breaking up in top end, dwell problem?

[vtechnik]

My car is breaking up after 4500 rpm. I hear dwell is supposed to drop at higher rpm but how low should it go? I am also going to check fuel pressure tomorrow but since my afr is below my target afr and I am nowhere near my 100% duty cycle, I figured its loosing spark.

m20b25
single coil
stock fuel pump
60lb injectors
gt3076 rep
3 psi with a boost leak
bpr7es'
new cap, rotor, wires
old fuel pump, fpr, and coil

[varg]

Can't tell what your AFR is in boost in that screenshot, but if it's too rich it might be the problem. At 3psi you don't really need to be significantly richer than you would be at WOT in a NA car. Failing that, you might be have to tighten up the plug gap a bit depending on what it is now. You can try increasing dwell to 3ms but at 4,500rpm you might have already passed the point where there is that much time available between firings.

[vtechnik]

I was at 13.2 afr at 5k rpm. I didnt think that was too rich for wot?

[digger]

have you ruled out a trigger issue?

[Fraser]

What's your plug gap? I had terrible breakup at high rpms that I spent waaay too much time troubleshooting that ended up a being a plug gap issue...I can't remember offhand the gap I'm running now but it's significantly tighter than stock.

[varg]

If it also happens in neutral then it could be a trigger issue. I have no idea if stock plug gap is too big for so little boost and such a lean AFR, I started out at 0.024" with mine and never ran less than 12psi at high rpm because of boost creep. I ran 3.2ms nominal dwell with my stockish ignition setup. This spreadsheet I created illustrates how rpm affects max theoretical available dwell time as rpm climbs.

I was at 13.2 afr at 5k rpm. I didnt think that was too rich for wot?

Definitely not.

[vtechnik]

My plug gap is .025 on bpr7es' and im fairly sure I set my trigger settings up right. The cars on stands right now because I'm doing wheel bearings but once shes on the ground again ill give her a redline in neutral. I'll also post a picture of my trigger settings to be sure.

I need to get it tuned but everything is upside down with the covid. I'm not sure if I can find someone in the Pacific northwest who will be able to tune it right now. Is it best to wait it out for a tuner or do you think i could manage it for a while with a non aggressive ignition table?