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Author Topic:   4 bolt vs 2 bolt mains
posted October 13, 2003 10:43 PM           
What are everyones thoughts on 2-bolt mains race engines? I know four bolt motors are best but does anyone run a 2 bolt motor? Hobby stock? Street stock? Certainly not in modified or late model?

Is running a 2 bolt common?


posted October 13, 2003 11:12 PM
Two bolts are just as strong if not stronger,more meat on the cap.When have you heard of a main bolt breaking?If it does something is wrong.


posted October 14, 2003 10:08 AM
If it's a 400 block, use a 2-bolt and have it splayed. On a 350 block, a 2 or 4-bolt will do fine. Personally, I prefer the hi-nickel 350 4-bolt blocks. I've got one I'm racin now that came out of a 70 sumthin Vette, started out as a standard bore 350, opened up to 355, then 358, over a 12 year period and still twistin hard! It has a GM steel crank, X rods, Manley forged slugs, and an unknown vacuum pullin cam that I think is finally startin to wear. It'll run with the bigger motors on dry slick, and hold its own on tacky, too. I may change the cam this winter and try it in my new mod next season. It's always been run in street or super street.

posted October 14, 2003 04:52 PM
I sell all the 4 bolts and allways run the 2 bolts.

Ive had up to 14.5-1 motors on stock caps at 7200, its all in the balance and machine work. I ran main studs in this combo.

4 bolt 400s are very weak I would never use one for a compression motor.

If your worried about caps go to billet splayed caps in a 2 bolt.

posted October 14, 2003 05:15 PM           
thanks for your answers... just one question... what does "splayed" mean? Does it mean that the outer bolts of a 4 bolt are at an angle (that's what it looks like to me)?


posted October 14, 2003 07:15 PM
We run a 360 dome in our late model and my father, who has built many races motors (lives by the words of Smokey Yunick), always makes us boys run a two bolt. We have never had the bolts (studs actually) break and the webbing (meat) on the cap is thicker. Just my 2cents.

posted October 15, 2003 04:13 AM
A 2 bolt would be fine like the others have said.
If its a 400 definitely use a 2 bolt and have the splayed (angle bolts) caps fitted.
I would definitely run studs rather that bolts though.
Like someone else said, its mainly in the quality of the balance job and machine work but most of all engine tune up - detonation will kill everything even the fanciest 4 bolt aftermarket block with all the "hollywood" parts, it will just cost more to replace.

GO 24
posted October 15, 2003 01:19 PM
I've been running 355 2 bolts in a limited late model for several years. Dyno's out at 430 or so and spins upto 7400rpms. Our new one which is more of a "super" late model motor has splayed caps but I've been told from our engine builder anything at 500hp or less is fine in the 2 bolts.

posted October 18, 2003 07:24 PM
I run a 383 stroker with 13.5 to 1 comp. and it's a 2 bolt.

posted October 18, 2003 10:13 PM
I've had good luck with the stock 4 bolt 400s...the secret is in the balance job and the crank. One has LA billet crank in it, the other is a cola. If the crank is made from cheap material, it will flex and break a cap (uaually # 2 or 4). The crank will fail a mag test if checked. Everyone blames the caps because they're easy to see because they are in two peices. These turn 72 to 7400 and aren't claimers. The claimer 400s I turn 6400 max (cheap cranks) and they still break. If you're running claimers, I'd suggest 350s.

posted October 19, 2003 01:18 AM
from what i'm led to believe, the disadvantage to a 400 4 bolt is actually in the block, because the bores are larger and the main journal larger there is less material around the webbed area at the base of the block (where the bolts thread into) and this becomes the weak point. i should point out that i have not seen one fail, but i don't know of any being run. most of the "building chev engines" books by reputable engine builders say the same. i would assume this is the reason why world products & dart went to all the trouble to start casting aftermarket blocks.
our engine is a 415 (dirt latemodel) using a factory 2 bolt 400 with the 3 centre mains fitted with splayed caps, i think the weak point in this setup would most likely be the front cap (at the end of the main journal oiling circuit).
if you don't want to fit splayed caps maybe you could try dowel pinning them, i think this is an old trick but i haven't seen it done, seems simple enough though.

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