More 3/16 boost control mod testing

Well after my last post and some discussion with various people, I decided it was worth doing a simple test to prove or disprove my theories about the 3/16 boost control mod.

My understanding about the boost control system as it applies to my MY02 Subaru Impreza WRX is as summarized as follows.
- The wastegate takes its pressure feed from the intake manifold (post compressor).
- The wastegate valve is set to around 7 psi.
- All other things excluded this gives a maximum boost pressure of 7psi.
- The pressure feed line contains a T-piece that feeds the boost control solenoid.
- This solenoid allows the ECU to bleed some pressure prior to the wastegate, thus giving more boost pressure overall.
- Inline with the solenoid is a restrictor.
- The restrictor is used so that the system is not sensitive to the internal diameters of all the piping and connectors, but rather to a single minimum point.
- This restrictor tends to govern the effect of the solenoid.

What the 3/16 mod is supposed to do (if you can believe what you read on the internet) is to enlarge the restrictor, and thus allow the solenoid to take effect quicker, and possibly also give a higher boost level from the Mitsubishi TD04 turbocharger.

If you know anything about control theory (and why would you! It can be amazingly boring stuff) you'd know that any system with a feedback loop can by pretty sensitive to changes. If you alter a part of the system you risk creating a situation where it's chasing its tail. In this case, if the boost rose too quickly, the ECU would peg it back, which would happen too fast, then it would open it up again. The result would be jerky and inconsistent power delivery, which has in fact been reported by others experimenting with this mod.

How to test my theory?

I figured the safest way to test things was to block the line to the boost control solenoid. If my theory was correct, this would cap boost at around 7psi and effectively give the WRX about ~120kW instead of the full whack 160kW. Why 120kW you may ask? Well 7psi is about 0.5 atmospheres (or 0.5 bar) which means that the engine will be getting 50% more air/fuel mixture than under natural breathing, which in broad terms should relate to 50% more power than a comparable naturally aspirated motor. This means that at 7psi the WRX is effectively running a 3.0 litre engine, and at full noise running around 14psi its effectively running a 4.0 litre, which is born out when you compare output figures of various cars.

Armed with all this knowledge and no small amount of consternation I pulled the restrictor from the hose, wrapped it with plastic and plugged it back in, thus blocking the hose completely.

Driving the car was quite interesting.

The characteristic WRX power delivery was altered quite a lot. The power came on smoothly up until around 3000rpm just like before, then... it just kept coming on smoothly. Instead of that grin-making whoosh that usually arrives, it just kept pulling strongly. It certainly felt stronger than a naturally aspirated 2.0 litre, and closer to a 6 cylinder in feel, but nothing like the usual WRX rush.

The turbocharger was definitely still working, because since I have the intake resonator removed I could still hear the spool up, and the factory BOV sneezing occasionally. However my theories seemed to be proved correct. The Mitsubishi TD04 turbocharger seemed to be making about 7psi with the hose blocked, and around 14psi (or whatever stock levels are anyway) with the restrictor in place. If the line was unplugged completely I'm guessing that the turbocharger would generate as much boost as it could, which is a pretty cheap way of upping your power, as long as you don't mind most likely detonating your engine.

My next tests will be to try some different restrictor sizes, or fit an adjustable valve. Stay tuned for more.

The (in)famous 3/16 boost control mod

Many a WRX enthusiast will have heard of the 3/16 mod. It's said to be a very cheap way of upping the performance of your stock, garden variety Subaru Impreza WRX. Unfortunately there's not much in the way of scientifically valid testing done on this modification, and opinions vary widely.

After a fair bit of research I decided to try the mod on my stock-as-a-rock MY02 Impreza WRX, and have been quite pleased with the results. However I will make the following disclaimer.... Fiddling with the boost control system on any turbocharged car is potentially dangerous. Overboost can destroy your engine in extreme circumstances. Make any changes AT YOUR OWN RISK.



What this mod does is give the stock WRX boost system a little kick. As I understand it, it allows the boost control solenoid to act faster and have more effect, which means that the boost comes on earlier and slightly stronger. It also means that if you overdo things, you'll end up with spiking, overboosting and underboosting, as the system chases its tail.

From what I've read about the WRX boost control system, it works like this... The wastegate is mechanically set at around 7psi. This is how much boost a car would run if the boost control solenoid was always shut.

The solenoid basically allows a small amount of air to bypass the wastegate, thus the turbo has to build up more pressure to have the same effect. The ECU thus controls the boost by opening and closing this solenoid. Solenoid open for longer means more air bypassed and more boost.



To avoid having to worry about the diameter of all the tubing in the solenoid circuit a restrictor is placed which gives you a set flow rate. Since this is the narrowest item in the circuit the restrictor is the deciding factor in how much air is bypassed through the solenoid.



