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Discussion Starter · #1 ·
Since I am getting ready for a big dyno session for the CRM header/exhausts and the Zard tuning, and because several S3 owners have recently contacted me about why their bikes showed low numbers on the dyno, I thought I would show what needs to be done prior to a dyno session.

Tuning on the dyno is all about getting consistent and repeatable results. If each pull on the dyno has a big variation, then you cannot tune accurately and know that the results your are getting are from the tuning, and not from the bike being inconsistent.

First, check the chain and sprockets. A worn sprocket can rob power like you wouldn't believe. The chain tension needs to be correct - a touch loose is better than a touch tight. The chain needs to be cleaned and oiled very well.

The cooling system needs to be in good shape. Old coolant or coolant with too much antifreeze cannot pull heat from the engine well, and the engine will need long cool down periods between runs if the cooling system is not working correctly. Each run needs to start at the same engine temperature.

The engine needs a tune up. Fresh oil, sparkplugs, and a good removal of all carbon in the cylinders and on the valves needs to be done, or each run can get a bit better (inconsistently) as the carbon is blown out, and really screw with your attempts to tune. High levels of carbon on the pistons will alter the compression, airflow, and combustion characteristics in the chamber. Fresh oil can make a big difference as well. Make sure the oil level is a touch low and not a touch high, which can increase windage in the sump as the oil is whipped around. make sure the air filter is CLEAN.

Make sure the exhaust gaskets are NOT blocking flow - especially at the collector mid-pipe joint.

Make sure the tire pressure is correct, or even a bit higher than you ride the bike. Low tire pressure increases friction on the dyno roller and in the tire itself.

If you are going to be spending a while with the bike on the rollers, pull the relay and fuses for the lights. This will save battery voltage. Also, TuneBoy users need to keep the cable connected for the least amount of time required - Leaving the ignition on robs battery voltage too.

Take a few tools with you. If you will need to pull the fuel tank, airbox, etc., then make sure you have the tools needed. Also take a USB flash card so you can copy the files from the dyno computer as well as have a printed copy. You can download the DynoJet file viewer here - http://www.dynojet.com/downloads/software.aspx

When you strap the bike down on the dyno roller, make sure that the straps are not too tight, and that the tire is positioned just behind the top of the roller. It will climb the roller when you apply throttle. You want the straps firm to support the bike and keep the tire in contact with the roller (no slipping). But too tight will add unneeded friction.

If the dyno operator does not get a tach signal, your graph will only show power and speed with air/fuel ratio (AFR). With a tach signal, you will get power and torque over rpm with AFR. To get a tach signal, you will need to place a small inductive clip (from the dyno) around the wire to one of the coils. The wires to the coil on cylinder number 1 (left side) are the easiest to reach. You may need to slot the cover on the coil wires so that you can have enough room to get the clip on them individually. Be careful, and use a sharp razor blade or similar. Do not cut the wires or their sheathing.

The dyno will have its own wideband oxygen sensor. This usually consists of the dyno operator sliding a copper tube into your exhaust. Make sure it is in the right side silencer on dual exhaust equipped bikes, and that the tube is not placed so that the end is against the bend in the exhaust. It needs to be in a good unobstructed flow of gases.

Before you make the first pull, get the bike (coolant and engine oil) up to temperature.

The first run will be low. This is due to the engine likely being a bit cool (not fully warmed up throughout the engine block) and the carbon still in the engine.

Runs through the gears will likely have little power peaks when you shift gears. This is false power, and cannot be trusted - it is NOT the peak power. Run the bike in the gear closest to 1:1 gearing. This is 5th gear on the S3. I like to tune in 4th gear, and test power in 5th gear. This tends to give a good tune even for lower gears as load will change the fuel and spark timing the engine wants for best power. For Drag racing, tuning in 2nd gear can make a difference on some bikes with heavy riders. ;)

After a tuning change, make 2-3 pulls and compare the torque and air/fuel curves. If they are consistent, then you can make another tuning change.

To get good numbers at the end of a tuning session, I like to make 5 pulls. I throw out the highest and lowest runs, and average the middle three. This gives you a good consistent idea of what power and torque the bike actually produces.

This is not all inclusive, but should give you a good idea how to prepare your bike for a dyno session. I hope it helps.

:wrench: :wrench: :wrench:
 

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We need a Devious2xs bible for engine tuning success. I would buy several copies, and give the gift of knowledge to several good friends.
 

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Discussion Starter · #4 ·
Nothing fancy guys. Just lots of lessons learned on dynos on several bikes and cars.

TOO much money spent on dyno time. :horse:
 

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And as Grant Matsushima mentioned in an interview about his 600cc Supersport bike something as simple as fitting the lightest available rear tire can be good for 10HP....
 

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nm3holer said:
And as Grant Matsushima mentioned in an interview about his 600cc Supersport bike something as simple as fitting the lightest available rear tire can be good for 10HP....
Another one is to stick a piece of tape in the rear tire. The tire spins and hooks up giving a mighty peak in the curve.
 
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