Ignition Advance Curve for 124" Engine

[Ron A]

I have a S&S VFI 124 with D&D Boarzilla 2:1 exhaust and teardrop air
cleaner in a 2003 Road King.

My question is about ignition timing advance curves for large
displacement V twins.

The 124 tune files available from S&S all have timing advance curves
that max out at about 23 degrees full advance at about 5,500 RPM at
WOT. Very mild curve I would say. I have tuned mine now to reach full
advance of 28 degrees at 5,250 RPM. Bike seems much quicker with the 5
degrees advance I added, and there's no pinging. A friend of mine, also
with a S&S 124, but carburated, has set his max advance at about 37
degrees, reached at 4,500 RPM and says he doesn't experience any
pinging. He recommends I do the same. I'm nervous about going to as
much advance as my buddy. I've read that large V twin engines should
not have full advance over 28 degrees.

What would you recommend for full advance at WOT and at what RPM should
that be achieved, for this size of V twin engine?

[Mike]

Timing seems to be all over the map on these. We have had 124's with Dyna ignitions run best on the least aggressive curves. In theory, we want as much advance as possible without detonation. This is exactly how the S&S IST system works. On race bikes we always wanted a lot of advance down low and early but then taper back as the RPM's gained. This seems to be the case with our Destroyer, it does not like a lot of advance up high but has much more at lower RPM's. We saw dramatic difference's in MPH when we tried uping the advance, yet ET's better with more in the mid range. I would advise trying advancing until yo get detonation then backingdown from there. Just be sure you are not masking possible detonation areas by overfueling. I.E., the fuel mix needs to be reasonbly close for timing changes to be readable. Generally, the richer your fuel mix the more timing you can run. But if you ramp up the timing and then lean out the fuel, you may get into detonation where it would not before the fuel change. To finish, we have much better combustion chambers than in the past so timing numbers tend to be lower than what we are used to. Most of the big motors we have built seem to like 26-28 degrees with full advance at 3200 RPM. Lower compression motors (8-9:1) will want 2-4 more degrees and higher compression (10-12:1+) will want 2-4 less as a function of that compression. Some motors may even make more torque with 32-35 degress from 2500-4000 then tapper back for HP. Detonation is the key, you may have to go there to find those limits.
Thank, Mike