turbo..and then boosted it to 13-14psi....ran 14.53....
i think that's good enough for $40..and the ecu didn't have to step in to interfere w/ it..
i did however (you might have seen my other posts) run into overboost, where the ecu dumped out all my boost for some reason..i'm sitll trying to find out why, but whatever the reason, i'm glad i sitll left the ecu in tact to protect my turbo, and from possible pinging...

I would tend to agree that if anyone is not sure of what they are doing they should prehaps allow the ECU to retain control. 

However the Dawes Devices website explains the installation of their MBC's and does so such that it by-passes the ECU controlled Boost Control Solenoid. They suggest raising the boost level to a point BEFORE the fuel mixture and EGT values begin to alter drastically ie O2 goes LEAN and EGT rises rapidly. Their instructions make important reading for anyone thinking of doing this sort of mod.

I have installed an MBC on my car and have the boost set to a limit of 13psi. There is no leaning of the fuel mixture. The characteristic of the car has transformed completely. There is now a much stronger low to mid band power surge. The turbo spools up very quickly on anything upto part throttle, where as before I would have to be on or approaching full throttle. 

I suppose to qualify the gains I'll need to get some dyno/track times. Maybe sooner than later. 
 

It seems that the MBC does a very similar thing as shortening the wastegate rod-delaying the opening of wastegate to shorten the spool-up time. Am I right? It can, however, eliminate spike when set up properly (by-passing the soleniod). It definitely improves performance more significantly under the stock ECU setting (with reasonable upper boost limit). 

My car has the IPD ECU and runs constant Max boost ~14 to 15 psi). With 3-turn adjustment on the wastegate rod, it spools up pretty quickly with spikes at 17~18 psi. I think the advantage of installing the MBC on my car will be to eliminate those initial spikes during boost as well as to take the vacuum load off the actuator diaphragm during normal operation. I haven't tried to raise the constant boost above 15 psi, which sounds a bit too high for the S70 T5 engine to bear.

Another thing is that I was told that the MAF sensor is able to communicate with the (stock) ECU to dump more fuel under higher boost, which seems to relief the concerns about running lean under the situation. Is that correct? 

Quote It seems that the MBC does a very similar thing as shortening the wastegate rod-delaying the opening of wastegate to shorten the spool-up time. Am I right?
 

Ummm, sort of I suppose. When you shorten the rod the wastegate has to receive slightly more boost pressure before it begins to open. The 'problem' is that the when under boost the wastegate is ALWAYS in receipt of a boost pressure signal and will begin to open proportionally in respect of this signal. Therefore as it opens it bleeds off some of the exhaust pressure. To overcome this the turbo has to produce more boost pressure to raise it back to the required value. This occurs continously as the wastegate 'creeps' open. This can increase the overall boost pressure rise time, or spool up period. 
 

Quote I think the advantage of installing the MBC on my car will be to eliminate those initial spikes during boost as well as to take the vacuum load off the actuator diaphragm during normal operation.
 

The standard ECU boost control is an open loop setup. With this I mean the ECU does not know what the actual boost is, it assumes it from other sensor data and responds accordingly. If you install a MBC between the turbo charger compressor housing and the wastegate actuator, you take control of the whole system away from the ECU. 

When boosting the ECU monitors many things and in particular the on set of knocking, pinging or whatever you want to call it. It retards the ignition and slightly backs off the boost level via the boost controller solenoid to compensate for this. In fact some people install a bright LED in the cockpit and have it wired such that it comes on as the ECU pulses the solenoid. This would give a visible indication of the ECU attempting to retard boost under near full throttle condition ie its detecting knock!! 

With only the MBC controlling the turbo, NO BOOST SIGNAL is passed to the wastegate actuator until the preset cracking open level is reached. This stops wastegate creep occuring and therefore the turbo spools up very quickly, even on light to part throttle input. When the MBC opens the wastegate is driven fully open and stops further boost rise. This set up gives consistant boost irrespective of the weather etc.

Obviously you have to consider other options for improving cooling of the inlet temperature under these higher boost levels ie charge cooler, water injection etc. Fuelling becomes an issue as well as boost rises, but is another subject in its own right.
 

Quote Another thing is that I was told that the MAF sensor is able to communicate with the (stock) ECU to dump more fuel under higher boost, which seems to relief the concerns about running lean under the situation. Is that correct?
 

