Section 8: General Performance Modifications

      8.1:   Chips
          8.1.1: Why can't BMW come up with the best chip?
      8.2:   Air filters
          8.2.1: K&N
      8.3:   Brakes
          8.3.1: Common Problems / fixes
          8.3.2: Performance Pads
          8.3.3: Custom brake lines
      8.4:   Differentials
      8.5:   Theory
      8.6:   Misc
          8.6.1: Water Wetter
          8.6.2: Indexing Spark Plugs

First you have to understand that to sell a car in the US, it must be "certified" by the EPA and/or CARB as meeting US/Calif. emissions standards for

1. Emissions performance (FTP test)
2. Emissions longevity (50k mile test)

To meet the FTP *AND* assure that your cat will last 50k miles, some *compromises* occur in the fuel and ignition mapping ..

If the car is also tuned for *economy* (as in the eta motors) even more power is lost ..

The basic fact is that the best emissions occur at a low fuel/air and the best power occurs at a richer fuel/air ratio ..

The balance and the compromises come into effect when you have to account for all 3 factors ..

Power, Economy, Emissions ...

Now, through in "bad gas" and you have slightly retarded spark timing

The knock sensored cars are better at this game, but the "base maps" are still slightly retarded from those of a car which would always be *assured* the finest 94+ octane fuel ..

Now, if you don't HAVE to pass the Emissions Warranty (50k) test, and you only modify points outside of the FTP procedure .. you can make a chip that "passes" but is REALLY significantly *dirtier* and also MAY have better overall performance ...

Some aftermarket guys are getting away with this (for now)

I must agree the K&N air filter is the easiest and best(for the cost) performance addition I have ever done to a car. The K&N seem to add .5 mpg (measured over a month) and eliminate the ping on hard acceleration.

The K&N filter in my 325es (stock engine with Dinan chip and 3.25 diff) gave me an extra 3-5 mph on the front straight at Lime Rock. I was pleasently supprised!

I was at Dinan Engineering for a seminar last wekend, and talked to Steve Dinan about exactly this issue (the benefits of adding a K&N air filter). He had two things to say:

1. The K&N filter is not as effective in taking particulates out as the factory paper filter is, so you will increase engine wear.
2. The factory filter pulls cool air from outside the engine compartment, while the K&N will pull warm air from the area behind the radiator. Warm air is less dense than cold, so this can cost 6-13 HP!!
3. According to their actual tests on th Dynomometer, you will *lose* horsepower, not gain it. He said he wished it were different, as lots o fpeople want to buy K&Ns from them, and he could make money selling them, but they have a policy of only selling things which *improve* performance.

I would argue that even though the particulates getting through the filter are indeed slightly larger (HOHO more airflow = larger holes; brilliant!) unless you live in the desert and you baha al lot, you are not likely to cause significant increased wear to your engine. Regarding the point about taking warmer air in; has it escaped Keith's mind that there are replacement K&N filters which fit in the original airbox? The air therefore comes the exact same place as before, and in fact it could be argued that since the airflow is higher the air would indeed be cooler, not hotter.

I have always put K&N filters on performance vehicles, and have found that usually the change is associated with a pleasant increase in performance. I will continue to use these filters since I have never found any proof of increased engine wear.

Readers,
A recurring question among many riders who do their own maintenance is what about alternatives for consumables such as air and, oil filters which we all go through so often. The following is a discussion of air filters and their efficiencies put together from a number of internet postings. Most of the hard information comes from Ed Hacket along with questions from others. (note that the standard filters which our dealers sell are paper, unless you have the K&N which is oild gauze and rated as plain gauze.)

Here's the info I have on air filter performance. Tests were done by Amsoil using SAE J726C Test Method 5-best --> 1-worst

Oiled foam Paper Oil bath Gauze

Large particle efficiency           5          5        5         4
Small particle efficiency           5          4        1         2
Airflow capacity                    5          2        3         5
Dust holding capacity               4          2        5         2
Load up charactaristic              4          1        5         1
Backfire charactaristic             3          2        5         3
Cleanability                        4          1        4         3

As you can see, K&Ns are great for airflow, which is what they were designed for. Their original application was on racing engines, where airflow is important and ultimate engine life was of little consern. They are not as good at filtering as paper or oiled foam types.

question > What constitutes oiled foam? Who makes one?

