2-3 kpa "flutter" logged at WOT in upper RPMS

[S351 R]

Reviewing some data logs for n/a SBF 427 with FAST Classic. From 5k rpm up the lines for kpa/vacuum are zig zagged thru 6k rpm shutdown. RPM likewise zigs that last 1000 rpms. It is very pronounced and eratic when overlayed in the VE table playback.

This was on a DTS engine dyno. The HP/Tq curves look smooth enough though it definitely peters out at 5700 and short of what HP I was expecting.
EGTs were 1250-1400 with couple cylinders with 1200's and couple with 1400's - any evidence here between a cold or hot cylinder? Standard full runner EFI intake.

Is this a valve or valvetrain thing that effected the vacuum signal or just something with the dyno?

Any $.02 is appreciated.

 

[HighPSI]

The 2-3kpa flutter you are seeing is not uncommon, depending on intake design and where your sensor is located. Are your valvesprings up to the task?

 

[S351 R]

Vavle springs should have been fine. Matched to cam with 160 seat / 410 open. Ramps shouldn't be too harsh - 293/307 @ .006 and 242/254 @ .050. and 585/585 lift

Would the corresponding bounce in RPM in the same area be fine too? More a matter of the sensitivity of the logging sensor?

Thx

 

[Blazer406]

lifter/pushrod/valve/valvespring/lock/retainer

They all play in to what a valvetrain is good for. My brother does valvetrain design for a living......one of the tools he uses is a "SpinTron"..........it spins a special engine at various RPM's and monitors valvetrain motion up to like 200,000 times per second.........

SpinTron

One thing for certain.......valve bounce off the seat is hard to predict......there are so many variables.

I would say... it "could" be valvetrain related. You could do some experimentation with some different springs....or something and see if it made a difference....

I know that doesn't help much....

 

[Chuck Leeper]

Ign going away??

 

[S351 R]

thanks gents,
I'm with ya on how all the valve train needs to be up to the task. Would not expect issues from new setup starting as early as 5k though.

As for ignition - dont know how to trouble shoot that one. Engine dyno was run off of Yellow top battery with 12.2 steady. FAST, TFI and Distributor all proven off of car and previous setup. Running cold AL 3922 plugs side gapped to about .030". Also, if I was losing spark I would have expected it to show something more obvious in the EGTs.

This may all be turbulance in the plenum effecting the MAP signal and nothing bad. As for the RPM roughness up top, maybe get this on a chassis dyno once complete and take it from there.

File attached - maybe legible...
Thx