mpg on my 340

brasil said
...I have a Carter Trick KIt... also jets from 95 -to 105
Rods..... so I can lean out the carb..
So the Carb is not the problem... the VC is the Issue...

Today I checked my timing.. ( after I changed the set up in the Distributor)
12 deg @ idle... 17 deg @ 1500 rpm 24 deg @ 2000
29 deg @ 2500 and 33 deg. @ 3000 rpm.. ( without the VC ! )
With VC... the timing goes up to 46 deg. @ 3000

But if I use the VC,,,I always have this klicking /pinging sound when I drive steady in the 50 to 60 mph range...
60 mph ...in my case equals 2650 rpm... more or less close to the peak of the timingcurve...with /or without VC... The engine accepts 33 deg... of timing...but the 13 deg from the VC... are too much...
The VC is connected to the Ported vacuum btw.
so perhaps I need to reduce the VC a bit more.. but then
I will end up with 42 deg.. all in..incl VC.
Greetings Juergen

Sounds like you know what's going on, thanks for the details... I think adjusting the vacuum advance can is all you really need to do. It won't reduce the total degrees from the VC but will make it so the advance doesn't come in until you have more vacuum. Does it ping all the time even on a flat road with the VC hooked up or is it more when you come to a hill and you give it a little more gas pedal to maintain speed?

Regarding the thread topic FWIW I average 16 mpg about 60/40 city/hwy with my 10.5:1 360 w/ Mag heads, 904 auto and 2.94 gears. Highway is probably closer to 19-20, city prob around 14-15. I'm expecting it to go down when I swap in a bigger cam and 3.55 gears, how much I'll have to wait to see.