Uni filters are oiled foam.

quest > After the first time Ed posted this, I went searching for an oiled foam quest > filter for the PD. Uni doesn't make one (at least that's what I've been quest > told). Does anyone know where to get one to fit the R's (flat of course)?

My room mate found a listing at a local shop that specializes in dirt bikes. They have the full Uni catalog. All three BMW types were listed (round and flat R, and K). The listings in Hap Jones, Parts Unlimited, ect. don't have the BMW listings.

He is thinking about ordering one as he says he definitely gets more fine dirt downstream of the K&N than with a stock BMW paper filter. He will only get it if it has a solid frame like the stock filter. Without the frame he feels installation and getting a good seal would be damn near impossible.

 Ed Hackett   edh_at_maxey.unr.edu           The Desert Research Institute
 DoD #0200  WMTC  BMWRA  DIOC             Reno, Nevada   (702) 673-7380
 KotLS  KotLE  DotD #0003            I'm not really a chemist, I'm just one of
 900SS  K100RS  501 CAMEL            them motorsickle sonsabitches.  __=o&o>__

>At Laguna Seca I experienced the
>following for the first time and hopefully last: >
>Spongy Brakes
>Fading
>Warped Rotors

Your enemy is heat. Boils the brake fluid causing the bad brake feel (and brake loss, in extreme cases). Overheated rotors warp as they cool - especially since the pads etc. make them cool at different rates in different places. So the problem becomes how to get rid of excess heat.

>But to prevent this from ever happening again and >hopefully raising my braking performance what can I do ??? >
>Comments / Suggestions / Nuances please.... >
>- Cross Drilled Rotors

Basically useless. Weakens the rotor, gives cracks a place to start, and does little if anything to improve cooling. (This from Derek Hanson(?), the owner of DECH, a highly respected Mustang performance shop in Canada, and classroom instructor at many BMW CCA schools).

>- Gas Slotted Rotors (What does "gas slotted refer to ?)

Refers to a rotor with several diagnol slots about 1/8 inch wide and deep running from the center to the outside rim of the rotor. Gives gases and brake particles a place to escape from between the pad and rotor.
Helps some with brake effectivness and how well they hold up under hard use, but not with cooling.
Increases pad wear.

>- Teflon/Kevlar/Stainless Braided Lines

Helps pedal feel when the brakes are working normally, but doesn't help prevent fade at all. More delicate than stock lines, check them often.

>- ATE Super Blue Racing Fluid
>- Castrol LMA

Super Blue has just about the highest boiling point of any DOT 4 fluid. This will resist boiling and so help prevent fading. You can still boil it though, so it isn't a cure-all. There are some DOT 3 fluids with a somewhat higher dry boiling point, but you have to change them often because they break down over time as they collect moisture. LMA has a reasonably high boiling point, but not as good as Super Blue. Its claim to fame is that it resists breaking down (to a lower boiling point) from moisture: LMA = Low Moisture Affinity. If you change your fluid as often as you should when you run your car on the track, that should not be an issue. Better fluid will help, but remember you can boil ANY fluid. Won't help with warping, either.

>- Cool Carbon Brake Pads

These will help as they have a ceramic layer between the pad and the backing plate that helps keep heat from getting to the caliper (fluid). They are a carbon/kevlar compound which works best when warm, so often feel like they don't grab well on the street. The braking force goes up quickly as they heat up, so even on the track you will find you get more braking force at the end of a brake application than you will at the begining. This can sometimes mean you will lockup your brakes unless you back off the brake pedal as you slow down. They tend to squeal if you dont' break them in well when you first put them on, and you should not switch between them and standard pads using the same rotors. So basically, they are great for the track, and will help with your fading, but they are finicky and not well suited for street use. Won't help with the warping problem.

>- Repco MetalMasters

A cheep pad that holds up reasonably well under hard use, but is harsh on the street. Better on the track than stock pads, but not in the same league as Cool Carbons, and won't help with your fading or warping problems.

