340 with a 273 distributor

[ElDavo64]

hello everyone
I have a 340 with a mild build with a stock 273 distributor how do I ascertain if th distributor has enough mechanical advance?

 

[halifaxhops]

Really depends what you have in the 340 modification wise. Compare the curves against each other and really go from there.

 

[teringer]

are they both duel points there likely verry close

 

[67Dart273]

Simple. Use your timing light. I "personally" distrust "dial up" lights (knob which is supposed to be accurate as to degrees) and tend to use older, simpler lights, with the balancer having been marked. This is easy. Take a small thin tape and measure around the balancer, then figure how many degrees per inch and use anything you like including masking tap, to mark the balancer out to 40 degrees.

Bear in mind that "the book" specs are in DISTRIBUTOR degrees which are half as much as crank degrees, same with the specs on RPM.

 

[pt70]

hello everyone
I have a 340 with a mild build with a stock 273 distributor how do I ascertain if th distributor has enough mechanical advance?

273 distributors vary greatly for mechanical advance. Initial advance can be 10* BTDC to 5* ATDC ! There are specs for them if you have the part number of the distributor. If not, you can get a ball park number by doing a little bit of checking.

Place a distributor in a vice horizontally. Hold it by the shaft. Mark the rotor tip in the center. -- mark the other end of the rotor in the center. Cut a piece of cardboard [cereal box ?] to the height of the rotor centerline. Rotate the dist. shaft so the rotor is parallel to the workbench. Tighten vice. The rotor is spring loaded in one direction. While using a taller piece of cardboard that sits on the bench, turn the rotor against the spring and trim the cardboard till it matches the angle of the rotor. This may take more than one try. Using a protractor measure the angle. Double the angle. This is your mechanical advance.

My unknown small block distributor ended up being 17* at the dist. So, 34* at the crank.
Initial timing at TDC is a good starting point.

 

[Mattax]

Or if the tag is still on the distributor, then at least we'll know what you're working with.
I've posted a graph of the engine timing for pre-CAP 273 4bbl a number of times for a reason.

But a 2 bbl or a CAP/CAS 4 bbl were different

 

[67Dart273]

^^Well no, ya won't. That tag is removeable, may not be the original dist, or it may have been recurved. Which is why I posted this.

WAY BACK in the 70's I bought a used hemi - tach drive dual point. It had been recurved. Turned out to be just right for my 440 with a big Sig Erson cam The tag on that dist had no bearing on what it actually was

 

[halifaxhops]

Really have to see what it started out as recurved lke most have been is always a crrapshoot. Great example look at say RA distributor listing for a 273 there are prob 50 numbers that it says it fits. Fits yes curved right? Probably not. Drop it in and using a timing tape see where it comes out to is the best bet no way I can answer this without running it up.