Category: Technical Information

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Oil quality and the life of your car

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Engine oil gets contaminated over time by moisture, fuel, and particulate matter.

Moisture generally being introduced as a byproduct of combustion, it is easily burned off by getting the oil up to temp. If you have a short commute, it is a good idea to take a long drive at least once a month in an effort to get the oil to a more reasonable temperature.

IMG_8121Fuel contamination is generally a result of cold starts. We generally gauge the life of the oil and the change interval based on mileage, but most of the degradation and contamination of the oil with short commute vehicles is a function of cold starts. It is best to crank the car and start driving immediately. This will cut down on the warm-up time and reduce the total contamination from the cold start event.

Particulate matter in the oil gets there one of two ways. The first is via the air filter. The air needs to be as clean as possible going into the engine. The fine particulate can cause engine wear. The oil filter will catch a lot of it eventually, but that may be after it has spent some time on the side of the cylinders causing wear. We recommend either paper filters or multi-layer foam such as is found in our intake kit. The other particulate matter in the oil is generally a function of the wear. This will be ring material, cylinder material, and possibly bearing material. Some wear is normal over time, especially on cold starts when the parts of the engine are not their ideal shape or size. Catching some of that wearing material before it gets run through the oil pump can help reduce some of the secondary effects, so a magnetic oil drain plug is a good idea.

An appropriate oil change interval with a suitable oil will be the best way to prolong the life of your engine. Not every application is the same, so it is a good idea to consult with experts regarding your particular needs. Collecting an oil sample and sending it off for analysis is a great way to see if you need more (or less) frequent oil changes as well as keeping an eye on what is going on with your motor over time.

 

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Ethanol and your fuel system

It is becoming common to blend Ethanol with Gasoline in many states. Most stop at 10%, but there have been cases where higher concentrations of Ethanol has been found in pump fuels.

Ethanol by itself is not bad. E85 (75-90% Ethanol, the rest Gasoline), if you have a readily available supply, can be great low cost high octane fuel.

The downside to ethanol, especially in low ratios such as E10, is that you do not get any of the benefit of ethanol’s high octane rating. You do get its cleaning properties though, and that is where the trouble begins. Ethanol will clean off the varnish and other deposits in your fuel tank and fuel system. Usually (hopefully) this is caught in the fuel filter. It is not uncommon for fuel filters to be come clogged very quickly as the switch to fuels containing ethanol is made. The good news is that this is not a perpetual case. The “dirty” stuff will be cleared out fairly quickly and it may only take killing a handful of filters before the change interval can return to normal.

The other potential problem is compatibility with the fuel system. Modern fuel systems should all take 10% ethanol fairly easily. It will speed up the deterioration of  older fuel lines, and it is always a good idea to replace all of the soft lines on the fuel system with some frequency.

E85 as a fuel is a lot harder on the fuel system than E10. You will need Viton or similarly chemical resistant fuel lines installed. You will also need a larger capacity fuel pump and larger injectors, as it will take approximately 30% more fuel to make the same power.

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Common Boost Leaks on Forced Induction M50-Series Engines

There are a number of common problem areas on the turbocharged (and some supercharged) M50 based motors.

With the OBD1 throttle body, there is a port on the bottom for the purge valve. It is generally best to disconnect this from the purge valve solenoid and cap the port on the throttle body, or install a check valve between the port and the solenoid.

On the M50 manifold, the ICV connector that connects the “turkey neck” to the intake manifold is held in with one clip. Under pressure, the connector can rock on its mount and compromise the o-ring seal. This can be especially difficult to find/troubleshoot as it often will snap back in place when the engine returns to vacuum based operation. The two common solutions are to either glue the fitting into the intake manifold, or to use zip ties to hold the fitting in the manifold.

In some cases the crankcase ventilation system will have been left connected to the intake manifold. This should not be the case. The crankcase must be vented to a non-pressurized location. On early M50 based applications, there is a small hose that, in stock form, connects the valve cover to the throttle body boot. That must be vented elsewhere. (We recommend connecting to a catch can, and then to a crankcase evac kit tied into the exhaust.) There is also a small hose that connects the valve cover to the ICV connector mentioned above. That should be plugged on the valve cover side, and plugged on the ICV connector side as well.

