Learn stuff - Lightweight & underdrive pulleys add wheel power
A potentially controversial question that our guys have decided to tackle with some useful testing and results that will surprise some.
The following is an extract summary of the whole GFB Discussion Paper on the subject titled "Lightweight Under-Drive Pulley Kit Performance Testing" which is available for download below.
GFB’s range of Lightweight Under-Drive Pulley Kits are designed to improve
acceleration by reduce the rotational mass (inertia) on the crankshaft as well as parasitic loads from the driven accessories.
The pulleys are manufactured from 6061 T6 billet aluminium on the latest precision CNC machines, and typically save up to 2.5kg of weight over the factory pulleys.
Under-driving is achieved through the use of a smaller diameter crank pulley, which reduces the amount of drag from the accessories, particularly at high RPM. Note that GFB take care to ensure that accessory performance is not affected.
The results shown above (refer article) are actually the pair of passes that show the smallest gains. Other tests could have been combined to show larger and better results, but this pair has the closest-matched conditions and represents the most honest results.
Gains or losses resulting from variations in boost pressure or ECU-related
adjustments are usually seen only in part of the rev range, as a bump or a dip, or a different shaped power/torque curve. The pair of runs chosen for comparison however, are very similar in shape, indicating that the engine is operating in as close to identical conditions as could be expected – the resulting improvement can therefore be said to be from the installation of the pulley kit only and not from external variations.
It can be seen in these results that fitting a GFB Lightweight Under-Drive Pulley Kit does in fact produce an honest, measurable and repeatable improvement in acceleration throughout the entire engine rev range.
The tests revealed that the minimum
recorded improvements after replacing the factory pulleys with the GFB Lightweight Under-Drive Pulleys were:
· 3% faster (0.1 seconds) from 30-90 km/h
· 4% higher average G-Force (0.02g) from 30-90 km/h
· 7.2% higher G-Force (0.03g) at 40km/h (2800 RPM)
· 5kW peak power increase (173.7kW to 178.7kW)
The results charts all tell the same story, which is a consistent improvement in GForce throughout the 30-90 km/h test, which results in more power and consequently a faster time to 90km/h.
Importantly (especially on turbo engines), the G-Force improvement off-boost and during spool-up are enhanced by a much larger percentage because of the limited engine torque available at low RPM. This gives the car what can be best described as a noticeably “livelier” feel in the lower rev range, and a greater willingness to rev during acceleration.
This is unlike many other engine modifications that improve power through increased airflow, since such gains are usually only available for a portion of the rev range, and often the ECU is required to be re-tuned to suit. The GFB pulleys however offer their benefits independently of the engine tuning, and regardless of how much power it makes.
Learn stuff - The truth about compressor surge. Part I
The following is an extract from a discussion paper put together by our engineers called "The truth about Compressor Surge -Part 1. Part 2 follows in the next thread.
Hopefully this should placate some fears and provide a reality check for turbo enthusiasts.
What’s in a name?
First of all, let’s get the terminology straight. Compressor surge often goes by many other names (usually in reference to the distinct sound made when surge occurs) such as turkey, pigeon, dove, dose, wastegate chatter, sequential BOV and undoubtedly many others I am not aware of or have yet to be invented!
Whilst I can’t argue that compressor surge noise does share a similarity to the noise made by certain avian species, the remainder of these names are either misleading or flat out incorrect. For example:
I have no idea how this name was derived, but it is most commonly associated with the Holden VL Turbo, since no factory diverter valve is fitted and it compressor surges readily. Going further, a “Dose Pipe” typically refers to any type of pod filter arrangement that makes the fluttering sound louder than with a factory airbox, therefore a “Dose Pipe” is not a device that creates the fluttering sound, but rather a means of making it louder.
This is a term that has found its way into common turbo vocabulary, and is often incorrectly used to describe compressor surge. Whilst it is possible for a wastegate to make a small clattering or rattling noise if it is just at the point of opening (exhaust pulses can make it vibrate on its seat before it lifts clear), it has nothing to do with compressor surge.
Compressor surge is often thought to be the sound made by a specific type of “sequential” BOV. In actual fact, no BOV makes the compressor surge fluttering sound, the noise actually comes from the turbo. This certain “sequential” BOV however is often responsible for causing compressor surge, which is how this misconception propagates.
What is compressor surge?
