Two Guys Rally

Volvo Project - Part 1 [ January 31st, 2011 ] By:Mark Ozimek

Being an engineer that always wants more power and likes wrenching on things can be a dangerous combination. Dangerous enough to allow one to decide that it would be a wise idea to start an engine build for his Volvo.

Last summer, I came across a great deal on a used engine out of a 2002 C70. It is a 5 cylinder 2.3L engine, basically identical to the engine in the S70, with a few changes to parts here and there that come from the advancement in technology over a couple of years. I tell the guy I want it, and behold, it arrives a week later:

It has the same 81mm bore, 90mm stroke, 4 valves per cylinder, but comes with a head that has more optimized port geometry for better combustion and a modest increase in flow. The cam geometry also changed, the exhaust cam got a VVT system that operates off oil pressure from a solenoid valve, both cams got a bit more lift and duration. Both good things for trying to get air to flow through the engine.

The overall plan is pretty simple at first glance. The engine has a turbo from the factory, but it’s a pretty small Mitsubishi TD04HL-16T. I wanted a bit more power than that, and I don’t mind waiting a bit longer for boost to avoid killing torque as the engine speed climbs. Between me being very indecisive on what I wanted out of the project, a lot of deliberation, a fair amount of math and “estimation” and some new product launches, I have settled on what the project should evolve to be.

While all that was happening, I was having fun getting my hands dirty and pulling the engine apart while it was still warm out.

Oil passages for the VVT gear that is inside the exhaust cam you see on the left side of the engine above:

A look into the head ports before any work has been done:

Combustion Engine Theory: Intro [ March 29th, 2009 ] By:Mark Ozimek

I was thinking the other day (rare, I know) it’s about time that I started up another interesting series. How about something that is at the heart and soul of almost every motorsport: The engine!

This is just the introduction to engines, I’ll cover the common terminology and give everyone a good starting point for understanding the finer design choices that I will cover later on.

Most automotive racing is powered by internal combustion engines. There are some variations within there to make things interesting. There are usually either two stroke or four stroke engines. I’m gonna focus on the latter, because two stroke engines are basically non-existent in rally. In four stroke engines, there are… wait for it… four strokes!

• Intake: The piston is moving downward, away from Top Dead Center (TDC) with the intake valve(s) open and the exhaust valve(s) closed. This draws in fresh air/fuel mixture to burn later.
• Compression: Intake valve closes, usually just after Bottom Dead Center (BDC), and the piston moves up to compress the air/fuel mix. Just before TDC (usually 10º-40º of crankshaft rotation), the combustion begins, either by igniting the fuel with a spark (gasoline) or injecting the fuel into the compressed air (diesel)
• Expansion: This is the stroke where the power comes from, the burning air/fuel mix generates a lot of heat and pressure that pushes the piston down, generating torque.
• Exhaust: Just before BDC, the exhaust valve opens up, and the piston moves back up to push all of the burnt gasses out of the engine. Once it reaches TDC, things start over again with the intake stroke.

The next choice is the type of fuel. Diesel engines run by compressing air a lot to generate very high temperatures, then inject the fuel, which combusts to generate pressure and heat that drives the engine. Spark ignition engines run a bunch of different fuels, usually gasoline, but can also include mixes of gasoline, ethanol, methanol, propane, compressed natural gas, and a few others. The air fuel mixture is ignited with a spark instead of relying on the sheer amount of heat in the diesel cycle.

There are also variations of the typical reciprocating piston engine, the most common being a rotary, or Wankel engine. The piston is replaced by a rotor with three faces housed inside of an oval-like housing that is technically known as an epitrochoid. Rotary engines have a very high power/displacement ratio because there are three power strokes for every revolution of the rotor, compared to the one power stroke every two revolutions of the crankshaft of a normal four stroke piston engine. However, sealing and lubricating the piston is a significant issue that hampers the reliability of this design

So now that this is out of the way, it’s time to get into the common terms used when describing or talking about engines. Let’s start at the macro level, things that everyone should be familiar with and move our way in.

