4 bolt main!? Tell me about it...

[OldCarPilot]

<small block chevy types>
You know when I put my engine together a while ago I bought into the whole 4 bolt main thing, but why? These days people are making HP with (at best) 93oct fuel and low compression. So I am wondering if any of you have had a “2 bolt main” come apart, and what was the situation? I don’t mean the drag racers running like 12:1 compression and 8000rpm or anything, but why not 2 bolt main at like 400hp or so?

[Tcoupe]

I have "heard" that the 4 bolts can actually be weaker in the main webbing areas....I have seen many 2 bolts take alot of abuse...now, splayed 4 bolts are a different thing all together.

[plan9]

my friends got an 11 sec nova without the bottle. its a 2 bolt main .30 over 350ci. its withstood some serious abuse.

id probably go 4 bolt main with a blower, depending on the boost.

i have heard alot of different things, but a 2 bolt with 400hp will be fine.... just make sure the block is sound before the building it.

anybody agree/disagree? id like to hear different angles.

[thirtytwo]

[ QUOTE ]
I have "heard" that the 4 bolts can actually be weaker in the main webbing areas....I have seen many 2 bolts take alot of abuse...now, splayed 4 bolts are a different thing all together.

[/ QUOTE ]

yep ..the machine shop i used to frequent back home (mostly dirt track stuff) told me the stock four bolts were worse cause the bolts were so close together they would crack between the bolts i guess the moral is if your that worried about it you should have splayed caps.

this seems to be opinion also for every one guy tells you better one more will say worse....even mech. engineers i have met dont agree....

all i know is the shop i used to go to did lots of motors for the roundy round guys and those motors saw lots more abuse than typical street motors.....he got hooked in with a rod mfg co. good deals .by the end of the season he stopped using them to high percentage of failure .real world is better than any lab

had a cast flat-top cast crank 2-bolt 350 constantly flogged it 6 grand for 3 yrs drove it 10000 mile road trip then sold it still runs as far as i know

[yorgatron]

i've seen plenty of connecting rods thrown through the sides of blocks,but haven't heard too many loose mains.most of the stuff i tinker with ain't hopped up though...

[lowandgold59]

.....tell me more!....

[Phil1934]

My machinist says all the SBC with spun main bearings he gets are 4 bolt mains. He doesn't know if it's just bad torquing sequences or a design problem, but he likes 2 bolts.

[colorado51]

For street use, a 2 bolt would be just fine.

If you were running a shit load of nitrous or a bunch of compression or spinning a lot of RPM`s, then a splayed 4 bolt is probably what you'd want.

[k9racer]

The 400 bolcks with 2 bolt mains are a lot stronger more meat around the bolts. I run 2 bolt blocks{ 400, 350 and sometimes a small journal} on my IMCA type open wheel racer and a street stock. I also use cast cranks I turn with good rods excess of 7000 all the time. I know that they are good for excess of 400 hp. I hope this helps. Bobby..

[**DONOTDELETE**]

I ran a 2-bolt cast crank 350 in this thing for two seasons. Didn't even freshen it over the winter. It had 9.25 : 1 compression. When I parked the car I sold the engine (cam changed) to a friend (1986) for his pickup truck. It's still going down the road today.

[OldCarPilot]

It sounds like no one has has a 2 bolt main engine come apart. Good news. I have one just laying around that I'm going to build next. Thanks all!