To the driver, compressor surge is apparent as a fluttering or repeated “choofing” sound, typically when closing the throttle.
Here's a good YouTube link showing classic compressor surge caused by the absence of a BOV
To the turbo, compressor surge is a condition that occurs whenever turbo boost pressure is high and airflow is low.
Read the complete PDF discussion paper for details including graphs and a full explanation of the mechanics of surge.
With an understanding of the mechanics of compressor surge and the conditions that cause it, it can be seen that in the majority of cases it will not cause significant turbo wear or damage, however there is the potential if it is severe enough.
There is however good reason for preventing compressor surge, and the fitment of a diverter valve that addresses the issues discussed is the best way to do so. The GFB TMS valve's are specifically designed as Turbo Management Solution.
Refer to part 2 for extra detail and the final conclusions.
Learn stuff - DV (Diverter Valve or Blow off valve) is it just performance noise?
Some more tech on potential myths and misconceptions about turbo boost management and BOV's, are they bad for your engine and why fit them at all This originated from an IClub thread asking "Is a BOV bad for an engine?" and draws on other comments on NASIOC.
Is a BOV (blow off valve) bad for my engine?
There are two main reasons why most people want to put an aftermarket BOV on their car: noise, and performance. We’ll take a look at these two separately.
Noise: venting a BOV to atmosphere has no benefit, other than to make noise. The aural benefits of this and your increased ability to pick up chicks is beyond the scope of this posting, and remains purely a personal choice!
It is common knowledge that venting a BOV to atmosphere on a car with a MAF sensor does have the potential to cause a few issues, although the scale of the problem is often blown out of proportion and is not well understood. GFB takes great care with the design of our BOVs to ensure that those who want to noise are able to get it without risking the commonly associated problems.
I’ll refer to the linked thread http://forums.nasioc.com/forums/showthread.php?t=468038
, as this is a very thorough and appropriate summary, although there are a few points I’d like to clarify. Dan has tackled the old “running rich” statement very well. Basically, when you shift gears and the valve vents, a certain amount of air passes through the MAF and is measured. The ECU continues to inject fuel for the amount of air measured, but some of it has escaped to atmosphere, resulting in a brief rich mixture. How brief? A lazy shift lasts for about a second, and the injectors will typically cut out after a second anyway on a closed throttle above 1200RPM in a Subaru. So really the longest you can have a rich mixture as a result of an atmo-venting BOV is about 1 second.
How rich? As Dan says, it may dip below 10:1, which is nothing serious, but it should also be noted that how rich the mixture goes for a given ECU tune is ENTIRELY dependent on how much
air you vent to atmosphere. Here’s where I would argue Dan’s point written about Hybrid BOVs:
“What about a 50/50 or BOVs that you can portion the VTA portion? This is a bad analogy, but if a BOV is a person in a wheelchair, a 50/50 BOV is a person in leg braces. It's not as bad, but not good enough to say bolt it up. If you find a deal on one or happen to like the sound of a particular model, go for it, but don't think you are doing your car better vs. a 100% VTA model”.
I’d have to disagree that it’s a bad analogy, or that it’s no better for the car than a 100% atmo model. As per my statement above, the amount of air vented to atmosphere is directly proportional
to how rich the mixture goes during this brief period. If you put on a large atmo valve, say like a GFB SV45 designed for 500-1000hp, as soon as that valve opens it will let out a HUGE amount of air, and the mixture will go measurable richer. This can be felt as you go into the next gear and the car needs to “clear its lungs” of the extra fuel.
If on the other hand, you put on a valve such as the GFB Hybrid or Stealth FX in which you can alter the venting ratio, and 50% of the air is recirculated, then the mixture will not go as rich, and the chance that you will run into problems such as backfiring or loss of performance is proportionally less.
There is typically a certain amount of air that you can vent to atmosphere without causing any problems. In most Subarus, GFB valves can usually be vented fully to atmosphere without any problems provided the spring is set correctly (Dan’s explanation of this procedure is quite thorough). Possible exceptions for this are on cars that run the standard ECU, but have other mods such as more boost, full exhaust, intake etc. This is because the factory ECU runs quite rich to begin with, and increasing airflow via these mods will cause the ECU to run even richer – we’ve seen cars with stock ECUs run down below 10:1 because of mods that haven’t been compensated for. Throw an atmo-venting BOV on top of that and the likelihood of problems increases.