Displacement: The amount of volume that all of the pistons displace in one stoke. This is dependent upon the number of cylinders, the bore and stroke.

Bore: The diameter of the cylinder when viewed from the top. The piston diameter is a small amount less than this, with rings to provide a good seal

Stroke: The distance the piston moves from TDC to BDC. This is dependent upon the crankshaft dimensions.

Compression Ratio: The ratio between the displaced volume (Vd) and the volume in the top of the cylinder (Vc) when the piston is at TDC. To calculate, CR = (Vd + Vc) / Vc.

Air/Fuel Ratio: Also known as AFR, or it’s reciprocal, FAR. Gasoline likes to burn within a specific range of ratios between the mass of air present and the mass of fuel present, typically between 8:1 to 20:1. the combustion can be considered the most “complete” when the AFR is stoichiometric (the wiki article does a better job explaining the chemistry than I ever could), 14.7:1 for pure gasoline, or ~14.2:1 for the 10% ethanol blend that almost all pump gas is now. This means that for every 14.7 kilograms of air that flows through the engine, the engine will try to supply 1 kg of gasoline. Ratios that are lower than stoich are called “rich”, and higher is “lean”. Given a constant set of parameters and optimized ignition advance, AFRs around 12.5-13 for gasoline give the most torque, because the fuel burns the fastest then.

Ignition Advance: Measured in the number of crankshaft degrees before the piston reaches TDC. Typically spark will be tuned to create maximum cylinder pressure around 14º after TDC. More advance is needed when the engine spins faster, because the burn speed of gasoline does not increase with the engine speed. However, the burn speed does increase with air density, and with AFR, with a maximum burn speed for gasoline being around 12.5-13. As such, timing is typically less advanced with more open throttle or higher boost pressure, but more advanced at higher engine speeds. Many design factors play a role in optimal ignition timing.

Volumetric Efficiency: This is essentially a measure of the amount of air that goes into a cylinder compared to how much a piston displaces. Since air is compressible, meaning the density changes with pressure, it makes more sense to think of it in terms of mass. A volumetric efficiency of 100% would imply that the mass of air that is in a piston is the same as the mass of whatever the displacement would weigh in the surrounding air. So taking the 100% efficiency example further, if it was a 4 cylinder 2.0L engine running at 100% efficiency at STP, the mass of air inside one cylinder would be equal to the density of air (1.184 kg/m³) multiplied by the volume (0.5L), the result is 0.592 grams of air. Doesn’t sound like a lot, but air is pretty light, and when you’re turning the engine at 6000 rpm, the engine is moving about 7 kg/min of air.

Mean Piston Speed: The average speed of the piston as it moves through a cycle. This is dependent upon the RPM (referred to as N in calculations) that the engine is running at and the stroke. To calculate, Sp = 2 * N * Stroke. Due to material strength and fatigue limitations, it is uncommon to see the mean piston speed exceed 25m/s or so, except in extremely high performance racing engines, like F1.

Brake Mean Effective Pressure: Commonly BMEP (or MEP when not measured at peak torque or power), this a way to measure how effective an engine is at making power in relation to it’s displacement and rpm. As a general rule of thumb, the more power you make per amount of displacement and the less rotational speed at that power level, the higher the BMEP is. Alternately, for those of you who know how torque, power and rpm relate to each other, the peak BMEP of the engine is at the peak torque of the engine. To calculate MEP, you need to know either the power and RPM, or torque, displacement, and number of strokes (2 or 4)

Calculating with power and rpm:

MEP = (P * Nr * C) / (Vd * N)

P is power, in HP or kW
Nr is the number of revolutions per power stroke, 1 for 2-stroke, or 2 for 4-stroke
C is a constant, use 396,000 for imperial (hp & ft-lbs) or 10³ for SI (kW & N-m)
Vd is displacement, cubic inches for imperial or liters for SI (61.02 CI per L if you need to convert)
N is the engine speed in RPM

Or with torque:

MEP = (T * C) / (Vd)

T is torque, ft-lbs or N-M
C is a constant, 75.4 for imperial, 6.28 for SI

Well, that’s it for the intro. I’m sure some of you have specific things that you would like me to go into detail on in this series, feel free to ask, and I’ll try my best to cover it!