No not really. The MAF sensor sends a 0 to 5v signal to the ECU which represents the air demand by the engine. When on full throttle and with max boost demand, the MAF voltage shoots upto about 4.9 volts on a standard car. If the boost is increased the air demand rises and the voltage can rise towards and infact go beyond the 5v max of the MAF. On the approach to this situation the ECU shuts down boost by fully opening the wastegate and dumping boost. At the same time the fuel cut off kicks in. This is why many sites on the web explain the installation of a 4.9v zener diode. This simple component 'caps' the voltage to a max of 4.9v and does not allow it to raise any higher when running extra boost. Its main function is to stop fuel cut off and the turbo dumping boost pressure. A supplementary fuel injector is then installed to provide the extra fuel required when running the higher boost level.

What is needed is for the fuelling maps under boost to be configured to supply the fuel under the new boost increases in respect of what the MAF is telling it is going on.
 

It is very important to monitor the fuel mixture when the car is on boost. If it suddenly goes lean, you are verging on seriously damaging your engine. 

--------------------
EOBD

'95 855 T5
Wow,
You are extremely educated EOBD, it seems you have been studying your 850 for a while... I feel I could learn alot from you... (geez, I thought I knew my stuff...) 
 
 
 

--------------------
EOBD

'95 855 T5

Jeff 

1987 244
1983 245 Ti
 

After chipping (PES) your volvo how many turns can you get away doing the wastegate? Can you go lets say 5-6 turns instead of the 3 for stock? I heard its safe to go up to 19 PSI but never go pass 20 so can I adjust it up to 18-19 PSI after chipping and won't be any problems since the car will be running better tuned 

Theoretically, what you propose is a great idea, but can you guaruntee you won't go over, i.e. an accurate boost gauge?
And be prepared to invest atleast one full day (12 hours) of tuning.

Then there are the issues of delivering enough fuel. When was the last time you changed your fuel filter, and how often and what fuel injector cleaners do you use?

And I think you won't need that many turns. Too many turns and the waste gate won't be able to dump boost in between shifts, i.e. say good bye to your engine. If you are that serious about holding higher boost, why not weld your waste gate shut, and get an accurate blow off valve. You will be able to REALLY control your boost, as well as get that mysteriously very popular sound of psssshh in between shifts.

> Theoretically, what you propose is a great idea,
Not really. Boost is controlled by the ECU. Additional turns will change the timing of the wastegate operation but not the maximum boost.
Otherwise why would one need to modify the ECU in the first place? Just keep dialing until you're happy!
 

If that's true, than why do people get higher psi with accurate vaccuum/boost gauges?
You know why? Because the OE wastegate with the actuator arm at it's stock position allows some boost to leak while at full throttle.
Yes boost is controlled by the ECU, but not exclusively.
"Otherwise why would one need to modify the ECU in the first place?"

One needs to modify the ECU because simply not allowing the wastegate to leak as much or at all under full throttle doesn't also change the other parameters of the engine that. After a certain increase, unless the parameters are changed, not enough fuel will be injected, ignition timing will be off from optimal, as well as proper valve timing, thus leading to a lean fuel to air ratio, which can cause damage. That's why many don't recommend over 3 turns to begin with, then if the engine is running fine still, try another half turn, then another, etc, until one pull's codes. When that happens back the actuator arm off.
Have you actually seen numbers on 850's with actuator arm adjustments? I've seen an S70 T5A SE and two 854Ts with actuator arm adustments. The S70 had a Haltech, two had GReddy's. The S70, and one of the 850's also had GReddy Air/Fuel ratio gauges. The both picked up psi throughout the rpm range, and both were still within operating parameters in regards to air/fuel. The S70 in question is the same S70 I mentioned with 18" x 8" Borbet rims. He has since welded his wastegate shut, and installed a blow off valve to hold 18psi of peak boost while also able to blow off enough boost between shifts on his auto trannied S70.

