401 crank questions

hohner0006

I'm taking the next step this off-season with my 401 and I need to know a couple of things first and want your opinions. I plan on either using my stock crank with the offset grind mod and 6" chebby rods or going with an aftermarket crank. My concern is how much rpm will the stock crank tolerate? What mods should I consider with respect to the main caps? Studs and Girdles? Who makes these parts? All said and done I'm looking for the 456 CI that my present pistons will net me with the 6" H-beam rods and strocker mod. I want the higher revs that an Indy single plane intake and 2" headers will allow. My cam will pull to 7500 + rpm and my heads will probably end up being the limiting factor ( 58 cc ported and polished). Please ask any questions or bring up anything you feel I may be over looking in my build. Thanks

jeepsr4ever

Your asking for a 4" stroke and a bore of 4.250 to net 457CI. You can do this with a honda journal of 1.88 instead of the chevy 2.00 or 2.100 due to the extended stroke. It is also possible to weld up that crank and then have it turned to 4" stroke with a 2.00 journal. A 6" rod with a Honda journal and a chevy .927 pin can be sourced from Eagle. A 6" 2.00 journal chevy rod can be found at many places. For what your asking you need to at least nitride the crankshaft. You will probly have around $800 into the crank with a chevy 2.00 journal and a 4" stroke. The Honda journal with a 4" stroke is something we have had done in the past however not all cores would take that stroke with that small of a journal. The rod oiling hole was eaten through on the crossdrill. Keep in mind your compression height of 1.200"-1.208" on the piston at a 4" stroke, 6" rod means you should run a ring land for oil and pistons can get a little expensive. I do not know of a BBC piston off the shelf that comes close to those specs. I have done the Chevy 2" and 2.1"- 420CI and 431CI and I can tell you its worth it...bigtime. I am messing with 445-462CI strokers right now using stock cranks that are nitrided and cryogenically treated. Curious, what is your application?

jeepsr4ever

Yes your heads will be the limiting factor. You may developing power at the wrong range for your head flow. When you are talking about a 450 cubic inch motor and a cam that will hit 7500RPM thats 1,687,500 cubic inches of displacement that needs to be fed every minute. To get the power you need a head flow of 275-323CFM for a volumetric efficiency of 25%@7500RPM. You can make your 680-730hp within this range but you would need head flow characteristics of the higher end 320CFM @7500 RPM or at the lift you will be at for that rpm. It can be alot to ask from a stock crank if your racing without proper prep of the crank. Prepping means you should have a nice large radius on the rod journals and the crank should be stress relieved using a nitriding at the least or Nitride/Cryo. The block at that range is entering the danger zone as far as thrust on the sidewalls of the cylinders. In my experience once past 750hp filler should be used at least to 75% of the cylinder depth. How much do you need out of this motor?

jeepsr4ever

Lastly do you need to have 4 bolt mains... Well that depends on the condition of your caps really. How would you know the condition is right to use stock caps? They must be crack free and the main journals must be aligned extremely well. Studs will allow you to get into that range but for the toughest lower end splayed caps will be needed. You can get 4bolt main caps off ebay of all places.

hohner0006

Application is 150 - 175 foot mud pits in side-by-side mud drags. I see were I made an error in my math off your strocker combo post. If I utilize the 6" chebby rod with the 3.899 stroke are the pistons "shelf" pieces or are they custom pieces? My current bore is 4.195 and I'd like to go as big as feasable without boring any further. I need to check with my machine shop to see if they can nitride the crank. I can't run aluminum heads so I guess I have to keep that limitation in mind when I make my decision. Something else I need to ask...who makes a real race application head gasket? I've been using a basic felpro (without any problems) but I intend on boosting compression from my current 12-1 to 14-1. I've already bought ARP studs for the heads and will have to order extras for the additional head studs after we drill through the heads/block. Any other thoughts?

jeepsr4ever

Pistons are not off teh shelf and I havent seen one set close enough to use. For head gaskets the High temp ROLs are the best. Get em quick becasue I heard through the grapevine that they are discontinued. We have sold out and I am not sure if we can get more.

ol' school power

jeepsr4ever wrote
The rod oiling hole was eaten through on the crossdrill.

Is that the one you brought to Kenosha?
Seeing that on a 401 crank brings a tear.

jeepsr4ever

ol' school power wrote
jeepsr4ever wrote
The rod oiling hole was eaten through on the crossdrill.

Is that the one you brought to Kenosha?
Seeing that on a 401 crank brings a tear.

Yes it does and it can be fixed but at a cost of over $800. It is a VERY common mishap when destroking :idea:

milnersXcoupe

I will be out of the office from Wednesday October 24 thru Monday SDecember 5th. Brian Owens 8)