Distributor big block vs small block

[Donald H.]

I'm helping a friend with a 66 big block 390HP engine. It has an aftermarket distributor of some type (no tach drive). The correct distributor for this car is a 1111141 non-TI distributor; however, these are rather pricy.

In looking at pictures of the 141 distributor the only difference I see in it and a small block distributor like the 156 (L79 distributor) is the 141 has 'notches' in the shaft down by the drive end and the 156 has a groove all the way around the shaft.

I realize the curves are different for these distributors with different springs, weights, and 'football' but otherwise can we use a small block distributor on this engine?

Thanks,
Don

001 distributor BB.jpg 001 distributor SB.jpg

[Joe L.]

I'm helping a friend with a 66 big block 390HP engine. It has an aftermarket distributor of some type (no tach drive). The correct distributor for this car is a 1111141 non-TI distributor; however, these are rather pricy.

In looking at pictures of the 141 distributor the only difference I see in it and a small block distributor like the 156 (L79 distributor) is the 141 has 'notches' in the shaft down by the drive end and the 156 has a groove all the way around the shaft.

I realize the curves are different for these distributors with different springs, weights, and 'football' but otherwise can we use a small block distributor on this engine?

Thanks,
Don

001 distributor BB.jpg 001 distributor SB.jpg

Don-----

Yes, you can use the small block distributor housing on the big block. Of course, you will have to have it re-curved to the specs for the particular big block.

Not all big blocks originally used the "half round" lower oiling groove. Some, in fact most, used the full round. In any event, GM approved the "full round" to be used in SERVICE for all 1962-74 small blocks or big blocks.

[Donald H.]

Thanks Joe.

Don

[Duke W.]

AFAIK small block and big block tach drive distributors are interchangeable, and I don't think a partial or small groove makes any difference. I recall the late John Hinckley so stated, but let's see what knowledgeable others have to say. I ran a '67 L-88 TI system in my SWC's 340 HP engine. The distributor probably had the partial groove, but I never noticed. It quit on me a couple of times between 1967 and 1975 at which time I had figured out how to make the OE single point system work better at high revs and sold the PoS to the then owner of the L-88 from whence it came in 1988.

Delco distributors are made from a family of parts, and you clearly understand the the spark advance maps were tailored to the specific engine, so it's easy to set up an optimized map for whatever engine you have from any "core" and you can buy a tag with the proper part number.

The "football" affects the shape of the advance curve - linear or some non-linear variant - but don't worry about it. Just get max centrifugal in as quickly as possible without detonation or low rev driveability issues.

Closed chamber blocks don't like as much low rev advance advance as small blocks and later open chamber big blocks. I recently set up a '66 L-36. Since we're in SoCal we visited David Sokolowski's warehouse and went through a box of cam assemblies and found a 32 degree (532or 732) that was OE on the '67 version. We ended up with 4-6 initial with 32 centrifugal in at about 3000-3500 (OE full centrifugal is all in at a lazy 5000) so at least we got into the bottom of the 36-40 best total WOT advance range on California 91 PON fuel. It you have 93 PON you can probably run 6-8 initial with a 30 degree cam assembly

Assuming the engine has an OE equivalent cam idle behavior is 15" @ 600, so you'll need a 12" B26 VAC. Read the following nearby thread.

https://www.forums.ncrs.org/forum/te...dvance-control

Duke

[Donald H.]

Thanks Duke. As always a lot of knowledge in your response.

Don