At the time of the waste gate adjustment, he only had a 2.5" cat-back, open element air filter, 1 coil of suspension clamped, and gauges. Now, he has a GIAC chip, 3" complete exhaust (downpipe to tip, with a 5" round chromed with rolled edged tip on a rear mount muffler), welded wastegate with a TIAL blow off valve, a number of turns on his wastegate, the iPd black mesh grill, blue bulbed head lights, DARK tinted windows, V70 R AWD front fascia, stock tranny, no other suspension or brake modifications and a shaved rear end except for a T5-R sign. He hasn't had it dynoed yet, hasn't raced it yet, hasn't had it clocked yet. All we know is even with the increased wheel diameter, his Yoko Paradas are taking major abuse.
And the highest boost he's seen is about 18psi.

Don't believe me, head to Magnus Motorsports on Keele St. just south of Rutherford Rd. and ask for Marco (the mod guy) or Rob (the owner of the S70) and ask them. They've been working on his car non-stop for the last little while.

> You know why? Because the OE wastegate with the actuator arm at it's
> stock position allows some boost to leak while at full throttle.

Nope, sorry.. You're talking about the bypass valve here.. It will leak at higher pressures. The wastegate is blissfully unaware of any ouput pressure unless the ECU on the Volvo engine will let it's actuator 'see' the pressure.
Keep in mind the difference between a wastegate and a blowoff or bypass valve. They are very different animals and serve different purposes.

The wastegate is in the exhaust side of the turbo and it's only purpose is to be able to bypass part of the exhaust gas around the turbo, so it will slow down and (slowly) drop pressure. It's controlled by the wastegate actuator and rod.

Bypass-valves and BOV's on the other hand are in the intake/pressure path of the turbo and their purpose is to control pressure-shock when the throttle is suddenly closed. They are conrolled by a vacuum line from the intake manifold and they open when the throttle is closed and vacuum is applied to their control port.

Volvo's don't use a BOV, but use a bypass valve, which feeds it's air back into the intake of the turbo when the throttle is closed. This is done to keep metered air from escaping the intake system as it would otherwise cause the engine to run (super)rich when this air is expelled to the outside. It's also more 'gentle' and controlled than a BOV and as such better suited for a 'family car'.

The bypass valves, however, *are* known to leak air back to the intake when pressure from the turbo is increased. This causes a loss of maximum boost. Welding these shut (as it's integrated on the mitsu turbo) and adding an external BOV is a well-known procedure to overcome this problem.
Also wastegate rod settings are known to be a little too 'loose', which causes the boost to come up too slowly, but it has very little effect on the maximum boost level unless you are really running the turbo outside it's specification.

Welding the wastegate shut is useless as you can get exactly the same result by just un-plugging the pressure line going to the actuator. In both cases the pressure, turbo rpm and air temperature will skyrocket out of control.

> Yes boost is controlled by the ECU, but not exclusively.

On the stock volvo's it's indirectly controlled by the ECU giving the wastegate actuator little 'blips' of pressure.

The way they do it is by using a wastegate actuator and rod setting which, if connected directly to the pressure output from the turbo, would open fully at about 40% of normal boost pressure. This is the so-called 'baseline boost' setting.

Now, the ECU has control of a (frequency)valve in the pressure-line going from the turbo outlet to the actuator. It will pulse this actuator to control the amount of pressure as seen by the wastgate actuator.

If it keeps the valve shut most of the time then the actuator receives little pressure, which keeps the wastegate closed and the turbopressure will rise. If it opens it up more cycles then the wastegate will open and exhaust gas will bypass the impeller and boost will drop.

The low 'baseline' boost setting is used to give a controllable boost-rise. As the boost is building up the ECU will start to mostly open the pressure line to the wastgate actuator once it reaches about 80 to 90% of the 'final' boost level. This will slow the boost rise and it will 'level out' at the factory spec where the ECU is constantly opening and closing the valve to the actuator to keep the pressure at the factory limit.

If you look carefully at the boost gague at WOT and keep it there for 30 to 60 seconds or so you will see it fluctuate constantly around the factory boost limit. This is the ECU in action while it pulses the valve.

This is also the reason why *only* screwing the wastegate rod tighter (without boost-controllers and such) only has a *temporary* effect on a stock Volvo turbo pressure. What it does is raise the baseline boost, but the ECU still only supplies pressure to the actuator at about 80 to 90% of max boost. But now it takes more pressure and time for the wastegate to open because the baseline boost has been increased.