>- Performance Friction / Carbon Metallic

Similar to Cool Carbons, but even more finicky. The braking force vs temp curve is even steeper, so you really need to come off them as you brake to avoid locking up. Derek Hanson says these also tend to destroy rotors if you don't drive them properly because they put so much heat into the rotor so quickly. Basically a top of the line race pad, but you had better know how to use them, and not at all well suited to street use.

The real solution to your problems is brake cooling. Vents in the airdam with a hose running around and out the control arm to blow the air directly at the caliper and center of the rotor. I've heard wheel fans also help, but I've never tried them. You can remove the backing plates, but I don't like to do that on a street car.
I used to often cook my brakes at high speed tracks like Watkins Glen. Now I use Ferodo pads (a standard compound (i.e. non-carbon) pad that takes heat better than Repco's but is still reasonably good on the street) with Super Blue and brake cooling vents. I have yet to cook the brakes while I am running, but I still often boil my brake fluid AFTER I come in from a run, that is while the car sits still and the brakes are no longer being cooled by any airflow. The brakes feel fine when I come in, but the next time I get in the car the pedal is soft. So now, after any run where I've given the brakes a good workout I drive around the infield for a few minutes to keep air going over them. It's also a good idea to always use thick pads and rotors - that is replace them before they wear too far. A thick pad insulates the caliper better, and a thick rotor can tolerate more heat.

rick
'87 325es
'90 325iX
'88 M3

*Why do brake rotors warp?

one explanation i've seen is that often newly manufactured rotors are stacked while still warm, and then machined flat later. the resulting rotors have inherent stresses, and when you heat them up sufficiently (such as at a race track) they stress relieve themselves by warping.

there are evidently sources of rotors which are manufactured more carefully; Brembo rotors, for example, seem to have much better behaviour under track abuse.

*Improving the rotor cooling depends on the type of rotor you have- *solid, or vented

if you have vented rotors, then any brake ducting should be aimed at the center of the inside of the rotor (the brake dust shields may need to be removed.) the vented rotor functions as an air pump, from inside to outside, and air aimed at the center will help cool the entire rotor (uneven cooling can contribute to warped rotors.)

if you have solid rotors, then you have a bit of fabrication ahead of you. what you need is a can with a slot that fits over the rotor, and a hole in one end to attach the duct to. you need to get cool air to both sides adjacent to the caliper; if you only cool one side, then the danger of warping still exists.

        |    _    |
        |   | |   |<=====ducted air goes in here
        |___| |___|

             ^--- rotor goes into this slot

but keep in mind this: for most any braking system you are likely to be able to build, there are drivers out there who can cook the damned thing. if you are having problems with brakes at driver's school, then in addition to attacking the mechanical and engineering issues, also consider modifications to your braking habits, if you want to keep brakes in the car all weekend.

From: "Carl Buckland" <buckland_at_alinc.com> Date: Thu, 16 May 1996 18:15:05 +0000

...
Brake pads are beginning to be much less of a mystery to me. Here is how I see it:

STREET PADS are cheap, clean, quiet, last a long time, and are rotor friendly. They tend to fade after they get hot. There are many available. I have been happy with the Rebco/PBR deluxes, available from BMP, among others.

AUTOCROSS PADS are what I would call the Hawk Y-5's. They are expensive, dirty, noisy, and "may" be a little harder on rotors and may not last as long as street pads. So far, Bob Tunnell reports that they are long lasting, and have not seemed to wear his rotors. I am sure that they are more fade prone than a true track/race pad. They do NOT require a lot of heat to work well. They are available from TC Kline, as well as others.

RACE/TRACK PADS are not for everyone. They are ALL, as far as my personal experience goes, expensive, dirty, noisy, short lasting, very hard on rotors, and, generally, don't work when cold. They do, however, work like an anchor around a tree when hot, and don't tend to fade (as much as street pads) when hot. The real key to using race pads is to WARM THEM UP BEFORE HEAVILY APPLYING THE BRAKES! Hard braking with cold race pads usually results in poor braking, lots of noise, and horribly grooved rotors. If you need race pads (and if you do a lot of hard track driving, you NEED race pads), be prepared for the above draw backs, and try to take them off as soon as you are off the track. The drawbacks make them unacceptable for street use, in my opinion. I have a stack of ruined rotors, and permenantly stained alloy rims to prove it. Even if you can stand the rotor and wheel destruction, you will tire of the dirt and noise.

