My guess is that atmospheric air is getting into your headers, right at the header flanges.
> you didn't mention your exhaust, but I gotta assume yur running headers.
My 276/286/110 cam (230/237), has 61 degrees of overlap. I suppose that yours has about the same.
The job of the headers is to create a low-pressure area, behind the exiting hot exhaust gasses. This helps draw plenum mixture into the chamber.
But, at lower rpms, some of the low-pressure pulses, that are created by the headers, now telegraphed into the intake, has time to pull mixture right across the piston-top, parked at TDC, and out into the primary pipes, where, if it finds even a hint of fire, it will explode, sending a reverse hi-pressure pulse back into the chamber. If the intake is still open at TDC/overlap that pulse can easily make it into the plenum. So now, your poor sniper is having to deal with all those pressure pulses going in different directions inside the common plenum, and in the single-plain, those pulses are all of them, right under the throttle-valves, and I bet in close proximity to, the load-sensing vacuum device..
>IMO, the TB spacers are likely helping to contain and dissipate this mess.
>IMO, fixing the header leaks will fix the problem, or most of it.
>IMO, a dual-plane will help contain and dissipate the rest.
>FYI the Edelbrock Airgap on my combo pulls hard to 7000, which is my typical shift-rpm, when ramming thru the gears.
Do not think that, on the street, you may need more intake than the AirGap. Mine makes enough power to post 93mph in the Eighth.
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My engine-combo is very similar to yours.
You said;
mine is;
Engine I'm working with is 360/40 over, 3.58 stroke
with 318 floating wristpin rods, and
KB107 pistons,
currently she is at 11.0 comp.
Cam is a Hughes 549/571 lift/ 276>286/110&230>237@050;
Heads are OOTB Eddies.
She runs an untouched Airgap/750 DP/no spacers.
She is getting fresh cold air from above the hood, and
She runs TTI headers with full-length 3" duals. And,
I run it at 207*F.
> IMO, she runs, perfectly at all throttle/load settings with no flat-spots and no hesitations of any kind.
> until recently, the plugs were new in 1999.
> As to Timing;
she will idle down to 500 in gear and smoothly pull herself along, at 5* advance. Her normal timing is 12>14 at idle, going to 28* at 2800, then tapering to no more than 34*@3400.
The V-can pulls in 22 degrees by 13 inches.
The cruize-timing is thus 50* at 2800, to which I can add up to 15 degrees from my dash-mounted, dial-back, timing module, but rarely does she run over 60*
At 2240=65mph, in GVod, the cruize-timing is usually about 14+10+22+6= 50*; but she gets a lil better gas-mileage at closer to 60*.
I know that cam. I've been running it since 2004. I run it straight-up with no advance. it likes a little bypass air from the carb.
In straight up, it doesn't clean up until about 2200>2400 rpm. Until it does, the vacuum is somewhat unstable. If I want to run something off the intake vacuum, I install a restrictor in the line, to smooth it.
I run a 4-speed/3.55s, so intake vacuum is always high enough to operate my power-brakes. Except for first thing in the morning. But by the time I get her backed out of the carport, the booster is on line.
Good luck.