Md
-I cant help you with the 440, as Ive never owned a BB.
-But, I may be able to help you on the 340.I have for 14 years striven for mpgs with my combo;360,10.7c/r, closed chamber eddies, .035quench, At that time;Hughes 223*flat tappet cam, 1.6arms,AG,Holley 600V-sec.I will tell you what worked for me, and you can take it from there.
-This assumes that the current tune is sharp.I see you have a 270* advertised cam, and 9.5 c/r. I see you have 24* initial and 34* total, and a 14* can.
For yours,if the the 34 is all in by2600(not likely) and the cruise vacuum is greater than 14", then the max timing available would be 34 + 14 = 48. For economy this is at least 10* short. My closed-chamber tight-quench Eddies liked 60ish degrees on 87 octane. Remember that 87 burns faster than 93, and open chambers like more timing than closed. I have been shopping for years for a 20* plus can, without luck. My timings were 14initial/34@ 3600, so at a cruise rpm of 2200, getting 60* was impossible.I think I was getting about 38*cruise timing, at the start. To overcome this I did 3 things. 1) modded my can,and 2)modded my mechanical curve, and 3) bought a dash mounted electronic dial-back advance unit.
-As to the can. This involves carefully grinding the stops back.I did this many years ago, so dont remember how much I got. Ima guessing 4*. So that got me an 18* can.
-As to the dial back device, theres only 15* max in it.
-So by now I was getting about 42*, at 2200rpm. The engine wanted more. I went back into the dizzy. I played around with springs for quite a while. i finally was able to build a 2 stage curve using a little spring and a big fat one with a long area where it didnt do anything. This gave me a very fast 16 *, and then the last 4* didnt come in til much later. So now I had 48* max. Still a lot short of what the engine was looking for.
The only option I had at this point was to increase the initial, bit by bit until the engine started complaining.But I had to bear in mind that power timing was running higher as well, so I would have to keep my foot out of it. To that end I blocked the secondaries disabled. This testing often went on for weeks so I wasnt sure if Id remember to not floor it. So what I discovered was the engine kept responding positively to more and more timing.Eventually it peaked around 56*.
-Now heres how I let the engine tell me what she wanted.Once I had the 2-stage curve in the dizzy, and verified that it wasnt detonating, and the can adjuster set full soft, I would pick a number out of a hat like 38*. Then with everything hooked up, and the dial-back device set to the midpoint of its adjustment,I just revved her up to 2200 and set the timing to 38*.Then with a large face vacuum guage installed in the cab, I would drive it.
-Oops I forgot to mention; I had previously fabricated a 2-stage throttle spring device that would work like normal and let the engine pull to 64mph(2200rpm)on the stop. Then I had a second stiffer spring engage from that point on. With this device I could always find the exact same throttle setting.
-So away I went. I had previously chosen a flat level stretch of highway, on my way to work.So every time I entered this stretch, I would check my v-gauge and mph.Then I would crank in 1/2 of the remaining travel on the D-back(about4*), and watched the mph.Honestly the V-gauge didnt help, so it didnt take long and I ditched it. The speedometer on the otherhand, told the story right off. So if the mph went up, I knew I was making more torque.So I would repeat this every day for a week and if the results were the same, then I would readjust the throttle stop the next week to get the mph back to the start mph. At the end of the week I would return the D-back to central and retime the engine another 4*.The following week was a repeat of the first and so on. As the weeks went by gains were harder to get and harder to verify, so I backed up to the last test that had good results. Then for weeks I drove with just playing with the D-back. Eventually, after 2 summers, or more, I came up with a number.
-Now lest you think that the secondaries were blocked the whole 2 summers, and I never had any fun,no not at all. There were lots of weekends in between where I returned the timing to the norm and blasted away on it.
-I should also mention this. I had previous to that time a selection of pumpkins to play with.The way I chose one for this test was; With a vacuum gauge hooked to manifold vacuum, and a fully warmed up engine, and all timing systems hooked up, I simply slowly reved the engine up until it vacuum-peaked.I reasoned that when this peak happened,reversion in the manifold had quit and now the engine was beginning to become more efficient.There would be no benefit, I reasoned, to gear it to run any slower than that,at cruise speed. The number was around 2200 so thats what I geared it for.This happened to be my favorite gears, the 3.55s, with a GearVendors O/D unit, behind my 3.09/Direct box.
So now I knew where the timing needed to be.Now I had to play with the Holley.The leaner I made it the earlier I had to start the fire.Thats how I ended up at 60* and 32 mpgUS, on a 600V-sec.
-Carb-tuning;Whole new story. But you have a TQ, which is way more adjustable in those circuits.
-So thats my story, as best as I remember.Hope it helps.
