Two Guys Rally

Camshaft Timing [ November 14th, 2008 ] By:Mark Ozimek

I found out recently that Volvo was generous enough to include adjustable camshaft gears on both the intake and exhaust camshafts in my car. Realizing that I really don’t know a whole lot about how the valve timing, I did some research on the matter. I’m not going to go into things like lift, duration, and cam profile too much today, and wait until I understand how all the factors interact well enough to write about it.

To set things straight, you don’t really gain or lose power when you change the valve timing, unless you change it so far away from the “optimal” spot that the engine can’t breathe properly.

Most modern engines have two camshafts, one for the intake and one for the exhaust, and they can be adjusted independently. This setup makes things pretty straightforward:

Adjust the intake to put the power band where you want it. Advancing the timing will “move” the torque lower in the RPM band, to make less peak horsepower, but greater power when in the low end to midrange. Retarding the timing will do the opposite, and will generate more peak horsepower, but at the expense of power in the low end.

Changing the exhaust camshaft will do the same thing to a lessor extent, but changing the timing between the exhaust and intake changes the overlap. For this part, I’m going to assume that you have a turbocharged car, as it significantly affects how much overlap is desirable.

Less overlap (advance the exhaust more than the intake) improve how well the cylinder fills with air in the upper RPM range and/or at high boost. It can also smooth idle some, depending on how it was configured before. One serious downside is that it raises the engine RPM needed to generate boost.

More overlap increases the amount of exhaust gas recirculation which reduces power a bit, but also lowers the temperatures, allowing for more aggressive ignition timing. Too much overlap creates an over-scavenging condition where a portion of the intake gasses flow right through the cylinder and out the exhaust to create a lean condition which would increase cylinder temperature. Alternately, under high load, the exhaust back pressure is much higher than the boost pressure due to the inefficiencies of the turbocharger, and the exhaust flows back into the cylinder.

All in all, overlap is a bad thing for an engine with forced induction, but if you’re messing around with it, experiment to see what gives you the best compromise between low end and high end power, fuel economy and smoothness. If there was a dyno I could use to test out a bunch of things, I would show how the shape of the power curve changes with different camshaft timing setups, but unfortunately, like many other things, that will have to wait a while.

I’ll be back with a part two of this article sometime in the future, so stay tuned!

WRC Japan Results [ November 6th, 2008 ] By:Mark Ozimek

Something slightly different this time around! Hirvonen stayed in first place from the start to the final stage of the rally. This bumps his overall score up to 102. Latvala came very close to taking the lead by the 25th stage, but stayed in second place. Loeb, the current points leader at 112, took third.

Hirvonen is catching up to Loeb, however, with one race left, there is no way that Hirvonen can pass Loeb to take the lead, so congratulations to Loeb for being the only one to win 5 championships! So, the battle is going to be for the 4th place position between Latvala and Atkinson, both with 50 points, and potentially 3rd, currently held by Sordo with a 9 point lead over 4th and 5th.

As always, WRC.com has their own highlights video that sums it up pretty well:

I also found a video of Solberg driving the shakedown run in the stadium. The concrete floor looks like a lot of fun to drive on! Quick warning, it’s much louder than the previous video.

To those in the USA [ November 4th, 2008 ] By:Mark Ozimek

Go vote!

—- 11:46 PM EST (an update)—–

So Obama is being projected as the next President of the United States of America. Congrats are in order to him. Both PA and VA voted for Obama, which happen to be our home states (NY is where we go to school). So do we get some sort of prize for that? That would be nice.

I wonder what four years of Obama will be like. We shall see!

The Volvo Chronicles: Solved It! [ October 30th, 2008 ] By:Mark Ozimek

So this should be the last chapter in the long saga I’ve had in trying to find the missing power in the upper RPM range of my S70. I’ve tried a lot of things, from doing some temporary testing with the downpipe loosened to check for catalytic converter blockage to replacing the compressor bypass valve diaphragm.

In my last post, I mentioned the turbo control valve (TCV) as the next part that I was replacing. For those of you who don’t know, the TCV is a little solenoid that controls the opening of the wastegate. In the case of the Volvo, there is no pressure sensor after the turbo (MAP sensor), and the boost pressure is calculated using the airflow values from the MAF sensor and the engine rotation speed. I believe the target is 0.7 bar, or 10.2 psi.

In order to keep the boost in check, the ECU uses the TCV to force air from the compressor housing into the wastegate actuator, opening up the wastegate. This allows air to bypass the turbine wheel, reducing the rotational speed, and dropping boost. I found a nice diagram of the turbo and associated parts:

The TCV is circled in red. As you can see from the hoses, the TCV simply allows or blocks air from going to the wastegate actuator. Since the air is coming from the turbo, it can be a little dirty, some excess oil from the crankcase ventilation and the turbo itself. This contaminates the solenoid over time, causing it to respond slowly, and sometimes outright fail.

So, if the TCV gets contaminated or fails, it won’t be able to maintain the proper boost levels, causing the performance of the engine to drop. One option is to do away with the TCV all together and put in a manual boost controller, which is basically a spring loaded valve that opens to open the wastegate at a certain pressure. Although you can use this to bypass the ECU’s control of the boost pressure, and potentially increase the boost higher than stock, you run the risk of overboosting and causing damage.

Anyway, I replaced the TCV, and everything is good. Power is strong up until I reach redline, whereas before it was falling flat past around 5,000 rpm. So at last, my search is complete, for now.

One interesting side note is that there used to be an interesting hesitation around 1,500 rpm in 1st gear, when pulling away from a stop. This no longer happens. I cannot figure out why this is, since the turbo is making no boost at this point. I’m certainly not complaining, since I love smoothness and predictible power response, however, perhaps one of you has an idea why this is happening?

