I know a couple of other people have done dyno runs on their 500E, but not everyone gets the car prepped properly. Since the W124 with M119 engine uses a 722.3 automatic transmission, you need to make a few changes prior to the dyno run to ensure you get a complete dyno graph (from low RPM to high RPM).
Chassis Prep:
You must disable ASR for the dyno run. This applies to all 500E/E500 models, and any 400E/E420 with optional ASR. If you have an ASR defeat switch on the console, this is easy - flip the switch. If you don't have an ASR defeat switch, disconnect a front ABS wheel speed sensor, the connector for the right front wheel is near the CAN box and easy to access (photo attached below). After you're done, re-connect the sensor and (if desired) clear the fault code.
Ideally, you want to pull from off idle to redline, usually in 3rd gear. The trick is, getting the car to begin at a low enough RPM (the torque converter won't allow anything under about 2000rpm though), and not letting the tranny downshift at full throttle. A dyno graph from 3000 or 4000 to redline just isn't as meaningful, you really want to see that low-end torque curve.
On the 500E, this is fairly simple to achieve:
Most dynamometers are the inertia type, which will measure true power that reaches the road. What this means is that any change in rotational weight in the drivetrain (driveshaft, differential, axles, brake rotors, and wheels/tires) will change the measured power output. Translation: You should bolt on stock wheels/tires (on at least the rear wheels) before going to the dyno. Most larger wheel/tire packages weigh more than stock, and this can reduce your power readings by roughly 5-15hp depending on how heavy they are. It's best to eliminate variables when possible, and using the stock wheels/tires is an easy way to do this. If you make a change to the car and go back to the dyno, use whatever wheels/tires you had on the first time! Otherwise you cannot compare the numbers from the two different sessions.
When you arrive at the dyno shop:
Try to keep the engine cool - when you arrive, pop the hood and let it cool off for at least 20-30 minutes prior to the first run. Better yet, park in the shade, remove the airbox (put it out of the sun), and run the heater with the temp dial set on 'max heat' for about 5 minutes after shutdown. The heater trick only works if your auxiliary coolant pump in front of the CAN box is functional... if the air blowing from the vents turns cool after 1-2 minutes with the engine off, your aux pump may be dead. Whack it with a screwdriver to see if it will come back to life. The pump only runs when the climate control temp wheel is clicked on max - not near max, it has to be fully on the max heat detent, or the pump won't turn on.
If possible, make the first run with the engine temp well under 80°C on the dash - this will likely be the best run. The first run should be with the dash gauge showing 60-70°C. The second run will probably have temps around 80-90°C, the third may be 90-100°C, and power will drop off slightly with each run as heat soak reduces power output. It shouldn't be much though, maybe 2-4hp difference for each run. Most of the time you'll see a 4-5hp loss from the highest to the lowest, this is normal. Past 100°C, power will probably drop significantly.
Note: Avoid letting the engine cool excessively... you want to keep the oil and ATF warm.
Optional: The factory documentation recommends using special tools (which are just fixed resistors) to "fool" the computers into thinking the intake air temp (IAT) is 20°C and the coolant temp is 80°C. The IAT tool (shown in attached photos) is relatively cheap, around $20 USD, and it plugs in at the wires behind the left headlight bucket. The coolant "tool" also shown below is much more expensive, it had been around $125, and is now $600+ with the Jan-2014 price increases. The effect can be duplicated using a couple of appropriate-spec resistors for a few bucks. This is less critical if you are able to get the engine temp down to 60-70°C prior to the first pull, so don't lose sleep if you don't have the temp simulators in place.
Ask if the dyno shop has a wideband oxygen sensor available. If so, request that you want the wideband readings. Some shops do this automatically, other shops only do this if you ask for it (and may charge a few bucks extra), some shops may not have this ability at all. This will show the air/fuel (A/F) ratio during the dyno runs at all RPM's.
Driving on the dyno:
With the tweaks above, you will be able to make the engine pull from approx 2000rpm to the ~6250rpm redline in 3rd gear, which will properly load up the engine. If you're behind the wheel (every shop does it differently - some shop owners will "drive" the car for you), put the shift lever in "3", accelerate just enough to get into 3rd gear, then back off the throttle slightly to bring the indicated speed to a bit under 20mph on a 500E with 2.82/2.65 gears (to bring RPM's down near 2000rpm), then nod to the dyno operator and FLOOR IT. When the tach reaches ~6250rpm, lift off the throttle, and move the shift lever to "D" to allow the engine revs to drop as the trans shifts into 4th gear. The end.
(Note: The starting MPH will be higher on a US/Japan spec 400E/E420 with 2.24 gears, and you may need to do the runs in 2nd gear if you have 2.24 final drive - especially if you have a 94-95 model with 130mph top speed limiter.)