Increasing the restrictor diameter means that opening the solenoid has more effect... or in other words the boost builds faster and potentially to a slightly higher level.

If the diameter is too big though, the boost will climb and fall quicker than the ECU can cope with, and it will overcorrect. The pressure will in that case be inconsistent and power delivery not smooth. You may get boost spiking to high levels and then cutting out as the WRX computer tries to compensate.

The replacement restrictor I sourced from my local hardware shop. It's original application was a hose coupler for a automated garden watering system. I then drilled it out to the required size and replaced the factory item.

Now I don't have a G-tech or boost gauge (although others with this mod have noticed boost arriving quicker and slightly higher).

Seat-of-the-pants-wise I found that on a hill that I'd previously have to down change to 3rd gear, I could now climb in 4th. I also found the traditional WRX Whoosh! arriving about 500rpm earlier.

All in all I've been pretty happy with the results, and have been driving the car with this modification for over a year now with no noticable down side.

Holden JS Vectra CD sedan

Background
The Holden Vectra has a heritage that many at Holden would rather forget. In Australia the J-series cars began with the infamous Camira. And while it managed to win the Wheels magazine "Car of the Year" for it's performance and roadholding, its quality left a little to be desired. The bits that fell off regularly tended to detract from its willing engine and high speed handling. Holden persisted with the Camira for many years, and just when they seemed to get it all right with the JE, which sported a 2.0 litre MPFI 85kW motor, they axed it and instead started selling rebadged Camrys as the Holden Apollo and expecting the car-buying public not to notice. At least the Camry was reliable but that was about the nicest thing you could say about it. The price of the Yen at least meant that it made economic sense.

Then in 1996 rumours of a new mid-size Holden began to leak out. It was the latest J-body car from General Motors in Europe, and the changing world economy made Euro imports a proposition once more. For Holden to re-use the name Camira would most likely result in sales suicide, and for a while the revival of the Torana nameplate was speculated. However Holden chose to use the same name as the European model, and in 1997 the JR Vectra arrived in Australia.
Holden had grand plans for the Vectra, and in late 1998 began locally assembling the JS Vectra at the Elisabeth plant in South Australia, planning to supply Australia and Sout East Asian markets, however changing Asian economic fortunes and the need to manufacture the Monaro meant that after only a few years of local manufacture, the Vectra returned to being fully imported.

This was a shame because the local car had some subtle but welcome tweaks over the imported model, the most significant being a boost in capacity in the 2.0 litre 4cyl to 2.2 litres, and revised suspension and gearing. The 2.0 litre was already putting out a class leading 100kW while offering excellent economy, and the 2.2 litre variant offered a welcome dose of low down torque, and an extra 4kW up top, without sacrificing much in the way of economy.

When the ZC Vectra arrived it really moved up an entire market segment into the medium size luxury class, leaving the niche vacant for the new Daewoo arm of General Motors to fill.

Vectra CD iD
This review of the 1999 JS Vectra CD can be considered a long term test... very long time. I've owned the Vectra since purchasing it new in February 1999 for the last six and a half years. In that time it's travelled over 120,000km. This was one of the Australian assembled cars with the 2.2 litre 4cyl and 5 speed manual transmission. Being the CD model it came loaded with all the good bits, such as Traction Control, Anti-lock brakes, dual airbags, Cruise Control, Trip computer, CD player, foglights and alloy wheels. The letters "iD" indicate that it has been fiddled with by a branch of HSV that provided various option to individualise the car. In my case the Vectra was fitted with an iD front and rear spoiler and sideskirts and alloy wheels. It even had an individual build number plate in the engine bay to make you feel special.



The iD body kit was actually supplied by the well known modifier of General Motors cars in Europe, Irmscher, located in Stuttgart.

Curiously enough I ended up purchasing the Vectra without ever driving one. Strange I know, however all the research I did and reviews I read seemed to point to it being a "good thing". In comparison to the other 4cyl cars in its class (the Mazda 626, Toyota Camry and Ford Mondeo) the Vectra had more power, better economy, more features, and outhandled all bar the Mondeo. It also looked by far the best to my eye. Another point in its favour was that in Europe the Vectra and Mondeo were pitched against the Audi A4 and Mercedes C-class, which made the prices in Australia a relative bargain. To buy a similar spec Vectra in the UK would cost up to 30% more that the Australian sticker price.

How does it Drive?
Once I was behind the wheel, the Vectra certainly didn't disappoint. The 2.2 generates plenty of torque from as low as 1000rpm, and so is virtually stall-proof. The torque delivery also makes for very relaxed driving around town, and minimises the need to change gears. The gearing is perfectly suited to the engines character, with fairly tall ratios that mean a leisurely 2000rpm or so at highway speeds. 2nd gear will take you all the way to 100km/h if you can sneak close enough to the limiter, and get you there in close enough to 9 seconds flat. If you have to grab 3rd before the 100 mark the time blows out to almost 10 seconds, as often published by less commited motoring journalists.

