1972 390 dist.advance
 

Went on a road trip last week and was not happy with my 390's power output.This engine has 6000 miles on it, 30 over, comp rv type cam (don't remember the part #),Edelbrock Performer,Edelbrock 600 4v,stock dist.& Petronix ignition,C6,3.54 gears,2wd and about 3000 lbs extra weight to boot. From a dead stop it will run ok but when going up hill it really falls flat and lacks any get up and go.I can not get the passing gear to kick in and the vaccume secondaries will not kick in.It rained all weekend and I have not had time to look at the carb secondaries or the kickdown but will try next week.

I checked the timing and it is still at 8 degree btdc and when I run up the rpms the timing reads 28 degrees btdc.Is this a standard swing for the advance or do I need to look further into the dist.At idle and any other rpm the timing holds steady and does not jump around.I am pulling vaccume from the front port on the carb and when disconnected from the dist there is little change to the timing.Any imput is appreciated as I do not know enough about this part of my engine and would be guessing at this point.

"bowties in the rearview mirror" 8D

Put a vacuum gauge on it and see what it reads, then see this:
vacuum gauge interpretation

Why did you rebuild the engine? Did it run better before the rebuild?
This sounds silly, but I knew a mechanic that replaced an engine and still had the same problem, it turned out to be clogged exhaust.
You should be able to run a little more advance on the timing. Try 16 degrees advance. If you hear it ping (sounds like shaking a can with a few marbles in it) back the timing off a bit.
Another simple thing, you probably already checked, make sure the carb goes to full throttle when the peddle is to the floor.

I would try advancing the timing to 12 initial 32 advanced.

I don't run a motor on anything less.

[QUOTE=Nod;9707989]Went on a road trip last week and was not happy with my 390's power output.This engine has 6000 miles on it, 30 over, comp rv type cam (don't remember the part #),Edelbrock Performer,Edelbrock 600 4v,stock dist.& Petronix ignition,C6,3.54 gears,2wd and about 3000 lbs extra weight to boot. From a dead stop it will run ok but when going up hill it really falls flat and lacks any get up and go...

3000LBS More going up hill.. I would say hopefully you build the motor for towing with a low end torque cam these will do your pulling up hills. Where as and mid range cam will not give you the pulling rpm range needed..

The vacuum carb port will not have much or any vacuum at idle, this will increase as rpm goes up advancing the the Vacuum-advance..so leave it their..

Remember you can't advance the timing much when towing very heavy loads.
Plus what size of tires and rear end ratio your running all adds up to the way you've camed the motor. All thing to think about..my 2cents
orich

timing
 

Well I just got back from another long road trip and this time I got better fuel mileage,about 10 mpg but not much else.I moved the timing up to 10 degree btdc and it helped a little with fuel mileage and a little more pulling horse power.I did build this engine for low end pulling,I had to rebuild it as the last engine had about given up the ghost.It has not quit raining but before my next long run I am going to run the timing up to 12 deg BTDC and check to make sure the carb is opening up all the way under full throttle position.I do not have a vacuum gauge but will try to borrow one as soon as possible and do a vac test as per the information above.Thanks for all the imput.
"bowties in the rearview mirror" 8D

Any kind of upgrade in a cam from stock will benefit with additional timing.Try setting your initial timing(idle)at 16-18 degrees BTDC.Then make sure your total timing is in the ballpark of 36-38 degrees BTDC.You want the total in around 2800-3000 rpms.To achieve the total,you have to play around with advance springs on the weights to find that sweet happy spot.You also need the right advance bushing to stop the total from going over 38 degrees.They make several size bushings to achieve this goal.In my 30 years of experience with working on motors,I find this setup,especially with upgraded cam to be very effective and beneficial for more performance and power gains.Obviously,if you are running a distributor with vacuum advance,you disconnect the vacuum line from the distributor and block it and then set up your initial timing and then zero in on your total.Make sure to do this procedure at a low rpm so that mechanical advance is not partially activated.Once you get the initial dialed in,move onto the total,and finally reconnect the vacuum advance to a full manifold supply port.This will help out with idle characteristics,fuel mileage,and partial throttle cruise additional advance.(Formula= 16-18 degrees base initial timing + 32-34 mechanical advance for a total of 38-40 degrees total advance + 12-14 degrees of vacuum advance for a total of 50-52 degrees of timing for partial throttle driving = a recipe for optimal engine performance.All engines react differently but this is a fantastic baseline to start from.Many factors come into the scenario as well(compression,duration of cam,carb,motor size)Try some more timing and chime back on here after you performed these experiments and I bet you have felt some power and performance gains.Im glad if I could help.Good luck