Two Guys Rally

Update on New Suspension Parts [ October 2nd, 2008 ] By:Mark Ozimek

I wrote about changing the suspension parts in my S70 a while back due to the damage from the rallycross Charles and I went to. Now that I’ve gotten a little bit of road time and testing with the adjustable shocks, I want to share my findings.

One important thing to keep in mind is that the Koni shocks I got are only rebound adjustable. The resistance to compression is fixed. This means that when they are set more firm, the car has a tendency to get lower over bumps, since the suspension takes longer to expand.

As a fairly obvious trend, the stiffer the setting on the shocks, the slower the car rolled. Hard corners were more predictable on smooth surfaces, but less predictable on rough surfaces. Acceleration and shifting feels much more solid, and really enjoyable.

Overall though, the ride quality near the hardest setting is just too harsh. Althoug the car does roll more with the softer settings, the improved traction on rough surfaces (which Rochester has a lot of) makes the tradeoff worthwhile.

Although I haven’t taken it to an actual race track, this general trend makes me suspect that the firmest setting would be ideal for track use, and the softest setting for rally style environments. Having more total suspension travel would be very nice for rally too, but I made the decision to keep the Volvo on the street, so I’m not too concerned about that.

A question for those of you with rally cars that have adjustable shocks, where do you prefer the damping firmness to get the car to handle the way you like?

The Volvo Chronicles: New Parts! [ September 11th, 2008 ] By:Mark Ozimek

As Charles mentioned the other day, the rallycross was pretty tough on my suspension. There were a few dips in which my suspension bottomed out going over it, and I’m sure the OEM dampers were having a tough time dissipating all the heat that the roughness was generating. Somewhere in all the chaos, the dampers broke. The rear dampers are not damping suspension travel at all, one of the front struts is making an awesome grinding noise, and the other is also not damping.

Tough, but it’s a reality we all face in rally; off-road surfaces are hard on cars, and you need durable parts engineered to take the abuse if you want to keep stuff around for more than a few races. In my case, it’s not really a big deal. I was aware that the dampers were degrading, and I have suspected them to be the same parts that were on the car when it rolled out of the factory in Sweden. Both rear dampers were leaking oil, and I’m sure the fronts were close to being in similar condition.

So I ordered some replacement parts, and decided to go more for better road handling than off-road handling, seeing as it’s a Volvo that really belongs on the highway at speed, not pitching around slow hairpins in the wet grass. I’m sure I’m not the only one, but I get really excited when big packages arrive in the mail! Looks like my kitty also gets really excited about packages too…

(click for larger picture)

H&R springs, should stiffen up the car a bit around turns and over bumps. There are also some Koni Sport dampers still in the mail that will hopefully be here tomorrow. I’m really looking forward to those, since the damping rate is adjustable, I can play around with it to see what firmness level gives the best handling. With 205-55-16r tires on the car, I’m suspecting I can get away with going pretty stiff before it becomes unreasonable.

However, over rough surfaces, stiffer is not better, since it reduces the amount of time the tires are in contact with the road when the surface suddenly changes height. The stiffer dampers will slow down the speed of the wheel significantly, but on the flip side, the stiffer springs will push harder against that damper to make the tire move faster.

There are a lot of things to consider when getting springs and dampers. Without delving too much into the mathematics behind it, a car can be modeled as a mass+spring+damper system mathematicaly. Solve a few second order equations and you can calculate things like the oscillation period, transient response, and all sorts of other neat things to try to match a spring rate and damping rate to your particular vehicle and preferred handling.

Really, there are three scenarios that occur, overdamping, underdamping, or critically damped. The latter is really hard to achieve, but it’s not difficult to get close. Here’s a relatively complicated picture for those uninitiated with system dynamics, stare at it for a while and try to make sense of it all, I’ll do my best to explain each one.

