Flutter below 2k rpm

mbaird said
I have spent much time trying to get my 360 to run crisper below 2k. It is what I would call a flutter.
Engine is a 5.9 with EQ IMM heads (9.7:1)
222/229 @ .050. And .509 lift on 112 cam
Airgap with an AVS2 650
Dougs headers
Timing at 19* mech adv of 14* starting around 1000 and all in by 3000.
17* of Vac adv starting @ 12” and all in by 18”
Idles at 800 rpm with 14” in nuetral/12.5 in drive.
AFR is around 13.5 at idle and 14.5 at light cruise.
Cranking compression is 168-175 psi

I have tried both HEI and mopar electronic.
Orange and chrome boxes. 3 different distributors and installed new plug wires/ gapped the plugs to .034

Maybe I am just imagining this and its just the way it will run ?

Any thoughts?

Hang on, 168 to 175 @ Scr of 9.7 and with that cam at 2500 ft elevation is sending up red flags to me. And the vacuum seems a lil low for that cam also.......(EDIT, oh wait 2500ft elevation I get it now)..and the vacuum drop is too much
That looks like a 268/276/112, and should have an ICA around 64*. And I get
Static compression ratio of 9.7:1.
Ica of 64/elevation 2500ft
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.78:1 .
Your dynamic cranking pressure is .........................144.48 PSI.
V/P (Volume to Pressure Index) is ........................122
So........... something's not right.......

are those heads aluminum;
cuz if your pressure truley is 168 to 175, then you got too much pressure for iron......And if they are iron;they better be closed chamber/tight-Q.

Here's what you would need to make your pressure
Static compression ratio of 10.7:1.
Ica of 60*/2500ft
Effective stroke is 2.88 inches.
Your dynamic compression ratio is 8.80:1 .
Your dynamic cranking pressure is....................... 171.60 PSI.
V/P (Volume to Pressure Index) is...................... 149

so any updates?

I ran a 223/230/110/.538/.549 Hughes FTH cam in my 367 for 4 years @ ~185psi, on an el-cheapo ignition with aluminum heads, ~10.9 Scr and a Q of less than .040(brainfart at the moment) Very smooth idle, could hardly tell it was a performance cam at all.

My guess is the low-speed circuit in that 650 is running too lean, because the throttle blades are too far closed, cuz the 19* idle-timing is too much. And/or the secondaries are not sealed up tight but not sticking.

The idle of 800rpm is too high, as evidenced by the 1.5" of idle drop going into gear. This occurs because of the torque loss at the new lower rpm. The trick is to not have so much torque difference between idle speeds in gear and out. Your first go-to is the timing. Take some out. Reset the mixture screws to mid adjustment (2.5 turns on the AVS IIRC) then backout the speed screw to get 650 in gear. If it goes lean, you'll have to give it fuel from the principle low-rpm/low load fuel delivery system, not cranking out the mixture screws and not increasing the rpm to cover the hole. On a Holley this is done by changing the transfer-slot exposure under the primary throttle blades. But on an AVS I can't remember. Ok I just checked; the Thunder 650 has transfer slots too, which are the principle low-rpm/low load fuel delivery system.
You gotta think of the mixture screws as idle trimmers and and the transfer slots as the main low-speed circuit; the two have to be balanced, one against the other.
If you give the engine too much timing, then these two go out of sync.
If you need a higher rpm after this is done, do NOT move the speed screw, get you some bypass air . You can do this with the pcv circuit, or bypassing air under the throttle blades into the PCV circuit, or thru the throttle blades, near to the idle discharge ports. But That Hughes cam in my engine did not need any bypass air.

My Hughes cam Vacuum- peaked in neutral at about 2000/2200rpm with 45* total timing including the Vcan (22*). I cannot remember right now what the actual number was. Maybe it'll come to me later.

What stall are you running?