Timing an 8ba

[AnthonyG]

Hi all, specs show for stock 1949 8BA timing s/b 2 degrees BTDC. Mine has a mild cam, a Merc crank & dome pistons. What should I set timing at. I think it s/b advanced from that but how much?

[tubman]

I set the initial timing on my engines with a vacuum gauge. Disconnect the vacuum advance (if any) and hook up a vacuum gauge. Set the idle to the desired RPM and adjust the timing until you get the maximum vacuum reading, and then retard it just a smidge. If you have a dial back timing light, check for maximum advance at the "all-in" speed. It should be around 36 degrees for an overhead valve engine and about 22 degrees for a flathead.

Note that this assumes a distributor with a correct curve for the engine concerned. If you have a dial back timing light, run the engine (with the vacuum advance disconnected) at the speed at which the centrifugal advance should be all in. At that speed, set the advance to the optimum advance for the engine. Hopefully, the engine will idle and start satisfactorily. If it doesn't, the advance curve has to be changed by changing the springs and advance limiter.

The hard part with this method is determining the proper advance when all in. If you have a dyno, it's pretty easy (but expensive). Otherwise. you'll have to use your "seat of the pants" dyno. Set the total advance until it runs the best and go with it. When we did the initial setup on the Chrysler hemi in my dirt modified, we were lucky enough to have unlimited track time. We kept fooling with the maximum advance until we got the best lap times. It turned out to ne 35 degrees total. On a flathead, you should start around 22 degrees,

[AnthonyG]

Wow tubman, good stuff! I’m typically a straight up timing light guy but what u say makes sense. I’ll start with the Vac gauge & get best Rpm & back off a bit seeing how it runs there!!

[Desoto291Hemi]

Tubman is pretty sharp on this stuff,,,,,,he usually knows .

Tommy

[Talkwrench]

A vacuum gauge is an underused tool...

[Bored&Stroked]

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I usually run about 24 degrees total advance - just to give you a reference point. This is on a 284 cube engine, heavily modified in all aspects - with a .040 quench over the pistons (Navarro heads).

[40cpe]

Originally Posted by Bored&Stroked

I usually run about 24 degrees total advance

Does "total" advance include a vacuum advance, or just initial and mechanical?

[tubman]

Originally Posted by Bored&Stroked

I usually run about 24 degrees total advance - just to give you a reference point. This is on a 284 cube engine, heavily modified in all aspects - with a .040 quench over the pistons (Navarro heads).

I will have to agree with Dale on this. (He builds hotter engines than I do.)

[Ol' Ron]

Need alittle more information here. Sounds like you maybe running more than a stock carb and distributor, with these mds. If so ther's not much you can do with these com components. actually the aftermarket cam will make the stock distributor useless. Convert to a converted SBC didt and get an AF meter. nd tune for cruise preformance and economy this usually calls for 26/28 degs adv, maybe more along with an AF of 15/15.5.
WOT should call for 18/20 deg adv AF around 13.
These numbers willvary alittle depending in compression and Cam. Works well with the L-100
Gramps

[AnthonyG]

Gramps, Running 2 Holley 94’s that Charley NY rebuilt & set up, Distributor is a 3 bolt E-Distributor no vac advance, mild cam, Ross Dome Pistons, Merc 4” crank. I used the vac gauge as tubman suggested, found highest rpm then retarded a bit. Then checked with timing light and it was 12-13 degrees advanced. Engine seems to like it there, no pinging & good pull. Think I’m done?
Thx all for great help / knowledge!

[flatjack9]

A hotter cam is always going to idle better with more advance. As long as you're not getting any detonation, you're good to go. It would be nice if someone could come up with a crab style distributor that incorporates mechanical and vacuum advance.

[Ol' Ron]

A modern engine uses an engine management computer. The computer runs the timing and regulated the fuel to give the best performance and economy under all load conditions. You can do the same with a modified GM distributor and the right carb. The best carb for this is the Edelbrock 500 CFM. There might be a better system but this is the one we used. Better control of the power valves (rods). The 276 L-100 cam engine got 22 MPG, and i was impressed with it's acceleration in a 3800 lb car
I'll admit he did make some of his own rods. Ya just have to do some putzing
Gramps