Underdamping is when the spring rate is too high in comparison to the damping rate. Most cars are underdamped, as this provides a more comfortable ride, and good traction in most conditions, despite the poor response time However, when the car is too underdamped, it will become uncomfortable and uncontrollable, as the car will be bouncing for a long time after hitting a bump. Think of your Grandfather’s old old Caddilac here.

Overdamping is the opposite, the damping rate is too high in comparison to the spring rate. This is bad because it puts a lot more strain on the suspension mounting hardware, as the bumps are barely absorbed by the suspension and is translated into chassis movement instead. This means that a moderate bump can cause your tires to be airborne for a moment. Obviously not good unless you’re racing on a really really smooth surface.

Critical damping is when the movement stops in the shortest time possible, technically the ideal balance between the spring and damping rates.

So which one is best? It really depends on a lot of things. Smoother surfaces can use higher damping rates to trade a little bit of traction for better response, while rough surfaces can do the opposite. the amount of suspension travel you want, the geometry of the suspension, the weight balance of the car, and even the driver’s preference all matter towards making the optimal setup for performance, or in some people’s case, comfort.

Personally, I am based towards critical damping, but only from a theoretical standpoint. More experience with suspension setup may change my opinion. Until then, I’ll just have to play with what I’ve got and make the most of it.

The Volvo Chronicles: Worn Suspension Parts [ July 14th, 2008 ] By:Mark Ozimek

Since there are more things going on with my S70 T5 than just some missing power, I decided it would be wise to just label everything that relates to my car the same way. After all, it’s a ten year old car with 150,000 miles on it. Things are gonna break, and I’m gonna have to replace stuff and write about it.

So what happened this time? Well, I had to get my car inspected, in order to remain road-legal. So I drop my car off at a local mechanic in the morning. After a few hours, I get a call from the mechanic, informing me that my inner tie-rods had too much play in them, and he couldn’t pass the car as it was. In case you are unsure, the tie-rods are the beams that connect the steering rack to the wheels so that you can turn the car. They have to allow movement in a few axes to account for turning and suspension travel. The parts the rub together are usually the parts that break after a while. If you break the rod itself, I’ll be very impressed.

Suspicious, because I never noticed excessive slop in the front end, I went down to check it out, and sure enough, there was a lot of play. I don’t know exactly how much is passable, but the wheels were pivoting about the vertical axis enough to move the front and rear parts of the tire tread around 3/8″ to 1/2″ on the driver’s side, a little less on passenger.

I give him the go ahead to replace the inner tie rods, and asked him to change out the outer tie-rods too, since it’s only 5 minutes of extra work once you’re in there. If the inners are worn out, the outers are likely to be pretty bad too. Unfortunately, since the car was already in the shop, and I was on a tight time schedule, I didn’t do the work myself. It’s not a very hard job, just somewhat time consuming, and you should get an alignment afterwards.

Curious to see how much of an effect the worn parts had, I took the car out for a spirited drive afterwards. The difference was almost surprising, especially over rough surfaces. I had never thought about it before, but when turning on a road that has bumps, or is generally rough, my S70 made some clunking noises, and tended to skip sideways every now and then.

Now with the new tie-rods, the car was much more settled and predictable, and a few of the clunking noises I had grown accustomed to and thought nothing of had disappeared. Of course, it wasn’t all better, since all the other bushings and ball joints are probably pretty old too. Someday I’ll have to take the time to rip apart my suspension and replace all the other worn parts.

Moral of the story? Check the amount of play in the suspension part joints, even something that was relatively unnoticeable could actually be a pretty serious issue!

Performance Loss Hunt: Part 3 [ July 8th, 2008 ] By:Mark Ozimek

A while back, I made two posts about my car, and how there is a lack of power in the top end compared to what it used to feel like. I verified that the exhaust isn’t causing significant restriction and that the turbo is making about as much boost as it should be.

Since this is turning into a guess and check thing, mostly because my car is 10 years old and has almost 150,000 miles on it, and I don’t know how it was treated for the first 130,000 miles of its life, I said “To hell with it”, and ordered two things that I highly suspect to be contributing to the problem: Vacuum hoses and a CBV diaphragm.