You can also let the engine pull to the rev limiter before lifting off the throttle, you will know when this happens as the motor very clearly hits a "wall" where the revs stop increasing. Some aftermarket chips increase the rev limiter to approx 6600rpm, so you may want to test your rev limit BEFORE going to the dyno. You can do this by driving in 1st gear with the shift lever in "B" and seeing what the max tach reading is when the limiter engages. The dash tach is not always exactly accurate but it should be within ~100rpm or so if it's stock. If the tach needle has ever been removed (for example, to install white-face gauges) then it is more likely the tach is not accurate. An aftermarket digital memory tach can be used to get more precise readings if desired. AutoMeter offers a number of tachs with this function.
Remember that the standard 500E transmission starts in 2nd gear, so you will only feel one upshift (from 2nd to 3rd). If you have an electronic FGS system (like Bergwerks), this will be disabled when the kickdown solenoid is unplugged, but will NOT be disabled if you unplug the kickdown switch behind the gas pedal. YOU need to figure this out so you know what gear the transmission is in before you nod to the dyno operator and floor the pedal. The 400E/E420, and any 500E with a first-gear-start valve body, will have two shifts (1-2 and 2-3) before it hits 3rd gear. Do not do the dyno run in 4th gear. A dyno run in 2nd gear is acceptable if necessary, i.e. if the dyno cannot handle ~120mph rear wheel speeds, but a 3rd gear run is preferred on a 500E/E500. Again, for a 400E/E420 with 2.24 gears, do the dyno runs in 2nd gear, not 3rd.
The max speed (at redline) in gear should be roughly between 80-120mph on the dyno rollers, so adjust as needed if you have custom gearing in your differential, and/or a manual transmission. A car with 2.65/2.82/3.06 gears (all 500E/E500, and Euro-spec 400E/E420) will be in this range in 3rd gear, a car with 2.24 gears (all US/Japan spec 400E/E420) will be in this range in 2nd gear, assuming it has a 722.3 automatic transmission and near-stock tire size.
After the dyno session:
If the dyno is a DynoJet, ask for the electronic .drf files from the session. Some dyno shops may be able to email these to you. Other shops do not have their dyno computer connected to the internet, and/or may not be computer savvy to know how to do this. Bring a USB flash drive so you can copy the .drf files to your flash drive. These files have ALL the raw data from the dyno pulls. You can download free software from DynoJet which will let you create any graphs you want from the data, you can change the scale on the graphs, only show hp, or tq, or both, show A/F ratio or not, wheel speed, etc, etc. This is far more useful than a single printout that most shops will hand you on the way out the door.
Don't forget to re-connect the Bowden cable before driving home, and if you unplugged the front wheel speed sensor, re-connect that too. When you get home, re-connect the kickdown wire or switch (depending which you had removed). Ditto for the CTS & IAT sensors if you installed the temp simulators.
To determine estimated crankshaft power, divide the peak rear-wheel horsepower & torque numbers by 0.82. Example: A 500E shows 265rwhp. 265/0.82 = 323hp. This is estimating about 18% driveline loss, which is typical (within a percent or two) for a W124 with 722.x automatic transmission, and stock wheels/tires/brakes. Note what correction factor is used... common ones are SAE and STD in USA, and DIN in Europe. For USA, the SAE factor is more conservative. I personally prefer to use SAE as it's the most conservative of all the correction factors (AFAIK). The correction factor accounts for the temperature, humidity, and barometric pressure at the exact time & location you were on the dyno. Dyno shops near sea level often have little to no correction factor applied, as elevation increases the correction factor also increases. If you see something like "SAE: 1.05" on the printout, that means that a 5% correction was applied using SAE standards.
SUMMARY:
A sample dyno graph is shown below, it is a 1993 500E with stock engine, stock 1993 LH module, stock wheels/tires/brakes/etc, run to the rev limiter. The average (SAE corrected) power readings of 258rwhp, divided by 0.82, equals 314.6hp estimated at the crank... darn close to factory spec of 315hp. Also note the A/F ratio averages right around 14.7 as expected for a 1993-up LH module which remains in closed-loop operation at all times.
The math can get tricky, especially when doing a 'reverse' conversion, i.e. from RWHP to estimated crank. It works like this:
Chassis Prep:
You must disable ASR for the dyno run. This applies to all 500E/E500 models, and any 400E/E420 with optional ASR. If you have an ASR defeat switch on the console, this is easy - flip the switch. If you don't have an ASR defeat switch, disconnect a front ABS wheel speed sensor, the connector for the right front wheel is near the CAN box and easy to access (photo attached below). After you're done, re-connect the sensor and (if desired) clear the fault code.
Ideally, you want to pull from off idle to redline, usually in 3rd gear. The trick is, getting the car to begin at a low enough RPM (the torque converter won't allow anything under about 2000rpm though), and not letting the tranny downshift at full throttle. A dyno graph from 3000 or 4000 to redline just isn't as meaningful, you really want to see that low-end torque curve.
