hey guys i'm trying to figure out the exact years Ford started using the butterfly pattern on the SB's. i looked in the 'BIBLE' but it didn't say years. figured i'd ask here next. thanks a lot- russel

What exactly is a butterfly pattern? Do you mean the throttle body EFI systems?

the 'butterfly' bolt pattern means the typical FORD bellhousing bolt pattern. i've never heard it called something else. so, that's as simple as i can get.

thanks...


russel

I have NEVER heard the term 'Butterfly' to describe the bellhousing bolt pattern of a small-block ford V-8.

The first year for the 6-BOLT pattern was 1965. prior to that (1962-1964) it was the 5-BOLT pattern on the 221-260-289 V-8's.

The 6-Bolt Small block pattern is on 289-302-351W, 240/300 Big Six, 351C and allegedly on 1973 only 400M, all other 351M/400M have the 429/460 tall pattern.

Eric

From Novak's website-

There are two completely different block bolt patterns used on the Ford small block V8s. The first small blocks were the 260 cubic inch engines in 1962-64 and the 289 c.i. in 1963-65. These engines are usually referred to as "5-bolt" engines because they had five bolts attaching the bellhousing to the block. 5-bolt engines have a transmission bolt pattern that measures about 6-1/4" wide by 7-1/2" tall and have a 4.687" bore in the bellhousing.

Some 1965 and all 1966 and later 289, 302, and 351 Ford V8s are referred to as "6-bolt" engines because of the six bellhousing to block attaching bolts. These 6-bolt engines have a transmission bolt pattern that measures about 8-1/2" wide by 6-5/16" tall with a bore diameter of 4.850".

I have a 66 parts bronco that has the 5 bolt bellhousing on a 289. I am brobably the 40 somethingth owner so no telling what has been changed but it is in there now. wierd.