Unfortunately, the vendor I’m getting the CBV diaphragm from does not have any in stock, nor does anyone else that I could find, replacing that part will sit on the back burner for now.

The silicon vacuum hoses from StylinMotors came in the other day, and sat in a corner of my apartment until I had the time to start ripping junk out of my engine compartment to get access to some of the hoses. Thanks to Independence Day being on Friday, I got a three day weekend to have fun. First order of business was figuring out what each hose does, and where it needs to attach to. Ideally, I would be able to just take one hose out, cut a new one to match and install. Knowing what everything does is something important to me, so I couldn’t make it that easy for myself.

After a couple minutes of fun wrestling with worm gear clamps and torx screws, the engine compartment of my S70 looked like this:

(click for larger image)

Although it looks like a disaster, all I really did there was take out the intake filter box and two intercooler pipes that were in the way of some hoses I needed to get to. Judging from the hose clamp style, the hoses are the original parts that were on the car when it rolled off the factory floor.

After prying the clamp off, I found something quite comical and frustrating at the same time. The hoses had rotted into place! I had to cut off every single hose I changed, since they would not come off any other way. Unfortunately, this meant that some of the hoses that are in tight spots did not get changed, since I couldn’t fit my knife into the area. I still plan on changing them though, I just need to remove more parts that get in the way.

Afterwards, the hoses in that picture had been replaced with silicone parts:

While changing out hoses, I found something very interesting. In the first engine picture, there is a small white thing on the very left edge in the center of the picture. This is a check valve that only allows air to flow in one direction. That hose comes from the intake manifold and leads downward to a T junction. The hose going to the right has another check valve, and connects to the intake hose just before the compressor inlet. The other hose goes to a solenoid that is part of the onboard fuel vapor recovery system.

Since the check valves are aligned in such a way to only allow air to be pulled out of the solenoid that is attached to a carbon filter, a broken valve from the intake manifold means that boost pressure can leak out of the intake manifold to before the compressor inlet or into the carbon filter. Both of these are things that should be avoided due to loss of efficiency and contamination of the fuel vapor recovery system.

Either way, I replaced the hoses I had relatively easy access to. Some will require the removal of the intake manifold, another is attached to the compressor housing, which the bottom part of the intake hose blocks, there is even a hose that runs over the top and back down to the back of the engine to the fuel pressure regulator. I’ll try to address the rest of these when the CBV diaphragm comes in.

So with all that said and done, did it fix the problem I’ve been seeing? Well, no. It actually did some things I didn’t really expect. Acceleration from a stop is now much smoother and more consistent as the engine speed increases. Fuel economy on the highway seems to have gone up by one or two MPG, but it is still too early to tell for sure. The most interesting is that the brakes feel much more responsive now. My suspicion is that there was a/some vacuum leak(s) that allowed air into the system causing minor problems, but not enough to make the ECU freak out. Knowing that is more motivation to go back and replace the rest of the hoses, since they surely have leaks too.

However, the top end power is still lacking, so the hunt to restore my engine to normal continues! I was joking with Charles earlier that I’m probably gonna replace everything under the hood short of the engine itself before I fix the problem.. I suppose time will tell. Until then, remember that preventative maintenance is the best thing to do to keep your car performing as it should.

Hunting for Performance Loss Causes [ May 20th, 2008 ] By:Mark Ozimek

Recently I have noticed a lack of power in the upper RPM range of my S70. Considering that it is now 10 years old and has just over 146k miles, I’m sure there are a whole bunch of things that are causing problems in one way or another, from dirty fuel injectors to leaks in the air hoses. Part of being a good driver or co-driver on a rally team is being able to quickly and accurately diagnose faults with your car that impact the performance. Also, being the engineering oriented car enthusiast that I am, I like knowing what is going on under the hood of my car.

So immediately, there is a list of probable causes to this performance reduction.

