ive got an 87 trans am gta with a 350 2 bolt main. my engine threw a rod so i need to do an engine swap. but all i see are mostly 4 bolt mains. will it still work? whats the difference?

 

The main difference for most guys is just bragging rights. It does sound more impressive to say you have 4-bolt mains. GM used them mostly in Corvettes and 1-ton pickups, but not in Camaros or 1/2-ton pickups.
Any real advantages? Not for a near-stock TPI L98. Any real disadvantages? Well, 4-bolt-main blocks are more likely to have cracks. And they're a few pounds heavier.

 

2-bolt and 4-bolt main engines used the same block castings. That should tell you something.

 

but it WILL work if i drop one in right? cuz its only a temporary engine till i get my original block back from the machine shop

 

Either block would be installed the same way into the car. They are more or less the same on the outside. Here are two sites describing the difference between 2 and 4 bolt mains:

http://67-72chevytrucks.com/vboard/s...d.php?t=379281

http://www.4wheelnoffroad.com/350.html

 

4 bolt main will handle more HP than a 2 bolt. other than that nothing

 

From the outside, you can't tell the difference between a 2-bolt and 4-bolt block. You have to pull the oil pan to tell one from the other.

That being the case, why would it not "drop right in"?

(It can be argued that a 2-bolt block is less likely to fail than a 4-bolt block. That doesn't mean you should pass on a 4-bolt block, because you aren't likely to make the kind of power that would break either one.)

 

And be aware, EVERYONE is going to say they are selling a 4-bolt, when 99% of them wouldn't know the difference anyway - they just know that some folks will pay more for a 4bolt. Remove the pan and look - might be able to talk yourself down a $100 or more if in fact it's not a 4bolt.

 

Nice theory, but with production 350 blocks it's not necessarily so.

 

maybe all the engine builders that only use 4 bolts know something we don't know

 

Yes, those of us who are famous engine builders, myself included, know that you novices won't buy a 500 horse 2-bolt-main engine. Wake the hell up already, damn!

 

so your famous that must be cool??

i my self use Jim Vance for my engine needs i build my own motors he does my machine work i would never make a claim I'm famous or i know it all far from it but novice?? i have been building and racing cars for 15 years. atilla i have got a lot of good info from you and appreciate that but you seem to have a problem with others having a say so..

how novice i am http://www.youtube.com/watch?v=E90aGBzSNiY
http://www.youtube.com/watch?v=GZF988vicjo
http://www.youtube.com/watch?v=9oiaF2fbWUo

 

2-bolt mains were around from 1954 to 1967. 4-bolts came out with the 350. They also went to larger main bearings at the same time. The factory used 4-bolts to help reduce cap walk. They have the effect of reducing the web material in the block, which weakens the block. 400 SBC's are even worse in that area, because they have even larger main journals.

Those first 13 years of SBC's didn't produce a bunch of failures that led the factory to go to 4 bolt mains. The 4 bolts don't enable the block to handle more power.

Splayed 4-bolt main caps are a different story.

 

well like i was saying i am no expert i only go by things i read and have been told over the years like Using 4 bolts to secure the main bearing caps reduces the amount of flex within the crankshaft as compared to 2 bolts high HP and high RPM increases flex.. i think its a matter of opinion I'm sure it been debated for years i for sure don't think 4 bolts are god but would have been interesting what my 383 would look like if it was a 2 bolt after this

 

I remember when I was a kid reading about Bill Grumpy Jenkins and his Camaro's. (Not many here are probably old enough to remember him I'd guess) He said he used either 2 or 4 bolt main in his cars. Said the 2 bolts walked around a bit but worked fine for him. And as far as I'm concerned, this guy knew his stuff.

Here is what I picked up last summer at U-Pull-It for $75. For my application it doesn't matter if it's 2 or 4 bolt, but for the $$$ I paid why not use it? Besides it was the only one I could find at the time.

 

Probably no different (unless it never would have broken at all).

The 4-bolt only keeps the cap stable side-to-side. It doesn't make it any stiffer up & down.

Get those cap pieces to me and I can tell you more about why it failed (assuming it hasn't had the two fracture surfaces put back together - but that's pretty hard for people to resist doing).

 

Nothing really 4 bolts are stronger in certain aspsects but it just mainly sounds better...

And yes they did put 4 bolt mains in 1/2 ton trucks

Most trucks had 4 bolt mains

 

ill send them to yeah i was told hard down shifting can make caps do this?

 

Yes it will work in your car. Externally ALL small block chevys are the same.

2 bolt vs 4 bolt

In a street engine it does nothing for you. Take into consideration the amount of power they engineer these blocks for(<300hp/380lb ft). Either or it doesn't matter at all.

If you are gonna build a high performance engine its really a waste of time. What you want is a VIRGIN (never been cut) 2 bolt block with NO core shift. The 4 bolt splayed cap is the strongest way to go. Its even stronger that the 6 bolt main in the ls engines.

Someone should do a scientific test and ruin a couple of perfectly good blocks with a hydraulic ram to see how many psi it takes to make both fail. I'm sure the difference in miniscule.

 

Maybe if you downshifted at redline, but usually the rods have something to say about it first. Trans abuse otherwise is usually contained within the trans

Pointless, 2 bolts, 4 bolts and splayed caps are all well documented and proven. A chat with a handful of machine shops/race shops should give you a decent list of the hows and whys several blocks failed

Besides, moden hotrodding is changing to the newer era of engine design so the old SBC info isnt as pertinent as it was 30 years ago

To the OP, it'll fit as long as the new engine is a 1pc RMS. If its an older 2pc RMS block, then the balancer and flexplate need to be swapped for the older stuff. Otherwise direct fit

 

No difference in the harmonic damper between one- and two-piece rear main seal engines.

 

Im thinking internal/external balance again