...
These are my opinions, but they are based on actual experience,

Carl

if you're going to do braided lines, consider a complete conversion to aircraft style single flares. you will need the following tools:

1. tubing cutter (available from lots of places; Eastwood has a decent one)
2. flaring tool (The Rol Aire from Aircraft Spruce and Specialty is very nice)
3. tubing bender (the one from Eastwood works well)

for hard lines, use 3/16" seamless Bundyweld tubing, available from better auto parts stores. avoid seamed and copper tubings at all costs.

for braided lines, the premade lines from Pegasus are good, tested, and available in various lengths.

you will need adapters to fit to the calipers and master cylinders; the thread should be M10x1.0. the adapter screws into the caliper/master cylinder and presents 37 degree AN flares on the other side; you then plumb the entire system with 37 degree flares. the only metric flares remaining in the system will be the ones where you've put in the adapters. oh, right. you'll need adapters for any proportioning valve that might be in the system, although if you're replumbing to this extent then a nice adjustable proportioning valve like the Tilton that Pegasus carries is a nice add on; bolt it to the floor next to the shift lever and route the rear brake line along the center tunnel.

and this is all legal in an IT car.

Aircraft Spruce and Specialty Company
201 West Truslow Ave.,
Fullerton, Ca 92632
714-870-7551

Rol Aire Imperial: 212 FB
Rol Aire for tight quarters: 507FB

The Eastwood Company
580 Lancaster Avenue, Box 3014
Malvern Pennsylvania 19355-0714
800-345-1178

The best improvement in acceleration you can get for the money.

John Allen commented on the higher redline and longer stroke of the '91-'93 M5 engine:
>It's interesting that the longer-stroke motor (S38B36) also >has the higher redline. Any thoughts?

John,

Yes, I can give you some "rules of thumb" about engine reliability versus rpm. I happened to research this some during the past week, so your question is timely.

The Metric Mechanic (MM) Catalog got me started with its section on engine rpm versus life. Basically, high rpm operation wears out engines faster, but there's more to it than that. MM also mentions the critical top piston ring area.

This sounded very familiar -- so familiar that I searched my attic for Gordon Jenning's "Two Stroke Tuner's Handbook". Now, M5s have four stroke engines, but the basics of pistons and rings are the same for either.

Mean Piston Speed

  Mean Piston Speed      Result
  ------------------     ------
  Under 3,500 ft/min     Good reliability
  3,500-4,000 ft/min     Stressful, needs good design
  Over  4,000 ft/min     Very short life

Mean piston speed is easy to determine. It's based on the piston stroke and rpm.

Cm = 0.167 x L x N

Cm = mean piston speed in feet per min L = stroke in inches
N = crankshaft speed in rpm

Using the 1988 E28 M5 as an example:
E28 M5, Bore and stroke 3.68 x 3.31 in (93.4 x 84 mm) At 6,900 rpm (factory redline)

Cm = 0.167 x 3.31 x 6900 = 3,814 ft/min

At 7,200 rpm (Dinan chip redline) = 3,980 ft/min At 6,500 rpm (max constant speed) = 3,593 ft/min

Here are some other piston speeds I figured for comparison.

             Redline   Stroke     Piston Speed
  Engine      (rpm)    in,mm       (ft/min)
  --------   -------  --------    ------------
  BMW 2002   6,400    3.15, 80      3,367
  BMW 318i   6,500    3.19, 81      3,463
  BMW 325i   6,500    2.95, 75      3,202
  BMW 3.0    6,400    3.15, 80      3,367
  BMW 535i   6,200    3.39, 86      3,510

  MM 4000    6,000    3.70, 94      3,707
  MM 3500    6,400    3.39, 86      3,623

BMW E36 M3 6,800 3.38, 85.8 3,838

  BMW E28 M5 6,900    3.31, 84      3,814
  BMW E34 M5 7,200    3.39, 86      4,076

CBR600 13,250 1.78, 45.2 3,939 (motorcycle)

Notice that most production cars stay below 3,500 ft/min, while the E36 M3 has the same 3,800 ft/min piston speed as the E28 M5. With its longer stroke, the E34 M5 piston speed is even higher than the screaming Honda CBR600 motorcycle! The two Metric Mechanic (MM) engines also go above 3,500 ft/min.