On the 500E, this is fairly simple to achieve:
First, you need to disable the transmission kickdown switch. I personally find it much easier to unplug the wire from the back of the transmission, under the car. It's the only wire in that area - it just pops out the rear. See attached photo. I normally do this at home, before driving to the shop. Some people disconnect the kickdown switch behind the gas pedal but I find this to be more difficult. Either method works, use whichever you prefer.
Second, you disconnect the Bowden cable from behind the airbox, on top of the engine (this is a breeze). I do this when I arrive at the dyno shop, only takes 30 seconds to connect or disconnect the ball/socket. It's no fun driving with the Bowden cable disconnected, the tranny will upshift at ~2000rpm for each shift. That's why you'll want it connected for the drive to & from the shop. But it MUST be disconnected on the dyno!
Most dynamometers are the inertia type, which will measure true power that reaches the road. What this means is that any change in rotational weight in the drivetrain (driveshaft, differential, axles, brake rotors, and wheels/tires) will change the measured power output. Translation: You should bolt on stock wheels/tires (on at least the rear wheels) before going to the dyno. Most larger wheel/tire packages weigh more than stock, and this can reduce your power readings by roughly 5-15hp depending on how heavy they are. It's best to eliminate variables when possible, and using the stock wheels/tires is an easy way to do this. If you make a change to the car and go back to the dyno, use whatever wheels/tires you had on the first time! Otherwise you cannot compare the numbers from the two different sessions.
When you arrive at the dyno shop:
Try to keep the engine cool - when you arrive, pop the hood and let it cool off for at least 20-30 minutes prior to the first run. Better yet, park in the shade, remove the airbox (put it out of the sun), and run the heater with the temp dial set on 'max heat' for about 5 minutes after shutdown. The heater trick only works if your auxiliary coolant pump in front of the CAN box is functional... if the air blowing from the vents turns cool after 1-2 minutes with the engine off, your aux pump may be dead. Whack it with a screwdriver to see if it will come back to life. The pump only runs when the climate control temp wheel is clicked on max - not near max, it has to be fully on the max heat detent, or the pump won't turn on.
If possible, make the first run with the engine temp well under 80°C on the dash - this will likely be the best run. The first run should be with the dash gauge showing 60-70°C. The second run will probably have temps around 80-90°C, the third may be 90-100°C, and power will drop off slightly with each run as heat soak reduces power output. It shouldn't be much though, maybe 2-4hp difference for each run. Most of the time you'll see a 4-5hp loss from the highest to the lowest, this is normal. Past 100°C, power will probably drop significantly.
Note: Avoid letting the engine cool excessively... you want to keep the oil and ATF warm.
Optional: The factory documentation recommends using special tools (which are just fixed resistors) to "fool" the computers into thinking the intake air temp (IAT) is 20°C and the coolant temp is 80°C. The IAT tool (shown in attached photos) is relatively cheap, around $20 USD, and it plugs in at the wires behind the left headlight bucket. The coolant "tool" also shown below is much more expensive, it had been around $125, and is now $600+ with the Jan-2014 price increases. The effect can be duplicated using a couple of appropriate-spec resistors for a few bucks. This is less critical if you are able to get the engine temp down to 60-70°C prior to the first pull, so don't lose sleep if you don't have the temp simulators in place.
Ask if the dyno shop has a wideband oxygen sensor available. If so, request that you want the wideband readings. Some shops do this automatically, other shops only do this if you ask for it (and may charge a few bucks extra), some shops may not have this ability at all. This will show the air/fuel (A/F) ratio during the dyno runs at all RPM's.
Driving on the dyno:
With the tweaks above, you will be able to make the engine pull from approx 2000rpm to the ~6250rpm redline in 3rd gear, which will properly load up the engine. If you're behind the wheel (every shop does it differently - some shop owners will "drive" the car for you), put the shift lever in "3", accelerate just enough to get into 3rd gear, then back off the throttle slightly to bring the indicated speed to a bit under 20mph on a 500E with 2.82/2.65 gears (to bring RPM's down near 2000rpm), then nod to the dyno operator and FLOOR IT. When the tach reaches ~6250rpm, lift off the throttle, and move the shift lever to "D" to allow the engine revs to drop as the trans shifts into 4th gear. The end.
(Note: The starting MPH will be higher on a US/Japan spec 400E/E420 with 2.24 gears, and you may need to do the runs in 2nd gear if you have 2.24 final drive - especially if you have a 94-95 model with 130mph top speed limiter.)
