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Author Topic:   2bolt or 4 bolt
jammin james
Dirt Full Roller

Total posts: 50
posted December 30, 2002 05:42 PM
looking to build a pure stock 350. how important is a four bolt main concerning durability and cost??? i know everyone says "get a 4 bolt" but what is the rule of thumb on this? thanks

Donnie Ross
Dirt Maniac

Total posts: 109
posted December 30, 2002 06:25 PM
in a pure stock its not important a 2 bolt is plenty tough.

sixwillwin
Dirt Freak

Total posts: 215
posted December 30, 2002 08:14 PM
Use whatever one you have, dont worry about it. In fact, alot of stock 4 bolts tend to develop cracks between the two bolts. Angled splayed caps are the best for high HP engines.

racer17j
Dirt Forum Champ
Total posts: 1565
posted December 30, 2002 11:03 PM UIN: 54865418
i've never ran a 4 bolt and never had a bottom end problem of cracked block

66jj
Dirt Freak

Total posts: 352
posted December 31, 2002 03:18 PM
saw a test 10 years ago in hot rod mag. they bolted blocks to the floor and pulled on the caps 4 bolt broke sooner...

i allways sell 4 bolts cus people want them everyone...... easy money..

ive ran 2 bolts with up to 14-1 comp, 383, 7400 rpm, all day long.......... i allways use main studs windage tray and make a crank scraper, even on a blow up motor.....

jammin james
Dirt Full Roller

Total posts: 50
posted December 31, 2002 04:16 PM
thanks everyone that's what i thought i'd hear

sdhnc29
Dirt Freak

Total posts: 467
posted January 01, 2003 03:53 PM
In your case the 2 bolt would be just fine , so long as the compression ratio stay's reasonable . If you have a 4 bolt block with the center 3 main cap's marked with part number 3412 , then these 4 bolt cap's are the same as 2 bolt cap's , and they crack exactly where sixwillwin said they would . But ........... If you happen to own a block that has the center 3 main cap's marked as part number 2482 , then these are nodular iron cap's , and superior in strength to the 3412 and 2 bolt cap's .

Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780

tilley88
Dirt Freak

Total posts: 353
posted January 02, 2003 02:41 AM
Surprisingly, I've had those break, too. In my experience(and I've blown a few), 2-bolt mains are superior.

RC Racing
Dirt Maniac

Total posts: 144
posted January 02, 2003 10:56 AM
Steve (of Hendren Racing), you said "as long the compression ration stay's reasonable". What would you define as "reasonable"? Thanks in advance for your reply & take care

sdhnc29
Dirt Freak

Total posts: 467
posted January 02, 2003 10:46 PM
I consider reasonable for stock 3412 main cap's or two bolt cap's , no more than 11:1 . I've found over the years that any more than about 11:1 , and you will start having problems with the center three caps . The rear cap does not seam to be much of a problem until you get up around 13:1 . Like anything else though , it's all about preventative maintenance . Regardless of what stock main cap's your using , they should still be magnifluxed every 12-14 races .

None of the stock cap's are bullet proof , as tilley88 has shown with the fact that he has broken 2482 cap's . The strongest combo , if you must use an OEM stock block , is a 2 bolt block with the center three cap's replaced with billet splayed cap's . If your up around 13.5:1 or higher , then you should also look at replacing the rear main cap as well , though this gets quite expensive for a wet sump engine .

Steve

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780

hamer36
Dirt Full Roller

Total posts: 61
posted January 04, 2003 11:53 AM
400 2 bolt caps have a stress riser where the flat is machined for the bolt head. I've tried polishing this out but the caps still crack at that spot. what can be done other than aftermarket caps?

66jj
Dirt Freak

Total posts: 352
posted January 04, 2003 03:08 PM
ive ran 13-1 motors at 6500 rpm max for up to 3 years and still going with stock 2 bolts and studs..


hamer36
Dirt Full Roller

Total posts: 61
posted January 05, 2003 09:20 AM
66 did you have a good crank in there? I often wondered if crank flex cracked the caps or were weak caps causing the crank to flex and crack. They were claimer 400s and were balanced. Back in my late model days I had a LA jet crank in a 4 bolt block and ran the thing forever. Even ran one year with a 350 hub, cut the outer ring off.(ya we were studid back then)But it stayed together. My theory is that a good crank save the block.

HIT THE WALL
Dirt Full Roller

Total posts: 36
posted January 05, 2003 02:28 PM
Hamer36 I agree with you, I have ran stock 400 cranks and had main problems, and i have had a 400 with a good 4340 crank 12.9to1 comp. and have not seen the main problems with it, i beleave flex is a problem in cast cranks or cheap cranks

66jj
Dirt Freak

Total posts: 352
posted January 05, 2003 07:30 PM
cast scat cranks in 355 motors.. are what i was running.

jeff

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