Getting into the story now I guess...
My engine and car at the present time:
- 461 cubic inches (4.25 stroke x 4.155 bore)
- Heads: 72cc Edelbrock round port. "Entry level" port work by Dave Wilcox. 2.190 intake valves, 1.77 exhaust valves.
- Cam: Bullet solid roller. 251/257 @ 0.050, 110 LSA, installed at 106 ICL. .625/.623 net valve lift after allowing for valve lash
- Rockers: Crower stainless, full roller, 1.5:1 ratio
- Lifters: Crower solid roller, HIPPO oiling, needle bearings, standard height, cutaway
- Valves: Ferrea - Ram Air IV length
- Springs: PAC double. Installed height 1.910. Seat pressure 230, open pressure 570
- Retainers: PAC Titanium
- Locks: Isky 7-degree super locks
- Timing set: Rollmaster double roller (.005 short due to align hone)
- Balancer: Romac - SFI rated
- Compression: 10.3:1
- Crank: Eagle forged
- Rods: Eagle H-beam forged 6.700 length
- Pistons: Ross forged, full floating pins (double spirolocks) D- shaped dish
- Windage Tray and Crank scraper: Spotts performance
- Rotating assembly neutral balanced by Butler performance
- Oil pump: Luhn Performance 80 psi
- Intake: Northwind - single plane
- Carburetor: AED Performance 850 HO Annular
- Fuel pump: RobbMc 1100 mechanical, set to 6 PSI output pressure, RobbMc regulator at carb inlet (set to 5 psi)
- Flex plate: TCI SFI rated - neutral balance
- Converter: Tri Shield Performance 9.5" (I'm REALLY liking this! Drives like a stocker until you hang your foot in it)
- Transmission: TH400
- Rear: Moser 9" - Wavetrac diff - 3.50 gears
- Instrumentation: Factory Rallye gauges supplemented by AEM Digital X-series Coolant Temp, Trans Temp, Oil Pressure, Wide band UEGO Air/Fuel meter
- Ignition: HEI with Davis "Dyna Mod" module
First challenge after getting it running and driving has been trying to balance the settings for idle and low speed part throttle cruise. When I first got it running, I was able to accomplish a reasonable idle "in gear" at about 750-800 RPM, A/F ratio in the 13 to 14 range which produced an idle vacuum of around 7-8 inches Hg. The idle was fine. However cruise was not. Even the slightest pressure on the throttle, enough to barely start the car moving and send the rpm up to about 1500 would send the A/F mixture plummeting into the mid 9's, even high 8's. There it would stay pretty much 'everywhere' at a steady state cruise. Getting up to around 60mph would see it creep up into the high 9's, low 10's but this was still WAY too rich. Getting dangerously into fuel wash territory - so rich that raw fuel could be getting into the cylinders and diluting the oil.
I tried jetting the carb down which did nothing really. I tried fiddling with idle mixture to get it as lean an idle as I possibly could. Right away I got into a Catch-22 situation. If I adjusted for a lean idle in neutral at around 900 to 1000 rpm, say mid to upper 14's on the A/F meter, as soon as I put it into gear it would shoot up WAY lean - 16's, 17's, 18's - and higher. A few times I saw it go so lean that it was above the gauge's ability to register it. I wasn't able to find an idle mixture setting that would let it idle at 800 rpm in gear without it going super rich driving. I couldn't figure out what was going on. I bought Dave Vizard's book on tuning Holley's but didn't find anything that addressed this specific problem. I started reading everything I could find on the net. That's when I found this thread on a Mopar forum:
Holley Rich at Light Throttle | Moparts Question and Answer | Moparts Forums
It seemed to fit with what I was seeing. The thread also mentioned getting into a situation of not being able to get both idle and cruise into an acceptable mixture range at the same time, and why.
I found threads that mentioned "transfer slot restrictors" that seemed to make sense. The transfer slots provide fuel to the engine during the 'transition period' when the throttle has moved off idle but hasn't yet been opened enough to cause the main circuit/boosters to come online and start feeding fuel. This engine makes so much torque that the majority of the time it's running on the transfer slots, even at 50-60 mph. The force that causes fuel to feed through the idle circuit and also through the transfer slots is primarily engine manifold vacuum - not air flow through the main venturis. The problem is, at an 800 rpm idle manifold vacuum is less than 10, but as soon as rpm starts to come up manifold vacuum comes up too, and fast. I hooked my gauge up so I could read it in the car, and once the car gets rolling and it's running at 1500 rpm or better, manifold vacuum is at 20 or better so it's "sucking" a lot harder on both the idle circuit and the transfer slot circuit. This explained how it could be 'right' at idle but sloppy rich at cruise. The problem then was how to get fuel flow to even out over such a wide range of manifold vacuum.
.... to be continued