1969 & 1971 350 sb
 

OK. So I have 2 350's w/ turbo 350 trans...
1 is from a 1969, the other from a 1971.

A few potential buyers have asked, "are they 2 bolt mains" or "4 bolt mains".

I know the difference in basic concept. However, I'm not sure on either.
Was 1 more likely than the other in a blazer of that era?

... I know I can check the #'s on the block, but didn't haven't gotten that deep under the hood to get the #'s yet.

Well if you've got the oil pan off its really simple to figure out

http://a4.sphotos.ak.fbcdn.net/hphot..._7233504_n.jpg

If it looks like this, then its a 4 bolt main.

As for rarity... not sure. The 4 Bolt Main is my '74 Block... so maybe they were more common is the earlier years.

Here's my old 2 Bolt for comparison, excuse the dirtyness, this is just after she blew 2 holes in my oil pan... lol

http://a4.sphotos.ak.fbcdn.net/hphot..._6948543_n.jpg

Not sure why everyone is asking... Other than they believe the 4 bolt main is way better for supping up.
And thus, they're getting more $$ for the 4 bolt blocks than the 2 bolt counter part.

I think I can get it from the block's stamp too, but I was trying to figure it out before getting dirty next weekend.

Thanks for the reply

Truck engines "tended" to be 4 bolt mains back in the day. So do the muscle cars. Not really sure that the numbers off the block will tell you one way or the other. Best bet is to drop the oil pan and verify.

There were many folks who swapped out the 2 bolt they had for a truck engine as back then truck engines were built for work. Can't say that for the past 30+ years, though.

EDIT: You replied, evidently, as I was typing my response. The reason folks want a 4 bolt over a 2 bolt is pretty simple. Lower end strength. If I'm not mistake, there were a few companies that came out with a way to make a 2 bolt into a 4 bolt. More power on the upper end means you need more strength on the lower end. A 4 bolt is stronger than a 2 bolt. Pretty simple in my eyes.

This is why people are asking.

The 4 bolt is supposed to be stronger. On a street engine a 2 bolt is just fine. You don't see the gains of a 4 bolt until you spin high rpms all day at high hp numbers. Way out of the range of anything you want to drive on the street or put pump gas in. People that pay more for a 4 bolt do so because they buy into hype. I have 4 blocks sitting in my shop and I actually gave less for the 4 bolt compared to the 2 bolts. Unless building something number matching one isn't worth anymore than the other.


There are a few cast numbers that are 4 bolt only but most numers are for a 350 block. They can be on either. Sometimes you can get the stamped number and look that up. In some years on some makes the 4 or 2 bolt was only offered. Still rare as if a 4 bolt was offered a 2 bolt was also. Its a 50 50 shot as what you have and honestly the only way to tell is to pull the oil pan.


Yes there are kits to turn a 2 bolt into a 4 bolt. The outter bolts are splayed and its a way stronger design. In the racing circles that know better this makes the 2 bolt the more wanted blocks.

The shape of the block is gonna be the main factor of the price. A block that's been bored out 40+ isn't gonna be worth much of anything if it needs a rebuild.

I have three 4-bolt main blocks and each of them has '010' at the end of the block pattern number located behind the driver side cylinder head on the bell-housing extension. But the pattern number doesn't tell the whole tale and can't be relied upon for determining whether the block is a 2-bolt or 4-bolt.

The easiest way I have found is to use a bore scope to look up through the oil plug hole & snake around until you can see the main bearing caps.

But as neo pointed out, 2-bolt main blocks can be built up just as reliably as 4-bolt main blocks. It's hard to make that point with many people though. 2-bolt main blocks also have the added benefit of being able to be a truly splayed 4-bolt setup instead of the straight in 4-bolt setup, but again, that's only if you're looking for high HP/RPM.

010 means 10% tin and 020 means 20% nickle. Deals with the alloy of the block and either of these numbers means its a stronger block compared to one with neither number.

Most all 4 bolt blocks had this but not all. Some 2 bolt blocks had it. It is more common on the 4 bolt blocks.

Great examples were the 302 and corvette 327s. All 2 bolt blocks and had high nickle blocks. Even being a 2 bolt design the chevy 302 was known to rev well into the 8k and even 9k range racing long term road racing.

If you can find somebody that buys into the 4 bolt hype then grab all the cash you can and use that as a selling point. Don't be surprised somebody that knows enough to ask knows better to buy into it. They are also gonna want to know the head numbers and that could be more of a selling point if they are good heads.

That's my hope. I'm not going to use either engine. I have another engine and tranny that I'm putting in my blazer...
I just have noticed a bigger "demand" for the 4 bolt.
~ And I hope to make some $$ selling them to roll back into mine to make it dirt pretty.