Timing?

[joelboxt]

hey, what is the timing suppose to be on a 71 350ci engine? 8 degree's advance or 4.. this is a stock motor.

thanks


joel

[joelboxt]

i think i found it in a book have here? 4 degree's sound right to you guys??????

thanks


joel

[JimKshortstep4x4]

The recommended setting for timing is 4 degrees btdc for the stick shift and 8 degrees btdc for automatic.

We set ours at 10-12 degrees btdc unless spark knock occurs and then we back off a bit if needed.

Jim

[joelboxt]

you get more power from using 10-12 BTDC?

thanks


joel

[JimKshortstep4x4]

Yes, you do get more power.

Jim

[CHEVY & GMC FOREVER]

I set my rebuilt 355 (350 Bored .30 over) at 6 instead of the "Factory" 4 BTDC.

[joelboxt]

is yours a manual transmission tho?

[CHEVIBUBBA]

first realize the stock advance curve is a compromise.if you are interested in good fuel mileage/good performance then, go read up on how to optimize your advance.

your camshaft duration has a huge effect on the required advance.
as does the head design.
a stock cam will have a mild factory advance curve that sometimes will continue adding timing all the way up to 4500rpm.not optimum!
a good basic advance curve for a 350 is to set base timing at 10-12 degrees.
have the mechanical advance all in by 300/3500 rpm
for total advance of 36-39 degrees depending on your cyl heads & cam.
i connect vacuum advance to manifold vacuum.this provides for a smoother, quieter idle, higher idle manifold vacuum & brisk takeoffs.not to mention it masks some of the lopiness from some cams.
using an advance curve this aggressive can yield part throttle cruise surging.
for this reason i highly recommend an adjustable vacuum advance.
this will allow you to keep the mechanical advance curve & be able to "pull out" some of the part throttle vacuum advance.
there is some good info on the net. try a google search for:"tuning ignition advance"

[joelboxt]

hey,

thanks for the info chevibubba.. my vacuum advance is hooked up to the carb. should put it directly to the manifold?

let me know

joel

[CHEVIBUBBA]

there are two different sources for vacuum on a carb: one is above the throttle plates & is called ported vacuum.the other is below the throttle plates & is called manifold vacuum.
i use the manifold vacuum port or connect directly to the manifold where the tranny modulator line connects.
you can use either port.
the ported vacuum will not provide vacuum at idle.
if you remove the vacuum advance line from the carb while the engine is running & it affects the engine you are connected to manifold vacuum.usualy increases idle speed.
you can experiment with the ports & see which one you like best.
just be sure to change your idle speed as needed when you change sources.