Now, let’s take a look at performance. It is fair to say that the factory Subaru valve is not completely useless. It will hold boost just fine at stock and slightly increased levels, but it’s not correct to say STi and WRX valves are the same. These valves are specifically designed to begin leaking above a certain boost pressure, which is set by the spring pre-load. Whilst unfortunately we don’t have a library of year models and factory bypass valve part #s, I can say with 100% certainty that STi and WRX factory valves have different spring pre-loads and will leak at different levels.
Now, a very important point. The fact that the spring pre-load on the factory valve dictates the point at which the valve begins to leak DOES NOT HOLD TRUE for GFB valves. A GFB valve will stay shut under WOT (wide open throttle) conditions REGARDLESS of the boost pressure or the spring pre-load setting. This is because manifold pressure and intercooler pressure are equal under WOT, and the piston area of the GFB valve top and bottom is equal, and since the manifold and intercooler pressure are fed to the top and bottom of the piston, the resultant force is zero – they cancel each other out. Therefore only a very small amount of spring pre-load is required to hold the valve shut.
Now, with the above in mind, let’s talk leaks. Here’s what Dan has to say:
“I have had XXXX brand valve for years, it has never leaked. How do you know? By looking at your boost gauge? Looking at the boost levels in your datalog? Neither of those prove that the valve isn’t leaking”.
I should also point out that a lower boost pressure reading doesn’t prove the valve IS leaking. “Losing boost pressure” is one of the most commonly assumed symptoms of a leaking BOV/BPV, but is in fact very close to useless for diagnosing leaking.
The term leak unfortunately does not in any way indicate a MAGNITUDE, and hence should be very carefully used. The pistons in your engine leak, but the engine still works. Your boost control solenoid leaks boost, but you don’t see a drop in boost pressure because of it. The SIZE of a leak is very, very important. For you to see a loss of boost on a gauge or data log, it needs to be quite significant – consider the amount of air entering your engine at full boost.
For argument’s sake, let’s assume your engine normally consumes 320CFM @ 14psi of boost. If the turbo does nothing to compensate for a leak (it will to a certain extent because of the nature of the wastegate system, but will be ignored for this example), and you see a boost loss of 2psi, for this to occur you would have to be losing 22CFM. The size of the leak would have to be the equivalent of an 8mm hole (derived from standard flow tables), which is pretty large.
So if you pull your aftermarket BOV off and find that putting a vacuum pump or compressor on it results in a few bubble coming out of it, you shouldn’t immediately panic. As I mentioned before, your boost control solenoid leaks in order to control boost (which is approximately equivalent to a 1mm hole), and if the leak you find on a BOV is similar, then you can be pretty sure it’s not costing you power. If on the other hand you could comfortably and constantly draw breath through it without suffocating, that’s a different story.
If you suspect a BOV leak IS causing a loss of boost/power, the only way to actually PROVE the BOV is the cause is to plug it up. You could perform a smoke test, you could put the car on a dyno and feel around for air leaks from the BOV under boost conditions, you could hook up a sophisticated air mass sensor in the BOV outlet to measure the air loss, but all of these tests either do not show magnitude, or are not feasible for most DIYers. Plugging off the valve and going for a lap around the block to measure boost is the simplest way to confirm the answer. One or two squirts without the BOV working won’t kill the turbo.
Finally, another point about performance. Fitting a GFB valve can give you a small but noticeable improvement in throttle response. The difference in the way the factory valve works compared to a GFB valve can be summed up as:
A factory valve is typically open until required to shut, whereas a GFB valve is shut until required to open.
This means that boost pressure can be made and held in the intercooler during conditions under which the factory valve would normally vent. A good example would be mid-corner, when modulating the throttle to balance the car – under light throttle, when the manifold is still slightly in vacuum, the turbo is capable of making boost, but not with the factory valve since it would be open under such conditions. A GFB valve on the other hand would be shut, the intercooler would be in boost ready for the throttle to open. The result is a quicker rise to peak boost when you do snap open the throttle. Connect your boost gauge prior to the throttle and you will see this effect.
In summary, atmo-venting BOVs aren’t “bad” for your engine. A correctly set-up GFB atmo-venting BOV should not cause any driveability issues, and does offer the benefit mentioned above. If anyone does have driveability issues with a GFB valve, I would invite them to speak to us about it and we can help.