>From the MM Catalog Engine Specification table, MM uses thinner (lighter) 1.5 mm (0.059 in) top rings than the standard BMW 1.75 mm (0.069 in) top rings. Lighter weight reduces vertical ring acceleration force at high rpm. MM talks about less "hammering" of the ring groove from the lighter ring, but it also reduces piston and ring overheating.

How Piston Rings Work

Rings don't seal just by their spring properties. Gas pressure above the ring forces it down against the bottom of its groove in the piston. The gas pressure also gets behind the ring, in the back of its groove, and forces it out against the cylinder wall. Normally this works well.

However, when piston ring acceleration exceeds the gas pressure holding it in place, the ring lifts upward in its groove (piston nears top of stroke and is being slowed to a halt at TDC). As the ring lifts, gas pressure releases above and behind the ring, causing the ring to hit up against the top of its groove. When the pressure behind the ring is released, high temperature and pressure combustion gases escape down the side of the cylinder wall causing piston and ring overheating. This hammering of the ring groove and overheating shortens engine life.

Here's a picture of how it works.

1. Normal Condition

   Gas pressure in the upper cylinder holds the ring down against the bottom of its groove and out against the cylinder wall, forming a seal.

        Gas Pressure
              :
              :
           \| :
           \| v
           \| :|----------------------------|
           \| v|                            .
           \| :|             Left           .   Right
           \| v|-------   Cross-section     .  Side of
           \| :.v.... |     of Piston       .  Piston
           \|[[[]] <: |\                    .  (not shown)
           \|  |-\----- \                   .
           \|  |  \       Ring Groove       .
 Cylinder  \|  |   \                        .
   Wall    \|  |     Piston Ring            .
           \|  |                            .
           \|  |                            .
           \|  |                            .
           \|  |----------------------------.
           \|
           \|
           \|

2. Too Much Piston Acceleration

Piston acceleration lifts the ring, shutting off pressure behind the ring and breaking the seal. The ring groove is damaged by constant mechanical pounding. Hot combustion gases get past the ring, overheating it and the piston.

         Gas Pressure
             :
             :
           \|:
           \|:
           \|: |----------------------------|
           \|v |                            .
           \|: |             Left           .   Right
           \|v |-------   Cross-section     .  Side of
           \|:[[[]]   |     of Piston       .  Piston
           \|v  \     |\                    .  (not shown)
           \|: |-\----- \                   .
           \|v |  \       Ring Groove       .
 Cylinder  \|  |   \                        .
   Wall    \|  |     Piston Ring            .
           \|  |                            .
           \|  |                            .
           \|  |                            .
           \|  |----------------------------.
           \|
           \|
           \|

Maximum Piston Acceleration

How much piston acceleration is too much for a piston ring? Well, first figure piston acceleration, and then use another "rule of thumb" for ring thickness versus piston acceleration.

The maximum piston acceleration formula is:

Gmax = (N^2 x L /2189) x (1 + 1/2A)

Gmax = max piston acceleration in ft/sec squared N = crankshaft speed in rpm
L = stroke in inches
A = ratio of rod length, between centers, to stroke

For example, the E28 M5:

L = 3.31 inch stroke
A = 2 (estimated) rod length/stroke
N = 6,900 rpm redline

Gmax = 6900^2 x 3.31/2189 x (1 + (1/2x2))= 89,989 ft/sec^2

Now use the following "rule of thumb" table from the "Two Stroke Tuner's Handbook" and interpolate to find the ring thickness for the M5's 90,000 ft/sec^2 piston acceleration.

