420 rotating assembly questions
Thread Starter
Racer
Joined: Oct 2006
Posts: 269
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420 rotating assembly questions
I have stock 400 block that is now ready for the rotating assembly. I have decided to use a 3.875 crank and make this a 420.
Does anyone know if there is a piston / rod combination that requires minimal machine work on the block? If not, is there a source for parts that are designed or clearanced for the 420 build?
Does the 420 build require more machine work than the 383?
Any tips or gotcha's for this build would be greatly appreciated. I intend to only drive this on the street. Looking to build a torque monster that will spin the tires and put me back in the seat while still using a thd350 and 3:08 gears.
Does anyone know if there is a piston / rod combination that requires minimal machine work on the block? If not, is there a source for parts that are designed or clearanced for the 420 build?
Does the 420 build require more machine work than the 383?
Any tips or gotcha's for this build would be greatly appreciated. I intend to only drive this on the street. Looking to build a torque monster that will spin the tires and put me back in the seat while still using a thd350 and 3:08 gears.
Le Mans Master
Joined: Oct 2006
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I'm not 100% sure, but I think you need to do some grinding on the block for a 383. A 420 may need more grinding AND a reduced base circle cam. Use some old bearings, drop the crank in and gently rotate it and see. Do a test assembly and find out for sure- that's the only way you can be sure about your specific combination anyway. It'd be a PITA to have someone tell you what they did, you put it together, and then find that you were off a little bit.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Eagle makes extra clearance rods for stroker applications. You need a small base circle cam for sure and as for pistons you are limited but they are out there
Thread Starter
Racer
Joined: Oct 2006
Posts: 269
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Are the rods you reference I beam or H beam? I am thinking of using a 4340 crank, I beam rods and forged pistons. If I use 6" rods will I have issues with the oil ring?
Any info on websites, part numbers or vendors would be much appreciated. I am having the machine work and assembly of the short block done by a professional but I am supplying the rotating assembly. For that reason I want to fully understand the machine work required based on the parts selected.
Thanks
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
The extra clearance rods are the H beam. I haven't looked into 420's but here is a good rotating assembly for a 434ci if you want to stuff a 4 inch crank into that blcck, that is what I am in the process of doing
http://www.cnc-motorsports.com/produ...00&CtgID=20652
http://www.cnc-motorsports.com/produ...00&CtgID=20652
Thread Starter
Racer
Joined: Oct 2006
Posts: 269
Likes: 7
The extra clearance rods are the H beam. I haven't looked into 420's but here is a good rotating assembly for a 434ci if you want to stuff a 4 inch crank into that blcck, that is what I am in the process of doing
http://www.cnc-motorsports.com/produ...00&CtgID=20652
http://www.cnc-motorsports.com/produ...00&CtgID=20652
Can you tell me if there is additional machine work required due to the 4 inch crank? I want to know what to expect before I begin discussions with the machine shop that is assembling the short block. I don't want to be in a position where the machinist tells me it will cost more to do a 4 inch if that is not true.
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I have not gone thru all the steps yet so I don't have a solid answer however, it should not be any more expensive than the 420ci, if he has to clearance then grinds a little more that's all. Everthing else is the same. I hope you do it, would be nice to see how it comes together
