Gas Mileage???

...good morning

So first of all Thank you for your help !! I apreciate this very much

@ aj/forms what does Squish mean ?

About the timing light... I have two a dial back from equs and a Bosch TL both show the same numbers...but the Dial back is not so good to use.. because of the MSD Dizzy...

About my engine....
340 block from 1973 ( with cast crank ) X heads from 1969 4bbl intake from 1971 ( Oem Cast Iron for Spread bore carbs )
MSD ready to run distributor ( so I can limit the advance very easy ) HP Manifolds
Passenger side: Part#2863549
Drivers side: Part#2863553

The pistons are Flat Top ( bought a endoscope to look inside the cylinders)
I am not sure if the former builder saved the heads.) The compression test showed
180-190 psi on all cyl. Vacuum @ idle with 16 deg initial is 15inches ROCK SOLID when I shift into DRIVE the vacumm goes down.... flucktrating very fast between 10 and 13 inches..

Sparkplugs are 65 Autolite

The Tranny is a 727 with stock TC ( still has the drain plug ) axle gears are 3.23
Tires are 225 / 60 /15

The engine runs with 180°F doesn´t matter if I drive on the highway...in the city..or whatever... So no cooling issues...

The Balancer seems to be o.k... I changed the timing chain /gears... and the TDC
mark showed exacatly 0 . ( Also the Problem existed before the chain change.. and the old chain had a lot of slash 1/2 inch )
Sadly I don´t know...what kind of cam is installed... also the CR is unknown.

Intresting thing.... I found out that the engine makes a lot more power ...if the curve is slower.... with a fast curve the engine sounds very stressed! Using the slow curve ( curve A or Curve B from the MSD Instructions ) the engine pulls like a
TRUCK... Using a fast curve makes the "pinging / rattling " issue worse

When I use less than 10 deg timing @ idle the engine shakes like hell... and I have to open the primary trottle blades too far...

I think to know whats going on ..I have to pull the engine ... pull the heads and the cam... also....:(

Greetings Juergen

Btw... forgot something.... The last curve I posted...is without VC ! The engine doesn´t accept the extra deg. of Timing....coming from the VC @ cruise speed ..50-60 mph till 45 mph everthing is fine... WOT also.... off the line... etc...