This causes the boost to 'overshoot' it's maximum (the boost-spike) until the wastegate has opened enough and the turbine is slowing down enough (the wastegate only bypasses the exhaust gasses around the turbo and does not 'vent' pressure) for the pressure to drop to it's factory maximum again after about 30 seconds or so.

So the wastegate mod in itself will give you a better/quicker pickup and initial 'push' as the ECU can't control the rise of the boost as well, but if you stick it at/near WOT for longer you will see it drop back to stock levels.

> adustments. The S70 had a Haltech, two had GReddy's. The S70, and one
> of the 850's also had GReddy Air/Fuel ratio gauges. The both picked
> up psi throughout the rpm range, and both were still within operating
> parameters in regards to air/fuel.

Of course! If you remove the ECU's pressure valve and substitute with boost controller then you probably also have to raise the baseline boost up, just to be able to reach the stock setting. Actually in this case I'd go for a stiffer actuator to start with..
You could also install the boost controller in front of the ECU-controlled valve in the pressure line, so you fool the ECU in thinking it's controlling the pressure.

> welded his wastegate shut, and installed a blow off valve to hold
> 18psi of peak boost while also able to blow off enough boost between
> shifts on his auto trannied S70.

I assume he welded his bypass valve shut. 18PSI? I hope he also has forged conn-rods? Most tuners I spoke to in Sweden say that the stock 5-cyl turbo will bend and sometimes even break rods at over 15PSI if you run it with enough fuel. Only the 265hp V70R AWD engine has stronger (forged) parts to cope with the added pressure (and now probably the 250HP S60T5)

Bye, Arno.
 

Thanks, Arno. I think you’ve answered my post to derspi above.

… Now let me go over your dissertation 2 or 3 more times to properly digest it … :)

So, bottom line is there is no ill effect to our efforts at tightening the wastegate actuator rod SO LONG AS we don’t tighten too much to the extent it causes a Check Engine lite, right? There seems to be much to gain too. Like I mentioned earlier, and I gather many boosted 850s/70series owners feel the same, post-chipping actually results in better fuel economy. So volvo programmed their ECU to run rich right from the factory.

Question: Does tightening the wastegate rod help to decrease fuel consumption, or actually increases it? I would imagine it is the former, isn’t it, as turbo lag (w/out tightening) results in the driver depressing the fuel pedal more in order to overcome lag.
I would like to describe my experience with my SAM chip here:

Prior to fitting the SAM-chipped ECU, I fitted a S/sprint downpipe and replaced the cat with a resonator. The results were fabulous – throttle response was immediate. Turbo lag practically disappeared.

THEN I fitted the SAM ECU. Turbo lag returned! It was just like stock ECU at low revs. The SAM tuning allows boost to build depending on how hard one steps on the throttle, and also depending on whether the gear mode is Econ or Sport.

Econ mode is almost exactly like stock ECU, only diff is it builds boost to max (1.0 bar) only at high rev range and only if one floors the pedal.
From cruising speed:

Light press on Sport - I get turbo lag, it's like there's absolutely no diff from stock ECU.

Medium step on Sport - 1 gear kickdown, still some turbo lag but it will climb (not "shoot" like a TME ECU I’d borrowed from a friend and tested on my car).

Hard flooring - 2 gear kickdown, it will rise rapidly to max on the stock gauge. Continue flooring the pedal and it will go to off-gauge at about 4500 rpm (looks like 1.1bar) before coming down again after awhile.
I dunno if this is the experience of others who’ve chipped their cars. I know it’s sure hard to say, “I’ve spent a grand on sumthing and the results show it loses out to the competition …” My experience is limited to 2 tuners – SAM and TME. Latter beats former hands down – no lag on TME reprogramming. Only consolation is, price-wise TME loses out a fair bit.
That’s why when I did the wastegate turns, I felt it was that much needed breath of fresh air lacking from my SAM chip. Those precious turns actually brought my SAM equal to TME standards. …

Thanks and rgds

Jeff from Malaysia

95 855T5A SAM chip, IPD swaybars, full S/sprint exos (no cat), Bilsteins
 

> So, bottom line is there is no ill effect to our efforts at
> tightening the wastegate actuator rod SO LONG AS we don?t tighten too
> much to the extent it causes a Check Engine lite, right?

