350 4 bolt

[otsenre]

Someone told me all chevy 350s out of 72s came with 4 bolt, I disagreed, can anyone comfirm this block casting is 3970010 Thanks in advance

[69halfton]

im not a information buff about stuff these trucks came with from the factory.

but i have herd that all trucks had "truck blocks" which were indeed 4 bolt mains.

my 69 has a four bolt.

[red69ss]

I have two 350's with same casting number and I know for sure one is a 2 bolt main, but have not had pan off other one you can check numbers on nastyz28.com ,but you probaly need numbers off pad in front of pass. head .

[cdowns]

thats a very common casting number i've seen more of them 2bolts than 4

[too much stuff]

Casting number is for a 350. Used for many years in low perf. to hi-perf. Could be had in 2 and 4 bolt mains...

[timcos]

2 bolts are good blocks. 4 bolt mains are used for high RPM or very high compression....not really needed but if you have 4 bolt does not hurt for daily driver apps.

Tim

[1969k10stepside]

Originally Posted by otsenre

Someone told me all chevy 350s out of 72s came with 4 bolt

Don't think so in the 10-30 series.What I've heard is that if they were from the C/40 and up series they were 4 bolt but I don't know...I've got a few 350 blocks around,one is a 4 bolt out of my old '69 Camaro I rolled over.If I really needed a 4 bolt I would make one out of a 2 bolt main block and go from there..

[PanelDeland]

From what research I have done;the casting # will not tell you whether it is 2 or 4 bolt main.Most performance engine builders prefer the 2 bolt main block even for very high performance because the webs are stronger and the aftermarket 4 bolt has splayed mains making them stronger and the webs remain stronger also.Also most agree that under 500 HP the 2 bolt is plenty strong.I have also been told the rods are weaker than the mains in a small block.

[57sailplane]

from the info i have found if your block has a 010 on the side by the motor mounts its is cast with thicker webs for the 4 bolt main.. making it stronger. now it is my understanding that if gm was short on 2 bolts it was not uncomon for them to drill out one of these as a 2 bolt.. it is still stronger than your average 2 bolt. if you put arp studs in a 2 bolt block it will be stro
nger than a 4 bolt...

by the way the picture you see here of my engine is a 3970010 casting block. it has the 010 on the sides and in the back.. it was a 4 bolt. but my machinest made cast iron studs and threaded them into the outer bolt holes with lock tight. then milled off the tops. then it was machined for splayed caps..

[special-K]

A steel crank is more important that 2-bolt vs 4-bolt.4-bolt stabilize against deflection,but 2 extra holes weaken the casting.So a more rigid crank solves that w/o weaking the block.I`m not saying 4-bolt are weak.I still prefer them.Just saying the emphasis should be on the crank more than which block.A steel crank 4-bolt is the ultimate.

I always heard that truck 350s all had 4-bolts up through`75.A truck block is a hi-perf block.The difference between HD and HP comes from all the other moving parts.

[Longhorn Man]

back to the original question, it is not uncommon at all to find a 4 bilt block in a 72 10 - 30 series truck.
It is also not uncommon to find a 10 20 high nickle block in a 72 10 - 30 truck too... which personally, I'd rather have the high nickle than the extra bolts.

[mrein3]

Originally Posted by otsenre

Someone told me all chevy 350s out of 72s came with 4 bolt, I disagreed, can anyone comfirm this block casting is 3970010 Thanks in advance

According to the factory stamp on the front pad of the 350 that was in my truck when I bought it, it was out of a 78 truck. It had a 3970010 casting number and 4 bolt mains. I replaced that engine with a 383 that was made out of a 350 that originally was in a 1971 Monte Carlo. It had the same casting number, 3970010, and 2 bolt mains. However, it also had 010 and 020 cast in the block under the timing chain cover.

Accoring to my machine shop guy, who has been doing this long enough to have ordered heads for a 396 out of a catalog BEFORE they were ever sold to the public, for 99% of the people out there 2 or 4 bolts won't matter.

[WorkinLonghorn]

for 99% of the people out there 2 or 4 bolts won't matter.

Probly not,but it sounds better "I got 4 bolt mains!" But I also wonder why the GM engineers opted for 4 bolt on low rev-ing trucks. Personally I always assumed that lugging and low rpm full throttle operation somehow required the up-grade to 4 bolts.Maybe it was just hype.
But hey,when I'm pulling away with 10,000 lbs GVW flat out at 1500 RPM I'm thinking " Damn,good thing I got 4 bolt mains!"

[Longhorn Man]

when most ppl run a plow, they hold it at WOT in first, same thing when trying to drag junk through the mud or anything like that.
I do agree though, 99% of these build ups that are more for street than track don't need them.

[PanelDeland]

So if you want the ultimate small block you need a 10 20 high nickle block with an 010 on the side and a steel crank.Then you have it machined for a splayed 4 bolt aftermarket main.Or you could just get an aftermarket block with all the above and probably save some money and even get a larger bore/stroke combo.Unless there's a class displacement requirement,or an originality issue building a 350 only makes sense if you already have good parts to build one.If you need a crank you can probably get a stroker for the same as a stock one,most other parts are the same,you can get better aftermarket for about the same money.

[Jtrux]

My k5's original block was a 4 bolt.

[57sailplane]

the 4 bolt main cap is not installed to strengthen the block. the extra 2 bolts are there to keep your bearing alive. i agree that a forged crank is way better than cast but thats a totally differant story..

what happens and most people dont realize is that under drastic loads or high rpm major amounts of down force are applied to the mains via the piston and rod force down on the crank combined with the resistive force wich would be the load your are towing or you hit the trans brake at launch... the piston and rod want to push downward rotating the crank wile the restive load wants to stop crank rotation thus putting a major down force on the mains wether or not the crank is flexing is to no value to this problem and actually one that flexes will actually counteract the problem cause some of the downward force is taken up by flex.. what the 2 extra bolts are there for are not to keep the cap on but to keep it from squeezing togather.. you see the center of the cap is taking all the down force wich is also the weakest point of the cap. now just a slight flex of the cap downward in the middle is not a problem but if the cap flexes to much the sides of the cap will tend to squeeze inward toward the crank thus causing bearing failure. gm added the extra bolt to help the clamping force between the cap and the block to help eleviate this problem.. it can still slide but not nearly as easy.. that is also why the splayed cap is used because the outer bolt is put in at an angle thus making it near imposible for any cap flex and bearing failure.

so you see for a steet engine being abused wile racing it or pulling the 4 bolt is a better deal.. keep in mind that i have read that an ARP studed 2 bolt is stronger than a stock 4 bolt and probably is cause you would get less flex from the stud and it has more clamping force than just 2 bolts. anyways i hope not to confusing...

[Billla]

Originally Posted by cdowns

thats a very common casting number i've seen more of them 2bolts than 4

• There is no way to tell a 2-bolt from 4-bolt SBC externally.
• 4-bolt mains are not required until 450+ HP *or* 6000+ RPM if studs are used. An align-hone is required if switching to studs
• It is not economically practical (IMHO) to install aftermarket 4-bolt caps.

IMHO the best buy is either a late-model roller block (one-piece seal) from your local junkyard or a new GMPP bare block (P/N 10066034) at around $700. The new factory block is a 4.00 finished bore with provision for a roller cam and a two-piece seal. You can drop a lot of money getting an old GEN I block up to spec.

For folks that have never actually seen a high nickel, high tin block - this is what it looks like