1. A hole or tear in an air hose.
2. Compressor bypass valve (CBV) failure.
3. Turbo control valve (TCV), AKA boost control solenoid (BCS) failure.
4. Significant restriction in the exhaust system.

A hole or tear in an air hose can cause a vacuum or boost leak, depending on where it is. This will cause the reading from the MAF sensor to be incorrect, and will throw off the base pressure upon which some of the turbocharger’s boost control devices operate on. A significant leak will cause the ECU to throw an error and turn on the Check Engine light, as well as significantly decrease fuel economy, neither of which have happened, so it’s actually rather likely that this isn’t the cause.

The compressor bypass valve (CBV) is a known weak spot, being integrated into the compressor housing, it has to endure a lot of heat and vibration. Tears in the valve diaphragm develop over time and allow air to circulate back to the compressor inlet when the engine is under load, which we definitely do not want.

Another part that is known to fail on this car is the turbo control valve (TCV), or boost control solenoid (BCS). Either name works, they’re the same thing. It operates based on a duty cycle from the ECU and the pressure difference before and after the compressor, and sends the ‘resultant’ pressure to the wastegate actuator to control the boost pressure. If this solenoid is stuck open, the wastegate will open before it should, and the turbo will never develop significant amounts of boost.

A restriction behind the turbocharger can also cause a significant performance decrease, for example, the catalytic converter failing and clogging up. Any backpressure on the turbine wheel increases how hard the turbine must work to generate a certain boost level by a lot, so this is also a sensitive spot. It is also the easiest to check for, and is what I am doing today.

As you can see, it is most likely related to the turbocharger. Unfortunately Volvo did not see the need to include a factory boost gauge in the instrumentation cluster, nor do I have a gauge on hand to test to make sure the pressure is at 10 psig like it should be.

So, with limited diagnostic resources at hand, there are really two choices I have; Check for leaks, or see if there is a restriction in the exhaust. I decided to check for the latter, since checking for vacuum leaks would entail replacing hoses to see if anything changes, and I do not have appropriate hose with me.

Starting off, there is a nice heat shield around the exhaust manifold and turbocharger to keep the engine bay temps down a bit, so I’ll remove that to get to the downpipe which I will unbolt to allow for gas to flow directly out of the turbine housing, bypassing any restriction. Be sure to do this work when the car is cold, as the exhaust system can get VERY hot.

Now with the heat shield out of the way, I have access to the bolts holding the downpipe on. A 13mm socket fit perfectly. After loosening the bolts, I pulled the downpipe off the turbo outlet flange:

After pulling it back enough to create a significant gap, I started the car, and went for a short test drive. I could tell that a significant amount of air was bypassing the exhaust system through that gap from the sound of the air blowing through, and the exhaust smell in the cabin. I ended up opening the windows to get some fresh air, since carbon monoxide poisoning sucks.

After doing some hard acceleration after the car had warmed up, I found that there was very little difference in the performance of the car. It had become significantly louder though, quite similar to the sound of a diesel truck, and surely in violation of noise ordinances. Fortunately, that rules out restriction in the exhaust causing the performance issues, since it would have been an expensive fix, working against the money Charles and I are trying to save up for the rally car. So I put everything back together. Always make sure to use proper torque for tightening things up in the exhaust to prevent leaks or cracking. Volvo specifies 30 Nm of torque for the downpipe bolts.

Before putting the heat shield back on, I decided to investigate two of my other leads: the CBV and the TCV. The CBV is totally caked in dirt and oil, which makes me highly suspicious of a leak there. The only way to find out if it has failed would be to replace it, which I plan on doing since it is an inexpensive part.

The TCV was harder to look at, since it was hiding underneath the air intake hose. It did appear normal aside from the electrical tape, but looks can be deceiving, so this is next in line if replacing the CBV diaphragm doesn’t do anything.

It looks like I need to brush up on my diagnostic skills a bit, since I was not able to find the fault in an afternoon’s work. When I find out what is wrong, I’ll post a guide on what happened and how to fix it, since boost related performance issues appear all the time on turbocharged cars as they age.