Flutter below 2k rpm
274/282/
[email protected];How in the world can you be making 168 to
[email protected], IDK. Might I suggest a second gauge?
And how in the world does that not ping with iron heads? Oh I see;290/
[email protected],
Are you running pumpgas?
Anyway, that's doesn't seem to be a problem for you and it ain't the source of your "flutter".
As for;
I did not realize I could adjust the blades on the transfer slot on an AVS other than the idle screw.
The idle screw is the only way;
You could try this;
>rev it up to 2000, using the fast idle cam. Check the timing and change it to 22*@2000, then connect the Vcan back up and recheck the timing, it should be about 39* with your 17* can. ( I would mod that can to pull in 22 or more and bring it in as fast as it can.
But that's another story.)
> now place a rag over the secondaries and monitor the rpm change; the secondary throttle valves should be closed up tight but not sticking. So there should be little to no rpm change, make it so.
> Next take that shoprag and bring it over the primaries, if the rpm rises, it's lean, so screw out your mixture screws; as far as 3 turns out. If the rpm goes down then it's already rich so screw them in up to 1.5 turns from lightly seated. If you can't get the rpm to stabilize between 1.5 and 3 turns out, then you will have to modify the slow-speed circuit. This assumes the PCV is working, The brake booster is not leaking and you have no uncontrolled air entering the engine, and that the cam-timing is about where it's supposed to be.., and that the 22*@ 2000rpm I guessed at is pretty close.
> kick the fast-idle off, remove all shoprags.
> Now you have the correct balance between low-speed circuit and the mixture screws. Don't touch them.
> if the idle speed is not what you want, then you will use idle-timing and idle-air bypass to get it. And then you will need to redo the 2000rpm balance test.
> I would suggest a slower than 800 idle speed to prevent a harsh N>D engagement, and a less drastic vacuum drop. You'll be targeting an rpm drop in the range of 75rpm+/- 25rpm, and a minimum in-gear rpm of 650/675, altho with those long slow clearance ramps, I guess another 50rpm might be required, those ramps are crazy-long.
Here is something to think about
with 295/301 durations (at .002tappet rise) on a 112, the overlap comes to 74*. That makes the total time for all events to be (360x2)+74=794*.. In at 108 the compression comes to just 105* and the power extraction is just 93* Ok so the total time when NO valves are open, is just 105+93=198*. Just over 1/2 turn of the crank. Jus saying.
So when you talk about "flutter", recall that the intake valve @.002T is opening at 40* BTDC, and The exhaust is not closing until 34* ATDC... so there are 74 degrees whilst both those valves are open. The idea is that with a good working header, it will create a favorable situation where the atmosphere at WOT will plow some extra air/ fuel charge into the cylinder.
But at idle, the atmosphere is not able to get in there. But the header is still working.
So picture this; with both valves opened, the exhaust header is directly connected to the intake plenum, and the header-pipe is at a lower pressure than the cylinder is..... so where do you suppose that A/F charge is headed? Hyup some of it is going straight into the header, never gets burned unless it finds fresh air in the exhaust system, and makes it's way into the atmosphere at the end of the pipe.If it finds fresh air at the header flange,and if catches fire, then it will burn right there... causing a pressure spike, and a portion of that may find it's way back into the intake, thru the still open intake valve.
But that's not the worst of it.
Consider that the intake valve may be at .003 open (.002 tappet rise) , as the valve is closing, at 75* after Bottom Dead Center, and the effective stroke is only 2.33 from that 3.58 actual stroke, and the piston is approaching half way up the compression stroke when it finally closes. So as the piston is rising, at idle, it is well able to push some of that A/F charge it is receiving, straight back past the still open intake valve, and into the plenum.
At 800rpm, this is happening about 7 times a second between all 8 cylinders, and this is why your vacuum gauge is reading 14" in N/P..
Ok so , is there any chance that your "flutter" is related to any of this activity?
Ok so when does all this crap activity stop? That's easy to figure out, with a vacuum gauge on the plenum, just slowly rev it up. The vacuum will increase steadily, then plateau, then begin to fall again. The lowest rpm that generates the highest vacuum, is the point that all the air,or at least most of it , is finally flowing in the same direction...
So, I gotta ask; is there any chance that one of your headers is leaking at or near the flange. As the exhaust is leaving the chamber with only 93* of burn time, the tail end of it may still be hot enough to ignite the fresh A/F charge coming in on the overlap cycle, in the presence of fresh air also coming in at the flange.
