im building a 350 v8 for my 92 s10 pickup. this is my first engine build so ill have plenty of questions. I can get a block for next to nothing that has a 1 peice rear main but i notice all the crate motors are 4 bolt main. which on is better advantages/disadvantages? thanks for any help

A 4 bolt main is way stronger, but not really needed unless you're gonna turn over 5000 RPMs or using over 10 to 1 comp.
it's kinda over kill for a stock motor. the one piece rear main seal is chevy's updated seal. If you are going with a mild motor, just get the one piece main block. that's My .02

Seals and main bolts are two entirely different things.The 1 piece rear main seal you are talking about has to do with the seal around the crankshaft. The main bolts have to do with the caps that hold the crank inside the block. Now a 2 bolt main is obviously going to weaker than a 4 bolt at higher RPM/HP levels. But you can always convert the 2 bolt main block to a 4 bolt main, but it would be cheaper in the long run to just find a good 4 bolt.

All in all, if you aren't going to be going over 400hp, a 2 bolt will suit you fine. Also, you might want to pick up a couple of books on engine assembly. The knowledge you gain from the books will help you avoid costly mistakes . ENGINE BOOKS (http://www.amazon.com/exec/obidos/search-handle-form/002-4389414-4168063)
:)

Also if you wanted, you could use ARP main studs in the 2 bolt block.

thanks i do have a book that im looking through.
Is there a way to tell a 4 bolt main from a 2 bolt main fromt he outside

Sometimes you can tell weather it is 2 or 4 by the casting number. But the only true way is to remove the pan. My .02$ :grinpimp:

yeah main bolts and rear main seals are WAY different things. I have a 4 bolt 1 piece rear main motor that I'm building a 383 from, so they exist.

Every SBC 4 bolt block I've owned has a number cast into the bellhousing flange (the second flat from the top) on the drivers side. The number will end with "010". That's usually a 4 bolt. I've heard a couple of guys say they've bought "010" blocks that where 2 bolt but I've never seen one.

if you look on Mortec, many casting numbers could be either one.

Hands down, the one piece rear main motor. I personally would rather have one of these only because oil leaks are few and far between. I have owned both, and worked on lots of each. Plus, honestly, how many motors blow apart because they were only 2 bolt mains. I can't think of any, usually lack of oil pressure, broken piston, timing chain, pinging, hyrdrolocked, etc.

so what applications had both the one piece rear main and 4 bolt mains. i thought all the ~86+ iron blocks were, sounds like i may have assumed wrong.

i have been toying with the idea of building my old 87 350 into a ~12:1 383 and running it on propane. i dont think i trust that high of compression to 2 bolt mains.

i have been toying with the idea of building my old 87 350 into a ~12:1 383 and running it on propane. i dont think i trust that high of compression to 2 bolt mains.

True, but how many by percentage run a 12:1 propane motor....

Every SBC 4 bolt block I've owned has a number cast into the bellhousing flange (the second flat from the top) on the drivers side. The number will end with "010". That's usually a 4 bolt. I've heard a couple of guys say they've bought "010" blocks that where 2 bolt but I've never seen one.


According to Chevrolet, the 010 casting # signifies a 4" or larger bore, so 350s and 400s can but wont always have these #s. it was after the 302/327s that they started with these 010 casting #s.

If you look on the passenger top bell housing bolt boss, where the block turns up vertical, theres a small block with a U shape on the top, this is usually a 4 bolt main block, but some 2 bolt motors made in mexico also have this, so it's not a constant.

According to Chevrolet, the 010 casting # signifies a 4" or larger bore, so 350s and 400s can but wont always have these #s. it was after the 302/327s that they started with these 010 casting #s.

If you look on the passenger top bell housing bolt boss, where the block turns up vertical, theres a small block with a U shape on the top, this is usually a 4 bolt main block, but some 2 bolt motors made in mexico also have this, so it's not a constant.

Basically the only constant is to pull the pan.

One worry with the 1 piece rear main motors is, the lifter valleys are thinner and weaker. Talked to a few folsk who have seen them simply collapse in on the cam. I already went through one block that was cracked in there and by the front Cam journal. My worry is that I will have spent the tons of money I have on my 383, and the lifter valley will collapse on my shiny new LT4 Hot Cam.