Yes. It can help to give you a quicker pick-up. Your chip-tune will take care of the long-term boost/power increase.
Some wastegates are set too loose from the factory (the new V70 and S60 T5's were waaay too loose a while back) and although it has little effect on the final boost level it does mean that the rise is much slower/delayed.
If it's tigtened up a little the pick up will be much better. Just keep an eye on the size of the boost 'spike' you get. If it gets too big (rod set too tight) then the overboost-protection comes in an it will probably trigger some errors.
'easy does it' is the motto here :)
Bye, Arno.

> You know why? Because the OE wastegate with the actuator arm at it's
> stock position allows some boost to leak while at full throttle.

It could occur for a short time until the ECU reacts and corrects it (there's a certain delay here, as in any control system with negative feedback).

> Yes boost is controlled by the ECU, but not exclusively.

Exclusively. What you're talking about is an overload condition, when the ECU can't cope fast enough with the input it's not designed/programmed to handle.

> One needs to modify the ECU because simply not allowing the wastegate
> to leak as much or at all under full throttle doesn't also change the
> other parameters of the engine that. After a certain increase, unless
> the parameters are changed, not enough fuel will be injected,
> ignition timing will be off from optimal, as well as proper valve
> timing, thus leading to a lean fuel to air ratio, which can cause
> damage.

Exactly! So you know the right way and WHY this is the right way...

> ... the same S70 I mentioned with 18" x 8" Borbet rims. He has since
> welded his wastegate shut, and installed a blow off valve to hold 18psi
> of peak boost while also able to blow off enough boost between shifts
> on his auto trannied S70.
> At the time of the waste gate adjustment, he only had a 2.5" cat-back,
> open element air filter, 1 coil of suspension clamped, and gauges. Now,
> he has a GIAC chip, ...

Ok, that sounds very intriguing, but his turbo can no longer be controlled by a Volvo ECU, stock or modded, in a normal way. And this story seems irrelevant, anyway.

Now, if you could produce some numbers (dyno, 0-60, etc) clearly stating that the actuator rod adjustment alone (all other parameters being the same) results in improvement - that would be relevant. But I doubt it. I've been monitoring this forum long enough not to miss someting this important.
Please don't take it personally. I'm just trying to couner-balance your opinion since you were giving an advice to someone who misunderstood some principles of ECU operation, and your advice could result in even bigger confusion.
Vadim.
 

He ran in the low to mid 12psi stock, and after chipping went up to around low 15. With all the other mods like exhaust, wastegate, etc, it went to around 18.
Sin
 

Well, you're both right but the only truth I know of is my own firsthand experience. I don't know what the other guys who have played around with their 850s and S70s have gotten but my results have been less than spectacular. You may gain just a tad more boost as a direct result of the wastegate adjustment, due to, as mentioned by Sin, poorly adjusted or leaky wastegates from the factory but I have yet to see any increase of more than 1 or 2 PSI. Full throttle or not but it makes no difference--I've had my wastegate rod shortened by 3, 4, 5 6 and now 7 turns. The only real difference is that the turbo kicks in earlier and with more ferocity. Lag is not as pronounced when the rod was at its normal, factory-spec length. I know for a fact that the car will eventually run a bit lean as the ECU adapts to my fiddling because I've been getting better gas mileage with the constant adjustments to wastegate rod. Whether or not these effects will be detrimental I don't know but I have yet to see any check engine lights.

In truth, there are two ways to go about getting more boost. The hard way entails much fiddling with BOVs, wastegates/linkages, bleed valves, electronic boost controllers. The end result may be more rewarding but remember that we're all limited to the engine internals of our particular car. Roughly 300 HP is all we're gonna see until you spend big bucks to beef up the engine. The easy and probably less expensive way is fine-tuning or custom mapping the ECU based on your needs and setup. This takes some professional help from chip tuners but would definitely serve to lessen the amount of headaches involved with getting more power and boost out of these 850/S70s. Another thing that seemingly no one ever mentions is the fact that extra boost is meaningless if you don't have more fuel to go with it. Sure, the ECU may be mapped to compensate for it but sooner or later, you're gonna find out that the stock 850 turbo injectors just aren't up to the task.

OK, I'm getting a bit off topic but I hope my own experience and some of the stuff I've read up on can shed some light on the subject.

Derspi