2000 Magnetti Marelli open look system, stage I flash, S&S 970 cam S & S 100" kit, ported heads, Thunderheader, Power Commander III USB

I could really use a little guidance from you tuning experts regarding ignition timing.

Had the bike dyno'd so the mixture is pretty close, but the shop does not tune ignition because they don't have the equipment to do it (which I think really means because my bike predates knock sensors.) So, I'm left to my own devices to get the timing right.

Had some pretty good detonation going on in the 2000 - 4000 range under load in hot weather, so I took away 3* timing across the board, and another 2* in those ranges where I had some residual knock.

It's running a little flat off-idle, so I added 5* to the idle RPM ranges, which caused the idle speed to increase noticeably but not hugely. I suppose that means peak cylinder pressure at idle was occurring later than optimal? My concern is that I might have the timing retarded too much now across the board, though I have cured all knock that I was able to hear by ear.

Anyone with expertise on this care to share their thoughts (other than my dyno shop should have done this)?

 

Sometimes a little extra fuel where it is knocking in that load range is better than retarding the timing.
I would put the timing back to where it was and just lower the AFR in those cells where you think knock is happening and see what happens.
Don't go overboard though as some extra fuel and 1 degree of timing removed can fix the problem

 

super duper +1 mr. scotty3

 

I suspect that the 970 is really a 570 cam. That cam will be flat off idle due to it's excessive exhaust duration. They do better if an exhaust reversion step is left in the cylinder head when porting. Another way to pick up some low end performance with the 570 cam and the thunder header is to bend the baffle tabs on the exhaust pipe outward to block off some of the exhaust flow.

It doesn't surprise me that you've had to pull a bunch of timing. Going from a stock motor to a built one with a cam that has overlap will increase dynamic compression a bit and 100 ci kit will increase the corrected compression as well. Also adding 1/4 inch to the bore increases squish area which increases combustion turbulence for a faster burn. All of these changes increase volumetric efficiency and pre-combustion pressures. Higher pressures mean fuel burns faster and timing needs backing off or detonation will occur.

As far as idle going up generally you can increase idle timing and have it go up on a fuel injection system if idle control is not closed loop. I don't know how the Magneti Marelli system controls idle.

 

Thanks guys for the tips, and thanks @Max Headflow for the very helpful write-up on my cam, what to expect from it (and why), and how to get the most from it. Really appreciate that!

Scotty and buster, appreciate the tip on enrichening as a means to combat knock and I'll toss that into the mix as I work through this.