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Old 11-04-2010, 08:20 AM
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How to Build a 421 SBC ???

Hi guys, Im new to this site, but I've heard of it in the past.
Anyways Im curious on how to build a 421 SBC. I have the "509" 2 bolt main 400 block. Its a complete virgin block, never been bored or undersized. I have around $3000 to build this motor.

What all has to be done to the block to allow a 3.875 stroke ? What kind of machinery ?
Im planning on converting the 2 bolt into a 4 bolt main. Im trying to get 525-575Hp out of the build. Can the stock block with a forged bottom end and racing heads hold up to the power ?
Any and all info appreciated.

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Old 11-04-2010, 08:27 AM
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If you want an honest NA 575hp that you plan on using I wouldn't run a stock block. I realize its a lot of money but you really need to be looking at an aftermarket block at that power level.

That is assuming you intend to drive it on the street, if its a drag only setup you may be able to get a few seasons out of it.

As far and the machining goes, for a 3.875" stroke it really comes down to the rods you use, you may need a small base circle cam, and you may need to have the block clearanced.
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Old 11-04-2010, 08:46 AM
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If all you have is a block, I seriously doubt $3k will get you to 575 hp. Machine shop alone I expect will be close to $1k, it cost that for my splayed caps, saddle machine work for outer cap to block clearances, line hone and a simple .030 bore/hone.

What parts do you already have?
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Old 11-04-2010, 10:27 AM
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How to Build a 421 SBC ?

I know $3000 wont get me to those power levels and Im sorry I wasnt specific enough, Im in school trying to sneak out these posts.
Ive also been looking at the 3.8 stroke aftermarket crank. With a .04 Overbore and that 3.8 stroke in a 400, I found it would put me close to 415 CI, Which I would be more that happy with. I was wondering if that extra .05 stroke would make any difference on whether the block would need machine work ? I want a engine bigger than a 400sbc, but not as heavy machined as the 421 CI. So I think I found my happy medium. Does anyone know if this crank will slide in and be fine with 6.0 rods ?
Does anyone also know if you can get a 3.8 inch rotating assebly thats forged and ultralight ?
Any other tips on a rare engine build like this ?
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Old 11-04-2010, 10:40 AM
How fast is fast enough?
 
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Quote:
Originally Posted by Chevy406power
I know $3000 wont get me to those power levels and Im sorry I wasnt specific enough, Im in school trying to sneak out these posts.
Ive also been looking at the 3.8 stroke aftermarket crank. With a .04 Overbore and that 3.8 stroke in a 400, I found it would put me close to 415 CI, Which I would be more that happy with. I was wondering if that extra .05 stroke would make any difference on whether the block would need machine work ? I want a engine bigger than a 400sbc, but not as heavy machined as the 421 CI. So I think I found my happy medium. Does anyone know if this crank will slide in and be fine with 6.0 rods ?
Does anyone also know if you can get a 3.8 inch rotating assebly thats forged and ultralight ?
Any other tips on a rare engine build like this ?
You don't have the budget for the build you're proposing. A superlight 3.8" rotating assembly won't leave you enough to even machine your block.


If you want any hope of getting it together for 3 grand, run a standard 3.75" stroke, 5.7" rods, about a 200-215cc sized head, a solid flat tappet cam, and a victor intake with a 750DP. If you get all of your parts used, in good working shape, and for a good deal, you MAY be able to get it together for 3 grand and hit 500hp.
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Old 11-04-2010, 11:02 AM
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How to build a 421 SBC

So from your post I take it you have to machine the block for a 3.8inch stroke ?
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Old 11-04-2010, 11:03 AM
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Quote:
Originally Posted by Chevy406power
So from your post I take it you have to machine the block for a 3.8inch stroke ?
You'll have to machine the block to use it at all. Doesn't matter if you run a 3" or a 4" stroke.
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Old 11-04-2010, 01:49 PM
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If you're on a budget...like most of us usually are then just build a good running 406. As said, you'll have to have some machine work done like bore, hone and some clearancing if necessary.

Stock crank will work after mag and polish, good Scat 5.7 rods and your choice of pistons. Keep it around 9.5 to 1 for a street motor, spend your money on the heads. If you shop around and spend wisely you can have a 500 hp STREETABLE 406. Just remember that money go's fast when buying performance parts. I don't think you can do it for 3k but good luck....and you'll need the right stall conv., trans and rear end to handle the hp.
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Old 11-04-2010, 02:07 PM
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spend your money on heads, intake, and carb.

power is in the heads. without good flowing heads, big cid's don't do much in the the hp department.

if you are on a budget then leave it a 2 bolt main 406 or even a 377 (350 crank).

500hp/500ftlb should be easy to make with a 406 and good heads.

build one like this (490hp/525ftlbs) and run 87 octane.

http://www.chevyhiperformance.com/te...ild/index.html
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Old 11-04-2010, 04:10 PM
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All good advice!
But little hint you dont need 421 cubes to make big power a 406 wil make all the power you can handle if built right.

Mentioned above about factory blocks not being able to handle big power complete "BS" if the block is prepped right and the right attention to detail is taken they can handle the power you will be making pretty easy now when you get at or over at 415 cubes probably a good idea to go aftermarket but again power wise those 406's will make more than you can handle good idea is to have it internally balanced.

But a good set of heads should make up your most expense in build thats where the power is.
also try a solid roller build if you can swing the cost. great power.
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Old 11-06-2010, 05:45 PM
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Quote:
Originally Posted by 327NUT
If you're on a budget...like most of us usually are then just build a good running 406. As said, you'll have to have some machine work done like bore, hone and some clearancing if necessary.

Stock crank will work after mag and polish, good Scat 5.7 rods and your choice of pistons. Keep it around 9.5 to 1 for a street motor, spend your money on the heads. If you shop around and spend wisely you can have a 500 hp STREETABLE 406. Just remember that money go's fast when buying performance parts. I don't think you can do it for 3k but good luck....and you'll need the right stall conv., trans and rear end to handle the hp.

Some good advice, I built my 406 last spring using a "509" casting block from 1975. I reused the stock crank and rods after having them checked, resized, and ARP hardware throughout the bottom end along with a windage tray and a stock pressure oil pump with a 6qt pan. I put the money in the heads, roller valve train, and hydraulic roller cam. My heads are a set of Dart Pro 1 Aluminum 200cc heads with 64cc chambers. My cam is a Trick Flow unit with .563"/.574" lift with 1.6 roller rockers. My compression is 10:5:1 using Speed Pro Hyper units. Even though I bought alot of this stuff from people who either didn't use or had a change of plans, I still have nearly 5,000.00 in my motor including the machining and assembly of the short block. Like some have said, "speed cost money" but I don't have regrets with my project, it flat out runs great.
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