As it says, I'm just wondering how much hp a 2 bolt main can handle shifting at no higher than 6000rpm.

Thanks for the help

Rob

 

I've been told "take that how you want to" A safe bet is around 400-450 hp. It could be more it could be less.
John
My 2 bolt 400 is just fine.

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Spud is correct. I've seen and built some very fast 2 bolt mains before. Good aftermarket Main bolts or even better Main Studs w/ a windage will add some addition strength and added insurance. The engine I recently took out of my 82 Z28 was a 2 bolt 350, and I was able to run 12.50's(1/4) and 7.80's(1/8) with a solid cam shifting at 6600RPM and had no problems.Incorrect clearances in a hot street/strip engine(or any engine for that matter) will be the death of it way before the fact that it is a 2 bolt.

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That's a funny issue because there are lots of factors and directions to look. I am not going to give you the run of the mill "as much horsepower as you can put on the street" answer. The RPM an engine runs has alot more to do with the stress on the crank and mains than the horsepower. So keep that in mind when building the engine, 450HP at 5000RPM is less stressful than 350HP at 7000RPM. 4 bolt mains do hold the bearings better. As a result even if the 2 bolt doesn't break your bearings are going to live longer in a 4 bolt block. However, talking pure racing I have seen cast cranks ran at 9000RPM in 4 bolt blocks and forged cranks ran to 10000RPM in 2 bolt blocks. Neither of which I would expect to live terribly long. Still the bottom end was not a problem for either engine. If what you are thinking of is building a 300-450HP street engine then don't worry about the 2 bolt main. Its more important that the bores are round and straight and supported with good bolts. Personally I prefer 4 bolt mains on a street engine for above 400HP or 6000RPM. This is preferred, but far from required. The only exception being the 400. The one I have ran on the street fine with 2 bolt mains. The 400 mains are a little stronger and the 4 bolt version cracks too easily for my taste.


[This message has been edited by Grand Prix (edited July 10, 2001).]

 

Perhaps you may simply wish to use good ARP studs and have the block line-bored. It would probably be fine for most everything you'll do short of road racing or circle track.


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According to Lingenfelter in one of his books, it doesn't really make a difference till above the 600hp level.

I'm inclined to take his word for it

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From 1955, SBC's (small journal, no less) were run at the strip, at Daytona, Bonneville, NA, blown, turbo'd, sprayed, nitro, alcohol - basically abused in about any way you can imagine. Main bearings just never seemed to be a problem.

Then, with the advent of the mighty 350 in 1968 (a few in 1967), the 4-bolt main was born. Perhaps Chevy got the idea from Lingenfelter or Smokey, but it's also been speculated that the way they went about it actually WEAKENED the main bearing web! Even then, they still made versions with 2-bolt mains.

True, the early engines mostly had steel cranks. But, how did they avoid problems all those years?

Conclusion: If it's a streetable engine, 2-bolt is probably fine. For race engines, there are other casting problems that are more likely to bite you first.

Oh, the new Motown block is a 2-bolt...

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...with 1/2" studs and thicker/stronger caps. Not exactly a fair comparison, its not really the # of bolts that is the important factor.

 

I have a 400 sbc that has been dyno'd at 462 hourse and 520 ft/lbs, it has a 2 bolt main has been fine for the two years that I have had it. The car is a daily driver in summer and I shift it at 6500 rpm.
Hope this helps.

 

I'd have to agree with spud. I've always heard 400hp, and no more that 6500rpms. But I think a massive torque set up would be more stressful. And I mean massive, like around 450lb.ft. and up.

Also like Grand Prix said, once the engine starts spinning higher, its more of a question of will the bearings take the heat and stress? But the main caps are more likely to break at lower rpms & high torque levels.

Where can you find most stock 4-bolt main blocks? In trucks, right? Usually 3/4 and 1 ton trucks. That's cause of the massive torque, plus the resistance to that torque from towing heavy payloads/trailers, etc.

Makes sense to me.

 

Don't forget a good balancing job.

 

i've done a few 2 bolt engines and have never had any problems with a few that made over 450 hp and some that were shifted at 7500. before i started worrying about the nuber of bolts in the main caps i'd pay some extra jack to have the crank blue printed, run arp bolts/studs, the block alighned honed, and maybe even some better main caps.

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Thanks for the help everyone, it's much appreciated.

Rob

 

I feel that allign boring is a waste of money, why concentrate on having it aligned to very strict tolerances when the crank will actually flex quite a bit under load??

Anyone agree?

Marck