Brake Dust vs Elbow Grease [ March 18th, 2009 ] By:Mark Ozimek

I was about to put my summer tires back on the Volvo today, but when I pulled the wheels out of the closet, I realized how dirty they are. I used the rain as an excuse to spend some time getting off some of the grime that had built up over the last 11 years and 150,000 miles!

Last fall, when I put the snow tires on, I tried to scrub down the inside of the wheel, and got a bunch of stuff off, but it still looked horrible:

So I made a quick run to a Pepboys down the road and picked up some Meguiar’s Hot Rim cleaning spray. It says to just spray on and rinse off. That’s a blatant lie. I effectively destroyed a sponge scrubbing all the crap off the surface. The spray really did help break down the baked on brake dust, and after rinsing everything off, that wheel now looks like this:

Much better! Not bad for about 10 minutes worth of scrubbing… hahaha. However, not perfect because quite a few of those black spots aren’t dirt, but damage to the surface of the wheel.

So why do this? Well, obviously it look nicer now. More practically, cleaning stuff off the surface prevents oxidation from occuring, and if there is too much dirt and grime, the balance of the wheel can be thrown off, requiring the wheel to be rebalanced to reduce vibration at high speeds.

Driving to Not Break Parts [ January 20th, 2009 ] By:Mark Ozimek

I came across some intruiging information earlier on the Nissan GT-R. While this may be old news to some of you, the gist of it is that Nissan is not honoring the warranty if the transmission fails after doing launches with the VDC off, and launch control on.

The GT-R has an interesting transmission, a computer controlled dual clutch sequential. So this means that Nissan has intentionally included a feature in their car that would void the warranty when used for anything other than getting the car unstuck from mud or snow. While this can be interpreted in a lot of different ways, it brings up an interesting, although blindingly obvious point to me.

Cars break.

The real question then is why do they break? For the average person, it’s likely due to improper maintainance, or simply normal wear and tear that takes out a component that may or may not be critical to the operation of the vehicle.

However, for people like Charles and I, and most likely you as well, we drive our cars hard. We expect the engineers who designed it to allow the car to be driven at full power and aggressively by including headroom in the strength and durability of critical components. But of course, even with that, there are things that you do that wear down parts, and will eventually break them.

Luckily, things are designed so that cheaper parts that are easy to replace take the brunt of the damage, protecting the more expensive components.

Aggressive turning will wear down suspension bushings, and tires a bunch. Hard shifting is hard on the clutch and engine mounts. Rough roads are also tough on the suspension bushings, and the dampers, and sometimes rattles the interior apart.

However, it’s not too hard to exceed the limits of some of these safety components and break something more important. For example, launching the car by dumping the clutch with the engine at a high rpm is very hard on the transmission, driveshafts, differentials, axles, and related bushings. It’s not uncommon for someone to break a differential gear or axle spindle when doing hard launches like so.

Something else transmission related that is hard to avoid is synchro wear. Synchros allow you to change between gears easily, and without rev-matching. In most modern manual gearboxes, the gears are always meshed together, but spin freely on a shaft. The gear is selected by engaging a ring, which then prevents the gear from rotating, and transfers the torque into the shaft. When engaging this ring, it needs to be spinning close to the same speed as the gear, or else there will be an awesome grinding noise and you won’t be able to select the gear. It is the synchro’s job to make sure everything is spinning at the right speed. However, the synchros wear out with use. Each gear shift puts a little more wear and heat into it. If you’re using the synchros a lot to make shifts that involve large RPM changes, they overheat and warp, creating a spot that rubs more than the rest, getting hotter and wearing faster, etc. So when downshifting, try to double-clutch whenever possible to reduce wear on those synchros! I know that was an awkward and cumbersome explaination, so I’m sorry, I’ll make a dedicated transmission post someday to explain it in more detail. However, we have made a video a while back on how to double-clutch if you’re not familiar with it:

In addition to that, there are plenty of other things. Keep the interior and exterior clean to avoid rust and damage to the finish. Don’t run into stationary solid objects. All those things that you generally can’t avoid when rallying, hahaha.