How do I set up my BOV to not leak/stand less chance of leaking?
Read the BOV manual/instructions first off. Learn how to adjust it. If it doesnt have a manual, just look at the valve. You can almost always figure out how to adjust it. Some have screws, some use washers under the spring, others use replacement springs. Now that you know how to adjust it, here is what you do:
First off, start the car, get out and open the hood. If you can see the piston of the valve (look in the hole it vents out of if its a VTA valve), check to see if it is moving at all at idle, or worse, partially open. You want that piston rock solid, not moving at idle.
Now give it a little gas. It shouldnt move when you step on it, and when you lift, it should pull up a bit. Depending how hard you hit the gas, it will either JUST move, or fully open.
If its doing anything but what it should be, adjust it a little tighter.
Now go drive the car
When you shift at light throttle, is it venting? If so, is it a pure straight vent, or do you get a little bit of a "chufchchchc" noise right before it vents? That noise is compressor surge. Which isnt as bad as some people like to think and say. Ideally, you are looking to hear a little surge then a vent. Or no sound at all. Either is ok. Now drive it hard, does it surge a little or just straight vent?
Get out of the car and tighten the valve and drive it again. Repeat this until you get a LOT of surge when you lift under boost. Now start loosening it until you JUST start to hear almost no surge.
What the surge means is that it fought opening just a little bit. If you hear a LITTLE surge just as it begins to vent, that means that the valve is holding itself shut as tightly as it is capable of, without being so tight that it doesnt vent properly.
Learn stuff - DV (Diverter Valve or Blow off valve) and ADR's
This was originally posted to the XR6 Turbo fprum in Australia in Feb 2009 in rsponse to questions about the GFB Stealth FX product, its fitment to the Falcon XR6 Turbo and the imploications ot ADR's (Australian Design Rules) a the time.
We think that there's some stuff here that might be useful and relevant to all BOV applications and fitment on turbo cars both in Australia and elsewhere.
In regards to the initial question asked, the GFB Stealth FX is available in a direct bolt-on configuration, part # 1013. The good news is no mods or changing of pipe required, and you can turn off the sound if you need to.
As has already been covered, the XR6 uses a MAP sensor, which means atmosphere venting with a BOV has absolutely no effect on AFRs. Regarding the laws, here’s the tricky part. The main thing is the ADRs – all cars need to comply to the relevant ADRs (Australian Design Rules), and whilst in theory it would be possible for an XR6 to pass these tests (both drive-by noise and exhaust emissions would be tested), the road authorities will typically label pretty much any aftermarket part that has not been ADR approved illegal. Why don’t we get ADR approval? The tests are prohibitively expensive, and need to be conducted on every single type and variant of car that the product could possibly be fitted to. The costs would run into tens and possibly even hundreds of thousands.
So we have the ADRs, then we have the local road authorities, who will usually say things like “atmosphere-venting BOVs and exposed air filters are illegal” as a blanket rule, to make it easier to enforce since they will not send a car to an ADR facility for testing. Interestingly, in NSW the RTA have two dynos available as a free service to conduct an internationally-recognised emissions test called the IM240 – it measures emissions through a set procedure of simulated road driving. Even on a car with an airflow meter (a WRX), GFB have proven that the Stealth FX set to atmo venting does not cause any measurable emissions changes according to the IM240, and the Stealth DID vent during the test.
So we could probably get the XR6 through ADRs, it would definitely pass a local road authority emissions test, but what next? The police has complete discretion over the issuing of vehicle defects. This is not to criticise the police force in any way, because it would be impossible for them to know the specifics of every type of vehicle modification – find me someone in the vehicle modification industry that knows this – however it does mean that EVEN if you had an engineer’s certificate, a copy of a passed emissions test, and an ADR approval, if in the officer’s opinion your modification is illegal, they can defect you. It is up to YOU to argue otherwise. This is simply the risk any person who modifies pretty much ANYTHING on their car takes. In my experience, driver attitude has a lot to do with it! If you give the cop attitude and wave a certificate in their face and scream at them to go buy some donuts, or that you pay their salary, or that you’ll have their badge, you’ll probably get done . On the other hand, I’ve heard of some pretty insignificant things get defected – such as an empty windscreen washer bottle on an otherwise brand new and un-modified car – the ADRs include things like this.