# 389 to 421



## wlawdog (Nov 27, 2015)

I have a sweet running super low milage 389 in my '64. Running '65 heads and an Edlebrock 4 barrel, otherwise stock. I am like everyone else I know, I want more horsepower. My dream has always been to run a 421. Can I get my 389 there, or close in a way that makes sense? I am thinking a stocker kit is a good starting place but honestly I have been a bolt-on guy with my cars in the past, and they have been Y block Fords and small block chevy motors. Only built one so I am far from expert. Turning to the Pontiac brain trust for some solid info here. Any insight regarding my dream (or nightmare) will be appreciated. 
wl


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## oldskool (Apr 26, 2015)

"...My dream has always been to run a 421. Can I get my 389 there, or close in a way that makes sense?..."


A 3" main 4" stroke crank will get you there.

RPM shows both a cast and forged 4" crank. Don't know if they are still available or not. They have BBC size rod journals. So you'll have to run BBC rods. I know the rods come in 6.635, 6.7 & 6.8 lengths. Will also need custom pistons, or just go with a stroker assembly.

NODULAR IRON

Spotts shows 4" forged cranks for $649. No price listed for the 4" stroker assembly. 

Crankshafts

Butler shows cast and forged crank, balanced 4" stroker assemblies. 

http://www.jbp-pontiac.com/products/engines_assemblies/rotating_assemblies.html#433-446

Sandoval sells the Scat 4" forged crank for $795.

http://www.sandovalperformance.com/#!product/prd12/3286612371/434-scat-4340-forged-4"-stroke-crank

http://www.scatcrankshafts.com/about-crankshafts/pontiac-crankshafts/


"...Any insight regarding my dream (or nightmare) will be appreciated...

Unless you are just set on using a 389 block, and the old style heads, I'd go with a 400 block stroker. You can still go with a 4" stroke if you prefer. But, the later model iron and alum heads have lots of advantages. Plus, you can keep your "sweet running super low mileage 389", for future use.


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## geeteeohguy (Feb 2, 2008)

Also, a 389 block with a stroker crank will be a stronger, more durable engine than the 3.25" main factory 421. My vote goes to stroke the 389...


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## ALKYGTO (Mar 29, 2010)

Yeah, Id go for a 400 block and leave the 389 intact since you are replacing all the reciprocating assembly anyway. Aftermarket rods are a must IMO and if you went with BBC rods you will have a larger choice and should be cheaper.



Oh, and why stop at 421? :reddevil: just tell everyone its "just" a 421 when you are actually packing 460++....:thumbsup:


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## wlawdog (Nov 27, 2015)

I have considered keeping what I have for future or fall back plan and starting fresh but leaning toward building mine out w/forged material. Dollars matter obviously so... Time to do some comparison shopping. thanks for the leads.


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