You can also let the engine pull to the rev limiter before lifting off the throttle, you will know when this happens as the motor very clearly hits a "wall" where the revs stop increasing. Some aftermarket chips increase the rev limiter to approx 6600rpm, so you may want to test your rev limit BEFORE going to the dyno. You can do this by driving in 1st gear with the shift lever in "B" and seeing what the max tach reading is when the limiter engages. The dash tach is not always exactly accurate but it should be within ~100rpm or so if it's stock. If the tach needle has ever been removed (for example, to install white-face gauges) then it is more likely the tach is not accurate. An aftermarket digital memory tach can be used to get more precise readings if desired. AutoMeter offers a number of tachs with this function.
Remember that the standard 500E transmission starts in 2nd gear, so you will only feel one upshift (from 2nd to 3rd). If you have an electronic FGS system (like Bergwerks), this will be disabled when the kickdown solenoid is unplugged, but will NOT be disabled if you unplug the kickdown switch behind the gas pedal. YOU need to figure this out so you know what gear the transmission is in before you nod to the dyno operator and floor the pedal. The 400E/E420, and any 500E with a first-gear-start valve body, will have two shifts (1-2 and 2-3) before it hits 3rd gear. Do not do the dyno run in 4th gear. A dyno run in 2nd gear is acceptable if necessary, i.e. if the dyno cannot handle ~120mph rear wheel speeds, but a 3rd gear run is preferred on a 500E/E500. Again, for a 400E/E420 with 2.24 gears, do the dyno runs in 2nd gear, not 3rd.
The max speed (at redline) in gear should be roughly between 80-120mph on the dyno rollers, so adjust as needed if you have custom gearing in your differential, and/or a manual transmission. A car with 2.65/2.82/3.06 gears (all 500E/E500, and Euro-spec 400E/E420) will be in this range in 3rd gear, a car with 2.24 gears (all US/Japan spec 400E/E420) will be in this range in 2nd gear, assuming it has a 722.3 automatic transmission and near-stock tire size.
After the dyno session:
If the dyno is a DynoJet, ask for the electronic .drf files from the session. Some dyno shops may be able to email these to you. Other shops do not have their dyno computer connected to the internet, and/or may not be computer savvy to know how to do this. Bring a USB flash drive so you can copy the .drf files to your flash drive. These files have ALL the raw data from the dyno pulls. You can download free software from DynoJet which will let you create any graphs you want from the data, you can change the scale on the graphs, only show hp, or tq, or both, show A/F ratio or not, wheel speed, etc, etc. This is far more useful than a single printout that most shops will hand you on the way out the door.
Don't forget to re-connect the Bowden cable before driving home, and if you unplugged the front wheel speed sensor, re-connect that too. When you get home, re-connect the kickdown wire or switch (depending which you had removed). Ditto for the CTS & IAT sensors if you installed the temp simulators.
To determine estimated crankshaft power, divide the peak rear-wheel horsepower & torque numbers by 0.82. Example: A 500E shows 265rwhp. 265/0.82 = 323hp. This is estimating about 18% driveline loss, which is typical (within a percent or two) for a W124 with 722.x automatic transmission, and stock wheels/tires/brakes. Note what correction factor is used... common ones are SAE and STD in USA, and DIN in Europe. For USA, the SAE factor is more conservative. I personally prefer to use SAE as it's the most conservative of all the correction factors (AFAIK). The correction factor accounts for the temperature, humidity, and barometric pressure at the exact time & location you were on the dyno. Dyno shops near sea level often have little to no correction factor applied, as elevation increases the correction factor also increases. If you see something like "SAE: 1.05" on the printout, that means that a 5% correction was applied using SAE standards.
SUMMARY:
- Disable ASR
- Disconnect kickdown & Bowden cables
- Install stock wheels & tires
- Get engine temp below 80°C prior to first pull
- Ask for wideband readings
- Run from 2000rpm to redline in appropriate gear (usually 3rd gear)
- Re-connect kickdown & Bowden cables
- Turn on ASR or re-connect wheel speed sensor
- Remove temp simulators, if applicable
- Request electronic .drf files if it's a Dynojet
- Divide rear-wheel HP number by 0.82 to estimate crank power
A sample dyno graph is shown below, it is a 1993 500E with stock engine, stock 1993 LH module, stock wheels/tires/brakes/etc, run to the rev limiter. The average (SAE corrected) power readings of 258rwhp, divided by 0.82, equals 314.6hp estimated at the crank... darn close to factory spec of 315hp. Also note the A/F ratio averages right around 14.7 as expected for a 1993-up LH module which remains in closed-loop operation at all times.
The math can get tricky, especially when doing a 'reverse' conversion, i.e. from RWHP to estimated crank. It works like this:
Crank HP x 0.82 = estimated RWHP
Example: 315hp x 0.82 = 258rwhp (stock 1993 500E)
RWHP / 0.82 = estimated crank HP
Example: 258rwhp / 0.82 = 315 crank HP
