Vacuum or Mechanical timing?

[billschroeder5842]

I'm doing some adjusting and tinkering........

My '69 has a 383 with a mild cam, headers, aluminum intake, Edlebrock carb and electronic distributor.

A car buddy said that the motor is sufficiently modified so that a mechanical timing adjustment is irrelevant. He suggested adjusting the timing using a vacuum gauge for a truer reading of the engine.

What do you all think?

[Musicman]

Take the car out for a good run, get it good and hot... pop the hood, pull the vacuum and plug it like usual... advance the timing 2 degrees and shut it off. Let it set a minute allowing your engine temperature to spike... now start the car... if it starts hard, pulling down on the starter like your battery is weak, or it backfires, you have gone past your optimal setting and you need to back it off 2 degrees again. If it starts normally, then simply repeat the procedure, advancing the timing 2 degrees at a time until you reach the point where it does show signs of straining... then back it off 2 degrees. This is the max initial timing that your current build can handle. Adjustments to the mechanical side can be made later to smooth out the upper end of the scale if necessary.

Sorry, there I go again... always doing things different 

[aifilaw]

save your money, and your time. Go spend an hour on a dyno with a wideband o2 (they will provide). Get it right and never worry about it again, or wonder if you could have another 10 or 20 HP you can't feel by the seat of the pants by being off 1 degree of timing.

[oldschool]

save your money, and your time. Go spend an hour on a dyno with a wideband o2 (they will provide). Get it right and never worry about it again, or wonder if you could have another 10 or 20 HP you can't feel by the seat of the pants by being off 1 degree of timing.

exactly......

[Musicman]

Go spend an hour on a dyno with a wideband o2 (they will provide).

Chassis Dyno is a good way to go if available and you can swing it 

[billschroeder5842]

Consider it "swung."

I think that a dyno is the way to go. I contacted Speedtek in the Dallas/FT Worth area and am working on an appointment.

Any tips for the "dynoMaster" would be appreciated!

[R2]

Are you talking distributor timing? 

Why would you need a dyno for this ?

Using a vacuum gauge is very helpful for engine tuning as well.....

I "curved" my own distributor,,,and adjusted the initial and total timing,,,,then the carb using a vacuum gauge to dial in the carb,,,, A/F mix testing would be really helpful as well....but might be tough to do "at home",,,

I would be happy to pass on any distributor curving stuff,,,,etc,,,if needed,,,

I have also taken mine to a chassis dyno,,,,they only did some "minor" tuning stuff,,,,ie,,,adjusting the timing,,,maybe some jetting,,,,BUT,,,,if your distributor curve is off,,,,and the distributor needs to be torn into,,, that might be tough to do on a time schedule.....(ps,,chassis dyno was very cool,,,,something else to see your car sitting there,,,screaming away on the dyno .... 

good luck,

DOUG.

[Ghoste]

I agree with using a vacuum guage but I disagree that your mechanical advance has become irrelevant.

[Musicman]

Timing first, then the idle circuit, etc,etc,etc... Start at the beginning, then work your way up...

[aifilaw]

If you are near Dallas, I can recommend a great mopar friendly shop with a dyno and a flowbench. he will take the time to help you get it right, if need-be, even re curve your distributor (weld and drill the slots). It's in Flint, TX

[billschroeder5842]

Thanks for the shop recommendation however Flint Texas would be a 2 1/2 hour drive. There is a shop "speedtek" that is a 20 min drive.

Thanks!

[oldrock]

any follow up report on speedtek? We rebuilt my sons 318 with new alum intake and 650 dblpumper and think an hour on a dyno might really help dial in the setup. Mind sharing cost and how it went?

[68chargerAG]

I have read that a good place to start with a bigger than stock cams is the following:

10- to 12-degrees of initial timing when the duration of the camshaft is less than 220-degrees @ 0.050" of valve lift; 14- to 16-degrees of initial timing with a camshaft duration of less than 240-degrees @ 0.050"; and 18- to 20 degrees of initial timing when the camshaft duration is less than 260-degrees @ 0.050" of valve lift.

Then you find max vacuum during driving conditions and set vac advance so timing is at about 36 when pulling that vacuum.  This is the tricky part, maybe trial and error, unless you have a hand pump to pull the dist to that vac setpoint while checking the timing with a light.  This is what I am still working on.