SDS:Tuning

I just wanted to offer some tips on tuning SDS for those with programmers and some warnings.

This is what I do when tuning a system in an aircraft:

You should have a wideband AFR meter such as PLX, AEM etc. before attempting any programming.

1. If your engine has been sitting for some time, injectors may be stuck shut or flow unequal rates. If there is ANY question about equal flow rates on your injectors, have them flow tested before any power runs. Unequal flow rates will cause lean and rich cylinders. The AFR meter only reads the average of all cylinders mixture. A cylinder running too lean can cause a piston failure and all EFI systems depend on having near equal mixtures in all cylinders. This is a mechanical issue that must be 100% right.

2. I like to have someone else adjust power while I work the programmer. This is also a safety thing. The other person can watch for people around the prop and making sure your prop blast does not impact other aircraft, watch water and oil temps etc. Not good having your head down in the cockpit. You have many things to watch here.

3. Have both people on the brakes, tie the aircraft down securely and chock the wheels too. Hold the stick aft.

3. Before starting fuel mapping, you should have already set the MAGNET POSITION parameter using a timing light. This is critical so you know what the actual ignition timing is.

4. Basic guidelines for ignition timing:

atmo engines running 100LL or mixes of at least 50% 100LL- no more than 32 degrees total timing at WOT

atmo engines running 91 octane fuel with less than 9.5 to 1 CR- no more than 28 degrees total timing at WOT

Turbo or supercharged engines running 100LL or at least 50% 100LL- no more than 32 degrees total timing at full boost running under 40 inches MAP.

Turbo or supercharged engines running 91 octane fuel- no more than 25 degrees total timing at full boost- less if you run over 35 inches MAP or if the CR is over 8.5 to 1.

5. Most adjustments will be with the RPM FUEL parameters. Don't mess with the MAP values initially.

6. Incrementally increase rpm in 250 rpm steps using the SDS programmer rpm as the reference. Stabilize at each point ie. 1750, 2000, 2250 rpm etc. Look at the AFR when stabilized at each rpm break point. Aim for an AFR between 12.5 and 13.0 to 1, Adjust the rpm fuel using the + or - buttons until you get this AFR, then move on to the next point. If the AFR gets leaner than 14.0 at any time, throttle down quickly and add some more fuel at that point before proceeding further.

7. Once programming all rpm fuel values, the power part of programming should be completed. You may still have to program for cold starting and want to tweak part throttle timing advance etc.

8. Do many ground verification runs to be sure mixtures are stable throughout the entire operating range.

I also recommend using one heat range colder plugs in all Subaru aircraft engines to reduce preignition possibilities.

On supercharged or turbo engines, IAT (intake air temps) should never exceed 60C (140F) as this seriously increases the chances of preignition, especially on mogas.

We prefer not to see EGTs exceed 1500F on Subaru engines. More fuel or more timing advance will reduce EGTs but be careful about getting close to detonation limits.

I am not a fan of running supercharged engines with cast pistons on 91 octane mogas as I've seen numerous piston problems. If you must, be very conservative with AFRs, ignition timing, EGTs and coolant temps.

rv6ejguy