Last week we spent time on the dyno with a couple of motorcycle projects that strongly demonstrated the benefits of individual cylinder tuning. The first one was a high-compression, high-revving small displacement 4 cylinder engine. The second was a 2 cylinder Ducati engine with relatively moderate compression and engine speeds. In recent years, we’ve been doing lots of work balancing air/fuel ratios, detonation limits and exhaust temps and found serious gains in both power and margin of safety.
There are a number of tools that help us do this quickly and economically. The new AEM 4
Channel UEGO amp quickly and easily allows for 4 lambda sensors to be installed in a motor, and for that information to be transmitted via analog inputs or CAN to your ECU or data logger. Their 4 channel thermocouple amp allows us to quickly and easily send 4 EGTs to the data logger as well, and the Pectel SQ6’s per-cylinder closed loop lambda control and knock detection makes all of this easy to do.
Here’s some of what we’ve learned:
- Having individual air/fuel ratio measurement doesn’t just help tuning fuel per cylinder, but can lead to improvements in your intake/exhaust system design. Especially in these engines where intake and exhaust tuning play a big role, there are dramatic differences in air/fuel ratio between cylinders. Often, its not just a “global” trim, but you find that the required fuel for each cylinder changes dramatically for different loads/engine speeds. There are general trends, but one of the most interesting phenomenons is “port robbing.” You’ll often find that richening 1 cylinder will cause another cylinder to richen as well, as fuel is actually being pushed back into the airbox. What this shows us is that either injection timing, intake trumpet length or exhaust header design can actually be modified for more efficient use of the fuel charge.
- A closed-loop multi-cylinder fuel trim is more effective than open loop. Fuel distribution seems to be much more sensitive to load and engine condition than overall fuel load. No matter how precisely we map individual trims on the dyno, the requirements seem to change on the street or track. An ECU that allows you to do closed-loop fueling adjustments per lambda sensor allows you to extract the maximum gain from individual fuel trims.
- Exhaust Gas Temperature Measurement (EGT) should be used as a guide, and care needs to be taken when balancing EGTs. EGT’s are an excellent tool for adjusting timing between cylinders as retarded cylinder will run hotter than ones near optimal timing. One challenge in using EGTs for trimming spark timing is that the installation can effect a lot. If one port is farther away from the others or too close to the exhaust valve, you will see significant temperature variations. The best way to look at EGTs is to find trends – what makes cylinders hotter or colder.
- EGTs can tell you when a cylinder is too retarded better than too advanced. For a lot of motors, cylinder temps rise pretty quickly as timing retards, but they stabilize over a wide range once you get close to optimal timing. This makes them a good tool for evaluating when you are close to optimal timing, but not always for if you’ve gone past it.
- Turbocharged engines have much more complex EGT demands. As boost increases, the backpressure and exhaust temps do as well. Also, its common to retard timing in order to prevent detonation. So to make sure that excessive heat doesn’t damage the turbocharger or exhaust components, its important to monitor exhaust temps in higher compression or high boost turbo motors, especially when ignition retard strategies like launch control, anti-lag or traction control are used.
- For detonation limited motors, individual cylinder knock control is a very important tool for maximizing power. On V8 supercharged offshore-powerboat engines, we were able to see over 10% power gains just from having individual cylinder knock control. We’ve seen similar situations on turbocharged Viper V10’s. Its amazing how much 1 or 2 cylinders can hold back the rest of a motor.
Our conclusion? When you’re ready to invest in maximizing your motor’s potential, put individual cylinder tuning near the top of your list. Take advantage of the great and reasonably priced products available to help with this, and find a tuner that understands the benefits and knows how to maximize them.