4 Bolt Caps

fifesjeep

Does anybody make 4 bolt main caps?

tufcj

Pro-Gram Engineering. http://www.pro-gram.com/

I believe it's a 401 mod, as the main webs are thinner on the 304/360 blocks and don't have enough meat to drill bolt holes.

Remember that the block will also have to be line bored after installing the caps.

Bob
tufcj

fifesjeep

tufcj wrote
Pro-Gram Engineering. http://www.pro-gram.com/

I believe it's a 401 mod, as the main webs are thinner on the 304/360 blocks and don't have enough meat to drill bolt holes.

Hmmm, I thought that there were thicker casted 360 blocks that would support this mod?

tufcj wrote
Remember that the block will also have to be line bored after installing the caps.

Bob
tufcj

Yup, sure do... Standard practice. :t:

Blown7

fifesjeep wrote
Hmmm, I thought that there were thicker casted 360 blocks that would support this mod?

Yep but those blocks are very hard to come by, I think they were cast for Trans Am racing.

fifesjeep

Blown7 wrote
fifesjeep wrote
Hmmm, I thought that there were thicker casted 360 blocks that would support this mod?

Yep but those blocks are very hard to come by, I think they were cast for Trans Am racing.

Cool, makes sense. I'd be nice to stumble upon one in good shape. :wink:

JERSEJO

fifesjeep;127920 wrote
Cool, makes sense. I'd be nice to stumble upon one in good shape. :wink:

Yes they were used in Trans Am but some of the later service replacement 360's came with the thicker webbing. I remember seeing one in a 74 Javelin that had a factory motor repalced in the mid 80's and it had the thick webs. Only one I ever saw

PagetHamington

The one at 74 Javelin was good enough. I still wonder why they did not make more in any of those ever.

ironman_gq

The factory service blocks were basically a blank with slightly heavier castings, it was up to the final user what they were at the machine shop (304/360) IIRC

SuperStockAMX

My first post here. AMC 1970 390 and all 401's will accommodate 4-bolt mains. The "service block" is as described above. It has the same bottom end as the late 390 and all year 401 and was a 4.08" bore 360 cylinders with enough material in the cylinder bores for the service department to bore to 4.165" 390 / 401 specs if required. There were some smaller 290 engine blocks made with 4-bolt provisions but that was a Trans-Am race block and very rare indeed. Milidon and Pro-Gram Engineering make excellent 4-bolt main caps. Milidon availability can be iffy, Pro-Gram will get them to you in a reasonable amount of time. You can buy the three middle caps with 4-bolt. Pro-Gram also offers billet #1 & #5 caps but those are 2-bolt. Just keeps the billet theme going. I have all 5 on my '70 390 race engine. You will need to line bore / hone ANY block if you change the caps (even if factory standard caps). Caps are married to the bore.