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Wish I grew up in the 60's
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Just a simple question, how much power (torque/hp) can a 350 with a 2 bolt main withstand without having to worry about breaking anything?
 

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Its not so much a question of what block, but the quality of the parts used. A good balanced assembly in a 2 bolt main motor will put out much better power than a stock assembly in a 4 bolt main.

In my mind, people put way to much importance in the 4 bolt main thing. Sure, its another improvement, but not the most important, by far.
 

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I couldnt tell you how many times this topic has already been brought up. do a search..youll be amazed.
But I totally agree...in most cases people make a much bigger deal out of needing 4 bolt mains than needed.
 

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Here is a good link to look over
http://www.chevelles.com/forums/showthread.php?t=38173

Here is a pic of a 2 bolt main block that was in a 410 horse engine that was sent our shop as it was loosiing oil pressure it had 4 circle track races on it and this is what the main caps and bearings looked like and this had an ARP stud kit as well and we have seen this many times on the 2 bolt main blocks but remember we see a couple hundred blocks a year not just a hallf a dozen blocks rorm what I have seen in the 32 years of building pefromance engines anything over 400 horse I would use a GOOD 4 bolt block. LOOK IN THE GM CATALOG AND SEE WHAT THEY RATE A 4 BOLT BLOCK AT as I don't believe the 2 bolt block is more.

As you can see the caps were walking it there registers as we see a few of these a year but have alot of calls and emails about this same subject.

We installed 3 center splayed caps and the crank had to be turned and the customer assembled it and it went the rest of the year and no more problems.
 

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CNC, arent the 2-bolts that are drilled and have splayed caps added supposed to be stronger than stock 4-bolts? Thats the route I would take, if its a good block, colin.
 

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CDJr said:
CNC, arent the 2-bolts that are drilled and have splayed caps added supposed to be stronger than stock 4-bolts? Thats the route I would take, if its a good block, colin.
Colin

Yes they are due to the 6 extra holes not being in the webbing of the block and the caps we put on are flat bottom caps and are 7.500 wide and these caps pull on the pan rails instead of just on the webbing of the block.

Stepped caps are OK but they are very hard to fit and and the contact area is not as good as a flat bottom caps.

And we use caps fron Kenny at Pro-Gram Engineering which have omly a 10 degree outter bolts beacuse when you start getting into caps that are 15 to 22 degree outter bolts there is a good chance of getting into the water jackets which is not a good.

Before we do anything to the block we sonic the cylinders for thickness and if thats fine we put caps on trom there.

Here is a pic of a block we did for another shop as this has all billet caps and a strap on the rear main cap and most street and strip 383 engines we build we just do the 3 centers.

Good luck with your build Carl
 

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Beater Driver
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I have a buddy who assembled a 9:1 compression 2-bolt main 350 in his garage. He home ported the -462 heads, slapped in a nice solid cam and ran 12.9x in his '66 Malibu. This engine has held together for several years of street and strip abuse. I would guess that this engine is in the 375-400 hp range. Get the balancing and machining right and you can do the same thing.
 

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I think that for a circle track car, which has extended high reving, a 4 bolt is a must....but a street car is not driven that way. For most street motors a 2 bolt should do................A 4 bolt is nice insurance.
 

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poncho62 said:
I think that for a circle track car, which has extended high reving, a 4 bolt is a must....but a street car is not driven that way. For most street motors a 2 bolt should do................A 4 bolt is nice insurance.
We don't care if its a street or strip engine, circle track or marine if its over 400 horse its over 400 horse and we use the proper caps for the proper horse power rating as we have seen plenty of street driven 383's and 355's with caps not as bad as the ones in pic but they have had problems in those areas.

We are not basing are info on just a few blocks or engines, Again we see a couple hundred blocks in a years time and we see a few a year where they have over powered the 2 bolt caps and we have an good reputation for we build for engines and blocks we machine and thats all we do is performance work a 2 bolt block over 400 horse is not a dependable as a block with good 4 bolt caps.

The guy that ownes the engine in the pic I posted run the engine this way cause his friend said it would be OK cause his friend did it and now they had to rebuild the engine again where it should have been done right the first time.

Why gamble.
 

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Wish I grew up in the 60's
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Discussion Starter #11
CDJr said:
CNC, arent the 2-bolts that are drilled and have splayed caps added supposed to be stronger than stock 4-bolts? Thats the route I would take, if its a good block, colin.
How can I tell if I have the drilled and splayed caps?? The 350 is out of a 1971 2bbl el camino.
 