Not All Is Lost In Racing [ January 13th, 2009 ] By:Mark Ozimek

Or is it…?

I know many of you guys realize my love for all things Volvo at this point, but this is something pretty interesting to me, and is proof that you can turn almost anything into a race car if you want to. I happened to find out that a team, K-PAX/3R Racing, is entering into the SCCA World Championship with two Volvo S60s.

This news is pretty contrary to me, with major teams pulling out of racing left and right. For a while, the future of automotive racing was looking pretty bleak to me. But this reminded me of something that we said a while ago: Smaller teams stand a chance of doing really well, since it seems that many of the top competing teams are taking a leave of absense. This announcement is proof of that. Who would think the epitome of safety and (maybe undeserved from my perspective) sluggishness would find it’s way to the track in racing form?

So to all of you smaller teams out there: Pull through! The future of rally racing may rest on your shoulders at this point, and it is your time to show everyone what you are capable of.

Turbochargers! - Part 5 [ January 8th, 2009 ] By:Mark Ozimek

Welcome back to the turbocharger series. Today’s lesson should be short and sweet; It is going to address some misconceptions I hear about size. And no, bigger isn’t better. I know I have covered turbo sizing to an extent in the second part, but I feel that there are some things that I have seen recently that I must comment on.

The first of those is about something called “Trim”. I have seen this used time and time again as a size descriptor for a certain turbo. It is not! A single turbo has two trims, one for the compressor wheel and one for the turbine wheel. Usually it is used in reference to the compressor.

So what is trim? Well, if you have read part two, you may recall that it is a ratio between the inducer diameter and the exducer diameter, Inducer²/Exducer² to be specific. Now, take note of that. It is just a ratio, nothing more. Yes, it does change the flow characteristics of the turbo a bit, but it has no bearing on the overall flow capabilities of the turbo, nor it’s size.

With that off of my chest, there is one other insane issue that I see crop up from time to time. Compressor wheel upgrades. It is often viewed as a cost effective upgarde to rebuild an engine’s stock turbo with a larger compressor wheel, without changing the turbine side at all. In some cases, this is actually a good idea.

However, in the vast majority, the stock turbo has a smallish turbine side to produce boost lower in the RPM band. When an even larger compressor is hooked up to that turbine, some not so good things can happen. First and foremost is compressor surge. The turbine has the potential to spin the compressor too fast and generate more boost than the compressor is capable of handling at that airflow, which leads to surge, which is extremely bad for the turbine.

The second is something that I mentioned in part four: Exhaust backpressure. A smaller turbine will result in higher backpressure, reducing the overall efficiency of the engine, and increasing exhaust gas temperatures. In other words, the engine’s power is reduced somewhat because it has more trouble flowing air, and is more susceptible to damage due to the higher temperatures.

Moral of the story: Before upgrading a turbo, make sure that both sides complement each other well. Flow capabilities should be similar on both sides.

The Volvo Chronicles: Upper Engine Mount [ January 5th, 2009 ] By:Mark Ozimek

With a new year comes new car parts that need replacing! I probably mentioned it in the past, but I noticed that my upper engine mount on the S70 looks like someone took a chainsaw to it. As you can imagine, this isn’t a good thing. Worn engine mounts allow more engine vibration, which can lead to poor feeling shifting, accelerated wear on other mounts, and in the extreme case, weird handling quirks and reduced power.

To fix this, I got a solid polyurethane upper mount from iPd to replace the hard rubber OEM piece:

As you can see, the Volvo part looks somewhat abused… it was originally a one piece design! Installation was pretty simple, I only needed 13mm and 15mm wrenches, along with a hacksaw and screwdriver to cut out the retaining ring on the old mount (the alternative was a bushing press to push it out of the mount, something I don’t have).

