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  #1  
Old 07-27-2005, 11:25 PM
benno318 benno318 is offline
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Default small block main girdles

just a question to see if anyone has ever seen a mopar small block with a main girdle fitted. i am rebuilding a poly 318 for road racing and the block cannot support a 4 bolt main cap conversion due to there being not enough meat in the web area. i was thinking of making a girdle for a bit of extra high rev insurance. anyone seen one on a mopar or am i going to be a pioneer of this? or can anyone advise me against it for any reason? thanks guys. ben simpson
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  #2  
Old 07-27-2005, 11:31 PM
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No such thing as a girdle for a small block. You don't need one anyway. It's good to 5 or 600 hp any way. We raced one for a season or two at a liottle over 400 hp and turning 6800 rpm all night long on a dirt track.
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Old 07-28-2005, 01:04 AM
skankweirdall skankweirdall is offline
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Not sure how much horsepower you are going to make with that poly but I would think not enough to worry about a girdle. I just use studs in my LA, no 4 bolt caps.
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Old 07-28-2005, 01:10 AM
sanborn sanborn is offline
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Keith Black made main girdles for 340s in the early 70s. They were used with the mating billet steel main caps. We had one, used it, took it off because it was very heavy(it also required a special oil pan). And we never had main problems with short track racing in the 550HP range.

When you get past the 600HP range on oval track racing, you probably need either four bolt mains or a main girdle. Drag engines probably can get by with 600HP without four bolt mains(fewer stress cycles).

It's not "rocket science" to make one, just requires precision machining.
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Old 07-28-2005, 02:50 AM
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What about steel main caps?

And sanborn, did you get my e.mail?
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Old 07-28-2005, 06:56 PM
benno318 benno318 is offline
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thank you all for the replies. i guess i was becoming a little nervous having seen a block from a truck with its guts well and truly ripped apart, but you guys have confirmed that it was more than likely caused by an abnormal problem. thanks again for the expert advice. ben simpson
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Old 07-28-2005, 07:52 PM
skankweirdall skankweirdall is offline
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I wouldn't worry about that, I can break stuff with a truck in a way that I never could with a car.
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Old 07-28-2005, 09:13 PM
littlecampbell littlecampbell is offline
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There is a guy on Moparts by the name of MR P BODY that spins his stock 340 2 bolt, no girdle to 8200....Shifts at 7800 rpm. It runs in the 9s and is obviously perfectly balanced.
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Old 07-29-2005, 12:19 AM
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This is the truck block he's talking about... and the crank...
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Old 07-29-2005, 12:45 AM
littlecampbell littlecampbell is offline
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Old 07-29-2005, 12:55 AM
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I can tell you, after driving 400kms in the rain, mucking around loading it into the utility and then waiting till the next day to check it out... Ben wasn't laughing!

Just check the Poly head cutaway thread to see how useful the heads were, too...
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Old 07-29-2005, 01:19 AM
sanborn sanborn is offline
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Ray, got your e-mail and sent you a reply. I will try to send it again.
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Old 07-29-2005, 01:33 AM
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Ray, just resent a reply. Let me know if you got it!
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Old 07-29-2005, 06:48 AM
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Yes, I got it... and I must apologise, I now realise I had got it before and in my delirium thought it was from someone else with whom I've had correspondence on another forum.

Thanks for the detail, I look forward to further discussion...
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Old 07-31-2005, 03:25 PM
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"Man now thats what i call a bad imbalance job" I have Read somewhere once that a 4 ounce imbalance at idel becomes a 64 pound sledge Hammer at 6000+RPM,So it pays to do a Good Balance Job, LOL.As in your case Ben just run it with a 2 bolt main it will be OK just Balance Everthing,We spun ours up to 8000 RPM on Numorus Occasions..
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Old 07-31-2005, 05:58 PM
benno318 benno318 is offline
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i have decided due to the answers recieved here that the stock bottom end will be adequate, although i may go steel caps. any problems i have seen are probably the exception rather than the norm. thank you guys for all of your answers and as i progress with the project i will keep you all informed. ben simpson
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  #17  
Old 07-31-2005, 06:55 PM
sanborn sanborn is offline
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The enemy of a block(or crankshaft) is torque. Torque causes the block to flex if too much is applied. Fortunately, Mopar blocks are beefier than either GM or Ford blocks. So you can get by with Mopar 2 bolt blocks where a GM or Ford block would fail---to a point.

The purpose of 4 bolt main caps (or girdles) is to keep the block rigid as possible under higher torque loads. You can load even an iron race "R" block to the point where it too will fail---but that requires a very high HP/RPM/Torque level.

That is one of the advantages of an aluminum block---they will flex without cracking---and absorb all that torque the engine is generating. But all is not perfect with aluminum blocks either.

The same is true for crankshafts, stock Mopar units are good---to a point. But you can easily overload the crank to the point where it will crack in the rod bearing cheeks----and if you keep overloading it----BAM!!!!!!!!!----and most then think it is a lubrication failure, not a material failure.
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