421sbc?????

[ucmydust68]

im planning on using a kit from here (http://www.ohiocrank.com/) for the 421 rotating assembly. does anyone know what kind of work im going to have to do to the block?

[Truckstr]

Originally posted by ucmydust68
im planning on using a kit from here (http://www.ohiocrank.com/) for the 421 rotating assembly. does anyone know what kind of work im going to have to do to the block?

Man, they don't seem to want to let a person navigate through their site! I almost didn't find such an animal.
Here's their real place to find the 421 kit: http://www.ohiocrank.com/html/newproducts.html

And it's no reflection on you, by the way. I'd have to "fault" their web management.

Now, back to topic. Sorry.

Most (if not all) of the aftermarket stroker kits on the market will still require some amount of "massaging" of the block in order to get them to "fit". In general, it's going to require (and behove) you to still talk to the machine shop's "in the know" folks.

Some of the best (IMO) companies out there will go to great lengths to make sure that whoever installs their rotating assembly, knows exactly what to do install it successfully.

Just talk with some people at their company. They'll give you a helping hand, if their worth dealing with.

[AirMale]

OHIO CRANK:
I just purchased their 550cu. BBC complete street motor. They are very helpful. Talk to Stan Ray and tell him your a friend of mine (John Vaughan) and ask for the best price on a rotating assembly. I spent over $9k with them. I bought the Merlin III block with Ray Franks ProFiler aluminum heads. I'm putting her in tommorrow, wish me luck!

[67Fleetsidedream]

Here 421 SBC

• SRP forced dome piston
• 4340 3.875 steel crankshaft
• 6" H-beam rods
• Internally balanced
• Race bearing and rings
$1795

You should have a machine shop do all the clearences for you.

[VTKidder]

Is it just me, or are the walls going to be getting thin on a 421 small block? There really isn't much to work with from the start.

[AirMale]

Not on a motown block(world products)

[VTKidder]

How do they make a block that will accept more machining than a standard 400 GM block? In order to make more wall, I'd think they'd need to space out the centers of the pistons, thus lengthen the crank? Make a rotating assembly that only works with a Motown or equivalent block? I've never seen why you can only bore a 400 so much; thought it was the thickness between cylinders, but if you'd punch into a water jacket, I see how Motown could sell a block with jackets moved away from the cylinder walls to allow for more machining? How do they do it?

[Truckstr]

The Motown block and the Bow Tie block, etc., all have the factory bore spacing. It's part of the SBC's "identity". A 421 (or other) kit "can" be installed in any one of those blocks - including the factory 400 block. The "trick" with using a production block would be to have it checked to make sure that it doesn't have an unacceptable amount of core-shift and, thus, thick enough cylinder walls.

If it were me, I wouldn't bore a production 400 block more than 0.040" over NO MATTER WHAT. It's just a matter of being "safe".

All that said, and I'm not to keen on the stroker small blocks (421, 434, 454, etc.) To me, there's just not that much more gained - if anything - by going with a bigger small block. The engine becomes too RPM limited due to piston accelerations and speeds - even with the 6.0" rods. It would be a better idea (to me) to build a big block for about the same money as one of the over-size SBC. But, to each his/her own.

[VTKidder]

So is a 421 a bore / stroke combo, or a straight up stroked or bored job? I'd tend to agree with you on steering clear of pushing a small block to it's end for a few more ponies and ftlbs.

[Truckstr]

421 cu. in. (actually 420.333) can be had from the above noted 3.875" stroke in a 4.155" bore (0.030" overbore). That's just 0.125" increase in stroke over stock (3.75"), but that is a whole bunch in internal engine terms.

The 6.0" rods help reduce the cylinder wall loading due to reduction in the rod angle, but it would still have the 2.65" diameter mains. That alone is largely the reason that 400 engines are RPM limited. A forged crank helps, but the bearing speeds still approach the critical limits. That's why a lot of race engine builders turn down the 400 cranks to 2.45" when they want to approach (and exceed) 7000 RPM reliably.

The piston accelerations increase with the stroke and the longer rods don't help there. The longer rods allow the piston to "dwell" at TDC longer, but - for a given RPM - the pistons will accelerate away from TDC at a faster rate. That can be detrimental to engine reliability. In a race engine, the tear downs occur more frequently, so it's not "as big" of a concern.

Comprende? Sorry, being that I'm in the throws of researching all of the little ins-and-outs for my 406 build, I tend to get a little anal about all of the details. Hope I've helped!

[VTKidder]

Yo comprendo.

You're not a dumb person. Thanks for the 0:30 rundown. I'm pretty ignorant when it comes to engine internals; my original 350 has probably never been apart, and it still runs strong. I'll prolly stick with that until it craps out, or I hit the powerball, then it'll most likely be a crate motor. Just one of those areas of trucks I tend to leave to the pros. I'll throw sheet metal, wiring and suspension stuff all over, but the powerplant I tend to shut the hood on. More power to folks like you!!!

[DMAN]

Truckstr, when building a 406 using 5.7" rods, do you need special pistons or do you use standard oversized pistons?
DMAN

[Truckstr]

Originally posted by DMAN
Truckstr, when building a 406 using 5.7" rods, do you need special pistons or do you use standard oversized pistons?
DMAN

The compression height is different when going from the standard 5.565" long 400 rod to the 5.7" long 350 type rod, so you'll have to go with different pistons.