Originally Posted by Ct Street Rod
To convert an L31 Vortec to carburetor is it as simple as the correct intake w/carb. & distributor w/vac adv ? IF so what would be the base line timing for start up? Thanks
Yep, pretty much. You'll need an electric fuel pump and filter and make sure not to exceed the pressure limit of the carburetor you'll be using. 5 1/2 lbs max for a Quadrajet, AFB or Performer. 6 1/2 lbs max for a Holley. This is not a case like EFI, where more pressure could make more horsepower. With a carb, you have to limit the pressure into the bowl to prevent over-powering the needle/seat and blowing raw fuel into the intake manifold. Set the float(s) properly and limit the pressure. Electric pumps work best when the push, not pull, so mounting the pump/filter back at the tank/cell is a good idea. That is also a good place to mount a regulator. Use one that will dump excess fuel back into the tank/cell rather than a deadhead regulator that will heat the fuel and wear out the pump quicker.
The blurb about distributor gears probably should have been worded differently, like....."Insure that the material that the distributor drive gear is made from is compatible with the material the camshaft drive gear is made from". The camshaft drive gear is normally part of the casting of the camshaft, so you would want to touch base with the tech at the cam grinder to find out what they like for distributor drive gear material compatibility with that particular camshaft.
With L31 heads, I would start at 34 degrees initial + mechanical, all in by 2800. More cam will want more initial ignition timing, so increase the initial and limit the mechanical to get to your 34. Once the motor is running, you can try rocking the timing back and forth a couple of degrees, but the L31 chambers are very efficient and should work best around 34.
The following is quoted from www.gnetworks.com
and says it best about the ignition timing with a larger cam.....
The chief function of initial timing is to provide a clean idle
and crisp throttle response. One of the best guides to
determine the initial ignition timing of V8 engines can be
found in the Barry Grant, Inc. catalog or at their website
under the Demon Carburetor Guide. Typically, they recommend 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."