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Pressure Testing the Intake System

Pressure testing the intake system on a turbocharged car is the best way to check for leaks. Any leak in the intake system can negatively impact the efficiency of the system. A leak after the MAF can also cause drivability and running issues. Pressurized leaks may not be apparent in vacuum testing, and may appear sealed when not pressurized. Post MAF leaks are generally noted by a rich running condition on boost.

Depending on the type of vehicle, there may be common leak areas that need more attention. This is true on applications such as the turbocharged M50 based motors.

Other common leak points are the silicone couplers and the turbocharger compressor housing. To ensure that the couplers hold right, verify that the hose clamps are on square to the tube as well as sufficiently tight. We recommend only T-bolt clamps for intercooler piping, but screw-type can work fine for compressor inlets.  The compressor housing on a turbo can be sealed to the center section in various ways.  Some use a paper gasket, some use a rubber o-ring, and others use nothing. Some that ship with nothing or with a paper gasket can benefit from switching to an o-ring. Most compressor covers use a 5.5 inch ID o-ring like this.

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Leak Down Test

A leak down Test can be performed on a warm engine. The appropriate leak down testing apparatus will be required, along with a good air compressor. You should not have a cylinder leakage of more than 10% in any cylinder for a fresh/healthy motor. You should also not have more than 5% variance between any two cylinders. If you do, then you will need to further investigate the cause of the leak. More than 20% leak down is an unhealthy motor and you should investigate further and find the appropriate course of action for repairing/replacing.

You will need to make sure you are exactly at TDC for the tested cylinder, and on the end of the compression stroke/start of the power stroke. If you are 360 degrees out, you can have a leak from the intake or exhaust valves which will make your results useless.

If you have a leak down of more than 10%, you should be able to track down the source of the leak, which will help determine the best course of action for repairs.

One of the benefits of a leak down test is that it can help isolate the problem areas. You should be able to hear the leak, or use a plastic bag and some tape to help locate leaks. An audible leak out of the intake indicates a problem at the intake valves (either valve seat issues, bent valves, etc). An audible leak from the exhaust (and you will still be able to hear the leak at the exhaust tip) will indicate an issue with an exhaust valve. If you can hear the leak in the expansion tank (with the cap removed) then you have a blown head gasket, cracked head, or an issue with the block. You will generally hear some leakage in the crankcase. A little is normal, but a lot is bad. This is why the leak down tester has a gauge.

Be sure to record your readings for each cylinder, and we recommend testing each cylinder more than once as a sanity check.

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Compression Test

Compression Tests should be performed on a warm engine, with the fuel pump fuse/relay unplugged (and the fuel rail drained/depressurized), and the throttle should be held fully open while testing. These pressure values will be less at higher elevations, and can be lower on engines with more mileage. Aggressive cams or cam timing will also reduce the measured cylinder pressure during a compression test, but should still give consistent readings. You should not have more than 10% variance between cylinders.
Typical compression test results should be approximately 150-170 psi per cylinder for ~8.5:1 CR, 210-250 psi per cylinder for ~10.5:1 CR.

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Before you get on the dyno

Before you have us tune your car, there are a number of important things to verify. If there is a “small problem” that is unknown before the dyno session, it can nullify

The pre-dyno check list is similar to the pre-track check list:

  • – Test the intake system for leaks
  • – Check, clean, or replace air filter
  • – Check engine oil level
  • – Check coolant level
  • – Check brake fluid level
  • – Check wheel bearings for excessive play
  • – Check that all suspension components are tight
  • – Check or replace fuel filter
  • – Bring plenty of fuel

It is very important to ensure that your vehicle is in good mechanical health before tuning it on the dyno. If you are using a custom tune (NA or turbo), we first send a base tune. This tune should be very close to the final tune in idle and part throttle drivability, so will be sufficient for startup and leak checking.

Before the tuning session begins, it is best to make sure you are tuning a healthy engine. We suggest you complete a compression test and a leak down test prior to your tuning appointment.

Please know that even if either of these test results look good, you can still have an engine that has some mechanical issue and the tuner/calibrator should be able to recognize any negative symptoms and consult with you about the consequences of further tuning your engine.

Make sure your air filter is clean and in good working order. Cleaning or replacing your air filter at regular intervals (according to the manufacturers instructions) is always a good idea, especially before a dyno tuning session.

