[Lugnutz65]

This is a fresh 1965 SBC 283 rebuilt by Carolina Machine Engines here in SC.
Rochester 2Jet carb. Cast iron manifold and ram horn cast iron exhaust. Bored 0.060 over. Hypereutectic pistons and a 268H Comp Cams flat tappet cam.
New points style distributor with Pertronix conversion. No points or condenser.

I’ve got the timing set to where it will start cold without any choke. Idles well at 750 RPMS and drives fine without stumbles. Engine is too fresh to do any hard pulls or hard accelerations. Medium acceleration is great though.

I did all this testing because the timing seems to have a lot of advance.

Here are some numbers for us to ponder.

I’m very methodical but have only one set of hands. I’m lucky to have a retired neighbor who enjoys helping me in the shop. I’m using an INNOVA timing light with flash delay and digital tach.

I brought the engine up to temperature and tested 4 things . . .
MECHANICAL ADVANCE with the vacuum line plugged.
MANIFOLD VACUUM from a large port behind the carburetor (see photo)
CARBURETOR vacuum line.
TOTAL ADVANCE with the carb vac line connected to the dizzy.

Like them or not, here are the numbers I got. If anything seemed unusual, I went back and tested again. I think I would get the same numbers if I did this again tomorrow.


MECHANICAL ADVANCE with the vacuum line plugged.
570 RPMs = 12°
750 RPMs = 12°
1000 RPMs = 15°
1300 RPMs = 23°
1500 RPMs = 24°
2000 RPMs = 27°
2500 RPMs = 32°
3000 RPMs = 35°
3500 RPMs = 40°


MANIFOLD VACUUM from a large port behind the carburetor
750 RPMs = 32 cm Hg (13 inches Hg)
1000 RPMs = 40 (16)
1300 RPMs = 47 (18.5)
1500 RPMs = 50 (19.5)
2000 RPMs = 54 (21)
2500 RPMs = 54 (21)
3000 RPMs = 54 (21)
3500 RPMs = 54 (21)

CARBURETOR vacuum line
750 RPMs = 20 cm Hg (8 inches Hg)
1000 RPMs = 24 (9.5)
1300 RPMs = 35 (13.5)
1500 RPMs = 40 (15.5)
2000 RPMs = 47 (18.5)
2500 RPMs = 50 (20)
3000 RPMs = 50 (20)

Timing results WITH the carburetor vacuum line CONNECTED to the distributor.
750 RPMs = 25°
1000 RPMs = 27°
1300 RPMs = 36°
1500 RPMs = 38°
2000 RPMs = 44°
2500 RPMs = 46°