RPM spike during WOT(FAST). Detonation? SC Belt?

[S351 R]

During a datalog for WOT 3rd gear, I had fluctuations in RPM, Boost, and corresponding Timing over about 4/10 of a second. Since it effected a few of the logged parameters I see this a engine related rather than FAST.

It created a malformed W and fluctuated between 4400 and 4800(middle of W) during that short time, and was much more pronounce than simply the usual "rough" rpm line. I remember the motor felt like it got a little soft at the top, but that seemed closer to the 5100 rpm that I shifted at as soon as I felt it.

FWIW, this was at 8-10 psi running 104 octane in 50*ambient.

Any thoughts? Momentary Supercharger belt slippage? Is this what detonation may look like in a log?

 

[Otto J]

email me a datalog and a gct file,id like to see them,Possible tire spin?

 

[S351 R]

I'd be surprised for tirespin only because Ive got BFG DR's and it was only for 4/10s of a second. Momentary clutch slip?

I cant seem to attach the files, but will try to email, and appreciate the look. In fact Id be indebted to ya if you gave them the once-over in general since no one else has helped me with tuning thus far.

 

[norbs]

What kind of belt are you running
?

 

[Otto J]

I tried to email back but it wont let my email go thru

 

[EightSecV6]

Are you using a DIGITAL MSD?

 

[S351 R]

The belt is a "Napa" brand. It was cranked on pretty good (+/- 85ft.lbs). Has belt dressing which makes it sticky to the touch. Standard Crane HI-6 for ignition.

Otto, got your email and very much appreciate the changes. I do not have a log showing such a pronounce but short variation; rpm is generally rough though thru the run (figure this is normal sampling).

At this point, I'll hope for a little momentary tire spin, (and not clutch!) and keep my eye on it. My concern about what detonation looks like in a log is what prompted such a hasty post.

Thanks again to all

 

[norbs]

If its not a coged belt it will slip over 10 psi no matter what. It desgined to slip to give more life to the unit.