Max Piston
Ring Thickness Acceleration
(inch) (ft/sec^2)

     0.125            40,000
     0.094            53,000
     0.063            80,000
     0.047           106,000
     0.039           138,000

The E28 M5 "rule of thumb" ring thickness works out to 0.057 inches. After figuring this, I hoped the actual rings were at least as thin as the MM 0.059in (1.5mm) rings instead of the standard BMW 0.069in (1.75mm) rings.

I quickly measured the M5 piston (with no rings) on my desk. Using a feeler gauge, the top ring groove measured 0.061 inch. Ring groove clearance is usually about 0.002 inch, so the M5 ring must be 0.059 inch or 1.5 mm, just like the MM rings -- thank goodness!

Recommendations

My suggestion is be most careful about sustained high (redline) rpms. It's probably okay to shift at redline, but don't hold it there very long, because the pistons and rings may suffer.

If you have a Dinan chip, maybe shift at the factory recommended redline (6,900 versus Dinan 7,200 rpm). Even shifting at 7,200 rpm won't cause any immediate consequences, but over time it causes extra wear.

M-engines are pretty rugged. Just don't expect miracles if you run hard all the time.

*Has anyone used this stuff? Miracle cure or snake oil? My bimmer's *stablemate doesn't like the hot weather.

it performs as claimed. it may or may not cure your problem, depending on what your problem is.

there are two formulations:

pink liquid, for cars that run water/glycol this stuff consists only of the surfactent; the function is to break up the large water bubbles that occur in some cooling systems and lodge in the cooling passages, causing severe localized overheating

pink crystals, for car that run straight water (real race cars) surfactent + corrosion inhibiters + water pump lubricant

if your cooling system has problems (clogged radiator, weak water pump, pressure leaks) then water wetter can't cure that, but in a normally functioning cooling system filled with glycol and water, water wetter can bring peak temps down by 10 degrees.

> The car I tried the Redline water wetter in had no known cooling problems. > I was looking for a drop in the gauged water temperature. There was none. > Hence my flame. Perhaps water wetter was not intended to drop gauged water > temperature. If anyone on the net has personally measured "hot spots" in > his cylinder head (or block), and the hot spots' response to water wetter, > please let us know. Somehow, I think water wetter is more an article of > faith than empiracal science.

First of all, you are not going to notice a difference in temperature as long as you are running a thermostat which is regulating flow based on temp. Where it is going to help is in situations where you are overheating, that is, the temperature is higher than 160-180 deg (whatever your application is) with the thermostat full open. Without this kind of condition, you will never notice that water wetter is beneficial.

This does not mean that you should not run water wetter if your temp is stable. The more efficient the heat transfer of a cooling system, the better. Your temp guage is only a sanity check and does not even begin to measure the effectiveness of a cooling system.

Technically, as a surficant, it is factual that water wetter reduces the tension of water. If you call Redline, they will be glad to send you a fact sheet. And, the company is reputable, so the facts will be accurate.

My understanding is that some racing organizations (e.g. BMW Club Racing in '97) require cars to run Water Wetter with no antifreeze because if a cooling system leak occurs, that combination is much less slippery than antifreeze, possibly causes less damage to the track as well.

>Read this in an Alfa Forum discussing a Performance Tip found in a BMW >newsletter......anyone know if this really works?

Yes, it does but... 6-8hp is a bit optimistic... maybe on an M3. This is a well known practice in big time drag racing. Of course, when you're tuning a 4000hp engine you might get 50-60 hp extra.

I indexed the plugs on my Mustang 5.0 and got no measureable performance gain. Idle quality and starting did improved though.

This is a 2-3 hp here, 2-3 hp there, kind of thing. It all adds up.

I've always been told to turn the open side of the electrode towards the intake valve. Trial and error experimentation will allow you to find the optimal placement of the plugs, but it's time consuming.

You can get the washers (that's all they are, thin washers made to the correct diameter for plugs) at your local performance shop. They'll know what you're talking about.

Indexing the plugs is really for those who seriously race their cars, and need that extra 5/100th's of a second, or those who just can't sleep at night knowing that there are a few HP's yet unleashed in their engine. It's certainly not a waste of time, the engine will like it, but it's not going to yeild a big improvement in most cases.

• -- Ron Katona ron3b_at_cris.com http://www.cris.com/~ron3b