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Old 12-10-2010, 05:24 PM
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Pontiac 2 bolt mains changed to 4 bolt mains

Has anyone ever heard of changing a Pontiac 455 with 2 bolt mains to 4 bolt mains? Can this be done and is this worth the money? I was told that the 3 center caps get changed from 2 bolt to 4 bolt? The block doesn't have any hole for a 4 bolt main I would have to have them drilled and taped

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Old 12-10-2010, 06:06 PM
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Quote:
Originally Posted by eztuld
Has anyone ever heard of changing a Pontiac 455 with 2 bolt mains to 4 bolt mains? Can this be done and is this worth the money? I was told that the 3 center caps get changed from 2 bolt to 4 bolt? The block doesn't have any hole for a 4 bolt main I would have to have them drilled and taped
It is done quite frequently. It can be done and might be worth it if you are building a race only engine, but for a street engine, You are better off just using ARP bolts or studs. I've have had a 4 bolt 455 block start to split between the main and cam journals at about 730 horsepower. Since your block is not drilled for 4 bolt mains, it would be a good candidate for splayed mains if you are planning on an all out engine.

Bill

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Old 12-10-2010, 06:30 PM
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I was planning on a 474 but my machinest said I should go up to 487. It should be under 500 hp and just a street driven car. I have never built an engine and I just keep on learning something new all the time and I haven't even started work on the engine yet. would splayed mains be worth the money on a 487 pontiac.
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Old 12-10-2010, 08:28 PM
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Quote:
Originally Posted by eztuld
I was planning on a 474 but my machinest said I should go up to 487. It should be under 500 hp and just a street driven car. I have never built an engine and I just keep on learning something new all the time and I haven't even started work on the engine yet. would splayed mains be worth the money on a 487 pontiac.
Has your machinist sonic checked the cylinders, and how much can your block be safely bored? Even .060" bore is pushing your luck without checking. Your machinist is apparently a Chevy mechanic as a BBC can easily be bored over .O60", but with Pontiacs, it can be a crap shoot! I wouldn't go bigger than the 474 inch that you were planning on. You would be throwing money away by having splayed caps installed on an under 600 HP engine. Just be sure to use good ARP bolts or studs.

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Old 12-10-2010, 08:45 PM
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If the power level is going to be under 500 HP, that can be done w/a 455 crank, no need for a 4.25" stroker (or bigger). No need for a 4-bolt caps, either. I would say to spend the money on a really good set of heads and good rods.

If the engine has to have a crank anyway, then a 455 block w/4.25" stroke crank using BBC rod journals would be fine. Better yet, build it out of a common c/n 481988 400 block.

BTW, billet 4-bolt caps are around $300/set, IIRC.
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Old 12-10-2010, 09:29 PM
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The caps themselves are expensive, yes, but the machine work for them is more than drilling and tapping holes, there are outer clearance requirements between the web and cap wings, I had my SBC done in Anchorage, Coker charged me about $500, with the line bore using my provided caps.
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Old 12-11-2010, 04:01 PM
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Quote:
Originally Posted by eztuld
I was planning on a 474 but my machinest said I should go up to 487. It should be under 500 hp and just a street driven car. I have never built an engine and I just keep on learning something new all the time and I haven't even started work on the engine yet. would splayed mains be worth the money on a 487 pontiac.
That sounds like a God awful lot of work for 500 horsepower, I can get that out of Chevy 350 with a cam and heads, that should be a no brainer on a 455 Pontiac.

The big Poncho's cap problems at high power is cap walk under the fasteners. This is usually solved with locating dowels rather than more bolts. This stops the walking and doesn't weaken the block by putting big holes in the bearing webs. Put your money into a good set of ARP studs which will require a rebore/hone of the main bores; a good balance job, a high quality damper. These go along way to reducing the dancing the crank does which takes a lot of load off the main caps.

Bogie
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Old 12-11-2010, 04:12 PM
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Thanks for all the help everyone...sound like I wouldn't get my moneys worth on splayed caps. I have a budget of $6000.00 to rebuild this engine and would like to use the money in places that it pays.

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