Before and after shots of the engine mount in question:

After installation, I took the car out for a test drive. One thing that I found a lot of complaints about was the increase in cabin noise and vibration. Granted, I am hard of hearing, but I honestly can’t see why someone would complain about the nice growl that is added upon acceleration.

However, the noise was the second most noticable difference, right after the feel when shifting. The actual shift engagement feel did not change, but rather the way the power is transferred to the ground when the clutch is released. In comparison to before, it feels much more solid, and throttle response is slightly better.

Those are really the only two things I noticed. No changes in handling through turns, which makes sense because that mount is designed to not support any load from the sides.

The moral of this story would be to make sure you stay on top of any bushings, especially on car that is exposed to racing conditions. The higher road speed, bumps, acceleration, braking, hard shifts, etc, all wear down the bushings that much faster, and introduce slop into components that usually do best without any.

Motorsports: A Sad State of Affairs [ December 18th, 2008 ] By:Mark Ozimek

The world of motorsports is in a sad state of affairs these days. I guess the economy is picking off teams left and right. The latest casualty is Subaru as they announced their withdrawal from the WRC. Oh we must really be in a recession when Subaru withdraws from the league that put them on the map.

But Subaru isn’t the only casualty, Suzuki withdrew from WRC also. Although for them it may have just been too big of an expense for too little of a return. However other leagues aren’t immune from this economic recession. Honda recently announced their withdrawal from Formula 1 AND the AMA(motorcylce racing). Porsche and Audi both widthrew from the American Le Mans Series.

While all this is sad and upsetting to the world of motorsports, there is a silver lining: it gives the amateurs a chance. While it may seem like amateurs and privateers get struck even harder by the recession, but their income is a little more stable than the advertising budgets of the factory teams. So there is hope for us all yet! It may just be a big enough shake up to make your way into the sport.

Do you know of any other teams/pillars of the sport that have been eaten by this economic recession?

AWD Systems [ November 21st, 2008 ] By:Mark Ozimek

I just came across an interesting video that brings up some curious points.

I would advise everyone who goes to view the video on youtube to take note of the comment, while the experiments are unbiased, the interpretation of results are quite the opposite. Even so, it is fascinating to see how different manufacturers’ implementation of putting power down to all four wheels compares in a synthetic and repeatable test like this.

AWD has always been a tricky situation to deal with. When all four wheels have similar levels of traction, things are easy, and open differentials will handle the job fine and split the torque evenly between all the wheels. But what happens when one or more wheels breaks loose? In an open differential system, all four wheels receive the same amount of torque, which will be equal to the amount of torque the spinning wheel can put to the ground (aka: not much).

The simplest way around this is to just lock the differentials when slippage is detected. This will provide the maximum amount of traction because all the wheels will be forced to spin at the same speed, but this reduces drivability a bunch if you’re trying to turn at all, since the inner tires spin slower than the outer tires in a turn, and the rear spin slightly slower ontop of that.

There are many (enough that I’d rather not take the time to list them all, since I’m sure I’d miss a few) limited slip differential technologies that bias the torque away from the spinning wheel(s) to put the power down to wheels that have traction. This is usually done with some sort of fancy gearing or internal clutches in the differetial. Most AWD systems use limited slip differentials with varying levels of success. As you can see from the video, Subaru has one of the better limited slip systems out there. I really would have liked to see how an Audi with Quattro performed in the same test, but oh well.

There is also what I consider a “lazy-man’s” limited slip system that applies brake pressure to the spinning wheels to increase the amount of torque at that wheel, thus the other wheels too. This is the method of “traction control” my S70 has. I put quotes around traction control because it requires a very responsive system for it to really be of any benefit outside of driving slowly slippery surfaces, something Volvo didn’t quite account for in the design.

Or you can just forgo driving the car with the wheels and use a giant turbine or something, but I don’t think many rally organizations allow propulsion in such a manner.