Hi guys i need your help some guy is selling his 350 that was in an 88 truck. but he cant tell me if its a four bolt main. How can i tell without actually going to look. Can i tell by the casting number? If yes what do i do with the number to tell.

thanks alot guys

 

get the casting number off of the block, behind the drivers side head, before the tranny, then go to Mortec.com and look under block/cylender head casting numbers, check your number and see what it says.

Now for example, i have a 350 out of a 71 pick up (probly not original motor) But anyways i took the casting number to mortec checked it out, and it says hi streigth, 2 or 4 bolt main, my point, it has info on the motor to see if it was original, and might or might not have what the mains are, sure way to tell, if its out of car, pull the oil pan.

 

Keep in mind that factory 4-bolt mains aren't all they're cracked up to be. The two side bolts go into an area of the main web that isn't very strong. For race or heavy duty use the ideal setup would be a 2-bolt block and then have it machined for aftermarket splayed 4-bolt main caps.

 

The block casting # won't tell you which caps the factory installed.

The ONLY WAY to know for sure is to look.

I agree, factory 4-bolt caps are designed for a different set of stresses than racing. Not worth paying extra for, or getting concerned about. There are other far more important things about a block that you should be making sure of.

 

Yeah exactly, like cylinder wall thickness and core shift.

 

And bore size (like, don't buy a .060" over block that's worn out), starter bolt holes, lifter bore alignment and condition, cam gear thrust wear, broken bolt hole bosses, etc. etc. etc. All of those things are important. Whether the factory installed 4-bolt caps in it, is way down low on the list by comparison. About the worst thing you could do, would be to get all starry-eyed over the 4-bolt caps, and pay too much for a block you can't use for some other reason, or will cause you extra trouble or expense repairing it.

Keep in mind that the block castings are always the same regardless of which caps they put in. You can always add aftermarket ones, which are vastly superior to factory ones. Factory 4-bolts are no better for a hot-rod application than 2-bolts.

 

Well said. A friend of mine runs a 409 small block in his race car, which I believe is a .040" over 400. When the engine finally went belly up under the pressure of 700HP on alcohol he went nuts trying to find another 4-bolt main 400 to create another engine just like the one that had failed. I kept telling him to get a dedicated race block like a Motown or Bow Tie, but he didn't want to pony up the loot. Some machine shop owner talked him into paying $400 for an unmachined 4-bolt 400 block. He went ahead and bored the block .040" over and had the rest of the work done, by that time he had $1,000 tied up in the block. 3 passes and the block failed. One of the cylinder walls failed because he never sonic checked it. It was paper thin in one small section, and that was all she wrote. Now it's a $1,000 4-bolt main door stop. He'd have been better off buying a $100 2-bolt core and having it properly checked out and machined for aftermarket 4-bolt caps. It might have lived.

 

The majority of all the truck blocks are 4 bolt but not all. Nothing external will tell you if it's a 2 or 4 bolt.

Even taking a 2 bolt block and having the mains studded is just as strong as having a 4 bolt block.

For most power levels, a 2 bolt block will work just fine. If you're going to use any power adder then consider going to a 4 bolt block.

 

If you are going to use a power adder then I'd still recommend getting a 2-bolt block and having it machined for 4-bolt caps with splayed outer bolts. These mains are much stronger than factory 4-bolt mains. You'll spend a couple hundred more having the machine work done and buying the caps, but 4-bolt main factory blocks command a premium anyway, and the added insurance is well worth it with a power adder.

If you're planning more than 550-600HP then seriously consider stepping up to an aftermarket block. Aftermarket blocks are typically worth about 20-25HP anyway all things being equal because they are more stable and consequently provide better ring seal.