The standing 400m is despatched in around 17 seconds, which is a far cry for the sub 15 time of my WRX, however the Vectra makes up for standing starts with its in gear and rolling start performance. Plenty of torque mean in situations where the WRX is left waiting for revs and boost to build the Vectra leaps away with a chirp of the tyres. Traction control is very much appreciated in wet weather.

Handling wise the Vectra is quite neutral and surprisingly quick. Two track days at Winton Raceway mixing mostly with V8 Commodores revealed how well it carved up the corners, and caused a few to ask if it was stock. It was only left wanting in top end speed down the main straight. In comparison with the WRX the Vectra does not feel as fast due in part to it's less supportive seats and lower revving engine, however if you have time to look at the speedometer in tight corners, the Vectra carries the same corner speed as the Subaru. It loses out on corner exits however, as the front wheel scrabble for grip and understeer relentlessly towards the outside of the corner while the traction control madly tries to keep things in check. Lifting off however tucks the nose back in and can even step the tail out nicely. On B grade backroads where the surface is bumpy or broken, the Vectra's 15" wheels and 60 series tyres just soaks it up and it corners flat and confident where the WRX will feel nervous and a bit harsh.

What does it cost to run?
The Vectra is amazingly economical for a car of its size and performance. Partially this is due to the relaxed gearing, and partially I think is due to the overrun cutoff feature that is common in many modern cars, which shuts down the injectors completely when the car is coasting in gear and the engine is being driven through the gearbox by the road speed. You can see this occuring by watching the fuel consumption in the trip computer which drops to 0l/100km as you start to coast down a hill.

Cruising around town it is quite easy to obtain 8.5l/100km and travelling interstate a figure somewhere below 7l/100km is quite common. The best ever obtained was 6.1l/100km, which gives the Vectra a range of almost 1000km from it's 60 litre tank. That means it will be able to travel Melbourne to Sydney on a single tank. In fact a friend once travelled to Sydney in their Hyundai Excel and only managed 7l/100km while the Vectra did 6.5l/100km.

Does the family fit?
One thing the Vectra does very well is haul things around. The boot is bigger than a Commodore at 500 litres, and can swallow our Emmaljunga pram without any disassembly required. While 5 adults can be a bit squashy, there's tons of room for kids, and the interior is comfortable and well appointed. There are the regulation anchor points for carseat and child restraints, however you'll have to get your own hardware. The Subaru has clip on points built into the seat. The Subaru also gets locking seatbelts for securing baby seats, while the Vectra does not.

Buttons and bits
Where the Vectra wins points is for locating all the window controls on the centre console, allowing the front seat passenger to operate windows for back seat children, and having a cruise control that doesn't need to be turned ON and OFF. Why Subaru feel I should have to press two buttons to activate cruise, and make one of them hard to see beneath the steering wheel is beyond me. The Vectra also wins praise for having the foglights on a toggle switch that turns off with the ignition, thus avoiding the problem of leaving them on and suffering the wrath of the anti-fog-light evangelists. The central locking in the Vectra also locks and unlocks the fuel cap and boot, thus removing the need for an inconvenient remote release. You also have the option of deadlocking the doors, which means that cannot be opened even from the inside.

Any problems?
Since owning the Vectra there have been a few minor issues and one major one. When virtually new it exhibited a stalling problem which was known to Holden and resolved immediately with a new Idle Air Control valve. Then sometime within the first few years there was a problem with the wiring of the indicators which caused the flash rate to vary. Once again Holden resolved the problem immediately. Then about a month from the end of the warranty and ticking/tapping noise was noticed, and the car was taken to the dealer to investigate. They diagnosed the problem as a chipped crown wheel in the gearbox/diff assembly, and since they couldn't get a replacement part, they replaced the entire gearbox and diff under warranty. This took a week, so was a little inconvenient, but I was nevertheless happy to not be paying for a new gearbox.

How do you rate it?
I'll admit that I love driving the Vectra, and have been more than happy with it.
I can't see any other medium size sedan doing anything better for the money.
5/5 stars - * * * * *

What's the point?

G'day all,
There are a lot of places you can read and see car reviews. Magazines, newspapers, television, and especially on the internet. So whats the point of producing more reviews? The short answer is that I love talking about cars! The long answer isn't much more complicated. I'm now 35 and have always loved driving, and have driven a lot of cars. I've done the odd track day, and I'm the type of guy who people ask for advice when buying a car. I've got a young family so need something practical, but also want something that's fun to drive. I don't think my perspective is unique which is why I think it might be useful. Currently I drive a Subaru Impreza WRX (MY02) and a Holden Vectra CD (MY99). They're both great cars for different reasons. Hopefully you'll find my opinions on these and other vehicles useful and amusing.
Matt