The Volvo Chronicles: CBV Diaphragm II [ October 16th, 2008 ] By:Mark Ozimek

It seems like all I post about these days is my own car. Hopefully Charles and I will get our hands on a rally car to work on, but for now, the Volvo will have to do as my source of entertainment. Anyways, a long while back, I ordered a CBV diaphragm to replace the old one in my car that I had suspected to be worn out and torn, allowing boost pressure to leak out.

I finally got around to replacing it last weekend. The old diaphragm was in much better condition than I thought it would be, however, the rubber was definitely worn. The sealing lip that gets compressed against the turbo was leaking, creating the huge mess on the turbo:

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However, there was something very significantly wrong. The hose that leads to CBV that supplies pressure or vacuum depending on throttle position had torn almost all the way off. Unfortunately, I missed this when replacing the vacuum hoses, so a new hose got put on with the new diaphragm.

After driving it for a week, there is a pretty noticable difference in power in the mid rpm range and top rpm range, though more in the mid than the top, which is opposite of what I expected. The turbo flows more air at higher rpm, so perhaps the leak, which would remain constant due to constant pressure, became less and less noticeable.

So in the end, the top rpm range still isn’t making the power it should, and I need to figure it out still. I have a new turbo control valve (TCV) that controls the wastegate actuation on the way, and I’ll try that out too. If the stock unit is fine, the new TCV has improved response over the OEM unit. At the very least, it should be able to control boost more precisely.

However, an important lesson can be learned from all this: Turbochargers are complex systems that have many parts to wear out and cause poor functionality. In a rally car, these components wear quickly due to the demanding conditions, so make sure you stay on top of the little small things in your car!

Another Reason to Strip the Interior [ October 7th, 2008 ] By:Mark Ozimek

Rattles.

Yes, you heard me. Rattles. Many people take out the interior of a rally car to make it lighter, but there are other unexpected benefits from doing so.

In a car that is flying over rough terrain all the time, all those plastic and metal parts inside the car have a tendency to vibrate loose. Clips wear or break, panels sag, screws come out, and so forth.

While this may not seem like a big deal, the resulting noise can be pretty distracting from listening to the normal sounds your car should be making. Worst case scenario, a piece breaks free and is floating around the cabin in an attempt to beat you and your co-driver up.

Why do I bring this up, you may be asking yourself. I tend to enjoy talking about things related to my own life, and in this case, it’s still my S70. The firmer suspension I put in a few weeks ago is starting to bring out a miniature chorous of fun sounds when I’m driving over rough roads. The Volvo has always made a few noises here and there, which is expected for a 10 year old car with 150k miles on it, but now it is distinctly noticable, and will take some getting used to because gutting my daily driver isn’t really an option for me!

So for those of you considering removing the interior of your racing car, you now have a bit more motivation to do so.

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?

Why Are Superchargers So Rare? [ September 24th, 2008 ] By:Mark Ozimek

One thing that I’ve noticed a lot is that rally cars seem to use turbochargers almost exclusively over their supercharger counterparts.

I have gone into detail on turbochargers in the past on how they work, and why they’re used to increase the amount of power an engine puts out. What is different about a supercharger? Well, both compress the intake air to increase power, but the supercharger’s compressor is driven mechanically (usually a belt off the crankshaft) instead of by the energy in the exhuast gas. So instead of reducing the efficiency of the engine by increasing exhaust pressure, energy is taken directly from the engine to increase power.

There are some plus sides to this, mainly no lag in waiting for the compressor to spin up. The compressor speed is directly related to the engine speed. This predictability makes design simpler, and the engine’s power response much more consistent.

However, ultimately a turbocharger setup can make more power with a similar amount of weight added to the car. The pressure increases non-linearly with engine speed, and can hit a high pressure before the supercharger would.

Each setup has it’s pros and cons, but to me, it seems like turbochargers are winning in popularity by a long shot. I know Charles and I both prefer turbochargers, and own turbocharged cars, mainly for the power efficiency and fun torque curve. Which do you prefer, turbochargers, superchargers, or even normally aspirated, and why?

The Volvo Chronicles: Parts Installed [ September 17th, 2008 ] By:Mark Ozimek

Unfortunately, it was raining over the weekend, so I had to delay the suspension work I had planned for the car. It was a really nice day yesterday, so I took the day off to have a full day in case something went horribly awry and I needed to go get more parts (I did, hahaha).

Unfortunately Charles had class for most of the day, so he wasn’t able to help me. No worries, as my tool selection really only allows one person to be working at a time, he would have just been sitting there and watching me and taking pictures.

One piece of advice, make sure you have all of the tools you need before you start. I thought I did, but it turns out that the jack stands were with Charles, and the spring compressors I was using for the struts required a 15/16th inch wrench, which I didn’t have, and required an emergency trip to Sears to get it.

Everything went more or less smoothly. I wasted some time on a few silly mishaps, like forgetting to put the dust boot on the first strut until I had decompressed the spring and had the strut assembly all together. This required taking the whole thing apart and getting the whole strut assembly into pieces so that I could get the spring seat out again to put the dust cap underneath it. Not a big deal, but annoying.

Before and after shots, since the springs I used lower the car about an inch to an inch and a half.

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And some pictures my lovely assistant, Sarah, took when she stopped by to see how things were coming along.

So now I get to play around with the shocks, since the rebound damping is adjustable, meaning the amount of resistance to the expansion of the shocks. This should have some interesting implications on the way the car handles, but I want to get used to how it feels now, since the difference is huge compared to the wallowy stock setup. I’m sure I’ll collect some data in true engineering fashion and post my findings from changing the suspension settings.

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…

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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.