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Discussion Starter · #1 ·
Just got a 2 bolt main block and was planning a 375hp range 355 build. I know everyone shoots for a 4 bolt main but I dont see this block tearing to pieces on 400hp. I have read that 2 bolt mains are good up to 750hp, Ive also read that they arent good for 400hp. Couldnt find a median.
Any suggestions?
 

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More for Less Racer
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350 2-bolt at 750 hp, no way!!, a 4-bolt won't even take that for long. General consensus at professional machinist and engine builder sites seems to be 450 hp for street/strip but only 375 hp circle track for the 350 2-bolt because of the small contact area between the cap and the block. The cap just wiggles around too much under rpm regardless of how good the bolts or studs are, and it gets even worse with longer strokes(like 3.75" used to make the 383).

400 SBC and the BBC's can take more because they have bigger caps and block registers.

We tried the 383 street/strip at 500 hp and at the first tear down for refresh(about 3000 miles with some strip action, low idle oil pressure was the reason for the refresh) it was plainly evident on the main bearings and fretting marks on the bottom of the cap and where the block and cap meet that things were moving around badly even with ARP studs, crank was found to also be cracked, we just got lucky that it hadn't flown apart. It got splayed caps and a new crank
 

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There are ALOT of different opinions on this. I think 375 you will be fine. That's 375 crank hp right? You can buy a brand new ready to 350 4-bolt block for $700 from GM or even get a long block for $1500. If your sticking with the 2-bolt I would throw in some main studs for extra insurance and you could always run a main girdle but personally for I think that would be wasted money for you. If the motor doesn't see much 6Krpm+ action and is more of a street thumper, 400-450 would be my personal limit. I know a guy running one on the Nova website pushing 500+ to the tires and has raced for 3 seasons and it's still together so you never know. Think of it this way, the Mustang guys talk about splitting stock 5.0blocks alot. You see some split at a measly 350hp, some hit 500 without issues. Up to you on if you want to take the chances, but I think 375 would be fine.
 

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All I can do is speak from my own experience with the only two bolt 350 I've ever had. I had no problems running a supercharger with 6 psi on a 9.7:1 cast crank 2 bolt main (with ARP studs) 350 and turning it to 6000 rpm regularly. I don't know how much horsepower it made but I can only guess that it was over 450, maybe 475. I sold it after two years and no issues.
 

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Yea, I know.

A lot of guy use em' and had good luck, and if I couldn't find a 4bolt I would too. But if you can afford 450+Hp you can afford a 4bolt. But what do I know I have 4bolt's coming out my ears.
 

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I forgot to mention, I ran one in a full size pickup for a bit with a Vortech supercharger on 7psi and a small shot of nitrous and then just nitrous at the tune of 150hp shot. The motor had 177K miles on it when I got rid of the truck, no smoking, no knocking, great oil pressure. As far as I know it is still running strong. Again, no concrete line of "it will break right at this HP level"
 
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