Vacuum, pressure, or smoke check all intake, charge pipe, intercooler, turbo, and vacuum lines. If it is a turbocharged car, pressure test the system to between 1.5 and 2 times the target boost pressure. Couplers can appear sealed and hold vacuum or low pressure smoke just fine, but leak when re-shaped by high boost pressure. Smoke test, vacuum test, or light pressure test naturally aspirated cars.

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The Science Behind Bolts

Materials can deform both elastically (returning to its original shape and structure) and plastically (permanently changed in shape, structure, or both). Every material under any sort of load (lets consider a fastener in tension) is deformed elastically, even if it is such a small amount that it’s impossible to notice. The strain (deformation, elongation in this case) in the sample is proportional to the stress on the sample (force over area) times Young’s Modulus which is a property of the particular material.

Stress vs strain: E, the slope of the curve in the elastic range, is Young’s Modulus. This is an indicator of the stiffness of the material.

When the stress on a test sample reaches the elastic limit (aka the yield point) of the material in question, the deformation becomes permanent. For example, a head bolt or stud will elongate slightly (and temporarily) as it’s tightened up to its yield point, then it will begin to elongate more per unit of stress applied to it, and the deformation will be permanent. The deformation at this point is generally uniform, that is to say it occurs evenly along the length of the bolt, until the ultimate tensile strength of the fastener is exceeded and it fails (no longer provides the correct tension). At this point, a noticeable “necked down” section appears If more stress is applied, and the bolt will eventually fracture (break). Some fasteners, such as BMW head, main bearing, and rod bolts, are designed to be torqued past their yield point and deformed plastically when installed. This leads to a joint that is very resistant to fatigue in the fastener, because the tension in the bolt cannot be released and reapplied. The bolts also strain harden as they are tightened, increasing their ability to hold further loads applied after they are installed.

What does this mean to me?

Never reuse a bolt that requires angle torque, or that BMW requires be replaced. BMW specifies torque angles for fasteners that are torqued to yield because they are a more consistent way to specify the installed strain in a fastener than a torque value that can vary with the specifics of the application, such as lubrication on the threads.

Also, whenever a torque value is specified with a particular lubricant on the threads, ensure that it is always used. Failing to do so can lead to different amounts of stress in the fastener (and thus different clamping loads) at the same applied torque.

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Suspension 101: Swaybars & Roll

IMG_8127Good suspension is meant to keep tires in maximum grip as much as possible. Maximum grip occurs when all 4 tires are in their “happy zone” temp and load wise. When cornering in a high-performance vehicle, load transfers from the inside tires to the outside tires due to the the lateral acceleration of the vehicle. Load transfer is a function of track width and CG height and it will happen no matter what suspension is installed. This transfer is what we aim to minimize with good suspension set-ups.

We want cg height as low as possible because for each unit of load we add to a tire, we have to take it off another tire. For each unit of load added, we gain less overall lateral grip than we lost from the removal of that same unit of load on the other tire. Body roll is only important in its effects on suspension geometry. We can control this roll with springs without changing the lateral load transfer. If we use sway bars to control this roll though, we are using what are essentially torsion springs to move load from the inside tire to the outside tire through the chassis. (the chassis is essentially *pushing down* on the outside wheels to try to level itself out, and its getting the force to push down on the outside tire by stealing it from the inside tire.) The other side effect of this form of roll control is limiting rebound travel of the inside wheels.

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Remember, we want to minimize the load transfer during cornering. This is why we try to get the CG (center of gravity) as low as possible. Change in spring rate = no change in lateral load transfer.    Sway bars = change in lateral load transfer. That is a fairly simplistic view of it, but that should hopefully give you a better idea of the basic functions.

As Milliken & Milliken from Race Car Vehicle Dynamics put it: “Anti-Roll Bars — these are usually in the form of a torsion bar spring which connects the vertical motions of the left and right wheels. No twist of the torsion bar takes place if the wheels move up and down together (ride), but in roll the bar is twisted as one wheel moves down and the other up from some initial position. Twisting of the bar adds load to one wheel and revoves it equally from the other. Anti-roll bars change the distribution of the lateral load transfer between the front and rear tracks, and also reduce the body roll angle and add to the one-wheel bump rate of the suspension.”

“Load transfer is independent of spring rate. If the wheels are truly independent, then the LLT is only a function of track width, CG height, and cornering force. When you add sway bars to the mix, they wheels are not fully independent anymore, and that is where the added load transfer comes from.”