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colincamaro said:
How can I tell if I have the drilled and splayed caps?? The 350 is out of a 1971 2bbl el camino.
Colin, no factory Chevrolet small blocks came with splayed mains. Since your engine was originally a 2 bbl carb engine, it more than likely has standard 2 bolt main caps. It should make a good candidate for upgrading to splayed mains if it passes a sonic test on the cylinder wallls.

Barry
 

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a 350 CI engine in the 400 +HP range is a pretty healthy normally aspirated street engine in my opinion. You need a good combination of compression, airflow, & RPM.
I think with carefull parts selection, like light weight pistons & pins to reduce the rotating mass. a roller cam rather than a flat tappet & good flowing heads, & good machine work, 400 HP can be acheived without hurting a 2-bolt motor.
A motor built with heavier pistons like KBs for example, or a flat tappet cam that requires higher RPM to make the #s as well as lack of careful blueprinting & clearancing, your in trouble.
On the other hand...the mony you may have to spend on those parts & machhine work to make it survive...you may as well have just either bought a good 4-bolt block, or have splayed caps installed.
Of course...we're talking SB Chevys here....BB Chevys is a little differant.
Also..I feel a 4-bolt is far more critical in towing applications, serious 4 wheeling & Marine applications.
 

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in my very early 20s a friend and I bought a 70 Nova SS no motor but fresh 400th with a 2800stall converter. and a low mi 12 bolt with a locker and slapper traction bars (so the seller said, and I believe it to be true) a $1500 70 Nova SS. it took us a yr but we built a low buck 355 maybe 400hp. we took a running 1969 350 2bbl engine out of a 69 impala 4dr & hot tanked it , polished the crank and new cam bearings and new rod & main bearings, honed the block, put a used set of pistons on the stock reconditioned rods. we bought a set of used camel hump heads ( when they were freshened they got new springs guides hard seats ect. I think when we bought them they were a couple 2 or 3yrs old since they had been freshened) they had 202 160s and had been ported & polished. I think it was 11.1 or 11.5.1 CR & solid flat tappet cam and some used headers & a used set of slicks. we run it 2yrs and it run a 13.02 and its best 1/4mi time was a 12.99 if I remember correctly, it barley got into the 12s. this was no seats ect. as big of a diet as we could put it on. but we rapped it high & hard, especially the 2nd season. (his wife made a scrap book with the pics & time slips thats in his garage) I sold my 1/2 after the 2nd season as my second child was on its way. but a yr later my buddie pulled the 2 bolt main motor and built a real motor (as real as he could swing), it was a 4 bolt 355 that took the nova into the mid and low 12s, he still owns the nova. my point is the 2 bolt main block held up, and I'm glad we did it as it was a unforgettable time in my life, hell we only had hand tools and had to borrow jack stands and a air compressor to build what we built. it went through as much hell as we could give it . he sold the 2 bolt engine to his dad. his dad completely rebuilt it (all new parts & bored, line honed & balanced it with a GM steel crank & aftermarket parts & heads) and put it in a 71 camaro. it has more nuts now than when we run it, its been to the strip a couple Xs. but mostly shows & cruses still to this day, 25+yrs later. the camaro is babied now days as his dad is in his late 60s or early 70s. maybe it was luck I'm not sure.

how much can a newer 1 piece rear main 2 bolt blocks handle or take ? some where near what the old 2 bolt LH dip stick could ?




Mustangsaly
 

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Race it, Don't rice it!
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It's about what CNC say's. When you see a few hundred engines a year you start seeing trends. Not eliminating those trends would be like building in a tolerance of failure. How many engine's could they sell if they said "Oh by the way, about 1 in twenty will wipe out a _____(insert part name), Go ahead and make that check out to..."


Listening to a few people on a web site like this is good for idea's and general knowledge of fact's but common mistakes can get spread around pretty easily. You got to remember, what worked for that ONE guy on the board may not be the best way of doing it. He may not of had problems, but he didn't tell you of other factors that affect the outcome.

In my daily driver right now, I broke a main cap and replaced it with one from a 4 bolt in street stock class with wiped bearings. I looked through five others I had laying around to find one close enough. The last one I tried fit to 3/4 of a thousandth and the size was changing fast because of the temp drop outside. I had to tighten the bolts an extra 15 FT LBS to pull it in shape though. The point I'm getting at is...I could tell you this works, it did for me, but probably got lucky and haven't had issues yet. I haven't looked at that bearing either.
 
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