Now a 2 bolt main is obviously going to weaker than a 4 bolt at higher RPM/HP levels. But you can always convert the 2 bolt main block to a 4 bolt main, but it would be cheaper in the long run to just find a good 4 bolt.

All in all, if you aren't going to be going over 400hp, a 2 bolt will suit you fine.

Cheaper to find a 4 bolt, but stronger to convert a 2 bolt main into a splayed 4 bolt main block if you were trying to make an obscene amount of power. If we're talking about 400s, the 2 bolt main is actually the desirable block, as the 4 bolt mains are actually weaker. On a 350 though you're fine either way.

Me personally, I wouldn't care either way. For a truck, there are very few applications where a 4 bolt main would ever be an advantage.

That said, my truck happens to have a 1 piece rear main, 4 bolt main motor in it, but its pretty much coincidence. I'd rather have a 1 piece rear main seal and a 2 bolt main, than two piece rear seal and a 4 bolt main.

tim84k10 is correct.the splayed two bolt main is way stronger than a 4 bolt.the 2 bolt had more webbing at the journals.I have a 010 2 bolt that makes close to 400 hp, it is not splayed,I dont believe you will need it.I had my motor align honed and balanced,if you have the money it is worth it,I have over revved it several times and it did not matter .the 302's were 010's also according to mortec.John lingenfelters books are a good idea.

so what applications had both the one piece rear main and 4 bolt mains. i thought all the ~86+ iron blocks were, sounds like i may have assumed wrong.

i have been toying with the idea of building my old 87 350 into a ~12:1 383 and running it on propane. i dont think i trust that high of compression to 2 bolt mains.


12.0:1 on a 2 bolt won't hurt it as long as everything is tuned right. Its not static compression that puts a lot of pressure on your mains. the true killer of main bearings, caps and cranks are things like detonation and crank flex. if you run a good crank such as a scat 9000 or better and keep detonation in check (detonation beats the hell out of your crank and mains, not just your pistons.) you should be ok with a studed 2 bolt main block in a motor that doesn't see a lot of rpm. I've had 600 hp 2 bolt main (with studs) big blocks run pass after pass after pass with 12.0:1 and higher compression.

granted, things like high rpm and long stroker cranks, make for more crank flex. a 3.75 stroker small block crank isn't really all that much stroke compared to big block strokers of like 4.25-4.5 or bigger

a 12 to one propane motor that doesnt see passed 6k with a good crank and main studs shouldn't have any problems.

this is just food for thought. a 4 bolt block or splayed 4 bolt does give you a better peace of mind...

I run a 4-bolt just because I'm old school. I really don't need it, but I didn't need a forged crank either. I'd run the 1 piece seal block because most are factory roller motors and the lifters are cheaper. Less oil leaks at rear seal. My two piece doesn't leak,,,,, Yet!
As for the two bolt mains, just by putting studs in the mains is said to be as strong as 4 bolt.
Most 010 blocks were 350's. The Mortec site shows some 302, 327's as being 010's, but this could only be really latemodel 69 production year which actually ran into the 70 model year. Hence, 70 1/2 Camaro. The 618 casting was the real 302, and high HP Large journal 327's for 69. Prior to this they were two bolts that saw 7000 rpm.
4-bolt blocks are said to have a higher nickle content. AND WHATEVER ONE DOES STAY AWAY FROM ANY MEXICO CASTINGS. The quality control at all levels is just not there. Do they cast LS motors there?

302 and the large journal 327, and a 350, are all the same block. 4" bore.

302 and the large journal 327, and a 350, are all the same block. 4" bore.
Actually they're all 3.998, but who's counting.

I have talked to a few machine shops that machine the bottom of the main caps flat and then cut 1/4" thick steel to fit on the bottom of the cap and install main studs. And they claim that they would rather have a 2 bolt block with this set up than a 4 bolt main because the block has more strength in the bottom end this way and that the steel solves the problems of the 2 bolt main caps splitting and you still keep the strength in the block. Its also cheaper than machining for splayed 4 bolt caps. My .02$ :grinpimp:

Note bottom of cap is closest to oil pan...

are you talking about main stud girdles? this is for a ford but you get the idea.
http://www.crateengine.net/imagespics/probe_trackdominatorgirdles.jpg

Essentiale yes but there making them and they are not tying the main caps together like a girdle does. My .02$ :grinpimp: